First-principles study of elastic and stability properties of ZrC–ZrN and ZrC–TiC alloys

• Published in: Journal of physics. Condensed matter 2009-09, Vol.21 (39), p.395503-395503 (8)
• Main Authors: Ivashchenko, V I, Turchi, P E A, Shevchenko, V I
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Elasticity, elastic constants; Electron states; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Methods of electronic structure calculations; Physics; Solubility, segregation, and mixing; phase separation
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/21/39/395503

Ab initio calculations of the elastic constants for several cubic ordered structures of zirconium carbonitride (ZrC(x)N(1-x)) and zirconium-titanium carbide (Zr(x)Ti(1-x)C) alloys were carried out. The calculations of total and formation energies, bulk modulus and elastic constants as functions of composition were performed with an ab initio pseudo-potential method. The predicted equilibrium lattice parameters are slightly higher than those found experimentally (on average by 0.2-0.4%). The predicted formation energies indicate that the ZrC(x)N(1-x) alloys are stable even at 0 K in the whole concentration range, while the homogeneous Zr(x)Ti(1-x)C alloys can be stabilized only at high temperatures. Spinodal decomposition of the latter alloys into cubic domains takes place over a wide range of compositions and temperatures. For the carbonitrides, the shear modulus G, the Young's modulus E and the Poisson ratio σ reach an extremum for carbon-rich alloys, and this is attributed to a maximum value of the shear modulus C(44) that corresponds to a valence-electron concentration in the range of 8.2-8.3. This extremal behavior finds its origin in the response of the band structure of ZrC(x)N(1-x) alloys for 0≤x≤1, caused by the monoclinic strain that determines this shear modulus. In contrast, the other shear modulus [Formula: see text] does not exhibit any extremum over the whole composition range. These results are in contrast with those for Zr-Ti carbides for which the elastic properties gradually increase from ZrC to TiC.