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1
Dabić, Predrag, Volker Kahlenberg, Biljana Krüger, et al. "Low-temperature phase transition and magnetic properties of K3YbSi2O7." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 77, no. 4 (2021): 584–93. http://dx.doi.org/10.1107/s2052520621006077.
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The new ambient-temperature hexagonal (space group P63 /mmc) polymorph of tripotassium ytterbium(III) disilicate (β-K3YbSi2O7) has been synthesized by the high-temperature flux method and subsequently structurally characterized. In the course of the temperature-dependent single-crystal diffraction experiments, a phase transformation of β-K3YbSi2O7 to a novel low-temperature orthorhombic phase (β′-K3YbSi2O7, space group Cmcm) has been observed at about 210 K. β-K3YbSi2O7 is isostructural with K3ErSi2O7, whereas β′-K3YbSi2O7 adopts a new type of structure. Both compounds can be built up from a regular alternation of layers of two types, which are parallel to the (001) plane. In the octahedral layer, YbO6 octahedra are isolated and linked by K1O6+3 polyhedra. The second, slightly thicker sorosilicate layer is formed by a combination of Si2O7 dimers and K2O6+3 polyhedra. The boundary between the layers is a pseudo-kagome oxide sheet based on 3.6.3.6 meshes. The phase transition is due to a tilt of the two SiO4 tetrahedra forming a single dimer which induces a decrease of the Si—O—Si angle between bridging Si—O bonds from 180° (dictated by symmetry in space group P63/mmc) to ≃164°. Magnetic characterization indicates that K3YbSi2O7 remains paramagnetic down to 2 K, showing no apparent influence of the phase transformation on its magnetic properties. Analysis of the magnetization data revealed the positions of the three lowest crystal field levels of the Yb3+ cations, as well as the corresponding projections of their angular momentum on the direction of the magnetic field.
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Romanenko, A. I., G. E. Chebanova, Tingting Chen, Wenbin Su, and Hongchao Wang. "Review of the thermoelectric properties of layered oxides and chalcogenides." Journal of Physics D: Applied Physics 55, no. 14 (2021): 143001. http://dx.doi.org/10.1088/1361-6463/ac3ce6.
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Abstract The current state of investigation on thermoelectric properties of layered chalcogenides and oxides is considered. The relationship between the quasi-two-dimensionality of electronic transport properties and thermoelectric properties is confirmed. A decrease in the dimension of electron transport from three-dimensional to quasi-two-dimensional in materials with a layered structure increases the thermopower with a slight change in electrical conductivity. The bismuth tellurides, bismuth selenides and its alloys are currently one of the outstanding state of the art bulk thermoelectric materials with layered structure. Layered transition metal dichalcogenides MX2 (M is a transition metal, X is a chalcogen) are efficient thermoelectric materials at higher temperatures (500–800 K). In these materials, an increase in thermoelectric properties associated with the two-dimensionalization of electron transport is also observed. Layered monochalcogenides MX (M = Sn, Pb, Ge; X = S, Se, Te) are also a promising class of thermoelectric materials. In SnSe single crystals, Z T ∼ 2.6 is obtained at 923 K due to the very low thermal conductivity along the b axis (0.23 W (m K)−1 at 973 K). Layered chalcogenides CuCrX2 (X = S, Se, Te) containing magnetic Cr atoms are effective thermoelectrics at higher temperatures (up to 800 K) due to the presence of phonon glass–electron crystal state led to a significant decrease in thermal conductivity at high temperatures. Magnetic atoms in CuCrX2 compounds lead to the presence of magnetic phase transitions affecting their thermoelectric properties. Interest in oxide-based thermoelectric materials has significantly increased due to their stability in air and higher temperatures for maximum efficiency. The most promising thermoelectric oxide materials Ca3Co4O9, Na x CoO2, Bi2Ca2Co2O x , and CaCo2O4 have a layered structure and contain magnetic Co atoms leading to magnetic ordering and influence on thermoelectric properties. The presence of phase transitions affects the thermoelectric parameters of thermoelectrics and the thermoelectric figure of merit ZT.
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Chiromawa, Idris Muhammad, Amiruddin Shaari, Razif Razali, Summanuwa Timothy Ahams, and Mikailu Abdullahi. "Ab initio Investigation of the Structure and Electronic Properties of Normal Spinel Fe2SiO4." Malaysian Journal of Fundamental and Applied Sciences 17, no. 2 (2021): 195–201. http://dx.doi.org/10.11113/mjfas.v17n2.2018.
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Transition metal spinel oxides have recently been predicted to create efficient transparent conducting oxides for optoelectronic devices. These compounds can be easily tuned by doping or defect to adapt their electronic or magnetic properties. However, their cation distribution is very complex and band structures are still subject to controversy. We propose a complete density functional theory investigation of fayalite (Fe2SiO4) spinel, using Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA) in order to explain the electronic and structural properties of this material. A detailed study of their crystal structure and electronic structure is given and compared with experimental data. The lattice parameters calculated are in agreement with the lattice obtained experimentally. The band structure of Fe2SiO4 spinel without Coulomb parameter U shows that the bands close to Fermi energy appear to be a band metal, with four iron d-bands crossing the Fermi level, in spite of the fact that from the experiment it is found to be an insulator.
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Han, J. P., and Y. Q. Guo. "Structure stability and magnetic properties of RIn3−xTx (R = Gd, Pr,T = Co, Fe, Mn)." Powder Diffraction 32, no. 4 (2017): 249–54. http://dx.doi.org/10.1017/s0885715617001142.
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The syntheses and crystal structures and magnetic properties of novel RIn3−xTx (R = Gd，Pr；T = Fe，Co，Mn；x = 0–0.3) intermetallic compounds in rare earth-In-3d transition metal ternary system have been systematically investigated. It reveals that RIn3−xTx crystallizes in cubic AuCu3 type structure with a space group of Pm$\bar 3$m and Z = 1. The 1a and 3c crystal positions are occupied by R and In atoms, respectively. The 3d transition metals substitute partly for In and prefer to occupy the 3c site. The lattice parameters and unit cell volumes decrease with increasing the content of 3d transition metal in RIn3−xTx intermetallic compounds. The magnetic properties of RIn3−xTx are sensitive to T content. With increasing T content, GdIn3−xTx alloys show the paramagnetic, mixture of ferromagnetic and paramagnetic and ferromagnetic behavior. T doping into RIn3 induces the presence of ferromagnetic phase in GdIn3−xTx, which is totally different from those of the pure binary RIn3.
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Zhang, Qin, Heng Chang Qian, Juan Pei, and Suo Jia Yuan. "Competing Effects of Band Filling and Steric Factors on Magnetic and Transport Properties of Double Perovskite." Advanced Materials Research 490-495 (March 2012): 325–28. http://dx.doi.org/10.4028/www.scientific.net/amr.490-495.325.
