Zeitschriftenartikel: „Incommensurable phase“

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Kubli, Martin, Matteo Savoini, Elsa Abreu, Bulat Burganov, Gabriel Lantz, Lucas Huber, Martin Neugebauer et al. „Kinetics of a Phonon-Mediated Laser-Driven Structural Phase Transition in Sn2P2Se6“. Applied Sciences 9, Nr. 3 (04.02.2019): 525. http://dx.doi.org/10.3390/app9030525.

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We investigate the structural dynamics of the incommensurately modulated phase of Sn 2P 2Se 6 by means of time-resolved X-ray diffraction following excitation by an optical pump. Tracking the incommensurable distortion in the time domain enables us to identify the transport effects leading to a complete disappearance of the incommensurate phase over the course of 100 ns. These observations suggest that a thin surface layer of the high-temperature phase forms quickly after photo-excitation and then propagates into the material with a constant velocity of 3.7 m/s. Complementary static structural measurements reveal previously unreported higher-order satellite reflection in the incommensurate phase. These higher-order reflections are attributed to cubic vibrational terms in the Hamiltonian.

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Kotovskaya, J. V., und Zh Kobalava. „How to characterize daily profile of pulse blood pressure?“ "Arterial’naya Gipertenziya" ("Arterial Hypertension") 12, Nr. 1 (28.02.2006): 59–65. http://dx.doi.org/10.18705/1607-419x-2006-12-1-59-65.

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The aim of this work is studying of double-phase rhythm characteristics of pulse pressure (PP) at untreated patients AH. The absent of night reduce of PP can be the consequent of night incommensurable change of systolic and diastolic pressure at night in comparison with day change. It was revealed two types of incommensurable double-phase rhythm of pulse pressure ( PP) on the basis of database analysis: Type 1 - with night increase of SHP (type 1a with night decrease DBP, type 1b with gap of increase DBP from SBP at night). Type 2 - with decrease of SBP and DBP at night. Ratio of daily index SBP and DBP ≥ 0,70 provide for decrease PP at night in comparison of day hours with probability ≥ 96 %. Accepting k = 0,70 as bench mark allow us to insert quantitative characteristics of double-phase rhythm of pulse pressure (PP), without using the traditional measure scale of daily index, the usage opportunity of which by BP demands more precise definition The presence of incommensurable daily rhythm of BP was associated with more expressed abnormalities from the point of target organs even with normal daily rhythm of SHP. Thus, I he estimation of proportionality of daily rhythm of SHP and DBP against their daily index is very important additional characteristic of daily profile of HP, allowing to identify patients in dipper and non-dipper groups, whose target organs condition can't be explained by the character of double-phase rhythm of SHP.

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Zwanenburg, G., C. P. Keijzers, E. de Boer und J. C. Krupa. „EPR-study of ThBr4:Pa4+ in the incommensurable phase“. Journal of Molecular Structure 173 (Januar 1988): 397–404. http://dx.doi.org/10.1016/0022-2860(88)80071-1.

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Zwanenburg, G., C. P. Keijzers, E. De Boer und J. C. Krupa. „Simulation of EPR spectra of ThBr8:Pa4+ in the incommensurable phase“. Chemical Physics Letters 140, Nr. 1 (September 1987): 11–14. http://dx.doi.org/10.1016/0009-2614(87)80407-4.

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Almairac, R., M. Siali, S. Vilminot, P. Saint Gregoire, G. Delplanque und G. Barre. „Phase incommensurable dans le composé mixte (NH4) 2(BeF4)0,82(SO4)0,18“. Journal de Physique Lettres 46, Nr. 23 (1985): 1123–31. http://dx.doi.org/10.1051/jphyslet:0198500460230112300.

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FRANCO, H. „WAVELET ANALYSIS OF A NONLINEAR OSCILLATOR TRANSIENT DURING SYNCHRONIZATION“. International Journal of Bifurcation and Chaos 06, Nr. 12b (Dezember 1996): 2557–70. http://dx.doi.org/10.1142/s0218127496001636.

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A forced nonlinear oscillator can exhibit complex transient spectra even in the absence of chaotic phenomena. Series of evenly spaced lines appear in spectrograms of the numerically computed oscillations. They can be explained by means of a simple model describing the dynamics of the energy exchange between the external oscillating force and the nonlinear system. The resulting amplitude and phase modulations are shown to produce the spectral line structures. Frequencies incommensurable with other present frequencies can be generated by the nonlinear system.

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Brown, M. G. „Phase space structure and fractal trajectories in 1½ degree of freedom Hamiltonian systems whose time dependence is quasiperiodic“. Nonlinear Processes in Geophysics 5, Nr. 2 (30.06.1998): 69–74. http://dx.doi.org/10.5194/npg-5-69-1998.

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Abstract. We consider particle motion in nonautonomous 1 degree of freedom Hamiltonian systems for which H(p,q,t) depends on N periodic functions of t with incommensurable frequencies. It is shown that in near-integrable systems of this type, phase space is partitioned into nonintersecting regular and chaotic regions. In this respect there is no different between the N = 1 (periodic time dependence) and the N = 2, 3, ... (quasi-periodic time dependence) problems. An important consequence of this phase space structure is that the mechanism that leads to fractal properties of chaotic trajectories in systems with N = 1 also applies to the larger class of problems treated here. Implications of the results presented to studies of ray dynamics in two-dimensional incompressible fluid flows are discussed.

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Новикова, Е. Р. „STUDY OF THE SINGULAR POINTS OF THE FRACTIONAL OSCILLATOR VAN DER POL-DUFFING“. Вестник КРАУНЦ. Физико-математические науки, Nr. 2 (20.07.2019): 47–54. http://dx.doi.org/10.26117/2079-6641-2019-27-2-47-54.

