First-principles calculations were performed on perovskite-type ScRh3Bx in order to understand the variation in the structural properties and bulk modulus as a function of the B concentration. The projected augmented wave method was used, with a super-cell, to treat various configurations of vacancies and B atoms. The generalized gradient approximation was used for the exchange-correlation functional. The calculated lattice constants were found to be in excellent agreement with experimental results. The maximum bulk modulus was found for x = 0.5; quite contrary to the expectation that vacancies should reduce the number of chemical bonds and hence the strength of the compound. This was explained by examining changes in the atomic and electronic structures upon B doping. It was found that doping enhanced the cohesive energy monotonically due to the strong covalent bonding between the B 2p and Rh 4d states. However, at x = 0.5, a configuration occurred in which each B atom was surrounded by vacancies at the cube centers, and vice versa. This reduced the strain in the structure and the Rh-B bonds were short; leading to a maximum in the bulk modulus. The density of states at the Fermi energy was also a minimum for x = 0.5 which added further stability to the structure.

Mechanism of the Increase in Bulk Modulus of Perovskite ScRh3Bx by Vacancies. R.Sahara, T.Shishido, A.Nomura, K.Kudou, S.Okada, V.Kumar, K.Nakajima, Y.Kawazoe: Physical Review B, 2006, 73[18], 184102 (9pp)