The C54 phases of ${\mathrm{TiSi}}_2$ and ${\mathrm{TiGe}}_2$ are known to be completely miscible, however, we have observed that thin films of C54 Ti(${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_2$ are not stable in contact with ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ when y=x. In this study it is shown that this interface instability can be related to the composition-dependent energetics that determine the Ti-Si-Ge ternary equilibrium diagram. Tie lines of the Ti(${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_2$ to ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ system were calculated on the basis of classical thermodynamics. The calculations indicate that for C54 Ti(${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_2$ to be stable in contact with ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$the compositions of the two phases must be such that y<x. The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamics of the interface reactions of C54 Ti(${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_2$ on ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ are related to the calculated tie lines, and the diffusion kinetics of the materials. Experimental results are presented that quantitatively support the model calculations. © 1996 The American Physical Society.

• Received 20 February 1996

DOI:https://doi.org/10.1103/PhysRevB.53.16279