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В работе проводится исследование на асимптотическую устойчивость точек покоя дробного осциллятора Ван дер ПоляДуффинга. Дробный осциллятор Ван дер Поля Дуффинга представляет собой колебательную систему двух дифференциальных уравнений с производными дробных порядков в смысле ГерасимоваКапуто. Порядки дробных производных характеризуют свойства среды (эффекты памяти), в которой происходит колебательный процесс и могут быть одинаковыми (соизмеримыми) или разными (несоизмеримыми). С помощью теорем для соизмеримой и несоизмеримой систем на конкретных примерах исследуется асимптотическая устойчивость точек покоя дробного осциллятора Ван дер ПоляДуффинга. Результаты исследований были подтверждены с помощью построения соответствующих осциллограмм и фазовых траекторий A study is conducted on the asymptotic stability of the rest points of the fractional oscillator Van der PolDuffing. The fractional van der PolDuffing oscillator is an oscillatory system of two differential equations with fractional order derivatives in the sense of GerasimovCaputo. The orders of fractional derivatives characterize the properties of the medium (memory effects) in which the oscillatory process takes place and can be the same (commensurate) or different (incommensurable). Using theorems for commensurable and incommensurable systems, the asymptotic stability of the rest points of the fractional van der PolDuffing oscillator is investigated with concrete examples. The results of the studies were confirmed by constructing the appropriate waveforms and phase trajectories.

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Липко, О. Д. „STABILITY OF THE REST POINTS FRACTIONAL OSCILLATOR FITZHUGH-NAGUMO“. Вестник КРАУНЦ. Физико-математические науки, Nr. 1 (04.05.2019): 63–70. http://dx.doi.org/10.26117/2079-6641-2019-26-1-63-70.

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В работе с помощью качественного анализа были исследованы на устойчивость точки покоя дробного осциллятора ФитцХью-Нагумо в соизмеримом и несоизмеримом случаях. Для соответвующей точки покоя, с помощью численного метода теории конечно-разностных схем, была построена фазовая траектория. Показано, что точки покоя могут быть как асимптотически устойчивыми, что соответствуют устойчивым фокусам, так и являться асимптотически неустойчивыми (неустойчивыми фокусами), причем для них фазовые таректории, как правило, выходят на предельный цикл. In this paper, using the qualitative analysis, we studied the stability of the point of rest of the fractional oscillator FitzHugh-Nagumo in commensurate and incommensurable cases. For the corresponding point of rest, using the numerical method of the theory of finite difference schemes, phase trajectories were constructed. It is shown that quiescent points can be both asymptotically stable, which correspond to stable focus, and are asymptotically unstable (unstable focus), and for them the phase trajectories usually go to the limit cycle.

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Chrzan, D. C., und L. M. Falicov. „Theoretical phase stability of incommensurable spin structures on the {001} surfaces of MnO-type antiferromagnetic semiconductors“. Physical Review B 39, Nr. 5 (15.02.1989): 3159–67. http://dx.doi.org/10.1103/physrevb.39.3159.

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Martínez-García, Alejandro N. „Artificial Intelligence for Sustainable Complex Socio-Technical-Economic Ecosystems“. Computation 10, Nr. 6 (08.06.2022): 95. http://dx.doi.org/10.3390/computation10060095.

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The strong and functional couplings among ecological, economic, social, and technological processes explain the complexification of human-made systems, and phenomena such as globalization, climate change, the increased urbanization and inequality of human societies, the power of information, and the COVID-19 syndemic. Among complexification’s features are non-decomposability, asynchronous behavior, components with many degrees of freedom, increased likelihood of catastrophic events, irreversibility, nonlinear phase spaces with immense combinatorial sizes, and the impossibility of long-term, detailed prediction. Sustainability for complex systems implies enough efficiency to explore and exploit their dynamic phase spaces and enough flexibility to coevolve with their environments. This, in turn, means solving intractable nonlinear semi-structured dynamic multi-objective optimization problems, with conflicting, incommensurable, non-cooperative objectives and purposes, under dynamic uncertainty, restricted access to materials, energy, and information, and a given time horizon. Given the high-stakes; the need for effective, efficient, diverse solutions; their local and global, and present and future effects; and their unforeseen short-, medium-, and long-term impacts; achieving sustainable complex systems implies the need for Sustainability-designed Universal Intelligent Agents (SUIAs). The proposed philosophical and technological SUIAs will be heuristic devices for harnessing the strong functional coupling between human, artificial, and nonhuman biological intelligence in a non-zero-sum game to achieve sustainability.

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Sastry, V. S. S., K. Venu, S. Uma Maheswari und R. K. Subramanian. „NQR Study of Dynamics in Incommensurate Phases“. Zeitschrift für Naturforschung A 55, Nr. 1-2 (01.02.2000): 281–90. http://dx.doi.org/10.1515/zna-2000-1-250.

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Dynamic processes in solids exhibiting structurally incommensurate phases are briefly reviewed, and the application of NMR and NQR is discussed. The unique utility of these methods, - arising due to, on one hand, the microscopic resonant nature of the probe used and, on the other, the presence of periodic, though incommensurable, structure - , is brought out by presenting recent results in a prototype system (Rb2ZnCl4) in the presence of randomly quenched disorder. In particular, the interesting new methodology of measuring, by analysing NQR spin echo modulation, ultra-slow diffusion like collective motions of ensembles of atoms in the presence of pinning effects due to disorder is illustrated with new results.

