Short-range order in disordered and ordered niobium carbide NbC0.83 from ab initio calculations

Abstract

Structural models of short-range atomic vacancy ordering in nonstoichiometric NbC_0.83 are proposed and investigated with and without allowance for long-range order. Using computer simulations, relations between the parameters of short-range and long-range order are derived, along with neutron diffraction patterns according to the Debye formula. Quantum-chemical calculations are performed using a super cell. The results show that short-range order is energetically advantageous in the disordered phase and in partially ordered modifications of an ordered phase at long-range order parameters η ≤ 0.4.