Surface Phase in the CaWO4–WO3 System: A Model for the Topological Structure of Composites

Physicochemical and transport properties of composites formed by CaWO₄ (mixed electron–ion conductor) and WO₃ (n-semiconductor) are studied. At x < 30 mol %, the CaWO₄ · xWO₃ composites display ionic conduction, which turns into electron conduction at x > 30 mol %. During contact of WO₃ with CaWO₄, both phases undergo a qualitative transformation at high temperatures, which is caused by the formation of a surface phase, CW-s. Electric properties of the composites at 900°C are considered within the model proposed for their topological structure.