Elastic properties of the [N(CH3)4]2 XCl4 (X=Co,Zn,Cu,Mn) crystals-possible application

Summary form only given. Crystals of the [N(CH₃)₄ ]₂XCl₄ class (X=Co,Zn,Cu,Mn) undergo a sequence of phase transitions (PTs), including PTs into the incommensurate, ferroelectric, and ferroelastic phases. The temperature dependence of the longitudinal and transverse ultrasonic wave velocities under the PTs was studied for this crystal by the pulse-echo method at a frequency of 10 MHz. Under the applied hydrostatic pressure significant changes of the temperature dependence character for the longitudinal and transverse elastic waves were found in the incommensurate phase. The results were explained phenomenologically, considering the interactions of elastic waves with normal coordinates of the incommensurate phase-phason and amplitudon