Isao Kawada

Crystal structures of V3S4 and V5S8

Abstract Crystal structures of the ordered phases of V3S4 and V5S8 were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS1.47, I2 m (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)A, β = 91.78(1)° and VS1.64, F 2 m (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), A, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe7S8, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.

Crystal growth of V6O13

Abstract V 6 O 13 single crystals were prepared by chemical transport method. From the electrical measurements of these crystals, a semiconductor/semiconductor transition was found. Based on the crystallographic and electrical measurements, we suggest that the transition is of the first order.

The phase relations and homogeneity range of the iron chevrel compound FexMo6S8−y

Abstract The phase relations of Chevrel phase compounds in the FeMoS system were investigated by performing experiments in sealed silica tubes at 1000 °C. The results of these experiments enabled the phase diagram of the FeMoS system to be constructed. The presence of the following ternary phase compounds was confirmed by X-ray powder diffraction examination of the quenched samples: monoclinic FeMo2S4, rhombohedral FexMo6S8−y and triclinic FeMo3S4. The iron Chevrel compound FexMo6S8−y coexists with molybdenum and Mo2S3 at low iron contents and with FeMo3S4 at higher iron contents. With respect to the homogeneity range it has been found that the iron and sulphur contents of rhombohedral FexMo6S8−y lie in the ranges 1.15

Behavior of vanadium dioxide single crystals synthesized under the various oxygen partial pressures at 1500 K

Abstract The effects of nonstoichiometry upon the behavior of vanadium dioxide single crystals in the vicinity of the semiconductor/metal transition temperature (Tc) were experimentally investigated. According to the electrical and thermal measurements, more stoichiometric vanadium dioxide exhibited the less electrical conductivity gap, the larger thermal and electrical hysteresis, and the lower transition temperature than the increased nonstoichiometric one near transition. Infrared absorptions and X-ray observations indicated the local and overall lattice distortion in the nonstoichiometric crystal due to the existence of V5+ ions. Furthermore, an intermediate phase between the low-temperature monoclinic and the high-temperature tetragonal phases was found in the nonstoichiometric VO2. On the other hand, no evidence for this intermediate phase was found in the stoichiometric one. Finally, some comparisons and discussions of our present data with the previously published ones were made.

Phase relations and structure of V3−xMoxS4 (0 ≤ x ≤ 2)

Phase relations, composition dependence of lattice constants, structure refinement, and electrical resistivity of the mixed-metal compounds, (V,Mo)3S4, are presented. Phase relationships in the system VMoS were studied by sealed silica tube experiments at 1373 K and an isothermal section of the phase diagram was constructed. The system VMoS is characterized by the following three solid solution series: cubic metal alloy VxMo1−x (0 ≤ x ≤ 1), monoclinic (VxMo1−x)2.06S3 (0 ≤ x ≤ 0.06), and monoclinic V3−xMoxS4 (0 ≤ x ≤ 2). The (V,Mo)3S4 phase coexists with MoS2 at higher S content, while it coexists with Mo at lower S content. The structures of VMo2S4 and V2MoS4 were determined and refined from X-ray powder data. A monoclinic Cr3S4-type cell with space group I2m was adopted. It was found that the contraction of the lattice constant b on substitution of Mo for V in (V,Mo)3S4 mixed crystals is due to formation of characteristic zigzag MoMo chains running along the b direction of the lattice. With respect to the metal distribution of Mo and V in the Cr3S4-type structure, Mo atoms have a great tendency to occupy metal sites in the metal-filled layers rather than those in the metal-deficient layers.

2H-type Ti1 + xS2 in the range x = 0.11–0.33

Abstract 2H-type Ti1 + xS2 (x = 0.11–0.33) was prepared by reducing TiS2 in an H2S-H2 atmosphere at 410 °C. At 1000 °C this specimen transformed to the 4H type which has already been reported within this composition range.

Needles of WO2.9 grown in an electron microscope

Abstract Small grains of WO 3 were heated by the illumination of an intense electron beam in an electron microscope. The grains evaporate and, instead, small needle-like crystals of WO 2.9 , i.e. W n O 3 n -2 with n = 19 to 27, were recrystallized on the adjacent microgr id. A needle consists of several domains, elongating along the growth direction and having a very small cross section. Each domain shares the common [010] direction along the needle axis. When the needles are illuminated by a more intense electron beam, further reductions to W 1 8 O 4 9 or even W occur. The thermodynamical background for the observations is discussed.

Effect of addition of vanadium on the chemical transport of TiSx, x = 1.40–1.70

Abstract Chemical transport of titanium sulfide TiS x was carried out using iodine as a transport agent in the temperature gradient 900→800°C. No tranport took place for x less than 1.67. The substitution of titanium in TiS x by vanadium broadened the range of composition to values much less than x = 1.67. while the transport rate remained considerable. It was found from total pressure measurements that for an experimentally appreciable transport to take place a sulfur pressure larger than 10 -2.8 atm is required.

(2H)2-2C type superstructure of TiS1.62, determined by high-resolution electron microscopy

A superstructure of TiS1.62 is determined by 100 kV high-resolution electron microscopy, in which the arrangement of metal vacancies is obtained from structure images. The crystal has monoclinic symmetry (pseudo-hexagonal) with lattice parameters a = 11.9, b = 6.85, c = 11.5A, β = 90°. The space group is considered as F2m. Metal vacancies are confined to every second metal layer and ordered within the partly filled metal layer, resulting in formation of a (2H)22C type of superstructure. The ordered metal vacancy layers are arranged in 2C-type stacking sequence along the c axis, while sulfur atoms are arranged in 2H-type stacking sequence along the c axis.

Stacking faults in nonstoichiometric titanium sulfide

Abstract The structure analysis of titanium sulfide with stacking faults was attempted by modifying the matrix method given by Kakinoki and Komura. The analyses were made for X-ray powder diffraction patterns of faulted Ti1+xS2 which were synthesized at relatively low temperatures. A low-temperature model was obtained by assuming that the slides, which cause the faults, occur only between the S-Ti-S sandwiches. The experimental result for 2H−Ti1.28S2, which was synthesized at 410°C, was interpreted satisfactorily. An extended model was attempted for 6R−Ti1.34S2, which was synthesized at 600°C, and the experimental results could be explained approximately.