Structural Study of the New Complex Oxides Ba 5- ySr yR 2- xAl 2Zr 1+ xO 13+ x/2 ( R = Gd-Lu, Y, Sc)

Abstract

New anion-deficient hexagonal perovskite-like complex oxides Ba 5 R 2Al 2ZrO 13 ( R = Gd-Lu, Y) and Ba 5- y Sr y Sc 1.33Al 2Zr 1.66O 13.33 were synthesized and studied by X-ray powder diffraction, electron diffraction, and high-resolution electron microscopy. All the compounds have similar crystal structures based on the 10H close-packed ( cchcc) 2 stacking of BaO 3- x layers. The anion vacancies are located in the h -type lamellae and may occur either in an ordered or in a disordered manner, depending on the R 3+ cation type. It is shown that the radius of the rare-earth element critically influences the composition and the possibility of ordering in the crystal structures of these compounds. High resolution electron microscopy revealed the presence of a large number of stacking defects, their number, and size, depending on the type of the rare-earth element. The crystal structures of these compounds can be formally described as intergrowth structures with an alternation of BaZrO 3 and β-Ba 2ScAlO 5-type blocks along the c axis.