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Journal articles on the topic 'Tetragonal Tungsten Bronzes (TTB)'

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Published: 22 June 2023

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1

Abdullah, A. M., T. Debnath, C. H. Rüscher, and A. Hussain. "Synthesis and Characterization of Vanadium Substituted Potassium Tungsten Bronzes, K_xV_yW_1-yO₃." Journal of Scientific Research 4, no. 2 (April 27, 2012): 507. http://dx.doi.org/10.3329/jsr.v4i2.9349.

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A series of vanadium substituted potassium hexagonal tungsten bronzes KxVyW1-yO3 (K-HTB) were prepared by conventional solid state method at 800 °C with compositions of x = 0.30 and 0.00 ? y ? 0.15. A mixture of K-HTB and non bronze phases with y ? 0.20 was observed. The proportion of this non bronze phase increases with increasing vanadium content. The non bronze phases in the mixture could not be indexed yet. In contrast, a very small amount of vanadium can be substituted in potassium tetragonal tungsten bronzes (K-TTB) at 800 °C with x = 0.50 and 0.00 ? y ? 0.02, however at 700 °C vanadium substituted K-TTB can be prepared with 0.00 ? y ? 0.05. Further substitution of vanadium in K-TTB decomposes to K-HTB and non-bronze phases. Keywords: Tungsten bronzes; Vanadium substituted bronze; Bronzoids. © 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi: http://dx.doi.org/10.3329/jsr.v4i2.9349 J. Sci. Res. 4 (2), 507-514 (2012)

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2

RAVEAU, B., M. M. BOREL, A. LECLAIRE, and A. GRANDIN. "NIOBIUM PHOSPHATE BRONZES — STRUCTURAL RELATIONSHIPS WITH PURE OCTAHEDRAL OXYGEN TUNGSTEN BRONZES." International Journal of Modern Physics B 07, no. 23n24 (October 30, 1993): 4109–43. http://dx.doi.org/10.1142/s0217979293003590.

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The phosphate niobium bronzes form a large family of structures characterized by pentagonal or hexagonal tunnels. The host lattices of these oxides, involving a mixed valency of niobium Nb(V)-Nb(IV) are described here. The close relationships with pure octahedral structures, mainly perovskites, hexagonal tungsten bronzes (HTB) and tetragonal tungsten bronzes (TTB), and K 3 Nb 8 O 21 are studied.

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3

Whittle, Thomas A., Siegbert Schmid, and Christopher J. Howard. "Octahedral tilting in the tungsten bronzes." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 71, no. 3 (May 29, 2015): 342–48. http://dx.doi.org/10.1107/s2052520615008252.

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Possibilities for `simple' octahedral tilting in the hexagonal and tetragonal tungsten bronzes (HTB and TTB) have been examined, making use of group theory as implemented in the computer programISOTROPY. For HTB, there is one obvious tilting pattern, leading to a structure in space groupP63/mmc. This differs from the space groupP63/mcmfrequently quoted from X-ray studies – these studies have in effect detected only displacements of the W cations from the centres of the WO6octahedra. The correct space group, taking account of both W ion displacement and the octahedral tilting, isP6322 – structures in this space group and matching this description have been reported. A second acceptable tilting pattern has been found, leading to a structure inP6/mmmbut on a larger `2 × 2 × 2' unit cell – however, no observations of this structure have been reported. For TTB, a search at the special points of the Brillouin zones revealed only one comparable tilting pattern, in a structure with space-group symmetryI4/mon a `21/2 × 21/2by 2' unit cell. Given several literature reports of larger unit cells for TTB, we conducted a limited search along the lines of symmetry and found structures with acceptable tilt patterns inBbmmon a `21/22 × 21/2 × 2' unit cell. A non-centrosymmetric version has been reported in niobates, inBbm2 on the same unit cell.

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4

Smirnov, M., and P. Saint-Grégoire. "Unified approach for determining tetragonal tungsten bronze crystal structures." Acta Crystallographica Section A Foundations and Advances 70, no. 3 (April 1, 2014): 283–90. http://dx.doi.org/10.1107/s2053273314003994.

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Tetragonal tungsten bronze (TTB) oxides are one of the most important classes of ferroelectrics. Many of these framework structures undergo ferroelastic transformations related to octahedron tilting deformations. Such tilting deformations are closely related to the rigid unit modes (RUMs). This paper discusses the whole set of RUMs in an ideal TTB lattice and possible crystal structures which can emerge owing to the condensation of some of them. Analysis of available experimental data for the TTB-like niobates lends credence to the obtained theoretical predictions.

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5

Shakil, Md Mahbubur R., Tapas Debnath, Claus H. Ruscher, and Altaf Hussain. "Study of Tantalum Substituted Potassium Tungsten Bronzes." Journal of the Bangladesh Chemical Society 25, no. 1 (September 3, 2012): 38–45. http://dx.doi.org/10.3329/jbcs.v25i1.11770.

