FIR spectroscopy study of the first-order phase transition of (CH3CH2NH3)2CdCl4

Abstract

The temperature dependence of the far infrared reflectivity of the layer compound (CH3CH2NH3)2·CdCl4 are investigated from 120 to 300 K. Only small frequency shifts are observed at the order disorder OLT‐ORT phase transition, but some normal modes are drastically broadened. The line broadening results are compared to the X‐ray investigation data on the disordered motions in the ORT phase. The anisotropy of the observed line broadening effects reproduces the thermal motions anisotropy and consequently it is proposed to explain this broadening by the disorder effects. The mechanisms connecting the motions of the ethyl‐ammonium chains and the linewidths are discussed and a comparison with NMR results suggests that the disorder may play a dynamical role in the line broadening.

Raman spectroscopic study of structural phase transitions in the layer crystals (EtNH3)2MCl4with M=Cd and Mn

“…The structural phase transitions of EAMnC and EACdC have been studied by NMR (Blinc eta1 1977), crystallographic (Chapuis 1977, Depmeier 1977, Depmeier and Heger 1978, optical (Brunskill andDepmeier 1982, Karajamaki eta1 1981): dielectric , calorimetric (Tello et a1 1977) and infrared (Oxton 1979, Peyrard andPerret 1979) measurements. They are summarised in table 1.…”