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Ordered double perovskite oxides (Sr2-3xLa2xBax)FeMoO6 (0≤x≤0.3) have been investigated in this work. X-ray powder diffraction reveals that the crystal structure of the compounds changes from a tetragonal I4/m lattice to a cubic Fm m lattice around x=0.2. Due to the electron doping, the lattice constants increase with x. Owing to the competing contribution of electron doping and steric effect, Curie temperature of the compounds is almost unchanged. The resistivity of the parent compound shows a semiconducting behavior below room temperature, but those of the doped samples exhibit a metal-semiconductor transition. A correlation between the resistivity and metal-semiconducting transition temperature (TM-S) is observed. The resistivity and TM-S of the compounds decrease with x for x 0.2 and increase for x≥0.2.
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Baker, Steve, Mervyn Roy, Chris Binns, and Martin Lees. "Controlling Crystal Structure in Embedded Magnetic Nanoparticles." Acta Crystallographica Section A Foundations and Advances 70, a1 (2014): C961. http://dx.doi.org/10.1107/s205327331409038x.
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"Magnetic nanoparticles and nanocomposite materials have attracted much interest due to their novel magnetic behaviour, and their potential use in a range of applications. One of the main reasons for their novel magnetism, appreciated for some time, is the high proportion of under-coordinated atoms at the surface of nanoparticles. In the case of magnetic transition metals this leads to a narrowing of the 3d bands that are responsible for magnetism in these materials, leading to size-dependent nanoparticle properties. The atomic structure adopted by nanoparticles is also a key factor in determining their magnetism. Unlike in bulk materials atomic structure in nanoparticles can be changed more readily by, for example, embedding them in suitable matrix materials. Here we describe how a high level of control over crystal structure in nanoparticles can be achieved, using EXAFS to ""fingerprint"" their crystal structure, and show how this in turn leads to a high degree of control over nanoparticle magnetism. We describe a flexible co-deposition process based around a gas aggregation source, which enables a high degree of control over structure in transition metal nanoparticles embedded in various matrices. EXAFS experiments and analysis used to probe atomic structure in embedded Fe and Co nanoparticles are described [1]. Examples presented include the system of Fe nanoparticles embedded in a CuAu alloy matrix where we show that is not only the ability to change the atomic structure of embedded nanoparticles that is important but the ability to fine-tune their structure once changed [2]. In this case, this enables the atomic magnetic Fe moment to be fine-tuned to a value higher than in the bulk Fe structure, in agreement with theory. In some systems alloying at the particle/interface can be significant. We describe how this is the case for Fe nanoparticles in Pd [3], and how such alloying could be useful in forming magnetic nanocomposites with superior properties."
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Moshkina E. M., Molokeev M. S., Eremin E. V., and Bezmaternykh L. N. "Influence of Ga-substitution to the structural and magnetic properties of (Mn,Fe)-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- bixbyite." Physics of the Solid State 65, no. 6 (2023): 1009. http://dx.doi.org/10.21883/pss.2023.06.56116.57.
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To study the dependence of the properties of ternary oxides (Mn,Fe,Ga)2O3 with the bixbyite structure on the composition, the temperature dependences of the magnetization and ac magnetic susceptibility of two single-crystal samples of different compositions obtained using the flux method were analyzed. A detailed study of the structure was carried out using single-crystal X-ray diffraction analysis, and the changes in structural parameters depending on the composition were analyzed. The dc magnetization and ac magnetic susceptibility of Fe1.1Mn0.76Ga0.14O3 and Fe0.65Mn1.1Ga0.26O3 bixbyites have been studied. Despite the qualitatively similar behavior of the magnetic properties, significant differences were also found, despite a small difference in the Mn/Fe/Ga ratio in the samples under study. It is shown that both compounds experience two successive low-temperature magnetic phase transitions from the paramagnetic phase at T=20-32 K as the temperature is lowered. Calculations of the Mydosh parameter for the detected phase transitions showed different degrees of ordering in the compounds under study. Keywords: transition metal oxides, magnetic phase transitions, spin glass state, bixbyite.
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Latushka, S. I., D. V. Zheludkevich, E. V. Budemko, K. N. Nekludov, M. V. Silibin, and D. V. Karpinsky. "Crystal Structure and Magnetic Properties of Bi1-yBa(Sr)Fe1-yTiyO3 Solid Solutions." Journal of Material Science and Technology Research 10 (August 29, 2023): 82–85. http://dx.doi.org/10.31875/2410-4701.2023.10.08.
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Abstract: Usages of various chemical substitution schemes of the initial multiferroic BiFeO3 can significantly reduce known drawbacks specific for the functional oxides based of iron ions and thus foster a creation of novel magnetoelectric compounds perspective for various technological applications. In the present study the co-doped compounds of the system Bi1-y(Ba1- xSrx)yFe1-yTiyO3 (x = 0.0 – 1.0; y ≤ 0.4) synthesized using sol-gel technique were analyzed focusing on the crystal structure stability and the correlation between the structure and magnetic properties. The concentration driven evolution of the crystal structure as well as the unit cell parameters were investigated based on the X-ray diffraction data, the correlation between the crystal structure and the magnetic properties of the compounds has been studied by magnetometry techniques. The compounds Bi1-y(Ba1- xSrx)yFe1-yTiyO3 with x = 0; y = ≤ 0.2 are characterized by single-phase rhombohedral structure, and increase in the dopant concentration to y = 0.4 leads to the stabilization of the pseudocubic phase. An increase in the Sr content leads to the phase transition in the compounds to the single phase state with the cubic structure which is accompanied by an increase in the value of the remanent magnetization.
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Demazeau, Gérard, Samir F. Matar, and Rainer Pöttgen. "Chemical Bonding in Metallic Rutile-type Oxides TO2 (T = Ru, Rh, Pd, Pt)." Zeitschrift für Naturforschung B 62, no. 7 (2007): 949–54. http://dx.doi.org/10.1515/znb-2007-0712.
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Abstract Synthesis routes to rutile-type oxides with 4d and 5d transition elements are summarized. Trends in electronic structure have been established through an analysis in the framework of density functional theory presenting the band structure, the density of states and the properties of chemical bonding. The metal-oxygen bond is found to play the major role in bonding of the system in the valence band. Throughout the series 4d → 5d (RuO2, RhO2, PdO2 and PtO2) the crystal field analysis of the band structure shows a lowering of eg towards t2g manifolds and a broadening of the overall density of states. In the vicinity of the Fermi level the role of the antibonding metal-oxygen character is investigated in the context of instability towards possible magnetic polarization, especially for RuO2.
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Yi, Di, Jian Liu, Shang-Lin Hsu, et al. "Atomic-scale control of magnetic anisotropy via novel spin–orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices." Proceedings of the National Academy of Sciences 113, no. 23 (2016): 6397–402. http://dx.doi.org/10.1073/pnas.1524689113.
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Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e., magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition-metal oxides (TMOs) by digitally inserting nonmagnetic 5d TMOs with pronounced spin–orbit coupling (SOC). High-quality superlattices comprising ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at the atomic scale. Magnetic easy-axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin–orbit state within the nominally paramagnetic SIO.
