Published online by Cambridge University Press: 15 October 1998
Temperature dependence of the dielectric constant ϵ and theelectrical resistivity ρ of Rb2ZnCl4 (RZC) along the threecrystallographic axes were measured between 260 and 360 K. The electrical measurementsclearly reveal the paraelectric incommensurate phase around 303 K. Peaks in thedielectric constants ϵa and ϵb were observed at this transitiontemperature. The results of the electrical resistivity were analyzed and the activationenergies of conduction at different temperature regions were evaluated. The dependenceof the absorption coefficient α on the photon energy and on temperature near thefundamental absorption edge was measured. Exponential dependence of that coefficientaccording to the Urbach's rule was observed and the Urbach parameters were determinedand their temperature dependence was investigated. The temperature gradient of the bandgap $(\partial E_{g}/\partial T)$ reveals an anomaly at the incommensurate paraelectricphase. The indirect band gap was shifted towards the longer wavelength (red shift)with increasing temperature. This behaviour could be interpreted in terms of electronlattice interaction and crystal field splitting.