Showing papers in "Phase Transitions in 1983"
TL;DR: In this article, the lattice parameters of LiKSO4 have been measured in the temperature range 155-300 K with an X-ray single-crystal Bond diffractometer.
Abstract: Lattice parameters of LiKSO4 have been measured in the temperature range 155–300 K with an X-ray single-crystal Bond diffractometer. Below 180 K LiKSO4 transforms on cooling into an orthorhombic phase. Above this temperature there is a broad range of an intermediate hexagonal phase which depends on the real structure of the sample and differs considerably on cooling and on heating. The anomalies in the physical properties of LiKSO4 reported in the literature have been explained. The crystal structure of the low-temperature and intermediate phase, as well as the mechanism of the phase transitions, are suggested and discussed.
72 citations
TL;DR: In this paper, a phase diagram has been prepared for AgNb, -Ta,O, solid solutions and a series of anomalies were found in the temperature dependence of the dielectric constant and loss tangent, as well as anomalies in the DTA curves associated with phase transitions.
Abstract: Dielectric investigations (65 K – 900K) and DTA investigations (300 K - 900K) have been carried out for AgNb, -Ta solid solutions. A series of anomalies were found in the temperature-dependence of the dielectric constant and loss tangent, as well as anomalies in the DTA curves associated with phase transitions. From the results a phase diagram has been prepared for AgNb, -Ta,O, solid solutions.
66 citations
TL;DR: From X-ray and DTA studies, a series of phase transitions in AgNbO3 at 333K, 510k, 609K, 643K,861K has been observed.
Abstract: From X-ray and DTA studies a series of phase transitions in AgNbO3 at 333K, 510K, 609K, 643K,861K has been observed. The existence of some of the phase transitions has been confirmed by domain structure investigations. e(T) and tan δ (T) variations are discussed from the point of view of the phase transitions.
45 citations
TL;DR: In this article, temperature and field dependences of magnetization, paramagnetic susceptibility, magnetic anisotropy and neutron diffraction for CuxZn1-xCr2Se4 spinels are investigated.
Abstract: We present detailed results concerning temperature and field dependences of magnetization, paramagnetic susceptibility, magnetic anisotropy and neutron diffraction for CuxZn1-xCr2Se4 spinels. Particular emphasis is put on the gradual transition from helimagnetism to ferromagnetism as a function of concentration x. The transition takes place through an intermediate structure for 0.05 ≤ x ≤ 0.8 with the ferromagnetic component growing with concentration. It is suggested that a double exchange mechanism predominates as x increases and this can be regarded as the origin of the transition.
32 citations
TL;DR: In this paper, it has been established that PbNb05B05O3 corresponds to a ferroelectric with a diffuse phase transition and PbNsb05Sc05OO3 shows a small diffuse nature.
Abstract: When studying the compounds of the PbNb05B05O3 series it has been established that with a critical ionic radius RB = 085A there occurs a transition from ferroelectric (B-Cr, Fe, Mn, Sc, In) to antiferroelectric (B-Lu, Yb, Tm) The structure of crystals and polycrystalline specimens has been studied by X-ray diffraction techniques, and also the dielectric properties of PbNb05Sc05O3 and PbNb05In05O3 located near the transition boundary from ferroelectrics to antiferroelectrics are discussed It has been established that PbNb05In05O3 corresponds to a ferroelectric with a diffuse phase transition The phase transition in PbNb05Sc05O3 shows a small diffuse nature The temperature-dependences of the unit cell parameters, dielectric constants and loss tangents have been obtained It has been established for the first time that PbNb05In05O3 at room temperature is rhombohedral (R3m) with cell parameters a = 41132 ± 00004A, α = 8997 ± 002° A preliminary determination of the PbNb05Sc05O3
25 citations
TL;DR: The density p of N(p-n-heptyloxy benzylidene) p-nbutyl aniline (HYBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase as discussed by the authors.