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Nocerino, Elisabetta, Ola K. Forslund, Chennan Wang, et al. "Magnetic nature of wolframite MgReO4." Journal of Physics: Conference Series 2462, no. 1 (2023): 012037. http://dx.doi.org/10.1088/1742-6596/2462/1/012037.
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Abstract Rhenium oxides belonging to the family AReO4 where A is a metal cation, exhibit interesting electronic and magnetic properties. In this study we have utilized the muon spin rotation/relaxation (µ +SR) technique to study the magnetic properties of the MgReO4 compound. To the best of our knowledge, this is the first investigation reported on this interesting material, that is stabilized in a wolframite crystal structure using a special high-pressure synthesis technique. Bulk magnetic studies show the onset of an antiferromagnetic (AF) long range order, or a possible singlet spin state at T C1 ≈ 90 K, with a subtle second high-temperature transition at T C2 ≈ 280 K. Both transitions are also confirmed by heat capacity (Cp ) measurements. From our µ +SR measurements, it is clear that the sample enters an AF order below T C1 = T N ≈ 85 K. We find no evidence of magnetic signal above T N, which indicates that T C2 is likely linked to a structural transition. Further, via sensitive zero field (ZF) µ +SR measurements we find evidence of a spin reorientation at T Cant ≈ 65 K. This points towards a transition from a collinear AF into a canted AF order at low temperature, which is proposed to be driven by competing magnetic interactions.
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Krisyuk, Vladislav V., Samara Urkasym Kyzy, Tatyana V. Rybalova, Ilya V. Korolkov, Mariya A. Grebenkina та Alexander N. Lavrov. "Structure and Properties of Heterometallics Based on Lanthanides and Transition Metals with Methoxy-β-Diketonates". Molecules 27, № 23 (2022): 8400. http://dx.doi.org/10.3390/molecules27238400.
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The possibility of obtaining volatile polynuclear heterometallic complexes containing lanthanides and transition metals bound by methoxy-β-diketonates was studied. New compounds were prepared by cocrystallization of monometallic complexes from organic solvents. Ln(tmhd)3 were used as initial monometallic complexes (Ln = La, Pr, Sm, Gd, Tb, Dy, Lu; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionate) in combination with TML2 in various ratios (TM = Cu, Co, Ni, Mn; L: L1 = 1,1,1-trifluoro-5,5-dimethoxypentane-2,4-dionate, L2 = 1,1,1-trifluoro-5,5-dimethoxy-hexane-2,4-dionate, L3 = 1,1,1-trifluoro-5-methoxy-5-methylhexane-2,4-dionate). Heterometallic complexes of the composition [(LnL2tmhd)2TM(tmhd)2] were isolated for light lanthanides Ln= La, Pr, Sm, Gd, and L= L1 or L2. By single crystal XRD, it has been established that heterometallic compounds containing La, Pr, Cu, Co, and Ni are isostructural linear coordination polymers of alternating mononuclear transition metal complexes and binuclear heteroleptic lanthanide complexes, connected by donor–acceptor interactions between oxygen atoms of the methoxy groups and transition metal atoms. A comparison of powder XRD patterns has shown that all heterometallic complexes obtained are isostructural. Havier lanthanides Ln = Tb, Dy, Lu did not form heterometallics. Instead, homometallic complexes Ln(L3)3 were identified for Ln = Dy, Lu as well as for Ln = La. The thermal properties of the complexes were investigated by TG-DTA and vacuum sublimation tests. The heterometallic complexes were found to be not volatile and decomposed under heating to produce inorganic composites of TM oxides and Ln fluorides. In contrast, Ln(L3)3 is volatile and may be sublimed in a vacuum. Results of magnetic measurements are discussed for several heterometallic and homometallic complexes.
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Struch, Niklas, Gregor Schnakenburg та Arne Lützen. "A novel crystal structure of {tris[4-(1H-pyrazol-3-yl-κN2)-3-azabut-3-enyl]amine-κN}iron(II) bis(tetrafluoridoborate) methanol monosolvate featuring a low-spin configuration". Acta Crystallographica Section C Structural Chemistry 71, № 12 (2015): 1048–52. http://dx.doi.org/10.1107/s2053229615020409.
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Mononuclear complexes are good model systems for evaluating the effects of different ligand systems on the magnetic properties of iron(II) centres. A novel crystal structure of the title compound, [Fe(C18H24N10)](BF4)2·CH3OH, with one molecule of methanol per formula unit exhibits a strictly sixfold coordination sphere associated with a low-spin configuration at the metal centre. The incorporated methanol solvent molecule promotes extended hydrogen-bonding networks between the tetrafluoridoborate anions and the cationic units. A less constrained crystal structure regarding close contacts between the tetrafluoridoborate anions and the cationic units allows a spin transition which is inhibited in the previously published hydrate of the title compound.
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Dissanayaka Mudiyanselage, Ranuri S., Tai Kong, and Weiwei Xie. "Crystal growth and physical properties of an antiferromagnetic molecule: trans-dibromidotetrakis(acetonitrile)chromium(III) tribromide, [CrBr2(NCCH3)4](Br3)." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 77, no. 4 (2021): 624–31. http://dx.doi.org/10.1107/s2052520621004662.
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The synthesis, crystal structure determination, magnetic properties and bonding interaction analysis of a novel 3d transition-metal complex, [CrBr2(NCCH3)4](Br3), are reported. Single-crystal X-ray diffraction results show that [CrBr2(NCCH3)4](Br3) crystallizes in space group C2/m (No. 12) with a symmetric tribromide anion and the powder X-ray diffraction results show the high purity of the material specimen. X-ray photoelectron studies with a combination of magnetic measurements demonstrate that Cr adopts the 3+ oxidation state. Based on the Curie–Weiss analysis of magnetic susceptibility data, the Néel temperature is found to be around 2.2 K and the effective moment (μeff) of Cr3+ in [CrBr2(NCCH3)4](Br3) is ∼3.8 µB, which agrees with the theoretical value for Cr3+. The direct current magnetic susceptibility of the molecule shows a broad maximum at ∼2.3 K, which is consistent with the theoretical Néel temperature. The maximum temperature, however, shows no clear frequency dependence. Combined with the observed upturn in heat capacity below 2.3 K and the corresponding field dependence, it is speculated that the low-temperature magnetic feature of a broad transition in [CrBr2(NCCH3)4](Br3) could originate from a crossover from high spin to low spin for the split d orbital level low-lying states rather than a short-range ordering solely; this is also supported by the molecular orbital diagram obtained from theoretical calculations.
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Yahsi, Yasemin. "X-ray characterization and magnetic properties of dioxygen-bridged CuIIand MnIIISchiff base complexes." Acta Crystallographica Section C Structural Chemistry 72, no. 7 (2016): 585–92. http://dx.doi.org/10.1107/s2053229616008974.
