Ultrasonic study of the structural phase transitions in [N(CH3)4]2CuCl4

Low-frequency elastic properties of the incommensurate ferroelastic [N(CH3)4Kityk1, Soprunyuk2, Fuith3 et al. 1996Phys. Rev. B311160View full textAdd to dashboardCite

“…Simultaneously we present also some results of ultrasonic measurements for comparison with the results of DMA measurements. In contrast to previous considerations 10,13,15 the obtained results are explained within the framework of plane-wave and soliton models.…”

“…The most appreciable softening occurs here in the elastic constant C 33 Ј which is in good agreement with previous acoustical measurements. 10,14 From the presented data it follows that the main contributions to the changes of the effective elastic constants C r Ј(i) at TϭT i are caused preferably by the first terms of Eq. ͑3͒.…”

“…On further cooling, another monoclinic proper ferroelastic phase ͓space group P112 1 /m (C 2h 5 )͔ appears below T 1 ϭ263 K. Ultrasonic studies showed an additional phase transition at T 2 ϭ127 K but the symmetry of the low-temperature phase is still unknown. 10 Phase transitions in TMATC-Cu crystals have been studied by various experimental techniques: neutron diffraction, 9 Raman scattering, dilatometric, and heat-capacity measurements, 11 dielectric and ultrasonic measurements, 10,[12][13][14][15][16] optical birefringence and optical-microscope observations of the domain structure. 11,12,14,15 Particularly, ultrasonic measurements 13 have revealed a remarkable change of the shear elastic constant C 55 ͑Fig.…”

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

“…These materials have attracted attention in the field of fundamental physics primarily because of a complicated sequence of structural phase transitions. These crystals are isomorphous, with space group Pmcn, and there are four formula units per unit cell with dimensions of approximately a=9 Å, b=15 Å, and c=12 Å 4 . In particular, the appearance of successive lattice transformations from a prototype structure to an incommensurate structure, and then to a commensurate structure is a ferroelastic phenomenon in the investigation of phase transitions.…”

Molecular motion study of [N(CH3)4]2Zn1–xCux Cl4 (x = 0, 0.01, 0.1, 1) mixed crystals by 1H NMR relaxation

“…Below 263 K, these crystals form a monoclinic phase (IV). On heating, they transform at 263 K into another monoclinic phase (III), then into an incommensurate phase (II) at 291 K, and finally to a commensurate phase (I) at 301 K. The highest temperature phase (phase I) has an orthorhombic structure with lattice constants a = 9.039 Å, b = 15.515 Å, and c = 12.268 Å, which are slightly deformed from the hexagonal values [4]. A fourth phase transition, at 200 K, was recently determined from the spinlattice relaxation time and with differential scanning calorimetry (DSC) [5].…”