| Summary: | Four types of oxides, ATiM2O8 (A: Mg, Zn; M: Nb, Ta) were prepared by high-temperature solid-state reaction. MgTiNb2O8, ZnTiNb2O8 and ATiTa2O8 had rutile-type, α-PbO2-type and trirutile-type structures, respectively. The crystal structures of these compounds were refined based on the synchrotron X-ray powder diffraction data with the following R-factors: Rwp = 4.34% and Rp = 2.21% for MgTiNb2O8; Rwp = 2.19% and Rp = 1.52% for ZnTiNb2O8; Rwp = 9.03% and Rp = 6.31% for MgTiTa2O8; and Rwp = 5.70% and Rp = 4.16% for ZnTiTa2O8. Their lattice parameters were a = 4.69585(8) and c = 3.04260(6) Å for MgTiNb2O8; a = 4.67138(6), b = 5.65916(7) and c = 5.00745(6) Å for ZnTiNb2O8; a = 4.6876(2) and c = 9.1385(3) Å for MgTiNb2O8; and a = 4.6987(7) and c = 9.1296(1) Å for ZnTiTa2O8. The optical band gap for these compounds ranged from 2.98 to 3.15 eV and every compound exhibited a small amount of photocatalytic activity for phenol decomposition under UV light irradiation. However, no photocatalytic activity was observed under visible light irradiation. The dielectric constants for these compounds were between 25 and 125 at a temperature range of room temperature to 400°C.
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