Effect of Bi substitution on the cationic vacancy ordering in SrMoO4-based complex oxides: Structure and properties

Abstract

The electronic and crystal structures of the Sr1−3xBi2xФxMoO4 series (0.025 ≤ x ≤ 0.30, where Ф represents cation vacancies) were studied. The 0.025 ≤ x ≤ 0.15 compositions showed a defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 < x ≤ 0.225 exhibited a tetragonal supercell with asup ≈ √5a, csup ≈ c where a and c are the tetragonal scheelite cell parameters. Strong distortion of MoO4 polyhedra was shown by Raman spectroscopy and described by the calculated phonon spectra of “virtual crystals” of Bi2+[MoO4] and Ф2+[MoO4]. The electronic structures were calculated for both types of structure. The decrease of the calculated energy gap is consistent with experimental data from Kubelka-Munk measurements. The electroconductive properties were measured by A.C. impedance spectroscopy. For Sr1−3xBi2xФxMoO4 compositions conductivity increases with increasing x-value, with maximum values of conductivity at 948 K of 2.82 × 10−5S cm−1 for the x = 0.20 composition.