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The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metalloproteins and metalloenzymes. Multinuclear CuIIand MnIIIcompounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen-bridged binuclear MnIIIcomplexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear CuIIcomplexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen-bridged copper(II) and manganese(III) Schiff base complexes, namely bis(μ-4-bromo-2-{[(3-oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu2(C10H10BrNO2)2], (1), and bis(diaqua{4,4′-dichloro-2,2′-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{μ-4,4′-dichloro-2,2′-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C18H16Cl2N2O2)(H2O)2]2[Mn2(C18H16Cl2N2O2)2(H2O)2](ClO4)4·2C2H5OH, (2), have been synthesized and single-crystal X-ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each CuIIatom is four-coordinated, with long weak Cu...O interactions of 2.8631 (13) Å linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each MnIIIatom is six-coordinated. The shortest intra- and intermolecular nonbonding Mn...Mn separations are 3.3277 (16) and 5.1763 (19) Å for (2), while the Cu...Cu separations are 3.0237 (3) and 3.4846 (3) Å for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2–300 K and reveal the presence of antiferromagnetic spin-exchange interactions between the transition metal ions.
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Suyolcu, Y. E., G. Christiani, P. A. van Aken, and G. Logvenov. "Design of Complex Oxide Interfaces by Oxide Molecular Beam Epitaxy." Journal of Superconductivity and Novel Magnetism 33, no. 1 (2019): 107–20. http://dx.doi.org/10.1007/s10948-019-05285-4.
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Abstract Complex oxides provide a versatile playground for many phenomena and possible applications, for instance, high-temperature superconductivity, magnetism, ferroelectricity, metal-to-insulator transition, colossal magnetoresistance, and piezoelectricity. The origin of these phenomena is the competition between different degrees of freedom such as charge, orbital, and spin, which are interrelated with the crystal structure, the oxygen stoichiometry, and the doping dependence. Recent developments not only in the epitaxial growth technologies, such as reactive molecular beam epitaxy, but also in the characterization techniques, as aberration-corrected scanning transmission electron microscopy with spectroscopic tools, allow synthesizing and identifying epitaxial systems at the atomic scale. Combination of different oxide layers opens access to interface physics and leads to engineering interface properties, where the degrees of freedom can be artificially modified. In this review, we present different homo- and hetero-epitaxial interfaces with extraordinary structural quality and different functionalities, including high-temperature superconductivity, thermoelectricity, and magnetism.
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Habermeier, Hanns-Ulrich. "Complex Oxide Interfaces: A Path to Design New Materials." MRS Proceedings 1454 (2012): 137–48. http://dx.doi.org/10.1557/opl.2012.924.
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ABSTRACTHeterostructures composed of transition metal oxides with strong electron correlation offer a unique opportunity to design new artificial materials whose electrical, magnetic and optical properties can be manipulated by tailoring the occupation of the d-orbitals of the transition metal in the compound. This possibility is an implication of symmetry constraints at interfaces with the consequence of a reconstruction of the coupled charge-, spin-, and orbital states of the constituents and their interactions. Novel architectures can be constructed showing functions well beyond charge density manipulations determining the functionality of conventional semiconductor heterostructures. Success in this endeavor requires the mastering of technological prerequisites such as structurally as well as chemically controlled interface preparation down to atomic scales. Additionally, a fundamental understanding of the modifications of the electronic structure at the interface imposed by structural boundary conditions and consequently by the constituent’s orbital occupation is required. A path towards a new generation of electronic devices with multiple functionalities can thus be opened by exploiting the correlation driven interface phenomena. In this paper, the technological challenges and experimental realizations along this concept are described with an emphasis of growth techniques based on the pulsed laser deposition method. As a case study, results of investigations of YBa2Cu3O7/La2/3Ca1/3MnO3superlattices are compiled and the conclusions regarding the orbital manipulation at the interface are used to pave the way for orbital engineering of oxides with electronic structures similar to the cuprates in order to find novel ordered quantum states at the interfaces including magnetism and superconductivity.
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Mondal, S., and A. K. Banthia. "Triethanolamine Molybdate, a New Polymeric Precursor for Molybdenum Nitride." Advanced Materials Research 29-30 (November 2007): 195–98. http://dx.doi.org/10.4028/www.scientific.net/amr.29-30.195.
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Nitrides remain a relatively unexplored class of materials primarily due to the difficulties associated with their synthesis and characterization. Several synthetic routes, including high temperature reactions, microwave assisted synthesis, and the use of plasmas, to prepare binary and ternary nitrides have been explored. Transition metal nitrides form a class of materials with unique physical properties, which give them varied applications, as high temperature ceramics, magnetic materials, superconductors or catalysts. They are commonly prepared by high temperature conventional processes, but alternative synthetic approaches have also been explored, more recently, which utilize moderate temperature condition. Transition metal nitrides particularly, molybdenum nitride, niobium nitride, and tungsten nitride have important applications as catalyst in hydrodenitridation reactions. These nitrides have been traditionally synthesized using high temperature nitridation treatments of the oxides. The nitridation temperatures are very high (> 800- 1000 oC). The aim of our work is to synthesize molybdenum nitride by a simple, low-temperature route. The method involves pyrolysis of a polymeric precursor, which was prepared from the condensation reaction between triethanolamine and molybdic acid. The melting point of the product is 180oC. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that molybdenum nitride (MoN) obtained from this method has hexagonal crystal structure. MoN is obtained by this method at very low temperature (~ 400 oC).
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Hamchaoui, Farida, Véronique Alonzo, Diego Venegas-Yazigi, Houria Rebbah, and Eric Le Fur. "Six novel transition-metal phosphite compounds, with structure related to yavapaiite: Crystal structures and magnetic and thermal properties of AI[MIII(HPO3)2] (A=K, NH4, Rb and M=V, Fe)." Journal of Solid State Chemistry 198 (February 2013): 295–302. http://dx.doi.org/10.1016/j.jssc.2012.10.007.
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Morozova, Polina A., Stanislav S. Fedotov, and Artem M. Abakumov. "(Digital Presentation) Prussian Blue Analogs – a Wide Variety of Promising Cathode Materials with Peculiar Electrochemical Properties." ECS Meeting Abstracts MA2022-01, no. 1 (2022): 59. http://dx.doi.org/10.1149/ma2022-01159mtgabs.
