Study of the local structure of Jahn-Teller distorted CuX^2-M₄ (X = Cl, Br) systems by polarized charge transfer spectroscopy: Influence of chemical pressure along A₂MX₄ (M = Mn, Zn, Cd, Hg)

Abstract

The aim of this work is to investigate the Charge Transfer (CT) spectra of CuCl^2- ₄ and CuBr^2- ₄ complexes formed in Cu²⁺-doped A₂MX₄ crystals and their dependence with chemical pressure when Cu²⁺ replaces the divlent cation at the MCl^2- ₄ tetrahedral site. A salient feature of this study is the weak sensitivity exhibited by the CT bands to structural changes of the complex. A similar phenomenon has also been observed for pure chlorocuprates. The analysis carried out on the available family of chlorocuprates indicates that the CT band-shift induced by structural distortions in CuCl^2- ₄ is smaller than that of the corresponding Crystal Field (CF) bands. We present a perturbative model for explaining the weak sensitivity of the CT bands. We present a perturbative model for explaining the weak sensitivity of the CT bands. in comparison to the CF ones. The estimates of the model accounts for the spectroscopic results observed along the A₂MCl₄: Cu²⁺ series.

Key Words:

• Tetrahedral complex
• Charge Transfer transition
• Jahn-Teller distortion
• CuCl^2- ₄
• CuBr^2- ₄