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Caracas, Razvan. „A database of incommensurate phases“. Journal of Applied Crystallography 35, Nr. 1 (22.01.2002): 120–21. http://dx.doi.org/10.1107/s0021889801017083.

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A database of incommensurate phases is currently available at http://www.mapr.ucl.ac.be/~crystal/index.html. The present database offers a fast direct retrieval system for structural, physical and bibliographical data of incommensurate phases. The database contains data about inorganic, non-composite, non-magnetic and non-superconducting incommensurate phases only. Classification is according to the physical mechanisms responsible for the incommensurate phase transition. The main classes of incommensurate phases thus obtained are: theA2BX4dielectrics family, zone-centre lock-in transition phases, cooperative Jahn–Teller incommensurates, tetragonal tungsten bronzes, charge-density wave systems and miscellaneous incommensurate phases. The latter class, because of the lack of available data, is classified on a chemical basis in several subclasses: silicates, perovskites, Mn-bearing oxides, other oxides, group VI compounds, intermetallics and other compounds. The database contains a brief description of the main physical, chemical and structural features of each phase, as stated in the literature. This description is very material- and bibliography-dependent and it is preceded by the phase transition sequence.

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Suárez, Almudena, Franco Ramírez und Sergio Sancho. „Prediction of odd-mode instabilities under output mismatch effects“. International Journal of Microwave and Wireless Technologies 9, Nr. 6 (Juli 2017): 1305–15. http://dx.doi.org/10.1017/s1759078717000885.

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A methodology is presented to predict odd-mode instability in power amplifiers under output mismatch effects, as in the case of amplifiers connected to an antenna. This kind of instability is often observed in multi-device configurations, due to their symmetry properties. Unlike the single-ended situation, there is a cancellation of odd multiples of the oscillation frequency at the circuit output, so there is no impact of the load-impedance values at the sideband frequencies. The odd-mode instability only depends on the impedance terminations at the fundamental frequency and its harmonic terms, and can only be detected within the circuit unstable loop, instead of the antenna-connection terminals. The possible unstable modes are related with the eigenvectors of an outer tier conversion matrix accounting for the symmetry properties of the circuit topology. Under sufficient low-pass filtering of the amplifier output network, the analysis parameters can be limited to the magnitude and phase of the reflection coefficient at the fundamental frequency. This analysis involves a computationally efficient graphical technique to detect potential instabilities and a bifurcation-detection method to determine the instability boundaries in the Smith chart. The two main types of instability from periodic regime are considered, respectively associated with incommensurable and subharmonic oscillations. Results have been validated through pole-zero identification and experimental measurements.

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Röthlisberger, Francois, Friedrich Seifert und Michael Czank. „Chemical control of the commensurate-incommensurate phase transition in synthetic melilites“. European Journal of Mineralogy 2, Nr. 5 (04.10.1990): 585–94. http://dx.doi.org/10.1127/ejm/2/5/0585.

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Nagakura, Sigemaro, Yoshihiko Hirotsu, Naoki Yamamoto, Katsumi Miyagawa, Yuji Ikeda und Yoshio Nakamura. „Modulated structures of Bi-based high-Tc superconducting oxides studied by High Resolution Electron Microscopy and electron diffraction“. Proceedings, annual meeting, Electron Microscopy Society of America 48, Nr. 4 (August 1990): 80–81. http://dx.doi.org/10.1017/s0424820100173534.

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In the superconducting Bi-Sr-Ca-Cu-O system, ideal compositions of the low Tc(Tc∼90 K) and the high Tc(Tc∼110K) phases are Bi2Sr2CaCu2Oy(y∼8:2212 phase) and Bi2Sr2Ca2 Cu3Oy (y∼10:2223 phase), respectively. The fundamental structures of these phases are tetragonal with parameters: at=bt=0.54 and ct=3.08 nm for the 2212 phase, and at=bt=0.54 and ct=3.71 nm for the 2223 phase. These phases have incommensurate structures with modulation along their b-axes. In this study, the modulated structures of Pb-doped 2212 and 2223 phases have been investigated by means of high resolution electron microscopy and electron diffraction. Samples Bi2-xPbxSr2CaCu2Oy(x=0-0.4, melt-quenched and annealed) and Bi2−xPbxSr2Ca2Cu3Oy(x=0-0.6, sintered) were observed in high resolution electron microscopes operating at 200 kV and 1 MV.Analysis of the incommensurate modulated structures of the 2212 and 2223 phases was made by using samples Bi2Sr2CaCu2Oy and Bi1.6Pb0.4Sr2Ca2Cu3Oy. The lattice parameters of the incommensurate superstructures are a=at and c=ct for both of these phases, but b∼5bt and b∼bt for the 2212 and 2223 phases, respectively.

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Sveleba, Sergii, Ivan Katerynchuk, Ivan Kuno, Ivan Karpa, Ostap Semotiuk und Volodymyr Brygilevych. „Calculation of the phase state of the [N(CH3)4]2CUCL4 crystals“. Computational Problems of Electrical Engineering 10, Nr. 2 (02.12.2020): 28–32. http://dx.doi.org/10.23939/jcpee2020.02.028.

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The calculation of the spatial changes of the amplitude and phase of the order parameter was performed in the Python environment with the use of the Skipy and JiTCODE libraries. In [N(CH3)4]2CuCl4 crystals, there is an incommensurate phase I1 at the small values of the magnitude of long-range interaction (T<0.6) and an incommensurate phase I2 at T≥1.0. This is the same incommensurate phase, although the behavior of the amplitude and phase functions in it is different under the different conditions mentioned above. At T = 0.6 ÷ 1.0, the coexistence of these two phases is observed which is manifested in the absence of anomalous changes of q during the transition from the sinusoidal mode of IC modulation to the soliton regime

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Randall, C. A., R. Guo, A. S. Bhalla und L. E. Cross. „Microstructure-property relations in tungsten bronze lead barium niobate, Pb1−xBaxNb2O6“. Journal of Materials Research 6, Nr. 8 (August 1991): 1720–28. http://dx.doi.org/10.1557/jmr.1991.1720.

