Structural, photocatalytic and electroconductive properties of bismuth-substituted CaMoO4

The Ca1−3xBi2xФxMoO4 system (0.025 ​≤ ​x ​≤ ​0.30, where Ф represents cation vacancies) was synthesized and studied. The 0.025 ​= ​x ​≤ ​0.15 compositions show a tetragonal defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 ​< ​x ​≤ ​0.225 exhibit a tetragonal supercell with asup ​≈ ​√5a, csup ​≈ ​c where a and c are the tetragonal scheelite cell parameters. Transmission electron microscopy shows that Ca0.4Bi0.4MoO4, crystals consist of three crystallographic domains: (1) defect scheelite; (2) tetragonal superlattice and (3) incommensurately modulated. Photocatalytic properties were studied using Rhodamine B water solutions under UV light. Catalytic activity increases with increasing Bi content. The conductivity of 0.15 ​< ​x ​≤ ​0.225 compositions is 10−7 to 10−8 ​S ​cm−1 in the range 500–650 ​°C, while compositions in the range 0.025 ​= ​x ​≤ ​0.15 show conductivity values from 10−3 to 10−8 ​S ​cm−1 from 500 to 800 ​°C. © 2020 Elsevier Inc.The study was done with a support of RSF, projects № 20-73-10048. The travel grant for neutron diffraction work was given by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006. The authors are grateful to the Science and Technology Facilities Council STFC for neutron beam time at the ISIS facility, Rutherford Appleton Laboratory, award No. RB1910306. Dr Ron Smith at ISIS is thanked for his help in neutron data collection

Effect of Bi substitution on the cationic vacancy ordering in SrMoO<inf>4</inf>-based complex oxides: Structure and properties

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