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A series of compounds KxTayW1-yO3 with x = 0.30, 0.00 ? y ? 0.30 and x = 0.55, 0.00 ? y ? 0.10 were synthesized by conventional solid-state method. The samples were characterized using XRD and FTIR spectroscopy. X-ray powder patterns reveal that the samples with compositions x = 0.30, y ? 0.30 show hexagonal tungsten bronze (HTB) type phase and the samples with x = 0.55, 0.02 ? y ? 0.10 show a mixture of two phases (K-HTB and tetragonal potassium tungsten bronze, K-TTB). The samples of the system, K0.30TayW1-yO3 with 0.00 ? y ? 0.15 shows no significant change in the cell parameters. However, for the composition y > 0.15, the cell parameter a decreases and c increases with increasing Ta content, which may be explained by the ordering of Ta for y > 0.15 suggesting the transformation to another space group. The appearance of absorption peak in the infrared absorption spectra of K0.3TayW1-yO3, y > 0.10 samples indicate the transition to non-metallic phase. DOI: http://dx.doi.org/10.3329/jbcs.v25i1.11770 Journal of Bangladesh Chemical Society, Vol. 25(1), 38-45, 2012

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Bursill, L. A., J. L. Peng, B. Jiang, and X. Li. "Crystal Structure of Red Lead Titanate Thin Films." Modern Physics Letters B 11, no. 26n27 (November 20, 1997): 1181–87. http://dx.doi.org/10.1142/s0217984997001419.

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Orange-red lead titanate thin films are examined by high-resolution transmission electron microscopy and diffraction. It is remarkable that the structure is based on that of tetragonal-tungsten-bronze (TTB) rather than perovskite-type. The chemical basis for this result is examined, it is deduced that the TTB structure is stabilized by inclusion of hydroxyl ions during synthesis by a sol–gel route involving hydrolysis of n-Butyl titanate.

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7

Krumeich, Frank. "On the Arrangement of Pentagonal Columns in Tetragonal Tungsten Bronze-Type Nb18W16O93." Crystals 11, no. 12 (December 5, 2021): 1514. http://dx.doi.org/10.3390/cryst11121514.

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The evaluation of HAADF-STEM images of a sample with the composition Nb18W16O93 provided new insights into its real structure. The basic structure comprises an intact octahedral framework of the tetragonal tungsten bronze (TTB) type. The partial occupation of the pentagonal tunnels (PT) by metal–oxygen strings determines the oxygen-to-metal ratio (O/ΣM with M = Nb,W). For a large area, the O/ΣM was determined to be 2.755, which is bigger than the value of Nb18W16O93, which is O/ΣM = 2.735. To a large extent, the three-fold TTB superstructure of Nb8W9O47 with a high oxygen content is present (O/ΣM = 2.765). In addition, a new four-fold TTB superstructure was found in small domains. Nb12W11O63 with an O/ΣM = 2.739 obviously accommodates part of the sample’s metal excess compared to the stable phase Nb8W9O47.

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8

Krumeich, F. "Order and Disorder in Niobium Tungsten Oxides of the Tetragonal Tungsten Bronze Type." Acta Crystallographica Section B Structural Science 54, no. 3 (June 1, 1998): 240–49. http://dx.doi.org/10.1107/s010876819701971x.

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Two superstructures of the TTB type (tetragonal tungsten bronze) exist in the system Nb2O5/WO3. They are caused by an ordered arrangement of pentagonal tunnels filled with metal–oxygen strings. Besides the well known 4:9 phase (Nb8W9O47), which has a tripled b axis, evidence for a new orthorhombic structure, Nb6W8O39 (a = b = 27.3 Å), has been found. The oxidation products of Nb7W10O47 and Nb4W13O47 frequently comprise less-ordered arrangements of filled tunnels, causing diffuse scattering. In Nb7W10O47.5 the electron diffraction patterns (along [001]) of many crystal fragments show circular diffuse scattering, which appears around the main reflections of the TTB substructure with two distinct radii (r*). r* \simeq 0.33a* indicates the predominance of 4:9-type domains, whereas r* \simeq 0.41a* corresponds to Nb6W8O39. In Nb4W13O49 the diffuse scattering pattern is cross-shaped; this is due to the presence of long slabs of diamond-linked pentagonal columns. Structure models for these particular states of order have been derived from high-resolution transmission electron microscopy images. Some general principles for the formation of the different arrangements are deduced. Apparently, two distinct types of link between the filled pentagonal tunnels are important features which lead to the stability of these structures.

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9

Namikuchi, Eliane Ayumi, Marcos Augusto Lima Nobre, and Silvania Lanfredi. "Selective Occupancy of Sites by Rare Earths in K₂Nd_(1-X)Eu_xNb₅O₁₅ Nanopowders, where X = 0, 0.0025, 0.025, 0.05 and 0.1, Prepared by Modified Polyol Method." Materials Science Forum 820 (June 2015): 361–66. http://dx.doi.org/10.4028/www.scientific.net/msf.820.361.

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Niobates with tetragonal tungsten bronze TTB-type structure have presented great technological potential due to their dielectric, ferroelectric, pyroelectric properties. The preparation by the modified polyol method and structural characterization of K2Nd(1-x)EuxNb5O15 nanopowders, where x = 0; 0.0025; 0.025; 0.05 e 0.1, were investigated. The structural parameters were analyzed as a function of concentration of europium ions in the K2NdNb5O15 host structure using the Rietveld method. From structural parameters was determined the TTB-type structure with tetragonal symmetry, where the pentagonal sites is occupied by K+ and Eu3+ ions and tetragonal sites is occupied only by Nd3+ ions. The addition of europium in the host structure led to a decrease in the lattice parameters, compatible with the increasing degree of distortion of NbO6 polyhedra. The average crystallite size showed values between 18.25 and 26nm.

