Vacancy short-range order in substoichiometric transition metal carbides and nitrides with the NaCl structure. II. Numerical calculation of vacancy arrangement

Using Babinet's theorem and certain results of the theory of short-range order originally developed for Cu₃Au alloys it is shown that the diffuse scattering intensity in the electron diffraction patterns of the substoichiometric transition metal carbides is related to a short-range order of carbon vacancies. Numerical values for the short-range order parameters can be obtained by integrating over the total diffuse intensity within one repetitive unit in reciprocal space. To perform such calculations on VC_0.75 an analytical function was identified which describes the shape of the diffuse intensity curves in reciprocal space. Making the simplifying assumption that the value of the diffuse intensity is 1 on the diffuse intensity curve and 0 everywhere else numerical values for the vacancy short-range order in VC_0.75 were obtained. The results, represented as average numbers of vacancies in different coordination shells around a vacancy, agree with the general principles of vacancy arrangement found in ordered transition metal carbides and nitrides.