Abstract: The density p of N(p-n-heptyloxy benzylidene) p-n-butyl aniline (HYBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase. The compound is tetramorphic exhibiting three smectic phases SG, SC, SA and a nematic phase. The density changes across the phase transformations and the calculated thermal expansion coefficient confirm the order of the SG[sbnd]SC, SA[sbnd]N and N[sbnd]I transitions as first-order, with SC[sbnd]SA transition as weakly first or second-order. The first-order SA[sbnd]N phase transformation in this compound, which is weakly polar, is in agreement with McMillan's theoretical predictions, and is different from other polar compounds.
23 citations
TL;DR: In this paper, the influence of controlled introduction of defects into the Pb and O sublattices of PbZrO3 was ascertained, and marked changes are caused in the dielectric parameters and the transitions between the antiferroelectric and ferroelectric states and the ferro electric and paraeiectric states.
Abstract: From studies of the influence of controlled introduction of defects into the Pb and O sub-lattices of PbZrO3 it was ascertained that marked changes are caused in the dielectric parameters and the transitions between the antiferroelectric and ferroelectric states and the ferroelectric and paraeiectric states. With increasing amount of defects the temperature range in which the ferroelectric state occurs is narrowed during the heating process and widened during the cooling process. An attempt has been made to explain the observed effects within the context of existing theoretical models.
20 citations
TL;DR: In this paper, the density ρ of N-(pn-octyloxy benzylidene) p-n-butyl aniline (OBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase.
Abstract: The density, ρ, of N-(p-n-octyloxy benzylidene) p-n-butyl aniline (OBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase. The compound is trimorphic, exhibiting three smectic phases, smectic-G, crystal smectic-B, and smectic-A phase. The changes in density across the phase transformations and the calculated thermal expansion coefficients confirm the order of the transitions as first order. Particular importance of the smectic-A to crystal smectic-B transformation, which is of first order, is apparent from the density jump across the transition.
20 citations
TL;DR: In this paper, the spectroscopic and crystallographic evidence for a symmetric (single-minimum) versus a double-minimum type O[sbnd]H[SBnd]O potential in KH2PO4-type crystals is reviewed.
Abstract: The spectroscopic and crystallographic evidence for a symmetric (single-minimum) versus a double-minimum type O[sbnd]H[sbnd]O potential in KH2PO4-type crystals is reviewed. The results clearly show that both the protons in KH2PO4 and the deuterons in KD2PO4 move between two off-centre sites and freeze onto one of these two sites below the ferroelectric transition temperature Tc . A self-consistent determination of the proton-tunnelling frequency from the observed soft-mode frequency, and other static and dynamic properties, requires the use of the four-particle cluster model as the short-range correlations of the protons around a given PO4 group cannot be neglected. The pressure and temperature-dependence of the proton-tunnelling frequency can be understood on the basis of some very general properties of the O[sbnd]H[sbnd]O potential.
18 citations
TL;DR: In this paper, the magnetic properties of CuxZn1−xCr2Se4 are explained in terms of the molecular field approximation assuming the existence of 90° exchange interactions, and the exchange parameters and integrals for the whole series under consideration are calculated.
Abstract: The magnetization, the susceptibility and the magnetic anisotropy field of Cu x Zn1−xCr2Se4 compounds have been studied at low temperatures (down to 2.9 K) in: high magnetic stationary fields (up to 14 T), high pulsed magnetic fields (up to 25 T), medium magnetic stationary fields (up to 0.6 T). The magnetic structure of these spinels was studied by neutron powder diffraction. The magnetic properties of CuxZn1−xCr2Se4 are explained in terms of the molecular field approximation assuming the existence of 90° exchange interactions, ferromagnetic for Cr-Se-Cr between the nearest Cr ions and antiferromagnetic for Cr-Se-Se-Cr between the second-nearest Cr ions. The exchange parameters and integrals for the whole series under consideration are calculated. Taking into account the three magnetic phase transitions observed in these spinels (Juszczyk, Krok, Okonska-Kozlowska, Broda, Warczewski, Byszewski, 1981) and the neutron diffraction studies a modification of the simple spin spiral forced by a strong m...
