Synthesis and characterization of new materials in molten salt fluxes.

摘要

The main goal of this research was to explore molten salts as growth media for the synthesis of new materials. The molten salt systems investigated in this work were ionic liquids and eutectic mixtures of metal halide salts. The primary characterization methods included: SED-EDS, X-ray diffraction, SQUID magnetometry, Raman and solid state NMR. The main focus was on the magnetic and structural properties of single crystal phases.;Hybrid organic/inorganic materials were synthesized from the reaction of metal oxides and metal powders in ionic liquids. Ionic liquid [bpyr][AlCl 4] was synthesized from the reaction of [bpyr]Cl and AlCl3 (1:1 molar ratio) and used as a solvent for the growth of single crystals of [bpyr]4[V4O4Cl12] and [bpyr] 4[Bi4Cl16] (bpyr = 1-butylpyridinium). [bmim][Bi(PO 2F2)4] was grown in ionic liquid [bmim][PF 6] (bmim = 1-butyl-3-methyl imidazolium). The structures of these hybrid compounds consist of inorganic anionic chains and clusters being separated by discrete organic cations.;A eutectic mixture is a combination of two or more phases at a composition with a significantly lower melting point. Mixtures of CsCl and NaCl in 13:7 molar ratio produce a eutectic which melts at 495°C. The reaction of vanadium oxide, iron oxide and iron in CsCl/NaCl melt produced a new salt-inclusion vanadium bronze phase, Cs5FeV5O13Cl 6. The structure of this compound consists of 1-dimensional vanadate sheets separated by Cs+ cations. Vanadium is in a mixed oxidation state (+4 and +5). Magnetic susceptibility measurements and NMR studies showed the unpaired electrons of V+4 ions to be delocalized. This compound appeared to order ferrimagnetically at 5K.The reaction of molybdenum oxide, iron oxide and molybdenum metal in CsCl/NaCl melt resulted in the formation of CsFeMo2O8 and an oxochloromolybdate phase, Cs 2Mo0.65OCl5. CsFeMo2O8 exhibits layered structure built of infinite slabs of MoO4 tetrahedra and FeO6 octahedra separated by layers of Cs+. The structure of Cs2Mo0.65OCl5 consists of isolated [MoOCl 5]- octahedra which are embedded in the CsCl structure. Magnetic susceptibility measurements showed that both compounds order antiferromagnetically with ordering temperature of 4.5 K for CsFeMo2O8 and 7 K for Cs2Mo0.65OCl5.