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10

Graetsch, Heribert A., Chandra Shehkar Pandey, Jürgen Schreuer, Manfred Burianek, and Manfred Mühlberg. "Incommensurate modulations of relaxor ferroelectric Ca0.24Ba0.76Nb2O6(CBN24) and Ca0.31Ba0.69Nb2O6(CBN31)." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 70, no. 4 (July 31, 2014): 743–49. http://dx.doi.org/10.1107/s2052520614011676.

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CBN crystals show a one- and a two-dimensionally modulated modification. The former is isotypic with orthorhombic Ba4Na2Nb10O30and the latter with the tetragonal tungsten bronze type of crystal structure. The orthorhombic form irreversibly transforms to the tetragonal polymorph at the ferroelectric phase transition near 603 K. Orthorhombic and tetragonal CBN24 slightly differ in the distribution of the Ba and Ca atoms over the incompletely filled Me1 and Me2 sites. The tetragonal symmetry is further broken in orthorhombic CBN24 by different amplitudes of the positional modulations of O atoms which are symmetrically equivalent in the TTB structure. A similar orthorhombic phase of CBN31 could be obtained by quenching from 1473 K.

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11

Drathen, Christina, Kirill Yusenko, and Serena Margadonna. "Structural modulations in multiferroic tetragonal tungsten bronze KxMnxFe1+xF3." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C52. http://dx.doi.org/10.1107/s2053273314099471.

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Multiferroic materials showing coupling of the different order parameters (ferroelectric, ferromagnetic, ferroelastic) are interesting not only from a fundamental perspective, but also from a technological point of view, e.g. for to the development of new storage technologies. However, the coexistence of (ferro)magnetism and ferroelectricity is considered a rare phenomenon. Whilst this may be true for perovskite oxides, where emptyd-shells favor the off-centering of ions but counteract magnetism, this intrinsic limitation can be avoided by moving to different structure types, and/or away from oxides. An example of non-perovskite, non-oxide multiferroic systems are the tetragonal tungsten bronze (TTB) fluorides KxM2+xM3+1+xF3(x= 0.4 – 0.6), which show coexistence of electric and magnetic ordering 1. Here we present a detailed structural study on a series of TTB fluorides, KxMnxFe1+xF3(x = 0.4 – 0.55). KMnFeF6has been previously described as tetragonalP42bcand orders ferrimagnetically belowT = 148 K 2. Additional satellite reflections were found in transmission electron microscopy experiments and attributed to ferroelastic domains arising from tilting ofMF6octahedra, but the reported bulk powder XRD measurements indicated only tetragonal symmetry 3. We used high-resolution powder diffraction techniques to reinvestigate the crystal structure as a function of temperature in comparison with DSC data. Our results reveal a structural distortion to orthorhombic symmetry (Ccc2) at room temperature, which diminished when moving to the end members of the series (x → 0.4 andx → 0.6). Although structurally subtle, this distortion may indicate a ferroelectric state, similar to KxFeF3, where ferroelectricity is observed only in the orthorhombic phase. On heating, an anomaly in thec-axis lattice parameter accompanies a phase transition to centrosymmetricP42/mbcaround 320 – 350 K, marking the transition from ferroelectric – paraelectric state.

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12

Krumeich, Frank. "Intergrowth of niobium tungsten oxides of the tetragonal tungsten bronze type." Zeitschrift für Naturforschung B 75, no. 11 (November 26, 2020): 913–19. http://dx.doi.org/10.1515/znb-2020-0107.

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AbstractSince the 1970s, high-resolution transmission electron microscopy (HRTEM) is well established as the most appropriate method to explore the structural complexity of niobium tungsten oxides. Today, scanning transmission electron microscopy (STEM) represents an important alternative for performing the structural characterization of such oxides. STEM images recorded with a high-angle annular dark field (HAADF) detector provide not only information about the cation positions but also about the distribution of niobium and tungsten as the intensity is directly correlated to the local scattering potential. The applicability of this method is demonstrated here for the characterization of the real structure of Nb7W10O47.5. This sample contains well-ordered domains of Nb8W9O47 and Nb4W7O31 besides little ordered areas according to HRTEM results. Structural models for Nb4W7O31 and twinning occurring in this phase have been derived from the interpretation of HAADF-STEM images. A remarkable grain boundary between well-ordered domains of Nb4W7O31 and Nb8W9O47 has been found that contains one-dimensionally periodic features. Furthermore, short-range order observed in less ordered areas could be attributed to an intimate intergrowth of small sections of different tetragonal tungsten bronze (TTB) based structures.

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13

SHEN, Chao, Sai-nan JIANG, Cui-min DING, Wei-shun XUE, and Ke-yu XIE. "Lithium-ion diffusion path of tetragonal tungsten bronze (TTB) phase Nb18W16O93." Transactions of Nonferrous Metals Society of China 32, no. 11 (November 2022): 3679–86. http://dx.doi.org/10.1016/s1003-6326(22)66048-5.

