Manifestation of phase transitions in the crystal field spectra of [(CH3)2CHNH3]4Cd3Cl10:Cu crystals

On the basis of absorption spectroscopy data the temperature evolution of the Cu2+ ion environment in the crystal of [(CH3)2CHNH3]4Cd3Cl10 doped with Cu2+ (IPACC:Cu) was studied. As it follows from the temperature dependences of heat capacity and absorption coefficient at a constant wavelength IPACC:Cu crystals are characterised by I order phase transitions at T1 = 358 K and T3 = 253 K whereas the continuous changes observed at T2 = 293 K would be related to the first order phase transition close to the second order. For the detailed analysis of the crystal field spectra in the temperature range from T3 till T1 the special program package Crys Tool 2.0 based on the quantum mechanical models first of all on the model of normalized spherical harmonics (NSH) has been employed. It has been found that similarly to the crystal of ((CH3)2CHNH3)4Cd3Cl10 (IPACC) the investigated doped crystal contains the distorted octahedral metal-halogen complexes of two types and the degree of their distortion is considerable changed in vicinity of the phase transition at T2 = 293 K. The phase transitions at T2 and T3 were found to be shifted toward the low temperatures in comparison with initial IPACC crystal whereas the high temperature transition at T1 is shifted to the higher temperatures.