  Herein we report on the synthesis of a metastable (Cr,Y)2AlC MAX phase solid
solution by co-sputtering from a composite Cr-Al-C and elemental Y target, at
room temperature, followed by annealing. While direct high-temperature
synthesis resulted in multiphase films, as evidenced by X-ray diffraction
analyses, room temperature depositions, followed by annealing to 760 {\deg}C
led to the formation of phase pure (Cr,Y)2AlC by diffusion. Higher annealing
temperatures caused decomposition of the metastable phase into Cr2AlC, Y5Al3 ,
and Cr-carbides. In contrast to pure Cr2AlC, the Y-containing phase
crystallizes directly in the MAX phase structure instead of first forming a
disordered solid solution. Furthermore, the crystallization temperature was
shown to be Y-content dependent and was increased by ~200 {\deg}C for 5 at.% Y
compared to Cr2AlC. Calculations predicting the metastable phase formation of
(Cr,Y)2AlC and its decomposition are in excellent agreement with the
experimental findings.
