共查询到20条相似文献,搜索用时 11 毫秒
1.
V. A. Nepochatenko 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(10):1358-1361
A new method for determining the lattice parameters near the first-order phase transition is proposed. The method is based on the model of a thin phase boundary and a linear dependence between the lattice parameters within a phase. 相似文献
2.
E. D. Yakushkin 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(9):1249-1251
The conductivity and heat capacity of tripotassium hydrogen trisulfate single crystals were studied. It was shown that these
single crystals undergo a solid-solid phase transformation upon heating with the formation of new phases, and that their properties
change considerably. Anomalies related to the sorption and desorption of water vapor were observed in the formed multiphase
system. Such anomalies were observed for the first time in measurements of the true heat capacity. 相似文献
3.
The structure of domain walls and new-phase nucleation are investigated in a four-sublattice antiferromagnet (AFM) of the La2CuO4 type placed in a magnetic field which initiates an AFM-weak-ferromagnet (WFM) magnetic structural phase transition. The critical fields for nucleus growth are found in the case of two types of domain walls present. The magnetization curve is calculated and a two-step mechanism is proposed for the AFM-WFM phase transition observed in La2CuO4. 相似文献
4.
The phase behaviour of K3H(SeO4)2 (TKHSe) above room temperature has been studied by differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), simultaneous thermogravimetric and mass spectroscopy analysis (TG-MS), impedance spectroscopy (IS) and X-ray powder diffraction (XRD). Our results show that the previously claimed superionic phase transition in TKHSe at around 388 K (114.85 °C) is also the onset temperature of a slow thermal dehydration that occurs at reaction sites distributed over the surface of the crystal. That is, we propose that the TKHSe undergoes simultaneously a superionic phase transition and a decomposition process with a very slow reaction rate that is evident when the sample is pulverized to fine powder, both starting at the same temperature. As a matter of fact, we observe a decrease of the magnitude of the dc-conductivity on successive thermal runs in powdered sample attributed to sample decomposition that starts at the surface of the TKHSe grains, but the jump in conductivity is only a consequence of the order–disorder transition in the TKHSe phase that remains inside the grains. 相似文献
5.
I. S. Lyubutin A. G. Gavriliuk V. V. Struzhkin S. G. Ovchinnikov S. A. Kharlamova L. N. Bezmaternykh M. Hu P. Chow 《JETP Letters》2007,84(9):518-523
The HS → LS spin crossover effect (high-spin → low-spin transition) induced by high pressure in the range 45–53 GPa is observed in trivalent Fe3+ ions in the paramagnetic phase of a Gd57Fe3(BO3)4 gadolinium iron borate crystal. This effect is studied in high-pressure diamond-anvil cells by two experimental methods using synchrotron radiation: nuclear resonant forward scattering (NFS) and Fe K β high-resolution x-ray emission spectroscopy (XES). The manifestation of the crossover in the paramagnetic phase, which has no order parameter to distinguish between the HS and LS states, correlates with the optical-gap jump and with the insulator-semiconductor transition in the crystal. Based on a theoretical many-electron model, an explanation of this effect at high pressures is proposed. 相似文献
6.
A. K. Radzhabov E. V. Charnaya B. Mroz C. Tien Z. Tylczynski C. -S. Wur 《Physics of the Solid State》2004,46(4):775-779
Ultrasonic studies of the temperature behavior of the velocity and damping of sound for the xx and zz longitudinal and yx and zx transverse waves in K3Na(CrO4)2 have been carried out in the temperature interval 185–295 K, which includes the region of the ferroelastic phase transition. The acoustic parameters for both shear and longitudinal waves were found to have anomalies in the region of the phase transition with a Curie temperature of 235.5 K. A theoretical analysis of the softening of the elastic moduli c44 and c66 was performed on the basis of the Landau expansion in terms of the strain tensor components ?4 and (?2-?1)/2 considered as the linearly coupled primary and secondary order parameter, respectively. The absolute values of the elastic moduli c11, c33, c44, c66, c12, and c14 at 295 K were calculated. 相似文献
7.
V. M. Egorov B. I. Smirnov V. V. Shpeizman R. K. Nikolaev N. S. Sidorov 《Physics of the Solid State》2005,47(10):1993-1997
An orientational phase transition in C60 crystals was studied by differential scanning calorimetry with the highest resolution provided by this method. The temperature dependence of the specific heat ΔC p (T) was found to have a double peak in the range 250–270 K. An analysis of the temperature dependences of heat capacity in the region of the peaks revealed that the lower temperature peak follows a power law of the type ΔC p = A/(T?T0)1/2 characteristic of order-disorder second-order phase transitions, while the high-temperature peak can be identified with a diffuse Λ-shaped first-order phase transition. 相似文献
8.
