ESTIMATION OF FORMATION ENTHALPIES FOR TRANSITION-METAL MONO-NITRIDES, CARBIDES AND OXIDES

Transition metal compounds with the NaCl structure are the constituent components of many metastable multicomponent layer materials deposited at low substrate temperatures. If transition metal nitrides, f or example, are combined with AlN (hex. ZnS structure) , a metastable ternary solution phase having either the NaCl or the ZnS structure is formed. Phase diagram calculations in these systems require a knowledge of the Gibbs energy G(T) of the binary components in both structures. However, formation enthalpies of the metastable modifications are difficult to obtain with sufficient accuracy. Therefore, a new method is proposed to enable estimation of such data. This method accurately accounts for the crystallographic characteristics of both structures under consideration. Its application is demonstrated in detail for the transition metal nitrides with NaCl structure. Calorimetric measurements in the metastable system (Ti, Al)N provide experimental refinement of the estimation method.