THERMOCHEMICAL ASSESSMENT AND SYSTEMATICS OF BONDING STRENGTHS IN SOLID AND LIQUID MEN 3D TRANSITION-METAL NITRIDES

Thermodynamic data provide a kind of information on the cohesive prope rties of materials which is appropriate for the analysis of regulariti es and trends across the periodic table. This approach has been applie d to the study of bonding trends in solid and liquid MeN nitride phase s 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 t he energy gained when forming the substance from the elements. This qu antity, 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 propert ies of metastable phases are obtained from calculations based on the c ompound energy model (CEM) for interstitial solutions. This analysis i s complemented with a study of the bonding enthalpy of MeN liquid nitr ides, which are considered in a special ordered state that is comparab le with the (cF8) structure. Information about these liquid phases is obtained from the interaction energies that are involved in the neares t-neighbour bond energy model (NN-BEM) for condensed mixtures. A compl ete account is given of the use of the CEM and NN-BEM in a thermochemi cal characterization of bonding strengths. The bonding enthalpies arri ved at in this work are used in establishing trends across the 3d tran sition series which are considered in the light of recent studies of t he electronic structure of NaCl-type structure carbides and nitrides. In addition, a detailed comparison is performed with the approach to c ohesion in alloys developed by Miedema and coworkers. Our analysis rev eals significant systematic discrepancies. Finally, the information ob tained by us is applied in examining theoretical and empirical general izations about the predominance of chemical bonding effects in the hea t of formation of compounds.