X-ray diffraction study of distorted perovskites R(Co3/4Ti1/4)O-3 (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho)

摘要

The crystal structure and powder patterns were prepared for the distorted perovskite series R(Co3/4Ti1/4)O-3 (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho). The R(Co3/4Ti1/4)O-3 members are isostructural with each other and are crystallized in the orthorhombic crystal system with space group Pnma, Z = 4. From R = La to Ho, the lattice parameters a range from 5.4614(3) to 5.5368(2) angstrom, b range from 7.7442(4) to 7.4859(2) angstrom, and c range from 5.5046(3) to 5.2170(2) angstrom. The unit-cell volumes, V which range from 232.81(2) to 216.237(11) angstrom(3) follow the trend of "lanthanide contraction". The structure distortion of these compounds is evidenced in the tilt angles theta, phi, and omega, which represent rotations of an octahedron about the pseudo-cubic perovskite [110](p), [001](p) and [111](p) axes. All three tilt angles increase across the lanthanide series (for R = La to R = Ho: theta increases from 8.34 degrees to 17.00 degrees, phi from 6.24 degrees to 8.53 degrees, and from 10.41 degrees to 18.96 degrees), indicating a greater octahedral distortion as the ionic radius of R3+ [r(R3+)] decreases. The bond valence sum values for the (Co/Ti) site and the R site of R(Co3/4Ti1/4)O-3 reveal no significant bond strain in these compounds. X-ray diffraction patterns of the R(Co3/4Ti1/4)O-3 samples were submitted to the Powder Diffraction File. (C) 2017 International Centre for Diffraction Data.