• Ponweiser, Norbert
• Lengauer, Christian
• Richter, Klaus W.
• Warczok, Piotr

Abstract

The section Hf5Ge4-Zr5Ge4 shows the existence of extended ternary solid solutions based on the binary compounds Hf5Ge4 (Pearson symbol: oP36) and Zr5Ge4 (Pearson symbol: tP36). The corresponding homogeneity ranges have been determined experimentally at 1350 °C. Partial ordering of the metal atoms at the three crystallographically independent metal sites of the structures was investigated by means of powder X-ray diffraction (XRD) followed by Rietveld refinement as well as by single crystal XRD. The two metals Hf and Zr exhibit site preferences throughout their respective homogeneity ranges. Using a simple thermodynamic model ("compound energy model") and employing ground state energies of hypothetical ordered compounds calculated from ab initio density functional theory, the experimentally observed site fraction data were reproduced with high accuracy. The obtained Gibbs energies were furthermore used to calculate the stability ranges of the two different phases at 1350 °C. The possible benefit of this approach for the prediction of phase stability and for the Calphad-type modeling of higher-order systems is discussed.

Topics

• density
• impedance spectroscopy
• compound
• single crystal
• phase
• theory
• powder X-ray diffraction
• density functional theory
• phase stability
• CALPHAD