Synthesis of Mixed Valenced Oxide Minerals

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(1) Making of Phase Equilibrium Diagram of the System Jacobsite (MnFe_2O_4) -Hausmannite (Mn_3O_4)Phase diagram of the system jacobsite-hausmannite was made by solid state reactions under hematite-magnetite oxygen buffers. Compositions of the two phase region where a cubic phase and a tetragonal phase coexisted were determined by electron microprobe analysis. A thermodynamical approach revealed that the equilibrium concentration relations among chemical constituents such as Mn^<2+>, Fe^<2+>, Mn^<3+>, Fe^<3+> and vacancy of metal in the cubic phase.(2) Observation of Thermal Decompostion Behavior of Pyrolusite by Means of Hihg Temperature Powder X-ray DiffractometerTwo kinds of thermally different pyrolusite (S) and (D) are known ; (S) shows one endothermic peak about 650^ﾟC and (D) has two endothermic peaks about the same temperature. High temperature X-ray measurements for these showed that (S) decomposed at about 650^ﾟC and transformed to bixbyite (alpha-Mn_2O^3) exclusively, whereas (D) converted to gamma-Mn_2O_3 and Mn_5O_8 in addition to bixybite. Thermal behavior of (D) was explicable from the oxygen deficiency in (D).(3) Thermal Transformation of Cryptomelane (A_xMn_8O_<16>. nH_2O, A=K, Na)Tetragonal cryptomelane was converted to a monoclinic cryptomelane and bixybite by heating at about 700^ﾟC in air. Alkali ions in the part were concentrated in the tunnel and caused the transformation to monoclinic phase accompanying with simulutaneous formation of bixbyite. Structural study in dicated that the Mn^<3+> ions were ordered in the monoclinic cryptomelane.(4) Valence State of Tellurium in BismuthtelluratesValence state of tellurium in the compounds appeared in the pseudo-ternary system Bi_2O_3-Sro-TeO_2 and Bi_2O_3-Pbo-TeO_2 in air was mostly in the state of Te^<4+>. In a superstructure of fluorite, Bi_2SrTeO_7, tellurium ion existed as Te^<6+>.