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14

Oualla, M., A. Zegzouti, M. Elaatmani, M. Daoud, D. Mezzane, Y. Gagou, and P. Saint-Grégoire. "New Gadolinium Based Ferroelectric Phases Derived from the Tetragonal Tungsten Bronze (TTB)." Ferroelectrics 291, no. 1 (January 2003): 133–39. http://dx.doi.org/10.1080/00150190390222628.

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15

de Lima, Caio Vinicius, Marcos Augusto Lima Nobre, and Silvania Lanfredi. "Changing of the Spontaneous Polarization in Niobate Nanoparticles Induced by Non Isovalent Doping." Materials Science Forum 820 (June 2015): 367–72. http://dx.doi.org/10.4028/www.scientific.net/msf.820.367.

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Ferroelectric niobates with tetragonal tungsten bronze TTB-type structure have shown great technology interest for application in pyroelectric detectors and piezoelectric transducers, sensor/filter in composite. The synthesis and structural characterization of the solid solution of iron doped potassium strontium niobate with stoichiometry KSr2(Fe0.25Nb4.75)O15-δ prepared by modified polyol method were carried out. The highest crystallinity was obtained for the precursor powder calcined at 1150oC for 10 hours in oxygen atmosphere. The structural characterization was performed by X-Ray diffraction. The average crystallite size obtained was equal to 25 nm. The structural parameters were determined by Rietveld method giving a tetragonal system with space group P4bm. The spontaneous polarization of the solid solution was calculated, being equal to 39.46 μC.cm-2. Polihedra distortion and its correlation with niobium off-center are discussed.

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de Lima, Caio Vinicius, Marcos Augusto Lima Nobre, and Silvania Lanfredi. "Dielectric Characterization at High Temperature of Iron Doped Potassium Strontium Niobate Ceramic by Impedance Spectroscopy." Materials Science Forum 820 (June 2015): 187–92. http://dx.doi.org/10.4028/www.scientific.net/msf.820.187.

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Tetragonal Tungsten Bronze structure TTB-type structure has attracted interest by the high anisotropy of the crystal structure. The dielectric characterization of iron-doped niobate of TTB-type structure, with stoichiometry KSr2(Fe0.25Nb4.75)O15-δ, prepared by Modified Polyol Method was investigated. Nanocrystalline single phase powders were obtained after calcination of the precursor powder at 1150 °C for 10 hours in an oxygen atmosphere. The dielectric characterization was performed by impedance spectroscopy, from room temperature to 600 °C, in the frequency range of 5 Hz to 13 MHz. The permittivity values obtained for KSr2(Fe0.25Nb4.75)O15-δshowed superior to the permittivity values of the KSr2Nb5O15host structure in all temperature range investigated. At room temperature, the permittivity values (2100) of KSr2(Fe0.25Nb4.75)O15-δis two times the permittivity values of KSr2Nb5O15. The substitution of niobium cation by iron cation in the KSr2Nb5O15host structure showed a suppression of the ferroelectric (P4bm)→paraelectric (P4/mbm) phase transition.

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Namikuchi, Eliane Ayumi, Ana Maria Pires, Marcos Augusto Lima Nobre, and Silvania Lanfredi. "Study of the Influence of Eu³⁺ Ions in the Bandgap of K₂NdNb₅O₁₅ Nanopowders." Materials Science Forum 820 (June 2015): 378–83. http://dx.doi.org/10.4028/www.scientific.net/msf.820.378.

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Ferroelectric semiconductors oxides with tetragonal tungsten bronze TTB-type structure doped with rare earth ions have been investigated in recent years due their promising optical properties. K2Nd(1-x)EuxNb5O15 nanopowders, where x = 0, 0.0025, 0.025, 0.05 and 0.1 were synthesized by the modified polyol method and characterized by X-ray diffraction and diffuse reflectance spectroscopy UV-Vis. Single phase and crystalline powders of tetragonal symmetry with non-centrosymmetric space group P4bm were obtained. The diffuse reflectance spectra were similar to the profile of a semiconductor material with the presence of thin transitions of Eu3+ in europium-doped K2NdNb5O15, as well as the transitions of Nd3+. The method of Kubelka-Munk was used for the estimation of bandgap energy. The values around 3.7 eV showed small variation with the concentration of Eu3+ ions in the K2NdNb5O15 host structure. The transitions were identified as direct ones type.

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Pugliese, G. M., F. G. Capone, L. Tortora, F. Stramaglia, L. Simonelli, C. Marini, Y. Kondoh, et al. "The Local Structure and Metal-Insulator Transition in a Ba3Nb5−xTixO15 System." Materials 15, no. 13 (June 22, 2022): 4402. http://dx.doi.org/10.3390/ma15134402.

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The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba3Nb5−xTixO15 (x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80–400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder.

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Es-soufi, Hicham, Hssain Bih, Lahcen Bih, Raman Rajesh, Alan Rogerio Ferreira Lima, M. I. Sayyed, and Rabih Mezher. "Rietveld Refinement, Structural Characterization, and Methylene Blue Adsorption of the New Compound Ba0.54Na0.46Nb1.29W0.37O5." Crystals 12, no. 12 (November 23, 2022): 1695. http://dx.doi.org/10.3390/cryst12121695.

