| Research Abstract |
1 Experiments were conducted to synthesize vanadate garnets of the following 5 types ; Type3:{A^+_2A^<2+>}[M^<2+>M^<3+>]-(V_3)O_<12>, Type 4:{A^+A^<2+>_2}[M^+M^<3+>](V_3)O_<12>, Type 5:{A^+A^<2+>_2}[M^<2+>_2](V_3)O_<12>, Type 6:{A^<2+>_3}[M^+M^<2+>](V_3)O_<12> and Type 7:{□_<0.5>A^<2+>_<2.5>}[M^<2+>_2](V_3)O_<12>, where A^+=Li^+,Cu^+,Na^+,Ag^+ and K^+;A^<2+>=Cd^<2+>,Ca^<2+>,Sr^<2+> and Pb^<2+>;M^+=Li^+;M^<2+>=Ni^<2+>,Mg^<2+>,Co^<2+>,Cu^<2+>,Zn^<2+>,Mn^<2+> and Cd^<2+>;M^<3+>=Cr^<3+> and Fe^<3+>. New variations of {Na_2Ca}[NiFe^<3+>](V_3)O_<12>,{A^+Ca_2}[LiCr^<3+>](V_3)O_<12>, where A^+=Li^+ and Na^+,{A^+Ca_2}[LiFe^<3+>](V_3)O_<12>, where A^+=Li^+,Cu^+,Na^+ and Ag^+,{LiCa_2}[M^<2+>_2](V_3)O_<12>, where M^<2+>=Co^<2+> and Mn^<2+>,{KCa_2}[Mn_2](V_3)O_<12>,{Ca_3}[LiCd](V_3)O_<12> and {Pb_3}[LiM^<2+>](V_3)O_<12>, where M^<2+>=Mg^<2+>,Co^<2+>,Zn^<2+>,Mn^<2+> and Cd^<2+> were prepared as phase-pure garnets for the first time. Garnets were formed only a few in both types 3 and 4. In types 5,6
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and 7, the variety of garnets formed was greatly limited by the replacement of Ca^<2+> by Sr^<2+> as compared with that being not so much limited by the replacement of Ca^<2+> by Pb^<2+>, though the effective ionic radius of Pb^<2+> is larger than that of Sr^<2+>. This is ascribed to "the hard and soft acids and bases principle". In types 5,6 and 7, in the case of M^<2+>=Cu^<2+>, the variety of garnets formed was fairly limited due to the "the Jahn-Teller effect of Cu^<2+>".
2 The morphologies of vanadate garnets (NaCa_2M_2V_3O_<12>,M=Ni,Mg or Co) were studied by growing well-formed crystals from sodium vanadate flux. The first rank F-faces were determined by growing crystals at low supersaturation levels and were found to be the {110} face at lower temperature and the {211} face at higher temperature. This change was ascribed to a change in the ratio of the bond lengths at the octahedral site to that of the dodecahedral site with increasing temperature. When crystals grew larger in the lower temperature region, predominantly {211} faces appeared in addition to {110} faces, whereas in the higher temperature region, {110} faces were predominant over {211} faces. The reason for these phenomena was ascribed to the surface kinetics caused by an increase in the rate of mineral nutrient transport to the surface of the crystal with increasing crystal size. Less
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