Acoustic studies of the ferroelastic phase transition in the K₃Na(CrO₄)₂ crystal

Abstract

PACS 62.20.Dc, 62.65.+k, 77.80.Bh Ultrasonic studies of the K 3 Na(CrO 4 ) 2 crystal were carried out within a temperature range of 185 to 295 K. Temperature dependences of the velocity and attenuation coefficient for the xx and zz longitudinal acoustic waves and the yx and zx transverse waves were measured. Noticeable anomalies in velocity and attenuation for transverse as well as for longitudinal waves were found near the ferroelastic phase transition which temperature was 235.5 K. The anomalies in the c 44 and c 66 elastic moduli were treated on the base of the Landau theory assuming the component ε 4 as the primary order parameter and (ε 2 -ε 1 )/2 as the secondary one. Six elastic moduli, c 11 , c 33 , c 44 , c 66 , c 12 , and c 14 were evaluated at room temperature.

Phase transition in sodium bismuth tungstate NaBi(WO4)2 – acoustic studies

“…1 and 2 are quite different. The transverse mode velocity decreases noticeably in the temperature range from 310 K to 325 K and reaches a minimum at a temperature of approximately 319 K. The general pattern corresponds to a linear relation between the order parameter responsible for the phase transition and the strains in the acoustic waves [9,10,16]. In contrast, the velocity of longitudinal waves show a slightly diffused step at about 319 K associated with the attenuation maximum.…”

“…1 and 2 are typical for the velocity and attenuation alterations near phase transitions (see, for instance, [9,10] and references therein). The reproducible character of acoustic anomalies and absence of a detectable thermal hysteresis allow us to assume that the observed phase transition is that of the second order or weakly first order; in the latter case the hysteresis is narrower than the experimental accuracy of temperature stabilization.…”

A nuclear magnetic resonance study of the ferroelastic phase transitions of K3Na(CrO4)2and K3Na(SeO4)2single crystals

“…Thus, to obtain information about the structural phase transitions that occur in K 3 Na(CrO 4 ) 2 and K 3 Na(SeO 4 ) 2 , it is useful to measure their NMR spectra, the spin-lattice relaxation times, T 1 , and the spinspin relaxation times, T 2 , for their 23 Na and 39 K nuclei as functions of temperature. However, very little experimental investigation of K 3 Na(CrO 4 ) 2 and K 3 Na(SeO 4 ) 2 has been performed; only Raman scattering results for the ferroelastic phase transition [13], elastic constants [3,14], and electron paramagnetic resonance (EPR) measurements [15][16][17] have been reported.…”