14 citations
TL;DR: In this article, a technique has been developed for refining the atomic displacements in perovskite-type structures by integrated intensity measurements of X-ray reflections obtained from polycrystalline specimens by separating the reflections sensitive to atomic displacement.
Abstract: A technique has been developed for refining the atomic displacements in perovskite-type structures by integrated intensity measurements of X-ray reflections obtained from polycrystalline specimens by separating the reflections sensitive to atomic displacements. In this way the temperature changes of atomic displacements in PbTiO3 and PbZrO3 at their phase transitions have been determined. It has been established that the displacements existing in PbTiO3 and PbZrO3 at room temperature monotonously decrease with increasing temperature to certain critical values at the phase transitions. A small abrupt change has been revealed in the atom displacements and unit cell parameters at approximately 150°C. For the first time, displacements of Pb and Hf at room temperature have been determined.
TL;DR: In this paper, the frequency of the microwave soft mode varies according to v2 r = A(T - T 0) with A = 1.1 × 1020 Hz2.
Abstract: Microwave dielectric investigations of SbS0.7Se0.3 I crystals were carried out over the frequency range 9 to 80 GHz. The main resonant dielectric dispersion caused by the soft mode occurs in the microwave range. On approaching the Curie point, the frequency of the microwave soft mode varies according to v2 r = A(T - T 0) with A = 1.1 × 1020 Hz2. K-1 and T 0 = 189 K in the symmetric phase, and with A = −3 × 1020Hz2. K−1 and T 0 = 193 K in the ferroelectric phase. The soft microwave mode does not belong to the set of normal modes. The phase transition is intermediate between the pure displacive and order-disorder types.
TL;DR: In this article, the incommensurate and commensurate superstructures of K2MoO4, Rb2WO4 and K2WOWO4 are shown to have orthorhombic symmetry rather than the hexagonal symmetry.
Abstract: The incommensurate and commensurate superstructures of K2MoO4, Rb2WO4 and K2WO4 are shown to have orthorhombic symmetry rather than the hexagonal symmetry, reported earlier. The structures belong essentially to the β-K2SO4 type. The β-K2SO4 structure can be regarded as a commensurate superstructure of the α-K2SO4 structure by doubling of the unit cell. In this sense β-K2SO4 and K2MoO4 have the same average structures. Rb2WO4 displays a lock-in transition at 681 K where the incommensurate distortion wave vector jumps from an incommensurate value to the value 0.5 which results in the β-K2SO4 type. The distortion wave vectors of the other compounds range from 0.25 to 0.5.
TL;DR: The successive phase transitions of [N(CH3)4,]2ZnCl4 have been investigated by means of EPR and DSC of Mn2+ doped samples as discussed by the authors.
Abstract: The successive phase transitions of [N(CH3)4,]2ZnCl4 have been investigated by means of EPR and DSC of Mn2+ doped samples. Changes in the EPR spectrum with varying temperature show the presence of six phases (I, II, …, VI) between 27 and −140°C. The spin Hamiltonian parameters and the orientations of the D tensor were determined in phases I and V. In phase II, the broadening and splitting of the spectrum are attributed to incommensuration. A discommensurate phenomenon is also detected. The spectra in phases III, IV and VI, are characteristic of modulated superstructures. The modulation amplitude and orientation angle for ZnCl2- 4 ion are related to the phase angle. The effect of changing temperature on the modulation amplitude and initial phase are shown.
