Ultrasonic study of the normal — incommensurate — commensurate phase transitions in [N(CH3)4]2ZnCl 4

Abstract

The shear elastic constants c44, c55, and c66 of single-crystal [N(CH3)4] 2ZnCl4 have been measured at 10 MHz near the normal-incommensurate transition at Ti ≃ 23°C, the incommensurate-ferroelectric commensurate lock-in transition at Tc ≃ 8°C, and the first-order ferroelectric-ferroelastic transition at T1 ≃ 4°C. A substantial variation in the velocity and attenuation of the c66-mode ultrasonic shear wave in the incommensurate phase can be understood qualitatively in terms of soliton-phonon coupling. The longitudinal attenuation α associated with the c11 mode was also studied as a function of frequency (10-70 MHz) near T i. The critical attenuation in the incommensurate phase could be well characterized by α ≃ f2(Ti - T)-0.9

Molecular Motions of [N(C2H5)4]+and [N(CH3)4]+ions by1H Nuclear Magnetic Resonance Relaxation in [N(C2H5)4]2CoCl4and [N(CH3)4]2CoCl4Single Crystals

“…changes; based on this information, it has been concluded that these phase changes are always accompanied by changes in molecular motion. [9][10][11] This study employed a pulsed nuclear magnetic resonance (NMR) spectrometer to investigate the temperature dependences of the line widths and the spin-lattice relaxation times, T 1 , for 1…”

“…Co, 63 Cu, and 67 Zn) single crystals belong to the group of A 2 BX 4 -type crystals. [1][2][3][4][5] The magnetic resonance relaxation times of nuclear spin systems have been widely used to elucidate various types of atomic motions in crystals because these relaxation times are related to the structures and internal motions of solids; in particular, the protons of these solids act as resonant nuclei, so the relaxation times of these nuclei reflect the ionic motions in the solid. 1…”

Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals. II. Raman Spectra of Low‐Symmetry Phases

“…However, considerable softening of the elastic shear constants C,, (by ~3 5 % ) has been detected in the incommensurate phase [15]. This softening has been attributed to the soliton-phonon interaction.…”

Structural characteristics of [N(CH3)4]2CdCl4determined by1H MAS NMR,13C CP/ MAS NMR, and14N NMR

“…The sequence of phase transitions in [N(CH 3 ) 4 ] 2 BX 4 (where B=Co, Cu, Zn, Cd; X=Cl, Br) compounds has made them the subject of numerous investigations in recent years [1][2][3] . These materials have attracted attention in the field of fundamental physics primarily because of a complicated sequence of structural phase transitions.…”