Accurate Crystal Structure Refinement of La{sub 3}Ta{sub 0.25}Zr{sub 0.50}Ga{sub 5.25}O{sub 14}

An accurate X-ray diffraction study of a La{sub 3}Ta{sub 0.25}Zr{sub 0.50}Ga{sub 5.25}O{sub 14} single crystal (a = 8.2574(4) A, c = 5.1465(4) A, sp. gr. P321, Z = 1, R/R{sub w} = 0.62/0.57% for 4144 unique reflections and 91 parameters) has been performed with a simultaneous neutron diffraction analysis. Tantalum, zirconium, and gallium atoms are found to occupy the mixed octahedral position (symmetry 32). Gallium atoms and a few zirconium atoms are in the position on axis 2 in the tetrahedron. The tetrahedral position on axis 3 is completely occupied by gallium atoms, while the large polyhedron on axis 2 is occupied by lanthanum atoms. The high resolution and averaging of the results obtained in two independent X-ray experiments with the same sample provided accu- rate structural data, in particular, on the anharmonicity of thermal atomic vibrations (atomic displacements). The X-ray and neutron diffraction data on the atomic displacements are compared.