Showing papers on "Ferroelasticity published in 1990"
TL;DR: In this article, the variation thermique du spectre RPE was studied and the temperature de transition between commensurable and incommensurable phases was determined. But this transition possede un caractere du second ordre.
Abstract: Etude de la variation thermique du spectre RPE. Determination de la temperature de transition vers la phase incommensurable. Cette transition possede un caractere du second ordre. Analyse et interpretation de l'eclatement des raies dans les differentes phases. Prediction de la co-existence possible d'une phase commensurable et d'une phase incommensurable en dessous d'une certaine temperature
32 citations
TL;DR: In this article, a phase transition from the prototypic to an incommensurate ferroelastic phase is observed at T = 150 K and the soliton density is equal to 0.45 at 139 K.
Abstract: EPR investigations of RbIn(MoO4)2 are presented. It is found that at TI = 163 K a phase transition from the prototypic to an incommensurate ferroelastic phase takes place. Below T = 150 K a transition from broad to narrow soliton limit is observed and the soliton density ns is equal to 0.45 at 139 K.
[Russian Text Ignored.]
28 citations
TL;DR: In this paper, the phase transition of TlH 2 PO 4 was shown to be a ferroelastic one induced by an instability of the transverse acoustic mode which corresponds to the shear strain x 5.
Abstract: Temperature dependence of the acoustic modes of TlH 2 PO 4 has been observed by the Brillouin scattering around its higher phase transition point at 357 K ( T tr ). The elastic constant c 55 obtained by the angular-dependent spectra shows softening with the Curie-Weiss law in both phases. The phase transition is concluded to be a ferroelastic one induced by an instability of the transverse acoustic mode which corresponds to the shear strain x 5 . The angular dependence of the spectra reveals a typical monoclinicity below T tr . The two-dimensionality of hydrogen-bonded network does not affect the dynamical property of the phase transition mechanism.
19 citations
TL;DR: In this paper, preliminary X-ray diffraction studies show that at room temperature [(CH3)2NH2]3Bi2I9 (DMAIB) is isostructural with Cs3Sb2I 9.
Abstract: Preliminary X-ray diffraction studies show that at room temperature [(CH3)2NH2]3Bi2I9 (DMAIB) is isostructural with Cs3Sb2I9. The crystals are orthorhombic, space group Pnam with unit cell parameters a = 22.565, b = 15.549 and c = 9.088 A, Z = 4, V = 3188 A3. Observations under a polarizing microscope at room temperature show that DMAIB crystal is ferroelastic. The ferroelasticity can be explained as a consequence of a hexagonal to orthorhombic 6/mmmFmmm phase transition. The successive structural phase transitions in DMAIB were studied by dielectric and DSC methods and polarizing microscope observations. DMAIB undergoes four transitions at 304 K (I⇒ II), 285 K (II ⇒ III), 230 K (III ⇒ IV) and 195 K (IV ⇒ V). The I ⇒ II and II ⇒ III transitions are of first order while the III ⇒ IV and IV ⇒ V are of second order. The III ⇒ IV transition is not revealed by DSC while the IV ⇒ V is not observed in a ⇒α(T) plot. The successive stages of the ferro-paraelastic (II ⇒ I) transition are shown in polarizin...
19 citations
TL;DR: A ferroelastic transition has been observed in yttria-stabilised tetragonal zirconia polycrystalline ceramics (TZP) via X-ray diffraction and ultrasound non-destructive testing (NDT), measured as a function of applied uniaxial stress.
16 citations
TL;DR: In this paper, the temperature dependence of the seven adiabatic elastic stiffness tensor compponents of the tetragonal-paraelastic phase were determined from ultrasonic measurements.
11 citations
TL;DR: In this paper, the Curie temperature Tc decreases from 490 K for x = 0 to 230 K for X = 0.20, and decreases with increasing x to es=0 for x≥0.20.
Abstract: Five compositions of K6−2x[FeII2 (FeII4−2xFeIII4+2x)]F30 with 0≤x≤0.20 have been investigated. The Curie temperature Tc decreases from 490 K for x=0 to 230 K for x=0.20. The spontaneous strain es=45×10−4 for x=0 at 300 K, and decreases with increasing x to es=0 for x≥0.075. The entropy change at the transition from the ferroelectric–ferroelastic to the paraelectric–paraelastic phase is 5.5 J mol−1 K−1 for x=0, decreasing to 1.5 J mol−1 K−1 for x=0.20. Calorimetric and dielectric measurements show that the phase transition broadens as x increases. The composition dependence of the phase transition is a function of the Fe2+/Fe3+ distribution. The presence of one Fe3+ ion on the Fe2+ sites of ten unit cells reduces Tc by 150 K. The entropy change at Tc for x≂0.2 corresponds to significant remaining displacements, from the tetragonal unit‐cell positions, being associated only with two of the three independent Fe atoms and with not more than two of the eight independent F atoms in each unit cell. UFAIPXR
11 citations
TL;DR: Linear biref ingence in LiRb4H4(SO4)4 and deuterated LiRrb4D3(SO 4)4 crystals was studied in the temperature range 25-300 K as mentioned in this paper.