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Using the solid-state process, the new compound Ba0.54Na0.46Nb1.29W0.37O5 was effectively produced in a single crystalline phase. The material’s characteristics were determined by X-ray diffraction and Raman techniques. The Rietveld method was applied to refine the structural properties of this sample using X-ray diffraction data and derive the diffraction line profile. The cell parameters a = b = 12.37843 ± 0.02 and c = 3.93526 ± 0.02 were accustomed to crystallizing this compound in the tetragonal tungsten bronze (TTB) structure of the space group P4bm. Thanks to Raman measurements, we were able to detect numerous vibration modes in this crystalline phase. The adsorption of methylene blue (MB) on crystalline phase was studied by UV–visible spectroscopy. On account of methylene blue adsorption on Ba0.54Na0.46Nb1.29W0.37O5, it was discovered that this material can be used to remove organic pollutants and thus be used for water treatment.

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Lee, Han-Young, and R. Freer. "High-Order Incommensurate Modulations and Incommensurate Superstructures in Transparent Sr0.6Ba0.4Nb2O6(SBN40) Ceramics." Journal of Applied Crystallography 31, no. 5 (October 1, 1998): 683–91. http://dx.doi.org/10.1107/s0021889898003550.

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Ceramics of strontium barium niobate (Sr0.6Ba0.4Nb2O6, SBN40), having the tetragonal tungsten bronze (TTB) structure, were prepared by a conventional processing route; sintering at temperatures in the range 1573–1723 K yielded products with three types of microstructure. Incommensurate superstructures were investigated by transmission electron microscopy (TEM). Modulation of the incommensurate superstructure (ICS) depended on microstructural development. The lowest-order ICS modulation was a common feature in all the SBN40 ceramics, regardless of microstructure. (h+1/2,h+1/2,l) reflections and unusually low δ (incommensurability parameter) were observed in SBN40 specimens having abnormally large grains and thus a certain degree ofA-site ordering was expected. Transparent SBN40 ceramics which exhibited large homogeneous grains were characterized by a shortenedcaxis, intense [001] X-ray diffraction reflections, a multiplication of (110) and (001) cell spacings and the appearance of higher-order ICS reflections. Planar defects, having the thickness of one d_{110} spacing, were observed aligned along \{110\}. The development of a higher-order structural modulation and of ICS reflections is believed to reduce the structural energy; the development of planar defects appears to stabilize the incommensurate phase.

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Yao, Y. B., C. L. Mak, and B. Ploss. "Phase transitions and electrical characterizations of (K0.5Na0.5)2x(Sr0.6Ba0.4)5−xNb10O30 (KNSBN) ceramics with ‘unfilled’ and ‘filled’ tetragonal tungsten–bronze (TTB) crystal structure." Journal of the European Ceramic Society 32, no. 16 (December 2012): 4353–61. http://dx.doi.org/10.1016/j.jeurceramsoc.2012.07.034.

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Rafiq, M. A., M. E. Costa, I. M. Reaney, and P. M. Vilarinho. "Transmission Electron Microscopy of Mn-doped KNN Ceramics." Microscopy and Microanalysis 19, S4 (August 2013): 99–100. http://dx.doi.org/10.1017/s1431927613001116.

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Smart materials like piezoelectrics and ferroelectrics play a crucial role in applications such assensors and actuators,radio-frequency switching, drug delivery, chemicals detection, and power generation and storage. K0.5Na0.5NbO3 (KNN) is one of the leading lead free piezoelectric materials being considered as an alternativeto Pb(Zrx,Ti1-x)O3 (PZT), which is currently the most widely used material for electromechanical applications. Although pure KNN has inferior electromechanical properties compared to PZT,efforts are on going to tailor and improve its piezoelectric coefficients by doping and texturing.Although the piezoelectric constant (d33) of undoped KNN is unsuitable for practical electromechanical applications, properties comparable to PZT at room temperature (d33>400 pC/N) have been reported for modified KNN ceramics. Electromechanical properties are however, very much dependent on the crystalline phase content, crystallographic orientation, microstructure, interfaces and domain configuration.Mn is an indispensable dopant for both PbO-based as well as PbO-free ceramics like BaTiO3, SrTiO3, KNbO3 and KTaO3. It has been reported to improve the density, mechanical quality factor, electromechanical properties and to reduce dielectric loss. Mn has been successfully used to reduce the leakage current and lower the orthorhombic to tetragonal phase transition temperature (TO-T) in KNN single crystals. It has also been shown to improve the density and properties of KNN–LiTaO3–LiSbO3. However, the effect of Mn on the KNN domain structure and phase assemblage has not yet been reported. In this work, KNN ceramics doped with Mn on the B-site (Mn content was 0.5, 1.0. 1.5 and 2 mole%) were synthesized by a conventional mixed oxide method. Transmission electron microscopy (TEM)(Hitachi 9000) studies were carried out to analyse the effect of B-site Mn doping on the ferroelectric domain structure and phase assemblage.Undoped KNN ceramics had large grains (>30 >m) which contained large (>1 >m wide) wedge shaped ferroelectric domains. KNN doped with 0.5 mole % Mn exhibited a smaller grain size (~2 mm) in which a well defined domain structure was observed with widths approximately an order of magnitude smaller than those in undoped KNN. For KNN doped with 2 mole % Mn, the presence of a second phase, Figure 1c, was often observed. Electron diffraction patterns from the second phase were consistent with a tetragonal tungsten bronze (TTB) structured compound although more work is required to definitively determine the phase assemblage. The domain structure became increasing complex as Mn concentration increased, suggesting that the presence of Mn on the B-site disrupts polar order.In conclusion, TEM analysis demonstrated that Mn doping changes the domain structure of KNN ceramics: for low Mn content, well defined ferroelectric domains and for high Mn content, tangled domains and second phase were the main features.These microstructure details elucidate reasons that may account for the inferior piezoelectric properties of KNN at higher Mn concentration.

