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

Abstract During thermal oxidation of binary amorphous Al x Zr 1− 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, (Al 0.33 Zr 0.67 )O 1.83 , emerges. The composition of this unexpectedly stoichiometric ternary amorphous oxide phase, that develops instead of the crystalline oxide phases Al 2 O 3 and ZrO 2 , under conditions far away from genuine thermodynamic equilibrium, is governed by thermodynamics, as demonstrated by thermodynamic assessment, adopting the amorphous (Al 0.33 Zr 0.67 )O 1.83 phase as a supercooled liquid oxide–oxide (Al 2 O 3 –ZrO 2 ) solution phase.