Depression of the ferroelastic phase transition in LiCsSO<Subscript>4</Subscript> by uniaxial stress
Zbigniew Tylczyński 《Central European Journal of Physics》2011,9(3):722-728
In the lithium-caesium sulphate crystal in the temperature range of ferroelastic phase transition, the uniaxial stress σ
X
induced changes in velocity and attenuation of the longitudinal ultrasonic wave propagating in the direction [010] are studied.
The phase transition is close to the three-critical point and the critical exponent is κ = 0.27 ± 0.02. The stress applied drastically decreases the stepwise change in the wave velocity at T
C
up to its disappearance at 2 MPa. In the temperature range between T
C
and T
C
− 6 K, the stress leads to an increase in the wave velocity and a decrease in its attenuation. This range was interpreted
as that of co-existence of ferroelastic and incommensurate ordering, in which the stress influences the density of solitons
leading to stiffening of the crystal lattice. 相似文献
9.
A theoretical phase diagram of the [N(CH3)4]2CuCl4 crystal with a new commensurate phase characterized by a dimensionless wavenumber q = 2/5 is constructed on a plane specified by two coefficients of the thermodynamic potential. This diagram is used as the basis for the construction of a theoretical pressure-temperature (P-T) phase diagram. The theoretical P-T phase diagram thus obtained is compared with the experimental P-T phase diagram. 相似文献
10.
R. Z. Levitin E. A. Popova R. M. Chtsherbov A. N. Vasiliev M. N. Popova E. P. Chukalina S. A. Klimin P. H. M. van Loosdrecht D. Fausti L. N. Bezmaternykh 《JETP Letters》2004,79(9):423-426
Cascade of phase transitions in GdFe3(BO3)4 at 156, 37, and 9 K has been detected by specific heat measurements and further studied by Raman scattering and Nd3+ spectroscopic probe method. A weakly first-order structural phase transition at 156 K is followed by a second-order antiferromagnetic ordering phase transition at 37 K and a first-order spin-reorientational phase transition at 9 K. 相似文献
11.
S. N. Zinenko A. A. Murakhovski L. P. Ol’khovik Z. I. Sizova E. V. Shurinova A. S. Kamzin 《Journal of Experimental and Theoretical Physics》2003,96(5):945-952
The equation of the magnetization of a hexagonal crystal is derived for the first time for an arbitrary orientation of the external magnetic field relative to the crystallographic c axis. In order to clarify the magnetization mechanism for a real ensemble of small particles in the framework of the given problem, surface anisotropy (which is significant for nanosize objects) was taken into account along with crystalline magnetic anisotropy and anisotropy in the particle shape. Model computer experiments prove that the magnetization curves for nanocrystals oriented in a polar angle range of 65–90° exhibit an anomaly in the form of a jump, indicating a first-order spin-reorientation phase transition. This explains a larger steepness of the experimental curve reconstructed taking into account the interaction between particles as compared to the theoretical dependence obtained by Stoner and Wohlfarth [IEEE Trans. Magn. MAG 27 (4), 3469 (1991)]. An analysis of variation of the characteristic anisotropy surface and its cross section with increasing ratio |K2|/K1 of the crystalline magnetic anisotropy constants upon a transition from a macroscopic to a nanoscopic crystal shows that surface anisotropy leads to a change in the magnetic structure. As a result, an additional easy magnetization direction emerges in the basal plane apart from the easiest magnetization direction (along the c axis). The direction of hard magnetization emerges from the basal plane, the angle of its orientation relative to the c axis being a function of the ratio | K2|/K1. 相似文献
12.
N. V. Sidorov M. N. Palatnikov N. A. Golubyatnik V. T. Kalinnikov 《Optics and Spectroscopy》2003,94(1):27-32
The ferroelectric-antiferroelectric phase transition in a ceramic solid solution Li0.12Na0.88Ta0.2Nb0.8O3 at 350°C was studied using Raman spectroscopy. A considerable broadening of the lines referred to the translational vibrations of the cations in octahedral and cuboctahedral voids and to the vibrations of the oxygen framework, along with a decrease to zero of the intensity of the line corresponding to the bridge stretching mode of the oxygen atoms from the octahedral anion BO6, was found to take place as the temperature of the solid solution approaches the transition point from below. It is shown that, during the transition, the solid solution loses its ferroelectric properties, probably owing to the preferential increase in the anharmonicity of the vibrations of the cations in the octahedral voids. 相似文献
13.
S. A. Sveleba I. V. Karpa I. M. Katerynchuk O. V. Semotyuk R. M. Shymkiv I. M. Kunyo O. I. Fitsych 《Journal of Applied Spectroscopy》2011,78(2):228-233
This a study of the optical transmission of [N(CH3)4]2ZnCl4 and [N(CH3)4]2CuCl4 crystals in the incommensurate phase when a defect density wave is present. It is found that an anomalous reduction in the
transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions
between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related
to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves. 相似文献
14.