TL;DR: In this paper, the variation of ultrasonic velocity in N-(p-n-hexyloxy benzylidene) p-nbutyl aniline with temperature in the isotropic, nematic, SA SB and SG phases is measured All the phase transitions are of first order The adiabatic compressibility β ad, molar sound veclocity or Rao number Rn, and molar compressibility or Wada constant A are computed
Abstract: The variation of ultrasonic velocity in N-(p-n-hexyloxy benzylidene) p-n-butyl aniline with temperature in the isotropic, nematic, SA SB and SG phases is measured All the phase transitions are of first order The adiabatic compressibility β ad , molar sound veclocity or Rao number Rn , and molar compressibility or Wada constant A are computed Molar sound velocity and molar compressibility of HBBA are compared with the values of other compounds They are found to be in good agreement with theory
TL;DR: In this article, the variations of molar volume Mv and ultrasonic velocity V with temperature in N(p-n-pentyloxy benzylidene) p-toluidine are presented.
Abstract: The variations of molar volume Mv and ultrasonic velocity V with temperature in N(p-n-pentyloxy benzylidene) p-toluidine are presented. The molar volume jump at the nematicisotropic transition suggests it is of first order. The adiabatic compressibility β ad, molar sound velocity or Rao number Rn , molar compressibility or Wada constant A, the thermal expansion coefficient α, and Van der Waals constant b, are computed. Molar sound velocity and molar compressibility are compared with the values of other members of the homologous series and are found to be in good agreement with Rao's and Wada's observations. The order parameter Sk, at the nematic-isotropic phase transition is 0.441 from our experimental results and the Maier-Saupe table and is found to be in good agreement with the theoretical value.
TL;DR: In this article, the temperature dependence of the neutron diffraction intensities of flux-grown nearly dislocation-free SrTiO3 crystals, upon cooling and heating through the structural phase transition at 105 K, for both the fundamental and the superlattice reflections, was reported.
Abstract: We report the temperature dependence of the neutron diffraction intensities of flux-grown nearly dislocation-free SrTiO3 crystals, upon cooling and heating through the structural phase transition at 105 K, for both the fundamental and the superlattice reflections. The results suggest that the transition is strongly controlled by macroscopic strains when the crystal is kept in the tetragonal phase and then warmed up, it., a time-dependent memory effect is observed.
TL;DR: In this article, the influence of a third constituent in a critical binary solution on the type of phase transition and on the value of the critical exponent defined by the relation has been investigated using nonlinear dielectric effect studies.
Abstract: Using the nonlinear dielectric effect studies have been made of the influence of a third constituent in a critical binary solution on the type of phase transition and on the value of the critical exponent defined by the relation Phase diagrams have been constructed indicating points of continuous phase transitions.
IBM1
TL;DR: In this paper, an electron-paramagnetic-resonance study of the 105 K phase transition in a flux-grown low dislocation density SrTiO3 crystal is described.
Abstract: An electron-paramagnetic-resonance study of the 105 K phase transition in a flux-grown low dislocation density SrTiO3 crystal is described. The rotational order parameter reveals no time-dependent effects, and the transition is within experimental accuracy continuous. These results agree with recent X-ray and neutron-scattering measurements of the lattice parameter, a = a(T c) × cos phi; being continuous at T c
TL;DR: In this paper, the lattice parameters of NH4BeF3 have been measured in the temperature range 235-365 K with an X-ray single-crystal Bond diffract meter.
Abstract: Lattice parameters of NH4BeF3 have been measured in the temperature range 235–365 K with an X-ray single-crystal Bond diffract meter. DSC measurements and Weissenberg photographs are also described in both the high-and low-temperature regions, and the phase diagram is presented. On heating, NH4BeF3 transforms at 334 K to an intermediate phase and at 347 K to the high-temperature phase.
TL;DR: In this article, structural phase transitions in 3,5-dichloropyridine crystal have been studied by calorimetry, X-ray diffraction, 35Cland 14N nuclear quadrupole resonance and vibrational spectroscopy.
