Eur. Phys. J. AP 4, 5-9 (1998)
https://doi.org/10.1051/epjap:1998239

Electrical and optical investigations of Rb₂ZnCl₄ crystals in the vicinity of the incommensurate phase

Physics Department, Faculty of Science, Assiut University, Assiut, Egypt

Corresponding author: assiut@frcu.eun.eg

Received: 27 February 1998
Revised: 28 May 1998
Accepted: 28 May 1998
Published online: 15 October 1998

Abstract

Temperature dependence of the dielectric constant ϵ and the electrical resistivity ρ of Rb₂ZnCl₄ (RZC) along the three crystallographic axes were measured between 260 and 360 K. The electrical measurements clearly reveal the paraelectric incommensurate phase around 303 K. Peaks in the dielectric constants ϵ_a and ϵ_b were observed at this transition temperature. The results of the electrical resistivity were analyzed and the activation energies of conduction at different temperature regions were evaluated. The dependence of the absorption coefficient α on the photon energy and on temperature near the fundamental absorption edge was measured. Exponential dependence of that coefficient according to the Urbach's rule was observed and the Urbach parameters were determined and their temperature dependence was investigated. The temperature gradient of the band gap reveals an anomaly at the incommensurate paraelectric phase. The indirect band gap was shifted towards the longer wavelength (red shift) with increasing temperature. This behaviour could be interpreted in terms of electron lattice interaction and crystal field splitting.