Synthesis, magnetic and transport properties of transition metal sulfides and oxides

The low temperature physical properties of known ternary sulfide phases, BaFe₂S₃ and Ba₆Fe₈S₁₅, have been studied. They show spin-glass like behavior at low temperatures and are semiconductors. BaFe₂S₃ is a rare example of a magnetoresistive sulfide that is one dimensional. Sr substitution into BaMnS ₂ structure produces Ba_0.93Sr_0.07MnS₂. Sr changes the coordination environment of Ba2+/Sr2+ and induces short range magnetic ordering. New perovskites and perovskite related oxides were prepared with Mn/Ru, Ni/V and Cu/V at the B site and La, Ba, Ca at the A site of ABO₃ lattice. The compounds show a wide range of magnetic and transport properties. Ba₃MnRu₂O ₉ adopts a hexagonal 9R structure. It displays spin-glass like behavior at low temperatures and shows temperature dependent spin at high temperatures due to metal-metal bonding. The Ca₃MnRu₂O ₉ and LaMn_xRu_1−xO₃ (0 < x < 1) series adopt GdFeO₃ type perovskite structure. Ca ₃MnRu₂O₉ is a ferrimagnetic semiconductor with very low room temperature resistivity. The LaMn_xRu_1−x O₃ series shows spin-glass like behavior with varying dominant interactions from antiferromagnetism (x ≤ 0.25) to ferrimagnetism (x > 0.25). There is an insulator to metal transition at x = 0.05. La₃Ni ₂VO₉ also has a GdFeO₃ structure and is a semiconductor. The magnetic susceptibility of this compound displays a spin-glass like behavior with suppressed effective magnetic moment. “LaCu₂VO ₉” possess a superstructure and the composition is best described as La₁₃V₄Cu₉O_38.5. It has a hexagonal structure with Cu₃ cluster units and V and Cu are trigonal bipyramidally coordinated. This compound is a semiconductor and the magnetic susceptibility follows the Curie-Weiss law with S = 1/2 per Cu2+ (T > 220K) to S = 1/2 per Cu₃ units (T < 50K). La₁₄V₆CuO _36.5 is a decomposition product of La₁₃V₄Cu ₉O_38.5. It is a transparent copper oxide which contains [OCuO] 3− sticks. Soft chemical synthesis methods have been utilized to prepare new metastable compounds. The ion exchange reactions of AMCuS ₂ (A = Rb, Cs; M = Mn, Fe) with various salts are complicated by the stability of the decomposition products. Concerted cation anion extraction from K₂La₂Ti₃O₁₀ with PPh ₄Br results in preparation of two metastable compounds, KLa₂Ti ₃O_9.5 and La₂Ti₃O₉. In the oxide system, Cs_0.5LaNb₂O_6.5X_0.5 (X = Cl, Br), Cs_0.5Mg_0.25LaNb₂O₇, and Cs_0.5Mg_0.5La_5/6Nb₂O₇ can be prepared via ion exchange of CsLaNb₂O₇ with PPh₄X, MgCl₂ and MgCl₂.6H₂O.