Atomistic simulation of sodium-gadolinium molybdate of stoichiometric compositions

Crystals of sodium-gadolinium molybdates of two compositions: stoichiometric ([Na.sub.1/2][Gd.sub.1/2]Mo[O.sub.4]) and cation-deficient ([Na.sub.2/7][Gd.sub.4/7]Mo[O.sub.4]) composition in which 1/7 of the corresponding cation positions are not occupied are simulated by the method of interatomic potentials. For cation-deficient crystals, two kinds of cation position distribution are considered: the statistical distribution of sodium, gadolinium, and unoccupied cation positions in the I[4.sub.1/a] structure and their partial ordering in the I[bar.4] space group. As a result of the simulation, structural characteristics of sodium-gadolinium molybdates agreeing well with the known experimental data are obtained. In addition, a number of important elastic and thermodynamic properties of these compounds are predicted. The results obtained in the partial-occupancy approximation and by constructing a 7 x 2 x 2 supercell are compared. The local structure of sodium-gadolinium molybdates are analyzed in detail. The influence of the deviation from the stoichiometry as well as cation ordering on the properties of these crystals is discussed. DOI: 10.1134/S1063783417050110