Spectroscopic evidences of the Jahn-Teller phase transition in the mixed crystals CsDy1-xBix(MoO4)2

Layered rhombic double molybdates of the family (MMIII)-M-I(MoO4)(2) reveal the sequences of phase transitions of different types which take place in the temperature region from 300 K down to helium temperatures. The aim of this work is to investigate the phase diagram of caesium-dysprosium and caesium-bismuth double molybdates and mixed CsDy1-xBix(MoO4)(2) crystals (x = 0.05-0.8). We have studied the low-temperature Jahn-Teller phase transition which takes place in CsDy(MoO4)(2) at 42 K and the influences of Bi doping on this feature. The polarized far-infrared spectre (40-500 cm(-1)), polarized reflectance spectra (400- 1000 cm(-1)), absorption spectra (13,000-13,500 cm(-1)), temperature dependence of birefringence and visual observations of the domain structure at phase transition were measured. Hysteresis loops at the phase transition of the first order type were obtained too. The results were discussed in terms of the simplified one-dimensional model of layered crystals. (C) 2001 Elsevier Science B.V. All rights reserved.