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Today, post-lithium energy storage technologies are now rapidly progressing due to the high price of a net Li-ion battery, which also depends on the desired capacity and power. Among sodium, potassium, calcium, magnesium, and even aluminum-based alternatives, young potassium-ion batteries demonstrate high capacity and energy density, notable ionic transport in electrolytes, the possibility to employ graphite anodes, and a wide variety of possible electrode materials: layered oxides, polyanionic, organic compounds, Prussian Blue analogs. However, the latter ones are generally considered as the most promising and practically viable. Prussian Blue analogs form a big family of electrode materials with the general formula KxM1[M2(CN)6]∙nH2O, where x=0...2, and Mi are any possible 3d transition metals. The most well-known and commercially available is based on a hexacyanoferrate anion [Fe(CN)6]n-, while other transition metals can also form hexacyanometallate complexes, but are poorly studied or not known at all. The most part of published works shed light on the morphology and low content of water defects inside crystallites counting the lack of hexacyanoferrate, and their influence on realized capacity and capacity fades, while the fundamental principles and real water position presence which guide the electrochemical activity of high- and low-spin cations in these materials are totally missed. In our work, we also started with the intrinsic water defects and their impact on crystal and physicochemical properties in K2Mn[Fe(CN)6]∙nH2O but with sensitive to light atoms neutron diffraction technique. We observed that water content does not effect the whole crystal symmetry but slightly amend unit cell parameters. Besides the fact of decreasing a decomposition temperature in “watered” Prussian Blue analog, electrochemical properties were found close. Therefore, we concluded that intrinsic water does not notably influence material properties. Continuing with potassium manganese hexacyanoferrate and electronic structure impact to the compound properties, to reveal the best synergetic stabilizing agent during cycling, we synthesized and studied the system K2-γMn1-xCox[Fe(CN)6]∙nH2O with x=0, 0.05,...1. In addition to symmetry and composition transformations, magnetic and electrochemical properties also significantly differ, while higher cobalt content increases the redox potential of iron, but drastically decreases total capacity due to the inability of reaching iron oxidation. The fact of notable changing of redox potentials in K2-γMn1-xCox[Fe(CN)6]∙nH2O is inspiring, and we have been extending with other hexacyanometallates. Hexacyanomanganate-ion [Mn(CN)6]n- is one of the promising pathways to investigate such systems with a more fundamental point of view, and the obtained experimental results confirm the hypothesis. We discovered that cation position exchange totally alters the electrochemistry of the Prussian Blue cathode materials, and the interpretation still raises a lot of questions and assumptions, and together with computational chemistry, we will try to answer the fundamental questions about electronic, crystal structures and electrochemical properties. In this report we will present the new correlations of redox potential in Prussian Blue analogs depending on transition metal position and electronic structure, evaluate diffusion of potassium in these materials, and try to answer the possibility to use these compounds in potassium-ion batteries.
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Hamchaoui, Farida, Veronique Alonzo, Diego Venegas-Yazigi, Houria Rebbah, and Eric Le Fur. "ChemInform Abstract: Six Novel Transition-Metal Phosphite Compounds, with Structure Related to Yavapaiite: Crystal Structures and Magnetic and Thermal Properties of AI[MIII(HPO3)2] (A: K, NH4, Rb and M: V, Fe)." ChemInform 44, no. 17 (2013): no. http://dx.doi.org/10.1002/chin.201317018.
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Méndez-Arriaga, José M., Itziar Oyarzabal, Álvaro Martín-Montes, Judith García-Rodríguez, Miguel Quirós, and Manuel Sánchez-Moreno. "First Example of Antiparasitic Activity Influenced by Thermochromism: Leishmanicidal Evaluation of 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine Metal Complexes." Medicinal Chemistry 16, no. 3 (2020): 422–30. http://dx.doi.org/10.2174/1573406415666190401120607.
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Background: The World Health Organization catalogues illnesses such as Leishmaniasis as neglected diseases, due to low investment in new drugs to fight them. The search of novel and non-side effects anti-parasitic compounds is one of the urgent needs for the Third World. The use of triazolopyrimidines and their metallic complexes has demonstrated hopeful results in this field. Objective: This work studies the antiparasitic efficacy of a series of 5,7-dimethyl-1,2,4- triazolo[1,5-a]pyrimidine first row transition metal complexes against three leishmania spp. strains. Methods: The in vitro antiproliferation of promastigote forms of different strains of leishmania spp. (L. infantum, L. braziliensis and L donovani) and the cytotoxicity in macrophage host cells are reported here. The antiparasitic assays have been complemented with enzymatic tests to elucidate the mechanisms of action. New crystal structure description, thermal analysis, magnetic susceptibility and magnetization experiments have also been carried out in order to present a whole characterization of the studied compounds and interesting physical properties besides the biological tests. Results: The results of antiproliferation screening and cytotoxicity show great antiparasitic efficacy in the studied complexes. The superoxide dismutase enzymatic assays exhibit a different behaviour according to the thermochromic triazolopyrimidine form tested. Conclusion: Antiproliferative assays and enzymatic tests corroborate the synergetic leishmanicidal effect present in coordination triazolopyrimidine complexes. The changes in coordination sphere derived from thermochromism affect the physical properties as well as the biological efficacy.
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Sengupta, Abhinanda, Ajit Kumar, Aakash Ahuja, et al. "Nano-Crystallites of P2-Type Layered Transition Metal Oxide High Voltage Cathode for Sodium-Ion Battery." ECS Meeting Abstracts MA2022-02, no. 64 (2022): 2332. http://dx.doi.org/10.1149/ma2022-02642332mtgabs.
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In this era of transitioning from conventional sources of energy to non-conventional, sodium-ion battery research has been burgeoning as an indigenous solution to energy storage applications, considering the sustainability, cost effectiveness, high availability and a familiar redox chemistry 1. P2-type Na2/3Ni1/3Mn2/3O2 is one of the preeminent cathode for sodium-ion batteries because of their environmental friendliness, open framework, superior specific capacity, higher operating voltage and air-moisture stability. However, rapid capacity decay on charging it to a higher voltage because of P2 to O2 phase transition and a large volume change leading to exfoliation of the layers have impeded the practicability of this as an electrode material for Na-ion battery 2,3,4. Here in this work, we report the preparation of hexagonal nanocrystals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, which is titanium doped in pristine Na2/3Ni1/3Mn2/3O2 via a novel and quick microwave synthesis technique. This provides sharp and clear facets that allows accelerated sodium-ion migration within the crystal during extraction and insertion of Na-ions, making this material a highly efficient cathode. Unlike conventional heating, which requires around 12-20 hours of synthesis time and high energy consumption, microwave radiation induces rapid solid-state reaction that heats the material on molecular level leading to uniform heating, thus retaining the nanocrystallinity of the structure 5. The distinctive hierarchical nanostructure having large surface area could efficiently facilitate the transportation of Na+ ions, fast utilization of active materials, overcome the effect of internal strain generated inside and reduces the pulverization of active materials, thereby restraining the P2 to O2 phase transition at higher voltage 6. Aiding from the combined effect of titanium doping at manganese site and designing hierarchical nanocrystrals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, we obtained a rate capability of 145 mAh g-1 at 0.1 C and a prolonged cycling life (87.3% capacity retention after 500 cycles at 1C) within a voltage range of 2.5 – 4.2 V, restraining the P2 to O2 type phase transition at higher potential. The combined analysis of X-ray diffraction, scanning electron microscopy and transmission electron microscopy along with density functional theory (DFT) calculations demonstrated the optimization of the structure and the physical properties of pristine Na2/3Ni1/3Mn2/3O2 and Ti doped structure along with their Bader charge analysis and electronic properties. Further the mechanical integrity of the nano Na2/3Ni1/3Mn1/2Ti1/6O2 and micro Na2/3Ni1/3Mn1/2Ti1/6O2 were analyzed through micro-compression test of the as prepared pellets. The underlying mechanism for the suppression of phase transition in Na2/3Ni1/3Mn1/2Ti1/6O2 was elucidated by ex-situ X-ray diffraction (XRD) and ex-situ Transmission electron microscopy (TEM). The electrochemical kinetics regarding Na+ diffusion coefficient was further studied through galvanostatic intermittent titration technique (GITT). An analytical model was established to probe deeper into the reason for exfoliation and thus, support our hypothesis. In addition, a sodium-ion full cell was constructed by pairing the as-prepared P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 with a hard carbon anode. This modification of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 nanocrystallites with comprehensive electrochemical performance can be a path breaking, highly efficient cathode material for large-scale energy storage applications. References: Larcher, D. & Tarascon, J. M. Towards greener and more sustainable batteries for electrical energy storage. Chem. 7, 19–29 (2015). Lu, Z. & Dahn, J. R. In Situ X-Ray Diffraction Study of P2-Na2/3Ni1/3Mn2/3O2. Electrochem. Soc. 148, A1225 (2001) Delmas, C., Fouassier, C. & Hagenmuller, P. Structural classification and properties of the layered oxides. B+C. 99, 81 – 85 (1980) Stansby, J. H., Sharma, N. & Goonetilleke, D. Probing the charged state of layered positive electrodes in sodium-ion batteries: Reaction pathways, stability and opportunities. J. Mater. Chem. A 8, 24833–24867 (2020) Muraligantha T, Murugan A. V, Manthiram A. Facile synthesis of carbon-decorated single-crystalline Fe3O4 nanowires and their application as high performance anode in lithium ion batteries. Commun. 7360 – 7362 (2009) Sun Y, Liu N, Cui Y. Promises and challenges of nanomaterials for lithium-based rechargeable batteries. Nature Energy. 1, 16071 (2016)
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Imamaliyeva, Samira Zakir. "New Thallium Tellurides with Rare Earth Elements." Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases 22, no. 4 (2020): 460–65. http://dx.doi.org/10.17308/kcmf.2020.22/3117.
