Synthesis and structural characterization of new perovskite phases, Ba ₂ Bi _0.572 TeO _6± <i> _δ </i> and SrLa ₂ NiFeNbO ₉

Ba 2 Bi 0.572 TeO 6± δ and SrLa 2 NiFeNbO 9 ceramics were prepared in polycrystalline form by conventional solid-state reaction techniques in air. The crystal structures of the title compounds were determined at room temperature from X-ray powder diffraction (XRPD) data using the Rietveld method. The Ba 2 Bi 0.572 TeO 6± δ structure crystallizes in a triclinic space group I –1 with unit-cell parameters a = 6.0272(2) Å, b = 6.0367(1) Å, c = 8.5273(3) Å, α = 90.007(7)°, β = 90.061(2)°, and γ = 90.015(4)°. The tilt system of the BiO 6 and TeO 6 octahedra corresponds to the notation a – b – c – . The crystal structure of the SrLa 2 NiFeNbO 9 compound adopts an orthorhombic Pbnm space group with lattice parameters a = 5.6038(5) Å, b = 5.5988(4) Å, and c = 7.9124(6) Å. The B O 6 octahedra ( B = Ni/Fe/Nb) sharing the corners in 3D. Along the c -axis, the octahedra are connected by O(1) atoms of ( x , y ,1/4) positions; while in the ab -plane, they are linked by O(2) atoms of ( x , y , z ) positions. The bond angle of B –O1– B is 168.7° and that of B –O2– B is 156.3°. The octahedral lattice corresponds to the tilt pattern a – a – c + ; it indicates that the octahedra tilt out-of-phase along the a , b -axes and in phase along the c -axis.