B-site ordered double perovskite LaBa1−xSrxZnSbO6 (0 ≤ x ≤ 1): Sr2+-doping-induced symmetry evolution and structure–luminescence correlations

Abstract

The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO₆, by selecting Zn²⁺ and Sb⁵⁺ with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr²⁺-doping-induced symmetry evolution from I2/m to P2₁/n was confirmed in the complete solid solutions LaBa_1−xSr_xZnSbO₆, where the tilting system also transferred from a⁻a⁻c⁰ to a⁻a⁻c⁺. The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr–O bond distances (revealed by Rietveld refinements) motivated us to study the Eu³⁺ luminescence in La_0.95Eu_0.05Ba_1−xSr_xZnSbO₆. Interestingly, the maximum of charge transfer absorption of Eu³⁺ shows a precise changing tendency with the A–O bond distances along with the Sr²⁺ doping, clearly revealing the structure–luminescence correlations.