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 t his work is to investigate the phase diagram of caesium-dysprosium and caes ium-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)), polari zed reflectance spectra (400- 1000 cm(-1)), absorption spectra (13,000-13,5 00 cm(-1)), temperature dependence of birefringence and visual observations of the domain structure at phase transition were measured. Hysteresis loop s at the phase transition of the first order type were obtained too. The re sults were discussed in terms of the simplified one-dimensional model of la yered crystals. (C) 2001 Elsevier Science B.V. All rights reserved.