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91.
The processes of melting and freezing of small mercury particles embedded in porous glasses with nanometric pore sizes are studied by an ultrasonic method for various values of the pore filling factor. The filling factor is found to have a threshold, below which the acoustic anomalies accompanying phase transitions change their character. The critical radius of mercury nanoparticles that corresponds to the zero melting temperature is estimated. 相似文献
92.
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
93.
The temperature dependence of 23Na spin-lattice relaxation in the polycrystalline Rochelle salt was studied by NMR within the range from 235 to 320 K covering
both Curie points. The spin-relaxation time t
1 versus temperature curve showed noticeable dips near the phase transitions against the background of the regular decrease
in the relaxation time upon increasing temperature. The dips observed were ascribed to critical contributions to sodium spin-lattice
relaxation caused by the slowdown of the correlation time for one of two relaxation modes in the Rochelle salt. The 23Na NMR parameters were also measured for the melted Rochelle salt.
This article was submitted by the authors in English. 相似文献
94.
A. L. Pirozerskii E. V. Charnaya K. R. Gabbasova A. S. Bugaev 《Acoustical Physics》2014,60(5):509-514
The temperature dependences of the elastic modulus in multiferroics-magnetoelectrics are analyzed, in which magnetic and ferroelectric orderings appear as the result of two successive phase transitions. The analytical relationships for the elastic modulus near the phase transitions to ordered states are obtained for the cases of either linear-quadratic or biquadratic contributions to magneto- and electroelastic coupling. The explicit dependence of the elastic modulus in the multiferroic phase on the magnetoelectric coupling constant was found. It is shown that the characteristic elastic properties in multiferroics can be treated using the Landau theory without taking into account fluctuations. The analysis includes changes in the phase diagrams due to the magneto- and electroelastic coupling. 相似文献
95.
V. F. Krivorotov G. S. Nuzhdov A. A. Fridman E. V. Charnaya 《Russian Journal of Electrochemistry》2013,49(12):1154-1159
The results of quantum chemical calculations of the potential profile in the LaF3 crystal lattice in the range of superionic phase transition are presented for clusters containing 24 to 1200 ions. It is found that the values of formation energy E a of vacancy-interstitial fluoride ion defects and potential barriers E d hindering the movement of fluoride ions and determining the efficiency of charge transport in the lattice grow monotonously from the minimum values E a = 0.12 eV and E d = 0.22 eV for a 24-ion cluster to the maximum E a = 0.16 eV and E d = 0.26 eV for clusters of 576 and 1200 ions. It is shown that the values of E a and E d obtained for the dielectric phase (T < T c) are several times the values of E a and E d for the superionic state (T ≥ T c) of LaF3. The values of E a and E d obtained by quantum chemical calculations from clusters of 576 and 1200 ions agree well with energies E a and E d obtained from the analysis of the data of the Raman and quasielastic light scattering. 相似文献