Abstract: Structural phase transitions in 3,5-dichloropyridine crystal have been studied by calorimetry (150–300 K), X-ray diffraction (300 K), 35Cland 14N nuclear quadrupole resonance (75–300 K) and vibrational spectroscopy (20–300K). Three phases have been shown to exist: phase I, between 338 and 287.5 K, phase 11, between 287.5 and 167.5 K, and phase 111, below 167.5 K. Phase I is characterised by the space group P 2,/m and Z = 2 whereas phases I1 and 111 remain centrosymmetric but double the unit cell. All the phases are ordered and contain crystallo- graphically equivalent molecules. The I ↔ I1 transition is of first order and probably of the reconstructive type while the II ↔ III transition is believed to be displacive. Both transitions are monitored by predominantly R′x and R′z librational motions.
TL;DR: In this article, the tricritical point at which the transition from a two-phase to a three-phase region takes place at the highest temperature is identified as the critical end-point.
Abstract: Applying the polythermal method the coexistence region of three liquid phases in an ethanediol-nitroethane-cyclohexane-methanol system has been found for several temperatures. From this the temperature and composition of the tricritical point has been determined as T TCP = 37.5 ± 1°C and mass fraction :x ethanediol = 0.09 ± 0.01, x nitroelhane = 0.45 ± 0.01 x cycelohcexane = 0.40 ± 0.02, x methanol = 0.060 ± 0.005. The point at which, for a given polytherm, the transition from a two-phase to a three-phase region takes place at the highest temperature is identified as the critical end-point. Functions of temperature versus heights of menisci separating the individual phases have been determined for selected values of concentration.
TL;DR: In this paper, the results of a detailed experimental study of the specific heat near the Curie temperature were reported for the Ni-Cu ferromagnetic alloy system, where the measuring technique and specimen preparation have allowed high enough resolution of specific heat for critical exponent analysis in the 0-10 weight per cent concentration range.
Abstract: In these papers (Part I and Part 11) the results of a detailed experimental study of the specific heat near the Curie temperature are reported for the Ni-Cu ferromagnetic alloy system. The measuring technique and specimen preparation have allowed high enough resolution of specific heat for critical exponent analysis in the 0–10 weight per cent concentration range. A simple data analysis without higher corrections gives very unsatisfactory results in respect of symmetry (α = α′) and universal behaviour of specific heat. The problem of rounding and the regular background term to the specific heat is analyzed.
TL;DR: In this article, the authors derived from the scattering of Mossbauer γ-rays from lead phosphate, Pb3(PO4)2, at temperatures above the transition temperature (180°C) were consistent with the idea that the crystal contains regions which have the symmetry of the low-temperature, ferroelastic phase.
Abstract: Results derived from the scattering of Mossbauer γ-rays from lead phosphate, Pb3(PO4)2, at temperatures above the transition temperature (180°C) are consistent with the idea that the crystal contains regions which have the symmetry of the low-temperature, ferroelastic phase. These microdomains are either very long-lived, a result which is inconsistent with findings from neutron scattering experiments reported in the literature, or have lifetimes which are considerably shorter than 10−7 seconds.
TL;DR: In this paper, the existence of the thermodielectric effect at phase transitions of cholesteryl esters (cholesteryl chloride and nonanoate) was confirmed.
Abstract: In this paper we confirm the existence of the thermodielectric effect at phase transitions of some cholesteryl esters (cholesteryl chloride, cholesteryl nonanoate and cholesteryl laurate). Significant sudden variations of the potential difference across the samples were detected at solid crystal → isotropic, isotropic → mesophase phase transitions of these liquid crystals. The variations are due to the formation of thermodielectric electrets by spontaneous polarization. The phase transitions are identified and their temperatures are in agreement with the literature.
TL;DR: In this paper, general expressions for the densities of a liquid and a gas in equilibrium are expanded in terms of the reduced densities and temperatures, and the resulting expansions are subjected to non-differentiability and symmetry requirements.
Abstract: General expressions for the densities of a liquid and a gas in equilibrium are expanded in terms of the reduced densities and temperatures. The resulting expansions are subjected to non-differentiability and symmetry requirements, and the gas density expansion is fitted to the Clapeyron-Clausius equation at low gas densities to achieve zero-parameter coexistence equations for the liquid and the gas.