Short-range order, atomic displacements and effective interatomic ordering energies in TiN0.82

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Abstract
The elastic diffuse neutron scattering of a TiN0.82 single crystal has been measured in thermodynamic equilibrium at 700, 800 and 900 °C. The diffuse intensity is maximum at the (1/2 1/2 1/2) type reciprocal lattice positions. Nitrogen vacancies are found to situate preferentially as third neighbours on the metalloid f.c.c. sublattice. Pair interaction ordering energies were calculated by mean-field approximation, Monte-Carlo simulations, and Cluster Variation Method ; the last two methods give very similar temperature independent pair energies : V1 ≃ 82 and V 2 ≃ 62 meV for first and second nitrogen neighbours respectively ; V3 and further interaction energies are very small. Titanium atoms are found to relax away, and nitrogen atoms to relax toward their first neighbour vacancies, by respectively 0.042 and 0.024 A