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Transmission electron microscopy (TEM) has been used to explore details of the structural phase transitions and corresponding microstructural features in the solid solution of Pb1−xBaxNb2O6 (PBN) tungsten bronze ferroelectrics at compositions embracing the morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases. In addition to the ferroelectric domain structures that were consistent with the expected symmetries, incommensurate ferroelastic phases were observed. The “onset” and “lock-in” transition temperatures are a function of the Pb/Ba ratio, and for lead-rich compositions it appears that the incommensurate distortion may occur above the ferroelectric Curie temperature in the paraelectric phase.

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Mizuno, Motohiro, Tetsuo Asaji, Masahiko Suhara und Yoshihiro Furukawa. „NQR and NMR Studies of Phase Transitions in R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4)“. Zeitschrift für Naturforschung A 51, Nr. 5-6 (01.06.1996): 721–25. http://dx.doi.org/10.1515/zna-1996-5-660.

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Abstract39K, 87, 85Rb, 133Cs, 205T1, and 1, 2H NMR spin-lattice relaxation times T1 and 14N NQR spin-lattice relaxation times T1Q were determined for R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4). T1 of 39K and 87Rb showed very short values in the incommensurate phase as compared with those in the other phases. When the commensurate-incommensurate phase transition point is approached from below, 14N T1Q of the R = K, Rb, Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond the corresponding transition point. The difference of the T1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.

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Couzi, Michel, François Guillaume und Kenneth D. M. Harris. „A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds“. Royal Society Open Science 5, Nr. 6 (Juni 2018): 180058. http://dx.doi.org/10.1098/rsos.180058.

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n -Alkane/urea inclusion compounds are crystalline materials in which n -alkane ‘guest’ molecules are located within parallel one-dimensional ‘host’ tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + 1)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n -nonadecane/urea and n -hexadecane/urea, two low-temperature phases II and ‘III’ exist and that one or both of these phases are described by a (3 + 2)-dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin–phonon coupling mechanism, which accounts for the mechanisms responsible for the I ↔ II ↔ ‘III’ phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + 1)-dimensional superspace groups. Around the temperature of the II ↔ ‘III’ transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a ‘crossover’ between two regimes involving different couplings between relevant order parameters.

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CAPRARA, SERGIO, MASSIMO CAPONE, LUCA CAPRIOTTI und FEDERICO BECCA. „COMMENSURATE VERSUS INCOMMENSURATE SPIN-ORDERING IN THE TRIANGULAR HUBBARD MODEL“. International Journal of Modern Physics B 14, Nr. 29n31 (20.12.2000): 3386–91. http://dx.doi.org/10.1142/s0217979200003708.

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The presence of incommensurate spin structures in the half-filled triangular Hubbard model, where frustration leads to a competition among different magnetic phases, is investigated using both the slave-boson technique, and exact diagonalization of finite clusters. We also investigate the metal-insulator transition which, due to the lack of perfect nesting, takes place at a finite value of U. Within the slave-boson approach, as the interaction grows the paramagnetic metal turns into a metallic phase with incommensurate spiral ordering. Increasing further the interaction, a linear spin-density-wave is stabilized, and finally for strong coupling the latter phase undergoes a first-order transition towards an antiferromagnetic insulator. No trace of the intermediate phases is instead found in the exact diagonalization results.

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Ishiguro, Takashi, und Hiroshi Sato. „Electron microscopy of the commensurate-incommensurate phase transition with the discommensuration network in 1T-TaS2“. Proceedings, annual meeting, Electron Microscopy Society of America 48, Nr. 4 (August 1990): 168–69. http://dx.doi.org/10.1017/s0424820100173972.

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Phase transitions of lT-TaS2 both on cooling from the incommensurate (IC) phase and on heating from the commensurate (C) phase are investigated by high resolution (HR) transmission electron microscopy because phase transitions are strongly hysteretic. The phases which had been identified were Normal(T>543K,no modurated wave, the Cdl2 type of structure, ao=0.336nm co=0.590nm), IC(354K< T< 543K), NC(non-commensurate or nearly commensurate, 185K<T<353K) and C(T<K). On heating from the C phase, the new phase called the T phase (nearly commensurate triclinic ) appears between 200K and 280K, and that has the discommensuration (DC) network. The HR observations at low temperature reveal both the three dimentional structure of the C phase and the DC network structure of the T phase.On cooling from the IC phase, the structure of the NC phase is essentially incommensurate in the basal plane and a continuous rotation of the moduration direction towards the C phase occurs.

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Zhang, Jian, Alexander Wolfel, Maxim Bykov, Andreas Schonleber, Sander van Smaalen, Reinhard Kremer und Hailey Williamson. „Transition between two Kosterlitz-Thouless phases in Sc-doped TiOCl“. Acta Crystallographica Section A Foundations and Advances 70, a1 (05.08.2014): C183. http://dx.doi.org/10.1107/s2053273314098167.

