It was recalled that congruently grown samples of this material were highly defective; because of its appreciable Li2O deficiency. Two stoichiometry-related models were extant. They could be distinguished with respect to the occurrence of Li or Nb vacancies. The Nb-vacancy model assumed an ilmenite structure, and predicted a Nb antisite concentration that was at least 5 times as high as that for the Li-vacancy model. It was argued here that the Mg-doping mechanism was essentially independent of such differences. It was suggested that extended stoichiometry-related defect clusters provided a key for the proper understanding of the defect chemistry of impurity cations. The analysis was based mainly upon recent shell-model simulations of the perfect and defective material.

H.Donnerberg: Journal of Solid State Chemistry, 1996, 123[2], 208-14