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Compounds of the Tl4LnTe3 (Ln-Nd, Sm, Tb, Er, Tm) composition were synthesized by the direct interaction of stoichiometric amounts of thallium telluride Tl2Te elementary rare earth elements (REE) and tellurium in evacuated (10-2 Pa) quartz ampoules. The samples obtained were identified by differential thermal and X-ray phase analyses. Based on the data from the heating thermograms, it was shown that these compounds melt with decomposition by peritectic reactions. Analysis of powder diffraction patterns showed that they were completely indexed in a tetragonal lattice of the Tl5Te3 type (space group I4/mcm). Using the Le Bail refinement, the crystal lattice parameters of the synthesized compounds were calculated.It was found that when the thallium atoms located in the centres of the octahedra were substituted by REE atoms, there occurred a sharp decrease in the а parameter and an increase in the с parameter. This was due to the fact that the substitution of thallium atoms with REE cations led to the strengthening of chemical bonds with tellurium atoms. This was accompanied by some distortion of octahedra and an increase in the с parameter. A correlation between the parameters of the crystal lattices and the atomic number of the lanthanide was revealed: during the transition from neodymium to thulium, therewas an almost linear decrease in both parameters of the crystal lattice, which was apparently associated with lanthanide contraction. The obtained new compounds complement the extensive class of ternary compounds - structural analogues of Tl5Te3 and are of interest as potential thermoelectric and magnetic materials.
 
 
 
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Norouzi, Nazgol, Darrell Omo-Lamai, Timofey Averianov, Farbod Alimohammadi, and Ekaterina Pomerantseva. "Molybdenum Oxide/Dopamine-Derived Carbon Electrodes with Enhanced Electrochemical Activity in Energy Storage Systems." ECS Meeting Abstracts MA2022-02, no. 2 (2022): 137. http://dx.doi.org/10.1149/ma2022-022137mtgabs.
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Herein, a versatile sol-gel reaction produces new electrode materials consisting of tightly integrated molybdenum oxide and carbon derived from chemically incorporated dopamine molecules, and the materials show enhanced electrochemical activity in nonaqueous Li-ion and aqueous Zn-ion energy storage systems. The novel synthesis entails the oxidation of molybdenum in aqueous solutions of excess and limited dopamine (Dopa) hydrochloride via a hydrogen peroxide-initiated process. The transformation of molybdenum under the condition of Dopa excess (Mo:Dopa molar ratio of 1:1) resulted in the formation of a metastable precipitate of polydopamine (PDopa) spheres encapsulated by Dopa-preintercalated molybdenum oxide, (Dopa)xMoOy@PDopa. Hydrothermal treatment (HT) of (Dopa)xMoOy@PDopa precursor was concomitant with concurrent Dopa carbonization and molybdenum reduction processes, resulting in a formation of spherical matrices of Dopa-derived carbon decorated by MoO2 nanoplatelets (HT-MoO2/C), as determined through FTIR spectroscopy, Raman spectroscopy, and SEM imaging. Annealing (An) of HT-MoO2/C at 600°C under argon atmosphere (AnHT-MoO2/C) led not only to improvements in MoO2 crystallinity, but also to an increased oxidation state of molybdenum and a facilitated interaction between molybdenum-based and Dopa-derived components, resulting in an intimate MoO2/C heterointerface. Consequently, while both HT-MoO2/C and AnHT-MoO2/C showed reversible intercalation-type behavior when evaluated as electrodes versus Li/Li+ in nonaqueous lithium-ion cells, AnHT-MoO2/C demonstrated higher capacities, enhanced capacity retention, better rate capability, and lower charge transfer resistance. The AnHT-MoO2/C electrode showed an initial specific capacity of 260 mAh/g and 67% capacity retention after 50 cycles at 10 mA/g, compared to an initial specific capacity of 235 mAh/g and 47% capacity retention shown by HT-MoO2/C at the same current density. Furthermore, in rate capability experiments, HT-MoO2/C and AnHT-MoO2/C delivered specific capacities of 93 mAh/g and 120 mAh/g respectively at 100 mA/g. When molybdenum was transformed in the presence of Dopa deficit (Mo:Dopa molar ratio of 5:1), a (Dopa)xMoOy powder precursor was isolated, and subsequent hydrothermal treatment of this precursor produced an MoO3 material with carbonized Dopa molecules, HT-MoO3/C. Reference α-MoO3 electrodes (α-MoO3-ref) were synthesized similarly but in the absence of Dopa molecules in the initial sol-gel reaction. The appearance of characteristic D and G bands in the Raman spectra and distinct vibrational modes in the FTIR spectra of HT-MoO3/C confirmed the presence of carbon in its structure. SEM images showed a uniform nanobelt morphology with fragmentation due to interactions between interlayer Dopa and MoO3 layers under the conditions of hydrothermal treatment. HT-MoO3/C delivered a second-cycle capacitance of 141.4 F/g when cycled at 2 mV/s in a -0.25–0.70 V versus Ag/AgCl potential window in 5M ZnCl2 electrolyte, while α-MoO3-ref delivered a nearly two-fold smaller second-cycle capacitance of 76.1 F/g under the same conditions. HT-MoO3/C also showed increased capacitance compared to α-MoO3-ref when cycled at increasing sweep rates up to 20 mV/s. The superior performance of HT-MoO3/C prompted a study of the electrode in an expanded potential window, based on previous reports in which MoO3 showed electrochemical activity at negative potentials versus Ag/AgCl. The HT-MoO3/C electrode exhibited a capacitance of 347.6 F/g on the second cycle when cycled between -0.85–1.00V versus Ag/AgCl at 2 mV/s in 5M ZnCl2 electrolyte. This work demonstrates a new strategy to improve the electrochemical performance of transition metal oxide electrodes for next-generation energy storage systems. Integration of oxides with carbon through the wet chemistry synthesis approaches that involve carbonization of organic molecules can be used to control oxide crystal phase and heterointerfaces leading to improved charge transfer and energy storage properties.
