Thermochemical assessment and systematics of bonding strengths in solid and liquid “MeN” 3d transition metal nitrides

Abstract

Thermodynamic data provide a kind of information on the cohesive properties of materials which is appropriate for the analysis of regularities and trends across the periodic table. This approach has been applied to the study of bonding trends in solid and liquid MeN nitride phases with Me being Sc, Ti, V, Cr, Mn, Fe, Co or Ni. The bonding strength is characterized by using a quantity introduced by us which measures the energy gained when forming the substance from the elements. This quantity, called the bonding enthalpy, is evaluated for both stable and metastable solid MeN phases with the (cF8) NaCl-type structure. Stable phases are treated by relying on calorimetric data, while the properties of metastable phases are obtained from calculations based on the compound energy model (CEM) for interstitial solutions. This analysis is complemented with a study of the bonding enthalpy of MeN liquid nitrides, which are considered in a special ordered state that is comparable with the (cF8) structure. Information about these liquid phases is obtained from the interaction energies that are involved in the nearest-neighbour bond energy model (NN-BEM) for condensed mixtures. A complete account is given of the use of the CEM and NN-BEM in a thermochemical characterization of bonding strengths. The bonding enthalpies arrived at in this work are used in establishing trends across the 3d transition series which are considered in the light of recent studies of the electronic structure of NaCl-type structure carbides and nitrides. In addition, a detailed comparison is performed with the approach to cohesion in alloys developed by Miedema and coworkers. Our analysis reveals significant systematic discrepancies. Finally, the information obtained by us is applied in examining theoretical and empirical generalizations about the predominance of chemical bonding effects in the heat of formation of compounds.