Metallic Bi3 Research Articles

Modifying optical and photochemical properties of bismuth oxyfluoride BiTe3O7F via stoichiometry alteration between Bi3+ and Te4+ ions

Bismuth oxyfluoride compounds have been intensively investigated as optical materials for multifunctional applications. In this work, preparation, optical and photocatalytic properties of a novel bismuth oxyfluoride BiTe3O7F were reported. To modify the performances, Bi1-4x/3Te3+xO7F (x = 0, 0.05, 0.1, 0.12, −0.05, −0.1, −0.12) was further designed with stoichiometry alteration between Bi3+ and Te4+. All the samples were synthesized via by sol–gel routine combined with a solid-state reaction method. Stoichiometry exchanges between nonmetal Te4+ and metal Bi3+ ions can be homogeneously realized in the lattices of Bi1-4x/3Te3+xO7F (x = 0, 0.05, 0.1, 0.12, −0.05, −0.1, −0.12). BiTe3O7F shows a typical indirect allowed transition with band energy of 2.917 eV. The deviation of Te:Bi from the stoichiometry requirement in BiTe3O7F (3:1) could modify the band gap in different ways, that is, the excess (x > 0) and lack (x > −0) of Te3+ make the band gap widen and narrow, respectively. The photocatalytic activities could be enhanced via substitution between Te4+ and Bi3+ cations in BiTe3O7F, especially, the improvement is more noticeable for the Te3+ excess (x>0) in the lattice. To discuss the mechanisms, XPS measurements and annealing treatments were conducted. The enhanced photodegradation could be ascribed to the changes of anion microstructure in the surfaces. The present results could be a reliable reference in the development of the photochemical application of bismuth oxyfluoride semiconductors.

Synthesis of Functional Oxides Using Cubic Anvil Press—BiNiO3 Exhibiting Inter-site Charge Transfer—

High-pressure synthesis is a powerful technique in searching for new materials. We have found a large number of functional oxides using this technique. BiNiO3 is a distorted perovskite compound with unusual Bi1/23+Bi1/25+Ni2+O3 valence state. High-pressure neutron diffraction measurements and bond valence sum calculations show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high-pressure phase is metallic Bi3+Ni3+O3. The same inter metallic charge transfer accompanied with 2.6% volume shrinkage is induced by heating Bi0.95La0.05NiO3 at ambient pressure.

Ｂｉ，Ｐｂ‐３ｄ遷移金属ペロブスカイトの構造物性研究

The interplays between crystal structures and physical properties in BiCoO3, PbVO3 and BiNiO3 are investigated. It is found that the t2g1 and t2g4eg2 electronic configurations of V4+ and Co3+ ions are the origin of the large tetragonal distortions in BiCoO3 and PbVO3. High pressure neutron diffraction measurements and Bond valence sum calculations on BiNiO3 with unusual oxidation state of Bi3+0.5Bi5+0.5Ni2+O3 show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high pressure phase is metallic Bi3+Ni3+O3.