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Kosov, A. V., O. L. Semerikova, S. V. Vakarin, A. A. Pankratov, S. V. Plaksin, and Yu P. Zaykov. "Formation of nanocrystalline tetragonal oxide tungsten bronzes on platinum." Russian Metallurgy (Metally) 2017, no. 2 (February 2017): 158–62. http://dx.doi.org/10.1134/s0036029517020070.

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24

Arnold, Donna C., and Finlay D. Morrison. "B-cation effects in relaxor and ferroelectric tetragonal tungsten bronzes." Journal of Materials Chemistry 19, no. 36 (2009): 6485. http://dx.doi.org/10.1039/b912535c.

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25

Botella, Pablo, Benjamín Solsona, José M. López Nieto, Patricia Concepción, Jose L. Jordá, and María Teresa Doménech-Carbó. "Mo–W-containing tetragonal tungsten bronzes through isomorphic substitution of molybdenum by tungsten." Catalysis Today 158, no. 1-2 (December 2010): 162–69. http://dx.doi.org/10.1016/j.cattod.2010.05.024.

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26

Miller, Andrew J., Andrei Rotaru, Donna C. Arnold, and Finlay D. Morrison. "Effect of local A-site strain on dipole stability in A6GaNb9O30 (A = Ba, Sr, Ca) tetragonal tungsten bronze relaxor dielectrics." Dalton Transactions 44, no. 23 (2015): 10738–45. http://dx.doi.org/10.1039/c4dt03936j.

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A series of isovalently A-site substituted relaxor dielectric tetragonal tungsten bronzes of general formula Ba_6−x−ySr_xCa_yGaNb₉O₃₀ were investigated.

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27

Heinrich, Christophe P., Matthias Schrade, Giacomo Cerretti, Ingo Lieberwirth, Patrick Leidich, Andreas Schmitz, Harald Fjeld, et al. "Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide." Materials Horizons 2, no. 5 (2015): 519–27. http://dx.doi.org/10.1039/c5mh00033e.

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Tetragonal tungsten bronzes Nb_8−xW_9+xO_47−δ allow a continuous variation of the charge carrier concentration while fulfilling the concept of a “phonon-glass electron-crystal” through intrinsic nanostructure.

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28

Ovchar, O., D. Durilin, A. Belous, V. Porokhonskyy, B. Jancar, and T. Kolodiazhnyi. "Tetragonal Tungsten Bronzes in Ba(M2+1/3Nb2/3)O3Microwave Ceramics." Ferroelectrics 435, no. 1 (January 2012): 176–82. http://dx.doi.org/10.1080/00150193.2012.740348.

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29

Rotaru, Andrei, Andrew J. Miller, Donna C. Arnold, and Finlay D. Morrison. "Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2009 (February 28, 2014): 20120451. http://dx.doi.org/10.1098/rsta.2012.0451.

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We discuss the strategy for development of novel functional materials with the tetragonal tungsten bronze structure. From the starting composition Ba 6 GaNb 9 O 30 , the effect of A- and B-site substitutions on the dielectric properties is used to develop an understanding of the origin and stability of the dipolar response in these compounds. Both tetragonal strain induced by large B-site cations and local strain variations created by isovalent A-site substitutions enhance dipole stability but result in a dilute, weakly correlated dipolar response and canonical relaxor behaviour. Decreasing cation size at the perovskite A2-site increases the dipolar displacements in the surrounding octahedra, but insufficiently to result in dipole ordering. Mechanisms introducing small A-site lanthanide cations and incorporation of A-site vacancies to induce ferroelectricity and magnetism are presented.

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30

Gardner, Jonathan, and Finlay D. Morrison. "A-site size effect in a family of unfilled ferroelectric tetragonal tungsten bronzes: Ba4R0.67Nb10O30 (R = La, Nd, Sm, Gd, Dy and Y)." Dalton Trans. 43, no. 30 (2014): 11687–95. http://dx.doi.org/10.1039/c4dt00126e.

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The structure of a family of ferroelectric unfilled tetragonal tungsten bronze oxides can be approximated to be metrically tetragonal allowing a simple correlation of tetragonality with Curie temperature.

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31

Aamlid, Solveig S., Sverre M. Selbach, and Tor Grande. "The Effect of Cation Disorder on Ferroelectric Properties of SrxBa1−xNb2O6 Tungsten Bronzes." Materials 12, no. 7 (April 10, 2019): 1156. http://dx.doi.org/10.3390/ma12071156.

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The versatile crystal structure of tetragonal tungsten bronzes (A12A24C4B10O30) can accommodate complex stoichiometries including cations in different valence states and vacant cation sites. Here, we report on the effect of thermally induced cation-vacancy disorder in the tetragonal tungsten bronze SrxBa1−xNb2O6 (SBNX). SBNX (x = 0.25, 0.33, 0.50, 0.61) ceramics, prepared by conventional solid-state synthesis, were annealed at varying temperatures and subsequently quenched to room temperature. The Curie temperature of all the SBNX materials increased with higher quenching temperatures, accompanied with ferroelectric hardening. The variation in thermal history also caused structural changes, specifically a contraction of the a lattice parameter and a minor elongation of the c parameter. These effects are discussed in relation to recent first principles calculations of the energy landscape of the cation-vacancy configurations and experimental evidence of thermally induced cation-vacancy disordering.

