Structural Correlations in Jahn–Teller Systems of Mn³⁺ and Cu²⁺: Unraveling Local Structures through Spectroscopic Techniques

Abstract

An experimental correlation study between the low-symmetry 3d orbital splitting pattern, Δe and Δt, determined by optical spectroscopy, and the local distortion ρ, determined by X-ray diffraction, for different Cu2+ and Mn3+ fluorides and chlorides is presented. Single crystals of different dimensionalities were explored, some of them studied under high-pressure conditions. The collection of structural and spectroscopic data provides structural correlations relating ρ and Δe and Δt in Cu2+ and Mn3+ systems, showing that Δe (and Δt) scales with ρ. Such correlations can be used to estimate local distortions of Cu2+ (or Mn3+) introduced as impurities in different chloride and fluoride host lattices from spectroscopic data. The results can be interpreted in the framework of the Jahn–Teller theory and provide support for the proposed structural scenario. The influence of the crystal anisotropy in the local structure is analyzed as well and compared with transition metal ion systems having E⊗e Jahn–Teller (Cu2+, Mn3+) and singly orbital (Ni2+, Mn2+, Fe3+) ground states in octahedral symmetry.