Spontaneous and electrical field-stimulated processes at the CaWO4∣WO3 interface

At the CaWO4∣WO3 interface in air at 900°C under a minimum external mechanical pressure, two oppositely directed processes—(i) spreading of WO3 on the surface of CaWO4 and (ii) penetration of calcium from CaWO4 (or CaWO4 itself) into the bulk of WO3—occur simultaneously. The electric field of a certain polarity accelerates both processes. To explain the experimental data, a model of the surface intermediate phase (CW-s) was proposed and proved in experiments. The key point is that the specific surface energy αCW-s is lower than αWO3 and αCaWO4.