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32

McNulty, Jason A., David Pesquera, Jonathan Gardner, Andrei Rotaru, Helen Y. Playford, Matthew G. Tucker, Michael A. Carpenter, and Finlay D. Morrison. "Local Structure and Order–Disorder Transitions in “Empty” Ferroelectric Tetragonal Tungsten Bronzes." Chemistry of Materials 32, no. 19 (September 9, 2020): 8492–501. http://dx.doi.org/10.1021/acs.chemmater.0c02639.

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33

Simon, Annie, and Jean Ravez. "Solid-state chemistry and non-linear properties of tetragonal tungsten bronzes materials." Comptes Rendus Chimie 9, no. 10 (October 2006): 1268–76. http://dx.doi.org/10.1016/j.crci.2006.04.001.

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34

Debnath, Tapas, Subrata Chandra Roy, Claus H. Rüscher, and Altaf Hussain. "Synthesis and characterization of niobium-doped potassium tetragonal tungsten bronzes, KxNbyW1−yO3." Journal of Materials Science 44, no. 1 (January 2009): 179–85. http://dx.doi.org/10.1007/s10853-008-3101-4.

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35

Tekaya, I., A. Tekaya, and B. Maximin. "Photo-Hall, photorefractive and photomagnetoelectric effects in tungsten bronzes and related tetragonal ferroelectrics." Ferroelectrics 551, no. 1 (October 26, 2019): 87–108. http://dx.doi.org/10.1080/00150193.2019.1658035.

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36

Börrnert, Carina, Wilder Carrillo-Cabrera, Paul Simon, and Hubert Langbein. "V2.38Nb10.7O32.7: A V2O5–Nb2O5 mixed oxide tunnel structure related to the tetragonal tungsten bronzes." Journal of Solid State Chemistry 183, no. 5 (May 2010): 1038–45. http://dx.doi.org/10.1016/j.jssc.2010.02.018.

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37

Zhu, X., M. Fu, M. C. Stennett, P. M. Vilarinho, I. Levin, C. A. Randall, J. Gardner, F. D. Morrison, and I. M. Reaney. "A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes." Chemistry of Materials 27, no. 9 (April 24, 2015): 3250–61. http://dx.doi.org/10.1021/acs.chemmater.5b00072.

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38

Gardner, Jonathan, Fengjiao Yu, Chiu Tang, Winfried Kockelmann, Wuzong Zhou, and Finlay D. Morrison. "Relaxor-to-Ferroelectric Crossover and Disruption of Polar Order in “Empty” Tetragonal Tungsten Bronzes." Chemistry of Materials 28, no. 13 (June 29, 2016): 4616–27. http://dx.doi.org/10.1021/acs.chemmater.6b01306.

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39

Zhu, X. L., and X. M. Chen. "Thermal hysteresis of ferroelectric transition in Sr4R2Ti4Nb6O30 (R=Sm and Eu) tetragonal tungsten bronzes." Applied Physics Letters 96, no. 3 (January 18, 2010): 032901. http://dx.doi.org/10.1063/1.3292209.

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40

Хуболов, Борис Магометович. "OPTICAL PROPERTIES OF AMORPHOUS THIN FILMS OF SODIUM-TUNGSTEN OXIDE BRONZES." Physical and Chemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials, no. 13 (December 23, 2021): 430–38. http://dx.doi.org/10.26456/pcascnn/2021.13.430.

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В работе измерены спектральные зависимости оптической плотности аморфных тонких пленок оксидной натрий-вольфрамовой бронзы тетрагональной структуры состава NaWO, конденсированной на стеклянные подложки, термостатированные при температурах 373,473 и 573 K, а так же отожженные на воздухе и в вакууме, и электрохромно окрашенных. В качестве исследуемой оптической характеристики была выбрана оптическая плотность D, пропорциональная, как известно, коэффициенту поглощения. Спектральные измерения пленок, осажденных на подложки в диапазоне температур 373,473 и 573 K показали однотипность спектральных характеристик, с пиком экситонного поглощения в ближнем ультрафиолете. Полоса минимального поглощения лежит в диапазоне длин волн 400÷460 нм, а примесного поглощения - широкой полосой в области 650 ÷1000 нм с максимумом в диапазоне 900÷1000 нм. Подобная спектральная характеристика и определяет сине-голубой цвет тонкой пленки на просвет. Изучение оптических свойств тонких пленок натрий-вольфрамовых бронз представляет собой актуальную задачу. The spectral dependences were measured of the optical density of amorphous thin films of sodium-tungsten oxide bronze of the tetragonal structure and the composition NaWO, condensed on glass substrates, thermostated at temperatures of 373, 473 and 573 K, as well as annealed in air vacuum, and electrochromically colored. The optical density D, which is proportional, as is known, to the absorption coefficient, was chosen as the studied optical characteristic. Spectral measurements of films deposited on substrates in the temperature range of 373, 473 and 573 K showed the same type of spectral characteristics, with a peak of the exciton absorption in the near ultraviolet. The band of minimum absorption lies in the wavelength range of 400÷460 nm, while that of the impurity absorption is a wide band in the region of 650÷1000 nm with a maximum in the range of 900÷1000 nm. This spectral characteristic determines the blue-blue color of a thin film in transmission. The study of the optical properties of thin films of sodium-tungsten bronzes is an urgent problem.

