Investigations of the Anisotropic Optical Reflectivity of Binary and Ternary Nb-W Oxides Possessing Block-Type Crystal Structure

Abstract

We have studied the anisotropic optical properties of binary NbO2.5-δ (0 < δ ≤ 0.083) and ternary Nb18-εW8+εO69 (ε = 0, 1,..., 9) compounds using the polarized regular-reflection method. We observed strong anisotropic behaviour for all reduced phases. The anisotropic effect can be related to the crystallographical structure principle and to the doping of charge carriers by the reduction of oxygen (δ) or substitution of W for Nb (ε) in the binary and ternary oxides, respectively. Our results indicate that the charge carriers are confined to the structural block units. For increasing δ and ε, metal-like properties occur (δ≥ 0.1, ε > 8) in the infinite block direction only.