Catherine E. Rice

Structural changes in the solid solution (Ti1−xVx)2O3 as x varies from zero to one

Abstract The crystal structures of (Ti1−xVx)2O3, x = 0.005, 0.01, 0.02, 0.04, 0.07, 0.30, 0.50, 0.70, and 0.90, have been determined from X-ray diffraction data collected from single crystals. The compounds are rhombohedral, space group R 3 c , and are isomorphous with α-alumina. The hexagonal cell dimensions range from a = 5.1549(6)A, c = 13.627(2)A, for (Ti0.995V0.005)2O3 to a = 4.9813(2)A, c = 13.996 (1)A for (Ti0.10V0.90)2O3. The most pronounced effects of V3+ substitution occur in the 0 to 7 at% V range and can be described as an increase in the metal-metal distance along the c axis from 2.578(2) A in pure Ti2O3 to 2.652(1) A in (Ti0.93V0.07)2O3 coupled with reorganization of the structure in order to maintain constant metal-oxygen distances. These structural changes have been related to both the change from semiconducting to metallic behavior and the disappearance of the 150–350°C resistivity drop which occur with increasing vanadium content in (Ti1−xVx)2O3 as x increases from 0.0 to about 0.07. They are consistent with the band theory proposed by others for this system. Indications of unusual structural behavior in the 90–100 at% V range are also noted.

Structural changes associated with the semiconductor-to-metal transition in Ti2O3☆

Single crystal x-ray structure determinations of Ti2O3 at 8 temperatures through the region where this material undergoes a semiconductor-to-metal transition show that the TiTi distance along the three-fold axis increases as predicted by previous theories. The slight decrease in the TiTi distance in the basal plane suggests that the conduction band in Ti2O3 is effectively nonbonding.

Dimethylgold(III) complexes of α-amino acids and related ligands

Abstract Dimenthylgold(III) complexes with the anions of glycine, alanine, valine, cysteine, histidine and imidazole, benzimidazole and 1,2,4-triazole, respectively, have been prepared. The structures of the complexes are discussed on the basis of their infrared spectra.

The effects of titanium or chromium doping on the crystal structure of V2O3

Abstract The crystal structures of five samples of (Ti x V 1− x ) 2 O 3 (0.011 ≤ x ≤ 0.077) and seven samples of (Cr x V 1− x ) 2 O 3 (both metallic and insulating phases, 0 ≤ x ≤ 0.05) were determined from X-ray diffraction data collected from single crystals. These compounds are isomorphous with α-alumina. The cell dimensions change such that the a axes increase and the c axes decrease with increasing Ti or Cr. In the CrV 2 O 3 system, from 0 to 1.25% Cr doping, changes in structure parallel those observed in the TiV 2 O 3 system. These changes are consistent with a slight weakening of the bonding metal-metal interactions in the basal plane, leading to an increase in the metal-metal distances coupled with changes which maintain constant metal-oxygen distances. A discontinuity appears at about 1.25% Cr as the transition from metal to insulating behavior occurs with increasing Cr content. No change in crystal symmetry accompanies this transformation. It appears that the metal-metal bonding interactions are retained even in the insulating phase of Cr-doped V 2 O 3 . A comparison of the structural variation in the Cr- and Ti-doped systems suggests that the change from metallic to insulating behavior cannot be a structure effect. These changes are, however, consistent with the band model proposed by others for these systems.

Metal-metal distances in vanadium, scandium, and aluminum doped Ti2O3 and their implications for the role of vanadium in (Ti1−xVx)2O3

Abstract Single crystal x-ray structure determinations of a series of V, Sc, and Al doped Ti 2 O 3 samples have shown that the metal-metal distance along the 3-fold axis in all of these corundum-like systems increases with increasing concentration of dopant. However, the effect of V is at least twice that of a corresponding amount of Al or Sc. The metal-metal distance in the basal plane decreases with increasing V and Al concentration and increases with increasing Sc concentration. These structural changes have been correlated with the electrical behavior of the doped systems and a cluster model has been proposed for the behavior of vanadium in Ti 2 O 3 .

Structural changes resulting from doping Ti2O3 with Sc2O3 or Al2O3

The crystal structures of (Ti1−xScx)2O3, x = 0.0038, 0.0109, and 0.0413, and of (Ti0.99Al0.01)2O3, have been determined from X-ray diffraction data collected from single crystals using an automated diffractometer, and have been refined to weighted residuals of 25–34. Cell constants have also been determined for x = 0.0005, 0.0019, and 0.0232. The compounds are rhombohedral, space group R3c, and are isomorphous with α-Al2O3. The hexagonal cell dimensions range from a = 5.1573(2)A, c = 13.613(1)A for (Ti0.9995Sc0.0005)2O3 to a = 5.1659(4)A, c = 13.644(1)A for (Ti0.9587Sc0.0413)2O3, and a = 5.1526(2)A, c = 13.609(1)A for (Ti0.99Al0.01)2O3. Sc and Al substitution cause similar increases in the short near-neighbor metal-metal distance across the shared octahedral face; for Sc doping the increase is from 2.578(1) A in pure Ti2O3 to 2.597(1) A in (Ti0.9587Sc0.0413)2O3. By contrast, changes in the metal-metal distance across the shared octahedral edge appear to be governed by ionic size effects. The distance increases from 2.994(1) A in Ti2O3 to 3.000(1) A in (Ti0.9587Sc0.0413)2O3 and decreases to 2.991(1) A in (Ti0.99Al0.01)2O3.