Double Non-Stoichiometry: The Lithium Vanadium Oxide Bronzes βLixV2O5-y

Abstract

The β (or β') LixV2O5 phases lose oxygen at high temperature, the approximate formula LixV2O5-y, leading to the formation of phases LixV6O15 LixV9O22 and LixV12O29. A general formula is proposed to relate this series, LixV3(1+n)O8+7n, to the corresponding n values of 1, 2 and 3. In fact, n, as an integer, can be formally varied in the range 0 ≤ n → ∞. Their crystal structures are derived by a structural mechanism based on extended Wadsley defects, denoted 1/10[051](100), affecting the LixV6O15 structure. Numerous syntheses performed in the Li2O-V2O5-V2O4 ystem have revealed that no intergrowth structure occurs between the n values 1-2 and 2-3, while, for n > 3, a defect structure has been evidenced by high resolution electron microscopic investigations. The LixV12O29-є phase is depicted as an intergrowth of the structure of the n = 4 member, i.e. LixV15O36, in the sequence of the LixV12O29 crystal structure. In a general discussion, the structural relationships between these phases are particularly emphasized, extended defects crossing tunnel structures being rather unusual.