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The compound TiOCl is a quasi-1-dimensional (1D) quantum magnet (Seidel et al., 2003). Upon cooling, TiOCl undergoes a phase transition at Tc2 = 90 K towards a state with incommensurate magnetic order, followed by a second phase transition at Tc1 = 67 K towards a spin-Peierls state (Seidel et al., 2003; Shaz et al., 2005; van Smaalen et al., 2005). Both low-temperature phases involve structural distortions that have been characterized by x-ray diffraction. The absence of any phase transitions has been reported for scandium-doped TiOCl with doping levels 0.01 < x < 0.1 for ScxTi1-xOCl (Glancy et al., 2008, 2010; Zhang et al., 2010; Aczel et al., 2011). We have synthesized ScxTi1-xOCl for x = 0.005. Based on temperature-dependent x-ray diffraction experiments and specific-hear measurements, we have found that the x = 0.005 compound transforms into incommensurate and spin-Peierls-like phases on cooling. Despite apparent large correlation lengths, these phases lack long-range order. A sluggish transformation is thus found between states of ScxTi1-xOCl that support different kinds of fluctuations.

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Knjazeva, Maria, Yurii Bronwald, Daria Andronikova, Georgiy Lityagin, Alexey Bosak, Parisiadis Paraskevas, Krystian Roleder et al. „Modulated Structures in PbHfO₃ Crystals at High-Pressure-High-Temperature Conditions“. Defect and Diffusion Forum 386 (September 2018): 149–55. http://dx.doi.org/10.4028/www.scientific.net/ddf.386.149.

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Lead hafnate single crystals were characterized using single crystal x-ray diffraction under simultaneous application of hydrostatic pressure and high temperatures. The information on the structure of two intermediate phases, situated between antiferroelectric and paraelectric phases in the pressure-temperature phase diagram, has been obtained. The lower-temperature intermediate phase is characterized by incommensurate displacive modulations in Pb sublattice. The higher-temperature intermediate phase is characterized by oxygen framework distortion, primarily in the form of anti-phase tilts of the oxygen octahedra, which is also present in the lower-temperature intermediate phase.

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Aizu, Kêitsiro. „Twofold Incommensurate Phase as Analogs of Semicommensurate Phases. On the Transitions [Prototypic→Ordinarily (or Onefold) Incommensurate →Twofold Incommensurate]“. Journal of the Physical Society of Japan 55, Nr. 5 (15.05.1986): 1663–70. http://dx.doi.org/10.1143/jpsj.55.1663.

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Pinheiro, C. B., A. Jório, M. A. Pimenta und N. L. Speziali. „Structural Analysis of Cs2HgBr4 in Normal, Incommensurate and Twinned Phases“. Acta Crystallographica Section B Structural Science 54, Nr. 3 (01.06.1998): 197–203. http://dx.doi.org/10.1107/s0108768197012032.

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X-ray diffraction and Raman spectroscopy experiments have been used to investigate different phases of Cs2HgBr4, dicesium mercury tetrabromide, from room temperature to 213 K. Structural analyses have shown that the crystal could be described, in the normal and in the incommensurate phases, both by ordered and disordered models, but the latter gave more consistent results. Raman results corroborate the descriptions based on X-ray analysis; the presence of an extra peak, which according to group theory should be forbidden in an ordered structure, indicates the lack of local symmetry and was associated with an orientational disorder of [HgBr4]2− tetrahedra. In the transition from the incommensurate to the commensurate phase a multi-soliton behavior was observed. The Cs2HgBr4 crystal in the low-temperature commensurate phase is composed of two types of ordered pseudomerohedral twinned domains.

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Andersen, S., Y. X. Guo und R. Høier. „Incommensurate Boundary Shifts in the AlMnSi Cubic Phase“. Proceedings, annual meeting, Electron Microscopy Society of America 48, Nr. 2 (12.08.1990): 522–23. http://dx.doi.org/10.1017/s0424820100136210.

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The icosahedral quasicrystalline (IQ) phases of rapidly solidified materials, and especially that of the AlMnSi type, have been subjected to intensive research in recent years. These phases have been found to be closely related to periodic phases of similar composition, and orientation relationships have been found between the IQ and its decomposition products. Consequently, they are also of great importance in the study of the IQs. The most recognized periodic phase in this respect is probably the primitive α-AlMnSi phase (a = 12.68 Å). The 138 atoms in the unit cell are arranged in large atomic clusters, the socalled Mackay Icosahedra, with slightly deformed icosahedral symmetry. These clusters are believed also to be the building blocks of the quasicrystals and of some additional periodic decomposition phases, the difference between the structures being realized through a different stacking of the clusters. A thorough understanding of these periodic phases is therefore clearly important. Here we present a study of some of the defects that frequently appear in the α-phase.

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Uhrig, Go¨tz S., und Ruud Vlaming. „Incommensurate phases vs. phase separation for interacting spinless fermions“. Physica B: Condensed Matter 194-196 (Februar 1994): 451–52. http://dx.doi.org/10.1016/0921-4526(94)90555-x.

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Parlinski, K., und F. Dénoyer. „Mechanisms of phase transitions between commensurate and incommensurate phases“. Physical Review B 41, Nr. 16 (01.06.1990): 11428–36. http://dx.doi.org/10.1103/physrevb.41.11428.

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Parlinski, K., S. Kwiecinski und A. Urbanski. „Phase diagram of a hexagonal model with incommensurate phases“. Physical Review B 46, Nr. 9 (01.09.1992): 5110–15. http://dx.doi.org/10.1103/physrevb.46.5110.

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31

Timirgazin, M. A., Anatoly K. Arzhnikov und A. V. Vedyayev. „Incommensurate Spin-Density Wave in Two-Dimensional Hubbard Model“. Solid State Phenomena 190 (Juni 2012): 67–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.190.67.

