Jahn-Teller effects in the mixed vanadate/phosphate crystalsTbV1−xPx

Y. Hirano

¹

,

N. Wakabayashi

²

,

C.‐K. Loong

³

et al.

Abstract

X-ray-diffraction measurements were performed on mixed vanadate/phosphate single crystals of the type: TbV 1Ϫx P x O 4 ͑where xϭ0, 0.10, 0.18, 0.24, and 0.32͒ in order to investigate the effects of P doping on the Jahn-Teller phase transition. The transition temperature, below which the tetragonal symmetry of the lattice is lowered to orthorhombic, decreases with increasing P concentration. In order to explain the order parameters of the transition and the striking reduction in the transition temperature with increasing P content, a modified mean-field model was developed for the mixed system. A simple calculation assuming only a distribution in the value of the quadrupolar crystal-field parameter B 2 0 is unsatisfactory. Since the local tetragonal symmetry is broken due to the random distribution of phosphorous, a term involving the operator P xy ϭ 1 2 (J x J y ϩJ y J x ) was introduced in the Hamiltonian that includes both the crystal-field and magnetoelastic effects. This term, in conjunction with the distribution in the magnitude of the corresponding crystal-field parameter, was essential in order to reproduce the observed temperature dependence of the order parameter ͑orthorhombic strain͒. The results of the diffuse scattering measurements performed on the xϭ0.32 crystal confirmed the existence of local strains that should give rise to variation in B 2 0 . The diffuse intensity due to strains having the symmetry associated with P xy could not be resolved, however, because of the overlapping thermal diffuse scattering.

Probing the Local Structure and Phase Transitions of Bi4V2O11‐Based Fast Ionic Conductors by Combined Raman and XRD Studies

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Comparative study of low-temperature x-ray diffraction experiments onR2Ir2O7(R=NdTakatsu1, Watanabe2, Goto3 et al. 2014Phys. Rev. B448200View full textAdd to dashboardCite

“…We have measured temperature dependence of the lattice parameter down to 4 K, since the temperature change in the lattice parameter can be precisely detected by our setup [39]. It is also a reason that if the crystal-structure phase transition occurs, a related structural change or a precursor of the phase transition are known to be observed in the T dependence of lattice parameters, strain, and elastic constants [40][41][42][43]: thus in addition to searching the emergence of a superlattice reflection and splitting of peaks in x-ray diffraction patterns, searching of an anomaly in the T dependence of the lattice parameter is also a simple and direct way for the clarification of small changes in the crystal-structure phase transition. We have found a negative thermal expansion that appears only for NIO at temperatures below T MIT = 34 K. The crystal structure retains the cubic pyrochlore structure (space group F d3m, No.…”

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“…TbVO 4 and TbAsO 4 show related behavior near and below their tetragonal-to-orthorhombic cooperative Jahn-Teller phase transitions at 33.1 K and 29.0 K, respectively [27,28]. Similar high resolution x-ray scattering measurements performed with the same experimental set up on these two materials show an extreme form of this pattern of splitting of Bragg peaks below T C [29].…”