- Conference date: 1990
- Location: Albuquerque, NM (USA)
We systematize available thermodynamic information on transition metal diborides, with emphasis on the enthalpy of formation, the vibrational entropy and the melting temperature. When experimental information is lacking, e.g., for metastable compounds, we obtain estimates through interpolation and extrapolation procedures introduced by us. Our results are used, i.a., to account for the change from stable to metastable transition metal diborides as one proceeds along a transition‐metal line in the Periodic Table. Our method of analysis combines available experimental thermodynamic and lattice–parameter data with CALPHAD calculations of phase diagrams and knowledge from solid state theory on electron states and lattice vibrations. An important point in the analysis is that in the high‐temperature vibrational entropy, atomic masses are separated from the interatomic forces. That allows us to introduce a quantity with the dimension of energy, which depends only on the electronic structure and shows a regular behavior along a transition metal row in the Periodic Table, and moreover co‐varies with the enthalpy of formation of the compounds. Thus we can study the trends in the Gibbs energy G=H−TS of the diborides and account for the systematics of their stability properties.
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