11 citations
TL;DR: In this article, it was shown that in the temperature range covered, this quantity is proportional to the optical polarization coefficient B6, which becomes spontaneous at the transition point, and the spontaneous strain has also been determined by means of X-ray diffraction.
Abstract: (N(CH3)4)2ZnBr4 undergoes a ferroelastic phase transition from an orthorhombic mmm structure to a monoclinic 2/m phase. Birefringence and optical indicatrix rotation about the monoclinic axis have been measured in the ferroelastic phase and their temperature dependences have been related to the order parameter of the transition. The spontaneous strain has also been determined by means of X-ray diffraction. It is shown that in the temperature range covered, this quantity is proportional to the optical polarization coefficient B6, which becomes spontaneous at the transition. This fact has allowed us to obtain a numerical estimate of the p66 elastooptic coefficient at the transition point.
11 citations
TL;DR: In this article, a comprehensive study of the ferroelastic domain structure in the DMACA crystal has been performed and it was concluded that the point group of the hypothetical paraelastic phase is 3 m.
9 citations
TL;DR: In this paper, the resonance theory of incommensurate (IC) phases in insulators studied by Heine and McConnell (1984) is reviewed and applied to ammonium hydrogen oxalate hemihydrate, in which and IC phase is stabilized above 3 kbar between the room-temperature paraelastic phase and the low temperature ferroelastic phase.
Abstract: The resonance theory of incommensurate (IC) phases in insulators studied by Heine and McConnell (1984) is reviewed and applied to ammonium hydrogen oxalate hemihydrate, in which and IC phase is stabilized above 3 kbar between the room-temperature paraelastic phase and the low-temperature ferroelastic phase. It is suggested that this IC phase is due to a structural resonance between the ferroelastic ordering mode and an incipient ferroelectric ordering mode. A simple pressure dependence of the latter reproduces the topology of the p-T phase diagram and the pressure dependence of the IC wavevector at TIC. Specific predictions concerning dielectric behaviour and diffuse scattering round satellite positions under pressure are made.
TL;DR: In this article, an analysis of DMABA single crystals with a polarising microscope has revealed its ferroeleastic properties, and it has been shown that the crystal belongs either to hexagonal 6/mF2/m or trigonal 3mF 2/m species in Aizu's terminology.
Abstract: Optical observations of DMABA single crystals with a polarising microscope have revealed its ferroeleastic properties. An analysis of ferroelastic domain pattern allow to suppose that the crystal belongs either to hexagonal 6/mF2/m or trigonal 3mF2/m species in Aizu's terminology. The temperature of ferroelastic phase transition has not been reached.
TL;DR: In this paper, the specific heat capacities of LaxPr1-xP5O14 crystals with x=0.9 and 0.7 were measured with a differential scanning calorimeter over the temperature range 350-450 K.
Abstract: The specific heat capacities of LaxPr1-xP5O14 crystals with x=0.9 and 0.7 were measured with a differential scanning calorimeter over the temperature range 350-450 K. A jump in the specific heat capacity at the phase transition temperature of 402 K and one thermal anomaly at about 385 K were found within experimental error. Factors contributing to the specific heat capacities were considered.
Abstract: We observed ferroelastic domain of LaNbO 4 crystals by micro-Raman spectroscopy utilizing a specific band (107 cm -1 A g mode) with the polarization condition. We found the variation of the Raman intensity corresponding to the ferroelastic domain structure, which is caused by the rotation of crystallographic axes in each domain. The results were in accordance with the optical microscope image with a good reproducibility, proving the feasibility of micro-Raman spectroscopy in the study of domain structures.
TL;DR: In this paper, the influence of random elastic fields on the impurity-induced ferroelectric phase transition is investigated in soft lattices with off-center ions characterized by elastic dipole moments.
Abstract: Results of a theoretical and experimental study of cooperative behaviour in soft lattices with off-center ions characterized by elastic dipole moments are presented. The influence of random elastic fields on the impurity-induced ferroelectric phase transition is investigated.
TL;DR: In this article, the Raman spectra of the phenothiazine crystal were measured at high pressures up to 20 kbar in a diamond-anvil cell (DAC) at several temperatures.
