Crystal chemistry and physics of selected transition metal compounds.

摘要

This volume contains two distinct parts. Part one focuses on the synthesis of single crystals of transition metals in oxy-anion frameworks, particularly the transition metals of chromium and manganese in a high oxidation state. The hydrothermal environment is clearly a reducing environment with respect to metals of a high oxidation state. While the formation of single crystals with a oxy-anion framework containing a metal with a redox potential greater than that of Mn3+ were not observed, two new Mn3+ compounds were synthesized. [Sr2Mn(P2O7)(PO 4) and BaHMnGeO5]. Speciation studies point out the immobility of the Mn3+ in the hydrothermal case and its propensity for disproportionation. Single crystals of Fresnoite, Ba2TiSi 2O8, and several derivatives were prepared hydrothermally and the E.S.R. spectrum for the Fresnoite analogue Ba2VSi 2O8 is reported for the first time with an isotropic g-factor of 1.94. An explanation is set forth to explain the intrinsic strain that exists in the Fresnoite structure type. A new compound Ba2TiGe 2O7 with titanium in an uncommon Ti2+ oxidation state and exhibiting the Melilite structure was synthesized hydrothermally.; The second part focuses on the thermoelectric properties of the layered transition metal chalcogenide, TiS2. Single crystals of doped titanium disulfides, many with at least one dimension in excess 1 cm, were synthesized using iodine vapor transport crystallization. The in plane electronic transport properties for single crystal titanium disulfides were measured for samples doped with the elements As, Ce, Co, Hf, Mo, Sb, Sc, Se, Sb, Y, and Zr. By doping the thermopower, alpha, was varied from -43 muV/K to -184 muV/K at 273 K. Similarly the electrical conductivity at 273 K can be varied from 0.2 mO•cm in the case of arsenic doping to 5 mO•cm for that of cerium doping. A linear correlation between the thermopower and the IR reflectivity was found for this system. The electronic power factors for materials of this type have values on the order of 0.3 W/mK with the power factor for nearly doping compositions of TiS2 still increasing at room temperature suggesting the viability of these materials as thermoelectric elements above room temperature.