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Ye, Xubin, Jianfa Zhao, Hena Das, et al. "Observation of novel charge ordering and spin reorientation in perovskite oxide PbFeO3." Nature Communications 12, no. 1 (2021). http://dx.doi.org/10.1038/s41467-021-22064-9.
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AbstractPbMO3 (M = 3d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6s and transition metal 3d orbitals. However, the detailed structure and physical properties of PbFeO3 remain unclear. Herein, we reveal that PbFeO3 crystallizes into an unusual 2ap × 6ap × 2ap orthorhombic perovskite super unit cell with space group Cmcm. The distinctive crystal construction and valence distribution of Pb2+0.5Pb4+0.5FeO3 lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb2+ and Pb4+) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a-axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b-axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe3+ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature.
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Lyubutin, Igor S., Alexander G. Gavriliuk, and Viktor Struzhkin. "Magnetic Collapse and Insulator-Metal Transitions in Some 3D Metal Oxides Under High Pressures." MRS Proceedings 987 (2006). http://dx.doi.org/10.1557/proc-987-0987-pp05-05.
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AbstractIn the systems with strong electron correlations, many theories predict the high-pressure-induced dielectric-metal transition, which is followed by collapse of localized magnetic moment and structural phase transition. In this report, summary results of many last experiments on the influence of high pressure on the magnetic and crystal structure as well on the electronic and transport properties of 3d metal oxides is presented. Along with X-ray diffraction, optical absorption, Raman scattering and electroresistivity measurements, several synchrotron radiation techniques have also been applied to perform the high-pressure experiments with compound iron oxides having different crystal structures.
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Yamaura, Jun-ichi, and Zenji Hiroi. "Crystal structure and magnetic properties of the 5d transition metal oxides AOsO4(A=K,Rb,Cs)." Physical Review B 99, no. 15 (2019). http://dx.doi.org/10.1103/physrevb.99.155113.
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Kumar, Harish, Matthias Köpf, A. Ullrich, M. Klinger, Anton Jesche, and Christine A. Kuntscher. "Fluorite-related iridate Pr3IrO7: Crystal growth, structure, magnetism, thermodynamic, and optical properties." Journal of Physics: Condensed Matter, October 13, 2022. http://dx.doi.org/10.1088/1361-648x/ac9a26.
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Abstract Spin-orbit coupling in heavy 5$d$ metal oxides, in particular, iridates have received tremendous interest in recent years due to the realization of exotic electronic and magnetic phases. Here, we report the synthesis, structural, magnetic, thermodynamic, and optical properties of the ternary iridate Pr$_3$IrO$_7$. Single crystals of Pr$_3$IrO$_7$ have been grown by the KF flux method. Structural analysis shows that Pr$_3$IrO$_7$ crystallizes in an orthorhombic phase with $Cmcm$ symmetry. The electron energy loss spectroscopy study indicates that Pr is in a 3+ valence state, which implies a 5+ oxidation state of Ir. Magnetization data measured at high and low magnetic fields do not exhibit any bifurcation between $M_{ZFC}$ and $M_{FC}$, however, a weak hump in $M(T)$ is observed at $T^*$$\sim$10.4~K. The specific heat data reveal two maxima at $\sim$253 K and $\sim$4.8 K. The optical conductivity $\sigma_1(\omega)$ spectrum shows 26 infrared-active phonon modes and reveals an insulating behavior with an optical gap $\Delta_{OP}$ of size $\sim$500~meV. During cooling down, the temperature-dependent reflectivity spectrum reveals seven extra phonon modes below the structural phase transition ($\sim$ 253 K). An anomaly is observed at around $T^*$ in the temperature evolution of infrared-active mode frequencies suggesting the presence of significant spin-phonon coupling in the system.
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Nenoff, Tina M., Nancy B. Jackson, William T. A. Harrison, Steven G. Thoma, and Steven D. Kohler. "Mixed-Metal Templated Phosphate Phases." MRS Proceedings 432 (1996). http://dx.doi.org/10.1557/proc-432-309.
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AbstractIn an effort to direct the structure formation and subsequently the catalytic properties of novel materials, both organic molecules and transition metals have been systematically incorporated into zinc phosphate materials, and various transition metals into zirconium phosphate materials. The resultant phases in the Zn/P experiments are determined not by the organic template, but by the type and stoichiometric amount of metal incorporated and by the organic template's anion. Furthermore, only one of the phases, a Ni/Zn/P, shows any acidic catalytic behavior. Similarly, the transition metals incorporated in stoichiometric amounts into the catalytically active novel zirconium phosphate are highly structure directing. Their presence inhibits the formation of the phosphate phase, instead promoting the formation of tetragonal ZrO2. The catalytic activity of the products are greatly diminished from the baseline material.The synthesis and characterization methods for each phase will be presented. Characterization techniques employed include single-crystal and powder X-ray diffraction, magnetic susceptibility, thermal analysis, DCP and FTIR.
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Lu, Qiyang, Changhee Sohn, Guoxiang Hu, et al. "Metal–insulator transition tuned by oxygen vacancy migration across TiO2/VO2 interface." Scientific Reports 10, no. 1 (2020). http://dx.doi.org/10.1038/s41598-020-75695-1.
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Abstract Oxygen defects are essential building blocks for designing functional oxides with remarkable properties, ranging from electrical and ionic conductivity to magnetism and ferroelectricity. Oxygen defects, despite being spatially localized, can profoundly alter global properties such as the crystal symmetry and electronic structure, thereby enabling emergent phenomena. In this work, we achieved tunable metal–insulator transitions (MIT) in oxide heterostructures by inducing interfacial oxygen vacancy migration. We chose the non-stoichiometric VO2-δ as a model system due to its near room temperature MIT temperature. We found that depositing a TiO2 capping layer on an epitaxial VO2 thin film can effectively reduce the resistance of the insulating phase in VO2, yielding a significantly reduced ROFF/RON ratio. We systematically studied the TiO2/VO2 heterostructures by structural and transport measurements, X-ray photoelectron spectroscopy, and ab initio calculations and found that oxygen vacancy migration from TiO2 to VO2 is responsible for the suppression of the MIT. Our findings underscore the importance of the interfacial oxygen vacancy migration and redistribution in controlling the electronic structure and emergent functionality of the heterostructure, thereby providing a new approach to designing oxide heterostructures for novel ionotronics and neuromorphic-computing devices.