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We consider the magnetic phase diagram of the two-dimensional Hubbard model ona square lattice.We take into account both spiral and collinear incommensurate magnetic states.The possibility of phase separation of spiral magnetic phases is taken into consideration as well.Our study shows that all the listed phases appear to be the ground state at certain parametersof the model. Relation of the obtained results to real materials, e.g. Cu-based high-temperaturesuperconductors, is discussed.

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Arakcheeva, Alla, und Gervais Chapuis. „A reinterpretation of the phase transitions in Na2CO3“. Acta Crystallographica Section B Structural Science 61, Nr. 6 (14.11.2005): 601–7. http://dx.doi.org/10.1107/s0108768105033008.

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Based on the structural data of phases α (hexagonal; 756–972 K), β (monoclinic; 605–751 K), γ (incommensurate, monoclinic; 295 K) and δ (lock-in, monoclinic; 110 K) of sodium carbonate, Na2CO3, we could draw a parallel between the phase transitions and the evolution of the second coordination sphere of the C atoms. The temperature-dependent structures observed in the β phase are reproduced in the incommensurate γ phase as a modulation wave, which relates to the content of the symmetrically equivalent {110} lattice planes in the α phase. By decreasing the temperature, the phase transitions are associated with a stepwise increase in the number of Na ions participating in the second coordination sphere of the C atoms. Over the full temperature range, this number increases from 3 to 7. The C—O distances and the mobility of the O atoms depends on the number of Na ions in the vicinity of the C atoms.

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Canadillas-Delgado, Laura, Lidia Mazzuca, Oscar Fabelo, J. Alberto Rodriguez-Velamazan und Juan Rodriguez-Carvajal. „Incommensurate structures of the [CH3NH3][Co(COOH)3] compound“. IUCrJ 6, Nr. 1 (01.01.2019): 105–15. http://dx.doi.org/10.1107/s2052252518015026.

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The present article is devoted to the characterization of the structural phase transitions of the [CH3NH3][Co(COOH)3] (1) perovskite-like metal–organic compound through variable-temperature single-crystal neutron diffraction. At room temperature, compound 1 crystallizes in the orthorhombic space group Pnma (phase I). A decrease in temperature gives rise to a first phase transition from the space group Pnma to an incommensurate phase (phase II) at approximately 128 K. At about 96 K, this incommensurate phase evolves into a second phase with a sharp change in the modulation vector (phase III). At lower temperatures (ca 78 K), the crystal structure again becomes commensurate and can be described in the monoclinic space group P21/n (phase IV). Although phases I and IV have been reported previously [Boča et al. (2004). Acta Cryst. C60, m631–m633; Gómez-Aguirre et al. (2016). J. Am. Chem. Soc. 138, 1122–1125; Mazzuca et al. (2018). Chem. Eur. J. 24, 388–399], phases III and IV corresponding to the Pnma(00γ)0s0 space group have not yet been described. These phase transitions involve not only the occurrence of small distortions in the three-dimensional anionic [Co(HCOO)3]− framework, but also the reorganization of the [CH3NH3]+ counter-ions in the cavities of the structure, which gives rise to an alteration of the hydrogen-bonded network, modifying the electrical properties of compound 1.

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Gorbatenko, V. V., B. N. Prasolov, S. A. Gorbatenko und N. V. Datsenko. „Harmonic Analysis of the Polarization Reversal of the Rb2ZnCl4 Crystal in the Incommensurate Phase“. Кристаллография 68, Nr. 5 (01.09.2023): 734–37. http://dx.doi.org/10.31857/s0023476123600453.

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The polarization reversal of Rb2ZnCl4 crystals in the incommensurate phase near a ferroelectric phase transition (PT) under the action of harmonic electric field has been studied using harmonic analysis. During polarization reversal of a test sample under the action of harmonic electric field, a PT induced by the electric field from the incommensurate phase to the ferroelectric phase and a PT from the field-induced ferroelectric phase back to the incommensurate phase occur. The study of the active and reactive contributions to the amplitudes of current density harmonics made it possible to determine the current values of harmonic electric field intensity at which the corresponding PTs occur.

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Yamamoto, Naoki, Makoto Kikuchi, Tooru Atake, Akihiro Hamano und Yasutoshi Saito. „Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4“. Proceedings, annual meeting, Electron Microscopy Society of America 48, Nr. 4 (August 1990): 172–73. http://dx.doi.org/10.1017/s0424820100173996.

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BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

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Xu, Z., Dwight Viehland und D. A. Payne. „An incommensurate-commensurate phase transformation in antiferroelectric tin-modified lead zirconate titanate“. Journal of Materials Research 10, Nr. 2 (Februar 1995): 453–60. http://dx.doi.org/10.1557/jmr.1995.0453.

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Antiferroelectric tin-modified lead zirconate titanate ceramics (PZST), with 42 at. % Sn and 4 at. % Ti, were studied by hot- and cold-stage transmission electron microscopy and selected area electron diffraction techniques. The previously reported tetragonal antiferroelectric state is shown to be an incommensurate orthohombic state. Observations revealed the existence of incommensurate 1/x 〈110〉 superlattice reflections below the temperature of the dielectric maximum. The modulation wavelength for this incommensurate structure was found to be metastably locked-in near and below room temperature. An incommensurate-commensurate orthorhombic antiferroelectric transformation was then observed at lower temperatures. However, an intermediate condition was observed over a relatively wide temperature range which was characterized by an intergrowth of 〈110〉 structural modulations, which was strongly diffuse along the 〈110〉. These structural observations were correlated with dispersion in the dielectric properties in the same temperature range. No previous reports of an incommensurate orthorhombic antiferroelectric state or an incommensurate-commensurate orthorhombic antiferroelectric transformation are known to exist.