Abstract: The Raman spectra of the phenothiazine crystal were measured at high pressures up to 20 kbar in a diamond-anvil cell (DAC) at several temperatures. A pressure-induced phase transition was found to occur at 2.2 kbar and 297 K. The high-pressure phase was shown to be the same as the low-temperature ferroelastic phase previously found at atmospheric pressure. The wavenumber of the fluorescence band R1 of ruby, used as the pressure monitor in DAC, was precisely measured to obtain its temperature dependence in the temperature region where the present Raman measurements were carried out.
TL;DR: In this article, the dielectric properties of single-crystal {N(CH3)4}2HgCl4 (structure at room temperature; orthorhombic Pmcn) have been measured in a temperature range from 4 K to about 370 K.
Abstract: Dielectric properties of single-crystal {N(CH3)4}2HgCl4 (structure at room temperature; orthorhombic Pmcn) have been measured in a temperature range from 4 K to about 370 K. The dielectric constant along the a-, b-, and c-axes shows a break at 278 K. No other anomalies are detected in the temperature range studied. The transition temperature increases linearly with increasing hydrostatic pressure at a rate of 0.20 K/MPa. Twin boundaries are observed in the low-temperature phase on b-plate specimens. The results indicate that the phase transition in {N(CH3)4}2HgCl4 is ferroelastic, as in {N(CH3)4}2XBr4 (X: Mn, Co, Zn).
TL;DR: In this paper, a new model is presented to describe the low temperature part of the phase diagram of M(CN)xX1−x mixed crystals, where the ferroelastic transition is lost at some threshold value xc greater than the percolation threshold pc.
Abstract: A new model is presented to describe the low temperature part of the phase diagram of M(CN)xX1−x mixed crystals. The ferroelastic transition is lost at some threshold value xc greater than the percolation threshold pc. Between xc and pc no phase transition occurs. However, cyanides are found to form ferroelastic domains with random orientations generated by local static strains. These results are consistent with molecular dynamics calculations and supported by very recent shear torque experiments.
TL;DR: In this article, the authors examined the temperature dependence of retardation of YBa2Cu30x single crystals and showed that the tetragonal-orthorhombic phase transition in yBa2cu30x is of the second order.
Abstract: YBa2Cu30x single crystals are found to show ferroelastic domain switching above 150[ddot]C. At about 300[ddot]C, {110} domain walls were clearly seen to move after application of an external stress. We also examined the temperature dependence of retardation of YBa2Cu30x single crystals. The continuous rise of the retardation evidences that the tetragonal-orthorhombic phase transition in YBa2Cu30x is of the second order.
TL;DR: In this article, a packing and lattice-dynamical study of the phenothiazine phase transition using atom-atom potential functions was made using a molecular rotation of 4° and a shear deformation.
TL;DR: A short review of the published experimental data on various physical properties and some new results of the measurement of dielectric and electromechanical properties of Cs2HgCI4 crystals in a wide temperature range are presented in this article.
Abstract: A short review of the published experimental data on various physical properties and some new results of the measurement of dielectric and electromechanical properties of Cs2HgCI4 crystals in a wide temperature range are presented. The crystal is shown to reveal anomalies at seven temperatures associated with structural phase transitions and hence to have eight phases. In two temperature regions there exists a small spontaneous polarization and the anomalous dielectric permittivity is a nonlinear function of the electric biasing field. Within the phase followed by the first polar phase on cooling the crystal, the effects of thermal, electrical and mechanical memory, specific for incommensurate phases, are observable.
TL;DR: In this article, a new ferroelastic material is characterized by microscopic observations, Brillouin and Raman scattering, and a molecular model of the transition is proposed to characterize the transition.
Abstract: A new ferroelastic material is characterized by microscopic observations, Brillouin and Raman scattering. A molecular model of the transition is proposed.
TL;DR: Ferromagnetic moments are due mainly to the ordering and coupling of electron spins and partly to changes in electron orbits as discussed by the authors, which impart a lowering of crystal symmetry to the host lattice, from cubic to tetragonal in the case of iron, for example.
Abstract: Ferromagnetism arises from the orientation of magnetic moments. Magnetic moments are due mainly to the ordering and coupling of electron spins and partly to changes in electron orbits. Ferroelectricity, a term first used to describe properties of barium titinate, arises from the orientation of electric moments associated with ions. Ferromagnetism and ferroelectricity are each accompanied by small, well-defined elastic displacements of atoms or ions, which impart a lowering of crystal symmetry to the host lattice, from cubic to tetragonal in the case of ferromagnetism in iron, for example. Such deformations are reversible and are not uncommonly referred to as “ferroelasticity. ”