Local tetragonal distortions of the (CrF₆)³⁻ and (FeF₆)³⁻ octahedral clusters in Cr³⁺- and Fe³⁺-doped tetragonal Rb₂KGaF₆ crystals

ABSTRACT

The local tetragonal distortions (α − α₀) (where α is the angle defined as tgα = R_⊥/R_//, R_⊥ and R_// are the metal–ligand distances parallel with and normal to the C₄ axis, α₀ = 45° is the same angle in cubic symmetry) of (CrF₆)³⁻ and (FeF₆)³⁻ octahedral clusters in the tetragonal Rb₂KGaF₆ crystals are estimated by analyzing their electron paramagnetic resonance (EPR) zero-field splittings D. The results indicate that the two impurity octahedra and hence the host (GaF₆)³⁻ octahedra are tetragonally elongated. The distortion (α − α₀) in magnitude differs from impurity to impurity because of the different sizes and natures of these impurities. These results are analogous to those in ABX₃ and doped ABX₃ perovskite crystals where the cubic-to-tetragonal phase transition is due to the rotation of BX₆ octahedra associated with the release or elongation of B–X bond along the C₄ rotational axis.

KEYWORDS:

• Defects
• local distortion
• electron paramagnetic resonance
• Cr³⁺
• Fe³⁺
• Rb₂KGaF₆

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project is supported by the Initial Foundation of Mianyang Normal University [grant no. MQD2011A05], the LPMT, CAEP [grant no. KF13003].