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Dorner, B., B. Schmid, K. Kakurai und D. Petitgrand. „The phase diagram of RbFeCl3 in a magnetic field perpendicular to the chain direction“. Canadian Journal of Physics 73, Nr. 11-12 (01.11.1995): 800–804. http://dx.doi.org/10.1139/p95-116.

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The temperature dependence of the position and line width of antiferromagnetic Bragg peaks were measured at different applied magnetic fields up to 1.4 T by means of elastic neutron scattering. Three different types of temperature dependences were observed that can be attributed to the commensurate–incommensurate, commensurate–paramagnetic, and incommensurate–paramagnetic phase transitions. Below 0.3 T the transition goes from commensurate to incommensurate. Between 0.3 and 0.5 T a phase boundary was observed, but there is some doubt as to whether the structure at temperatures below this boundary is commensurate. Between 0.5 and 1.2 T the phase transition goes directly from commensurate to paramagnetic at around 2.5 K. For fields higher than 1.3 T and temperatures above 1.5 K no commensurate phase could be identified. But above 1.2 T and still at 1.4 T there exists an incommensurate phase. Based on these temperature dependences at different magnetic fields, phase boundaries in the H–T phase space are proposed and compared with the phase diagram obtained by previous susceptibility measurements.

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Bosak, Alexei, Volodymyr Svitlyk, Alla Arakcheeva, Roman Burkovsky, Vadim Diadkin, Krystian Roleder und Dmitry Chernyshov. „Incommensurate crystal structure of PbHfO3“. Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, Nr. 1 (01.02.2020): 7–12. http://dx.doi.org/10.1107/s205252061901494x.

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Controversy in the description/identification of so-called intermediate phase(s) in PbHfO3, stable in the range ∼420–480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00γ)s00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO3-like antiferroelectric and Pm3m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.

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Dolinšek, J., und R. Blinc. „A Note on the 14N Electric Field Gradient Notizen: Tensors in Incommensurate [N(CH3)4]2ZnCl4“. Zeitschrift für Naturforschung A 42, Nr. 3 (01.03.1987): 305–6. http://dx.doi.org/10.1515/zna-1987-0318.

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The 14N electric field gradient tensors of [N(CH3)4]2ZnCl4 have been re-determined in the paraelectric phase at 26 °C and in the incommensurate phase at 16 °C. The results in the incommensurate phase show the “non-local” nature of the 14N EFG tensor interaction.

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Nakano, Hiromi, Shota Ando, Konatsu Kamimoto, Yuya Hiramatsu, Yuichi Michiue, Naoto Hirosaki und Koichiro Fukuda. „Incommensurately Modulated Crystal Structure and Photoluminescence Properties of Eu2O3- and P2O5-Doped Ca2SiO4 Phosphor“. Materials 13, Nr. 1 (20.12.2019): 58. http://dx.doi.org/10.3390/ma13010058.

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We prepared four types of Eu2O3- and P2O5-doped Ca2SiO4 phosphors with different phase compositions but identical chemical composition, the chemical formula of which was (Ca1.950Eu3+0.013☐0.037)(Si0.940P0.060)O4 (☐ denotes vacancies in Ca sites). One of the phosphors was composed exclusively of the incommensurate (IC) phase with superspace group Pnma(0β0)00s and basic unit-cell dimensions of a = 0.68004(2) nm, b = 0.54481(2) nm, and c = 0.93956(3) nm (Z = 4). The crystal structure was made up of four types of β-Ca2SiO4-related layers with an interlayer. The incommensurate modulation with wavelength of 4.110 × b was induced by the long-range stacking order of these layers. When increasing the relative amount of the IC-phase with respect to the coexisting β-phase, the red light emission intensity, under excitation at 394 nm, steadily decreased to reach the minimum, at which the specimen was composed exclusively of the IC-phase. The coordination environments of Eu3+ ion in the crystal structures of β- and IC-phases might be closely related to the photoluminescence intensities of the phosphors.

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Fukuda, Takashi, Tomoyuki Terai, Hidefumi Maeda und Tomoyuki Kakeshita. „Stress-Temperature Phase Diagram of Ni₂MnGa and Structural Relations between its Constituent Phases“. Materials Science Forum 684 (Mai 2011): 61–71. http://dx.doi.org/10.4028/www.scientific.net/msf.684.61.

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The ferromagnetic shape memory alloy Ni2MnGa exhibits a successive martensitic transformation from the L21-type structure to the so-called intermediate phase and then to the martensite phase with an incommensurate structure during cooling under zero stress. In addition to these phases, a new phase, which we call the X-phase, appears when Ni2MnGa is cooled under compressive stress applied in the [001] direction. In this paper, we discuss the structural relations between the X-phase and the other phases on the basis of experimental results of compressive tests, transmission electron microscope observations and neutron diffraction patterns. It is likely that a multicritical point exists in the stress-temperature phase diagram of Ni2MnGa.

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Меньшенин, В. В. „Магнитные фазовые переходы в несоизмеримую магнитную структуру в соединении FeGe-=SUB=-2-=/SUB=-“. Физика твердого тела 61, Nr. 3 (2019): 552. http://dx.doi.org/10.21883/ftt.2019.03.47251.269.

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AbstractA symmetry analysis of possible magnetic structures in an incommensurate magnetic phase in FeGe_2 compound, resulted from phase transitions from the paramagnetic phase, was performed based on a phenomenological consideration. It is shown that two possible approaches to a such an analysis, the first of which uses the magnetic representation of the space group, and the second one is based on the expansion of the magnetic moment in basis functions of irreducible representations of the space group of the paramagnetic phase, yield the same results. Space group irreducible representations are determined, according to which the transition to an incommensurate structure can occur. The set of these representations appears identical in both approaches. Ginzburg–Landau functionals for analyzing the transitions according to these representations are written. A renormalization group analysis of the second-order phase transitions from the paramagnetic state to the incommensurate magnetic structure is performed. It is shown that a helical magnetic structure can arise in the incommensurate phase as a result of two second-order phase transitions at the transitions temperature.

