Phase formation and electrical properties in the system BaO–Li2O–TiO2

Abstract

A survey of compound formation and phase equilibrium in the system BaO–Li₂–TiO₂ for compositions containing >50% TiO₂ has been made at subsolidus temperatures, ca. 1150–1200 °C. Four ternary phases were encountered, all of which have variable composition. These are phase A, centred on Ba₃Li₂Ti₈O₂₀, phase B centred on BaLi₂Ti₆O₁₄, phase C based on the line Ba₂Ti_{10 –x}Li_4xO₂₂ and phase E, a hollandite-like phase Ba_3xLi_{(2x+ 4y)}Ti_(8-2x–y)O₁₆. Phase A is new; phase B is the phase responsible for high Li⁺ ion conductivity reported by Zheng et al.(Solid State Ionics, 1989, 35, 235); phase C is related to one reported by Tillmanns and Wendt (Z. Kristallogr., 1976, 144, 16) whose formula coincided with x= 0.75; phase E was reported by Sucket et al.(J. Mater. Chem., 1992, 2, 993). In addition, an extensive area of ternary solid solution based on Ba₄Ti₁₃O₃₀ is reported. Mechanisms of solid-solution formation are discussed; the two principal mechanisms appear to be Ti⁴⁺⇌ 4Li⁺ and 2Ti⁴⁺⇌ 2Li⁺+ 3Ba²⁺. Electrical conductivity data are reported; phases A, C and D appear to be very modest electronic conductors.