D. G. Sannikov 《Physics of the Solid State》2005,47(2):324-326
The formation of a new commensurate phase with a dimensionless wave number q = 1/3 in an [N(CH3)4]2CuCl4 crystal under the action of an external electric field is analyzed theoretically. The phase diagram is constructed on a plane specified by two coefficients of the thermodynamic potential in the presence and in the absence of an external electric field. 相似文献
15.
R. M. Shymkiv S. A. Sveleba I. V. Karpa I. N. Katerynchuk I. M. Kunyo E. I. Phitsych 《Journal of Applied Spectroscopy》2012,78(6):823-828
Optical absorption spectra in thin [N(CH3)4]2CuCl4 crystals in the thickness range 10 μm ≤ d < 100 μm have been studied. Strengthening of the crystal field has been found with
a decrease in the [N(CH3)4]2CuCl4 crystal size. The reasons for absorption band shifts in the visible region depending on the [N(CH3)4]2CuCl4 crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure are discussed. 相似文献
16.
17.
K.?S.?Aleksandrov V.?N.?Voronov A.?N.?Vtyurin A.?S.?Krylov M.?S.?Molokeev M.?S.?Pavlovski? S.?V.?Gorya?nov A.?Yu.?Likhacheva A.?I.?Ancharov 《Physics of the Solid State》2009,51(4):810-816
Pressure-induced phase transitions in the ScF3 crystal were studied using synchrotron radiation diffraction, polarization microscopy, and Raman spectroscopy. The phase existing in the range 0.6–3.0 GPa is optically anisotropic; its structure is described by space group R 3 c (Z = 2), and the transition is due to rotation of ScF6 octahedra around a threefold axis. The pressure dependence of the structural parameters and angle of rotation are determined. The number of Raman spectral lines corresponds to that expected for this structure; above the phase transition point, a recovery of soft modes takes place. At a pressure of 3.0 GPa, a transition occurs to a new phase, which remains metastable as the pressure decreases. The results are interpreted using an ab initio method based on the Gordon-Kim approach. 相似文献
18.
L. Khusravbekov E. V. Charnaya S. D. Vasil’kov I. K. Rakhimov M. I. Salakhutdinov A. Kholov 《Physics of the Solid State》2007,49(3):516-518
This paper reports on the results of acoustic investigations of a NaBi(MoO4)2 crystal in the temperature range from 20 to 70°C. The temperature dependences of the velocity of longitudinal ultrasonic waves propagating along the crystallographic axes z and x are measured at a frequency of 4 MHz. The results obtained demonstrate that a structural phase transition occurs in the NaBi(MoO4)2 crystal at a temperature of 309 K. The experimental findings are consistent with the assumption that the observed phase transition is either a second-order ferroelastic transition or a first-order ferroelastic transition that is very close to being a second-order phase transition. 相似文献
19.
The Rb3(HSeO4)2.5(H2PO4)0.5 compound was prepared and its thermal behavior and electric properties were investigated. The thermogravimetry (TGA) analysis and the differential scanning calorimetric (DSC) show the presence of a structural phase transition of the title compounds at 374 K which is confirmed by the variation of fp and σdc as a function of temperature. The complex impedance of the Rb3(HSeO4)2.5(H2PO4)0.5 compound has been investigated in the temperature range of 295–453 K and in the frequency range 209 Hz–1 MHz. The impedance plots show semicircle arcs at different temperatures, and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance Rp and constant phase elements CPE1 in series with fractal capacity CPE2. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity dc follows the Arrhenius relation. The near value of activation energies obtained from the analysis of modulus, conductivity data, and circuit equivalent confirm that the transport is through the ion hopping mechanism, dominated by the motion of the H+ proton in the structure of the investigated materials. 相似文献
20.
S. V. Myagkota P. V. Savchin A. S. Voloshinovskiĭ T. M. Demkiv Ya. V. Boĭko R. S. Vus L. S. Demkiv 《Physics of the Solid State》2008,50(8):1473-1476
Crystalline materials of the compositions Cs4SnBr6, CsSnBr3, and CsBr-Sn (0.1 mol %) are investigated using x-ray diffraction and luminescent methods. The formation of the CsSnBr3 phase is found to occur in metastable Cs4SnBr6 and CsBr-Sn. It is established that the CsSnBr3 crystalline phase in the Cs4SnBr6 metastable phase is a more stable compound as compared to the CsSnBr3 bulk crystal, which undergoes oxidation and hydration in air. 相似文献