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RUSTAMOV, K. A., und B. R. GADJIEV. „THEORETICAL MODEL FOR THE HIGH-FREQUENCY DYNAMICAL SUSCEPTIBILITY IN THE IMPROPER SEGNETOELECTRICS“. Modern Physics Letters B 07, Nr. 20 (30.08.1993): 1335–42. http://dx.doi.org/10.1142/s0217984993001387.

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Description of the temperature and frequency dependences of the dynamical susceptibility in improper segnetoelectrics in the incommensurate phase near the incommensurate–commensurate phase transition is presented. The used model is based on the theory of three interacting nonlinear oscillators.

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Nakayama, Hirokazu, Nobuo Nakamura und Hideaki Chihara. „NQR Parameters in Incommensurate Cs2CdBr4 and Cs2HgBr4 Crystals“. Zeitschrift für Naturforschung A 41, Nr. 1-2 (01.02.1986): 261–64. http://dx.doi.org/10.1515/zna-1986-1-246.

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The temperature dependence of the 81Br spin-lattice relaxation times for Cs2CdBr4 and Cs2HgBr4 was measured in the low temperature and the commensurate phases. For the commensurate phase of Cs2CdBr4 rapid shortening of the T1 of νB ~ νC was observed on approaching the “lock-in” transition point. It is probably due to an anisotropic critical fluctuation. On the other hand, T, in the low temperature phase of Cs2HgBr4 behaves like an order parameter but no critical decrease of T1 was observed in the commensurate phase.

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Jacobs, A. E. „The incommensurate phase of“. Journal of Physics: Condensed Matter 8, Nr. 5 (29.01.1996): 517–26. http://dx.doi.org/10.1088/0953-8984/8/5/002.

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Weigel, Dominique. „Commensurate incommensurate phase transitions“. Phase Transitions 16, Nr. 1-4 (Juni 1989): 341–49. http://dx.doi.org/10.1080/01411598908245708.

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Markgraf, S. A., C. A. Randall, A. S. Bhalla und R. J. Reeder. „Incommensurate phase in Ba2TiSi2O8“. Solid State Communications 75, Nr. 10 (September 1990): 821–24. http://dx.doi.org/10.1016/0038-1098(90)90758-4.

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Zheng, Yufeng, Dong Wang, Rajarshi Banerjee, Dipankar Banerjee, Yunzhi Wang und Hamish L. Fraser. „Exploration of Nano-scale Structural Instabilities in Metastable β Titanium Alloys Using Advanced Electron Microscopy“. MATEC Web of Conferences 321 (2020): 12001. http://dx.doi.org/10.1051/matecconf/202032112001.

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A variety of nano-scale structural instabilities formed in different metastable β titanium alloys have been systematically investigated using advanced characterization techniques. The characteristics of three different types of nano-scale structural instabilities, the transformation mechanisms and pathways involved and the critical experimental conditions to generate such nano-scale phases will be reviewed and summarized, including athermal ω phase with hexagonal structure, O’ phase with orthorhombic structure, and incommensurate modulated nanodomains. The athermal ω phase has been observed in the as-quenched state in Ti-xMo (x=12, 15 and 181), Ti-18Mo-5Al, Ti-20V, Ti-5Fe, Ti-5Al-5Mo-5V-3Cr (Ti-5553) and Ti-24Nb-4Zr-8Sn (Ti-2448). O’ phase has been characterized to co-exist with athermal ω phase in the as-quenched state isomorphous titanium alloys, including Ti-26Zr-2Al (at.%), Ti-18Mo, Ti-18Mo-5Al, Ti-5553 and Ti-2448. Incommensurate modulated nanodomains were found in compositionally graded Ti-xFe alloy when the athermal ω phase is suppressed. These various nano-scale structural instabilities need to be taken into consideration when designing novel metastable β titanium alloys to optimize the mechanical performance by microstructure engineering.

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NONNE, H., E. BOULAT, S. CAPPONI und P. LECHEMINANT. „PHASE DIAGRAM OF ONE-DIMENSIONAL ALKALINE-EARTH COLD FERMIONIC ATOMS“. Modern Physics Letters B 25, Nr. 12n13 (30.05.2011): 955–62. http://dx.doi.org/10.1142/s0217984911026668.

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The phase diagram of one-dimensional alkaline-earth fermionic atoms and ytterbium 171 atoms is investigated by means of a low-energy approach and density-matrix renormalization group calculations. For incommensurate filling, four gapless phases with a spin gap are found and consist of two superconducting instabilities and two coexisting bond and charge density-waves instabilities. In the half-filled case, seven Mott-insulating phases arise with the emergence of four non-degenerate phases with exotic hidden orderings.

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Lauter, H. J., H. P. Schildberg, H. Godfrin, H. Wiechert und R. Haensel. „Neutron diffraction studies of two-dimensional quantum systems“. Canadian Journal of Physics 65, Nr. 11 (01.11.1987): 1435–39. http://dx.doi.org/10.1139/p87-226.

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The phases of D2 monolayers on graphite between the commensurate and the incommensurate phase have been investigated by neutron diffraction, revealing new features including domain-wall constructions. For the related systems, 3He and 4He adsorbed on graphite, the structure of the solid first and second layers and the interaction between them have been analyzed.

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