Alloy heats of formation: Theory versus experiment

Comparison is made among calculated heats of formation of ordered transition metal compounds, experimental heats obtained by Kleppa and coworkers, and parameters appropriate to CALPHAD constructs. The calculated heats are precise representatives of band theory granted the class of local density potential which was employed; comparison with experiment suggests that they are less accurate than is desired. The issue of the stability of excited phases against local distortion is explored indicating that some systems,which are normally presumed to be metastable, are not. This has consequences for CALPHAD phase diagram constructs and suggests that entropy is an important contribution to the local stability of some high- temperature phases.