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, [Formula: see text], 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, Sr(2+)/Pr(3+) 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 [Formula: see text] 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 [Formula: see text] phase transition.
ABSTRACT
The crystal and magnetic structures of SrLnFeRuO(6) (Ln = La, Pr, Nd) double perovskites have been investigated. All compounds crystallize with an orthorhombic Pbnm structure at room temperature. These materials show complete chemical disorder of Fe and Ru cations for all compounds. The distortion of the structure, relative to the ideal cubic perovskite, has been decomposed into distortion modes. It has been found that the primary modes of the distortion are octahedral tilting modes: R(4)(+) and M(3)(+). The crystal structure of SrPrFeRuO(6) has been studied from room temperature up to 1200 K by neutron powder diffraction. There is a structural phase transition from orthorhombic (space group Pbnm) to trigonal (space group R3c) at T = 1075 K. According to group theory no second-order transition is possible between these symmetries. Magnetic ordering for all the compounds is described by the magnetic propagation vector (0,0,0). SrPrFeRuO(6) shows ferrimagnetic order below ca 475 K, while SrLaFeRuO(6) (below ca 450 K) and SrNdFeRuO(6) (below ca 430 K) exhibit canted-antiferromagnetic order. The magnetic moments at low temperatures are m(Fe/Ru) = 1.88 (3)µ(B) for SrLaFeRuO(6) (2 K), m(Pr) = 0.46 (4)µ(B) and m(Fe/Ru) = 2.24µ(B) for SrPrFeRuO(6) (2 K), and m(Fe/Ru) = 1.92µ(B) for SrNdFeRuO(6) (10 K).
ABSTRACT
Single crystals of the mixed valence compound Pb3Ni1.5Mn5.5O15 were successfully grown. Polarized Raman spectroscopy revealed that they belong to the point group D(3d), in accordance with single-crystal x-ray diffraction data which were refined within the trigonal space group P3c1 (No. 165), with lattice parameters a = 9.941(3) Å and c = 13.543(3) Å. Strongly anisotropic long range magnetic order is established below 65 K.
