Structural study of SrPrZnRuO6, SrPrCoRuO6, SrPrMgRuO6 and SrPrNiRuO6 double perovskite oxides by symmetry-adapted mode analysis

Abstract

Powder SrPrZnRuO6, SrPrCoRuO6, SrPrMgRuO6 and SrPrNiRuO6 double perovskites were synthesized by the solid-state reaction method, and their crystal structure was investigated by Rietveld analysis (using the symmetry-mode procedure) by x-ray, synchrotron and neutron powder diffraction data. SrPrMRuO6 materials are monoclinic perovskites at room temperature, adopting the space group P21/n, , c ≈ 2ap, Z = 2. The unit cell parameters increase through the series as the B-cation size increases. The tilting of the octahedra is associated with irreducible representations GM+4 and X+3. In the studied series, Sr2+/Pr3+ are in eight-fold coordination and are displaced from the center of the Sr/PrO8 polyhedron along [010] by the X+5(A10) mode. The size of the first coordination sphere of Sr/Pr increases and the second coordination sphere reduces with temperature, suggesting an actual change in coordination. While changing the interatomic distances, the distortion of the structure diminishes, as observed in distortion mode amplitudes and octahedral tilt angles. The temperature driven phase transition was observed for Ni and Mg materials at ≈1025 K and 950 K, respectively. Tilting of the octahedra in the trigonal phase is associated with GM+4, which is the unique active mode associated with the not experimentally observed phase transition.