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41

Boerrnert, Carina, Wilder Carrillo-Cabrera, Paul Simon, and Hubert Langbein. "ChemInform Abstract: V2.38Nb10.7O32.7: A V2O5-Nb2O5 Mixed Oxide Tunnel Structure Related to the Tetragonal Tungsten Bronzes." ChemInform 41, no. 33 (July 24, 2010): no. http://dx.doi.org/10.1002/chin.201033017.

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42

Geguzina, G. A. "The complex oxides with octahedral structures: Existence areas and phase transitions." Journal of Advanced Dielectrics 10, no. 01n02 (February 2020): 2060013. http://dx.doi.org/10.1142/s2010135x20600139.

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The experimental and calculated data on the existence of complex oxides in solid state with the octahedral structures of four families, namely perovskites, Bi-containing layered perovskite-like ones, tetragonal tungsten bronzes and pyrochlores, and about their phase transitions are systematized and summarized on the basis of the quasi-elastic or geometric models of these structures. It has been established that similar existence areas and similar correlations between the interatomic bond strains in their structures, on the one hand, and the temperatures of their ferroelectric or antiferroelectric phase transitions, on the other hand, are observed for all of them, despite the differences in the compositions and structures of these oxides, but taking into account their similar parameters.

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43

Tegg, Levi, Georg Haberfehlner, Gerald Kothleitner, Erich Kisi, and Vicki J. Keast. "Crystal structures, electrical properties, and electron energy-loss spectroscopy of the sodium and potassium tetragonal tungsten bronzes." Journal of Alloys and Compounds 868 (July 2021): 159200. http://dx.doi.org/10.1016/j.jallcom.2021.159200.

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44

Slater, P. R., and J. T. S. Irvine. "Niobium based tetragonal tungsten bronzes as potential anodes for solid oxide fuel cells: synthesis and electrical characterisation." Solid State Ionics 120, no. 1-4 (May 1999): 125–34. http://dx.doi.org/10.1016/s0167-2738(99)00020-x.

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45

Botella, P., E. García-González, B. Solsona, E. Rodríguez-Castellón, J. M. González-Calbet, and J. M. López Nieto. "Mo-containing tetragonal tungsten bronzes. The influence of tellurium on catalytic behaviour in selective oxidation of propene." Journal of Catalysis 265, no. 1 (July 1, 2009): 43–53. http://dx.doi.org/10.1016/j.jcat.2009.04.008.

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46

Prades, Marta, Héctor Beltrán, Nahum Masó, Eloisa Cordoncillo, and Anthony R. West. "Phase transition hysteresis and anomalous Curie–Weiss behavior of ferroelectric tetragonal tungsten bronzes Ba2RETi2Nb3O15:RE=Nd,Sm." Journal of Applied Physics 104, no. 10 (November 15, 2008): 104118. http://dx.doi.org/10.1063/1.3021460.

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47

Pan, Fengjuan, Xiaohui Li, Fengqi Lu, Xiaoming Wang, Jiang Cao, Xiaojun Kuang, Emmanuel Véron, et al. "Nonstoichiometric Control of Tunnel-Filling Order, Thermal Expansion, and Dielectric Relaxation in Tetragonal Tungsten Bronzes Ba0.5–xTaO3–x." Inorganic Chemistry 54, no. 18 (September 8, 2015): 8978–86. http://dx.doi.org/10.1021/acs.inorgchem.5b01098.

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48

Prades, Marta, Nahum Masó, Héctor Beltrán, Eloisa Cordoncillo, and Anthony R. West. "Synthesis, Structural Characterization, and Electrical Properties of New Oxygen-Deficient Tetragonal Tungsten Bronzes Ba2NdTi2+xNb3–xO15–x/2." Inorganic Chemistry 52, no. 4 (January 29, 2013): 1729–36. http://dx.doi.org/10.1021/ic301156c.

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49

Kim, Nam Gil, Maxim Avdeev, and Young-Il Kim. "Tunnel structure of tetragonal tungsten bronzes BaTa2O6, Ba0.8Ta2O5.8, and Ba0.5Ta2O5.5 studied using synchrotron X-ray and neutron diffraction." Journal of Alloys and Compounds 815 (January 2020): 152420. http://dx.doi.org/10.1016/j.jallcom.2019.152420.

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50

Cerretti, G., M. Schrade, X. Song, B. Balke, H. Lu, T. Weidner, I. Lieberwirth, M. Panthöfer, T. Norby, and W. Tremel. "Thermal stability and enhanced thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47 (0 < x < 5)." Journal of Materials Chemistry A 5, no. 20 (2017): 9768–74. http://dx.doi.org/10.1039/c7ta01121k.

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Engineering of nanoscaled structures allows to control the electrical and thermal transport in solids for thermoelectric applications where a combination of low thermal conductivity and low electrical resistivity is required.

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