Dependence of the Cl⁻ → Cu²⁺ charge transfer with hydrostatic pressure in the pure and Cu-doped A₂MCl₄ (M = Mn, Cd, Cu) layer perovskite. Structural correlations

Abstract

This work investigates the dependence of the Cl⁻ → Cu²⁺ Charge Transfer (CT) bands with the local structure around Cu²⁺ in the Jahn-Teller CuCl^4- ₆ complexes formed in layer chloroperovskites with the K₂NiF₄-type structure. We present experimental results on the variation of the first CT band of CuCl^4- ₆ with hydrostatic pressure in the 0–80 kbar range. The study has been carried out in CuCl^4- ₆ formed either as impurity in Cu²⁺-doped crystals or in pure A₂CuCl₄ compounds in order to establish structural correlations. A noteworthy feature is the redshift undergone by the first CT band at about 26000 cm⁻¹, upon pressure in all the investigated systems. This redshift is interpreted in terms of anisotropic distortions of the octahedral elongated CuCl^4- ₆ complex. MS-Xα and Extended Hückel calculations of the electronic structure around the D_4h equilibrium geometry allow us to establish correlations between the energy shift and the structural distortions of the complex.

Key Words:

• Jahn-Teller
• CuCl^4- ₆
• Impurity
• Charge transfer
• Hydrostatic pressure