Thermodynamics controls amorphous oxide formation: Exclusive formation of a stoichiometric amorphous (Al0.33Zr0.67)O1.83 phase upon thermal oxidation of Al-Zr

During thermal oxidation of binary amorphous AlxZr1−x solid solutions over wide alloy-composition (0.26 ⩽ x ⩽ 0.68) and oxidation-temperature (350-560 °C) ranges, a single amorphous ternary oxide phase of well-defined stoichiometry, (Al0.33Zr0.67)O1.83, emerges. The composition of this unexpectedly stoichiometric ternary amorphous oxide phase, that develops instead of the crystalline oxide phases Al2O3 and ZrO2, under conditions far away from genuine thermodynamic equilibrium, is governed by thermodynamics, as demonstrated by thermodynamic assessment, adopting the amorphous (Al0.33Zr0.67)O1.83 phase as a supercooled liquid oxide-oxide (Al2O3-ZrO2) solution phase.