Influence of phase transitions in the charge transfer spectra of TMA₂MnCl₄:Cu²⁺

Abstract

The local geometry and the orientation of the CuCl₄ ^2- complexes formed in TMA₂MnCl₄:Cu²⁺ are studied through the polarized Charge Transfer (CT) spectra in the 10 - 300 K temperature range. The analysis of these spectra indicates that CuCl₄ ^2- complexes display distortions of D_2d symmetry along only one of the tetrahedron S₄ axes, with bond angles of 124°. The structural phase transitions undergone by this crystal mainly involve reorientational motions of the CuCl₄ ^2- complexes. Below the P112₁/n→P12₁/cl phase transition temperature, 171 K, the CT spectra experience the highest variations due to the formation of domains.