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Lee, Sang A., Hoidong Jeong, Sungmin Woo, et al. "Phase transitions via selective elemental vacancy engineering in complex oxide thin films." Scientific Reports 6, no. 1 (2016). http://dx.doi.org/10.1038/srep23649.
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Abstract Defect engineering has brought about a unique level of control for Si-based semiconductors, leading to the optimization of various opto-electronic properties and devices. With regard to perovskite transition metal oxides, O vacancies have been a key ingredient in defect engineering, as they play a central role in determining the crystal field and consequent electronic structure, leading to important electronic and magnetic phase transitions. Therefore, experimental approaches toward understanding the role of defects in complex oxides have been largely limited to controlling O vacancies. In this study, we report on the selective formation of different types of elemental vacancies and their individual roles in determining the atomic and electronic structures of perovskite SrTiO3 (STO) homoepitaxial thin films fabricated by pulsed laser epitaxy. Structural and electronic transitions have been achieved via selective control of the Sr and O vacancy concentrations, respectively, indicating a decoupling between the two phase transitions. In particular, O vacancies were responsible for metal-insulator transitions, but did not influence the Sr vacancy induced cubic-to-tetragonal structural transition in epitaxial STO thin film. The independent control of multiple phase transitions in complex oxides by exploiting selective vacancy engineering opens up an unprecedented opportunity toward understanding and customizing complex oxide thin films.
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Nallagatla, Venkata Raveendra, Harisankar Sasindra, Hyoung Gyun Kim, et al. "Graphene Quantum Dots as an Oxygen Reservoir for Topotactic Phase Transition‐Based Memristive Devices." Advanced Electronic Materials, August 22, 2023. http://dx.doi.org/10.1002/aelm.202300401.
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AbstractA novel class of transition metal oxides, capable of reversible topotactic phase transition between the oxygen‐deficient brownmillerite and oxygen‐rich perovskite, has emerged as a promising material for memristive and magnetoelectric devices. However, the absence of a local oxygen source in the device structure necessitates an oxygen exchange process between the surrounding atmosphere and the switching layer during operation, which can lead to unreliable device performance. In this study, graphene quantum dots (GQDs) are introduced into a SrFe0.5Co0.5Ox memristive device as an oxygen reservoir for the nanoscale topotactic redox process. The SrFe0.5Co0.5Ox memristive devices with GQDs exhibit reliable resistive switching performance compared to SrFe0.5Co0.5Ox devices without GQDs. To understand the effect of GQDs on the device structure, a pulse endurance test is carried out in a high vacuum. The devices with GQDs show rather good endurance behavior, while devices without GQDs exhibit endurance failure. These results provide a deeper understanding of the potential use of GQDs in enhancing the performance of SrFe0.5Co0.5Ox memristive devices, with implications for tuning nanoscale topotactic phase transition for multi‐functional properties.
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Blanchet, Miles D., Bethany E. Matthews, Steven R. Spurgeon, Steve M. Heald, Tamara Isaacs-Smith, and Ryan B. Comes. "Jahn–Teller-driven phase segregation in MnxCo3−xO4 spinel thin films." Journal of Vacuum Science & Technology A 41, no. 5 (2023). http://dx.doi.org/10.1116/6.0002329.
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Transition metal spinel oxides comprised of earth-abundant Mn and Co have long been explored for their use in catalytic reactions and energy storage. However, understanding functional properties can be challenging due to differences in sample preparation and the ultimate structural properties of the materials. Epitaxial thin film synthesis provides a novel means of producing precisely controlled materials to explore the variations reported in the literature. In this work, MnxCo3−xO4 samples from x = 0 to x = 1.28 were synthesized through molecular beam epitaxy and characterized to develop a material properties map as a function of stoichiometry. Films were characterized via in situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, and polarized K-edge x-ray absorption spectroscopy. Mn cations within this range were found to be octahedrally coordinated, in line with an inverse spinel structure. Samples largely show mixed Mn3+ and Mn4+ character with evidence of phase segregation tendencies with the increasing Mn content and increasing Mn3+ formal charge. Phase segregation may occur due to structural incompatibility between cubic and tetragonal crystal structures associated with Mn4+ and Jahn–Teller active Mn3+ octahedra, respectively. Our results help in explaining the reported differences across samples in these promising materials for renewable energy technologies.
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Muneta, Iriya, Takanori Shirokura, Pham Nam Hai, Kuniyuki Kakushima, Kazuo Tsutsui, and Hitoshi Wakabayashi. "Ferromagnetism modulation by ultralow current in a two-dimensional polycrystalline molybdenum disulphide atomic layered structure." Scientific Reports 12, no. 1 (2022). http://dx.doi.org/10.1038/s41598-022-22113-3.
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AbstractLayered materials, such as graphene and transition metal dichalcogenides, are able to obtain new properties and functions through the modification of their crystal arrangements. In particular, ferromagnetism in polycrystalline MoS2 is of great interest because the corresponding nonmagnetic single crystals exhibit spontaneous spin splitting only through the formation of grain boundaries. However, no one has reported direct evidence of this unique phenomenon thus far. Herein, we demonstrate ferromagnetism modulation by an ultralow current density < 103 A/cm2 in 7.5-nm-thick polycrystalline MoS2, in which magnetoresistance shows three patterns according to the current intensity: wide dip, nondip and narrow dip structures. Since magnetoresistance occurs because of the interaction between the current of 4d electrons in the bulk and localized 4d spins in grain boundaries, this result provides evidence of the current modulation of ferromagnetism induced by grain boundaries. Our findings pave the way for the investigation of a novel method of magnetization switching with low power consumption for magnetic random access memories.
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Takeda, Airi, Hidenori Hiraoka, Kota Nakamura, et al. "Polyol Synthesis of Ni and Fe Co-Incorporated Tungsten Oxide for Highly Efficient and Durable Oxygen Evolution Reaction." Journal of The Electrochemical Society, July 8, 2022. http://dx.doi.org/10.1149/1945-7111/ac7fbe.
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Abstract The development of inexpensive transition metal-based catalysts for water splitting has attracted global attention, which should be accomplished in the simplest and most scalable way feasible. In this study, nickel and iron co-incorporated tungsten oxides (NixFe1-xWO4) were synthesized using a simple polyol method, and the materials achieved a highly efficient and stable oxygen evolution reaction (OER) in an alkaline electrolyte. The product as-synthesized using the polyol method consisted of an undeveloped wolframite structure, which was converted to its complete crystal by heat treatment at 600°C, with an increase in crystallite size. The OER properties of NixFe1-xWO4 could be controlled by the ratio of Ni and Fe present and heat treatment temperature. A ternary tungsten oxide (Ni0.5Fe0.5WO4) with a Ni:Fe:W molar ratio of 0.5:0.5:1 deposited on a glassy carbon electrode required 297 mV to reach a current density of 10 mA cm−2 in 1.0 M KOH solution. The 10 mA cm−2 electrolysis with the electrode was continued for at least 100 h. This was quite different from a similarly-synthesized NiFe oxide without W, which required an additional 47-mV overpotential to reach 10 mA cm−2 and had inferior durability.