| Research Abstract |
The present project has been focused on the hydrothermal synthesis of novel vanadium oxide compounds with layred structures by incorporationg foreign metals in the interlayr space, aiming at the developments of new functional materials. As a results, compounds with novel layr structures such as sigma-Zn_<0.25>V_2O_5・H_2O, Cs_2V_4O_<11> and BaV_6O_<16>・nH_2O have been obtained and characterized. Also have been synthesized and characterized new layred compounds such as Rb_<0.5>V_2O_5, AV_3O_8 (A=K, Rb, CS) , delta-M_<0.25>V_2O_5・H_2O (M=Ca, Ni) and new layred-tunnel compounds M_XV_3O_8 (VO) _y・nH_2O (M=K, Rb. Ba) . Further, single crystals of metastable FeVO_4-II were hydrothermally synthesized and its structure has been solved as well as its magnetic properties. Brief description of selected compounds synthesided in this study is given below. sigma-Zn_<0.25>V_2O_5・H_2O, a new vanadium bronze, has first been synthesized here, consisting of novel V_2O_5 layrs and hydrous Zn ions ; thus th
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is phase is designated sigma phase. Isomorphous phases have been synthesized with other divalent metals such as Co, Ni, Mn and Mg. Cs_2V_4O_<11> adopts a unique layred structure with V_4O_<11> layrs made up of VO_4 and VO_5 polyhedra in a random array. The striking feature is that there is single crystallographic V atom site with two different oxygen coordinations. BaV_6O_<16>・nH_2O has turned out to be a member of hewettite group compounds that are structurally related to monoclinic gamma-Li_<1+X>V_3O_8, a promising cathode material for secondary Li batteries. This compound shows a layr structure similar to that of gamma-Li_<1+X>V_3O_8 but exhibits orthorhombic symmetry with a long-period structure due to interlayr Ba distributions and a stacking mode of V_6O_<16> layrs. delta-M_<0.25>V_2O_5・H_2O (M=Ca, Ni) is classified into delta-type vanadium bronze represented by delta-Ag_XV_2O_5 and the structures of its hydrated phases have first been determined here. The interlayr hydrous Mions are surrounded by four water moleculeds and also by apical oxygens of V_2O_5 layrs resulting in 6 and 7 oxygen coordinations for smaller Ni^<2+> and larger Ca^<2+> ion, respectively. M_XV_3O_8 (VO) _y・nH_2O (M=K, Rb. Ba) basically have layred structures with V_3O_8 layrs but appear as tunnel structures with bridging VO polyhedra. The formation of this phase seems to be confined for limited cation sizes. Less
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