B.L. Chamberland

Alkaline-earth vanadium (IV) oxides having the AVO3 composition

Abstract The preparation and properties of the perovskite-type metavanadates, CaVO3 and SrVO3 are reported. The calcium phase has orthorhombic symmetry while the strontium phase has the cubic perovskite structure. They are both metallic conductors and exhibit Pauli paramagnetic behavior. The BaVO3 composition was only obtained at high pressure and may be nonstoichiometric. Single crystal data indicate that the predominant phase has a 14-layer hexagonal stacking sequence, previously observed in the BaCrO3 system. Curie-Weiss magnetic behavior was observed on this phase above 77°K.

The characterization of calcium iridium oxides

Abstract Several calcium iridium oxides were prepared by solid state reactions and by a hydroxide precipitation technique. These phases were characterized by X-ray powder diffraction data, electrical and magnetic properties. The calcium-rich phase, Ca4IrO6, was an insulator exhibiting Curie-Weiss behavior above 77°K with a Weiss constant of −47°K and a magnetic moment of 1.76 μB. Ca2IrO4 is a semiconductor and the temperature-dependent susceptibility above 77°K was analyzed in terms of one-dimensional linear chains of octahedrally coordinated Ir4+ ions. Two CaIrO3 phases were isolated, but only the orthorhombic perovskite modification was sufficiently pure for magnetic studies. It was Pauli paramagnetic with metallic conductivity.

A study on the PbCrO3 perovskite

Abstract The perovskite compound PbCrO 3 has been prepared from CrO 2 and PbO at high pressure. The product was formed as small black cubes suitable for electrical resistivity measurements. Magnetic susceptibility data were obtained in the region 77 to 550°K. The oxide phase was found to be a semiconductor with antiferromagnetic behavior below a transition temperature of about 160°K.

Structure d'un oxyde double de rhénium à charpente de type KSbO3 cubique: SrxReO3(0,4 ⩽ X ⩽ 0,5)

Abstract The compound Sr x ReO 3 (0,4 ⩽ X ⩽ 0,5) has been prepared under high-pressure and high-temperature conditions (50 kbar, 900°C). Its structure (cubic KSbO 3 type, a = 9.192A, space group Im3) was solved using conventional methods from 819 unique reflections collected on an automatic four-circle diffractometer. The framework formed by ReO 6 octahedra pairs definites, along (111) axis, tunnels occupied by Sr 2+ ions. These strontium atoms are randomly distributed (occupancy factor = 0.30) on the 16 f positions of the Im3 space group.

The characterization of Ba3Re2O9 and Sr3Re2O9

Abstract The compounds Ba 3 Re 2 O 9 and Sr 3 Re 2 O 9 were prepared by the solid state reaction of the corresponding alkaline-earth oxide with ReO 3 at 750 to 900°C in sealed, evacuated, fused silica tubes. The two compounds are isostructural, having the nine-layer ABO 3 structure with vacant central octahedra. The unit cell parameters are given. The magnetic susceptibility for Ba 3 Re 2 O 9 indicates Curie-Weiss behavior with a Re 6+ moment having localized electrons. The magnetic data for Sr 3 Re 2 O 9 suggest delocalized electron behavior from its temperature-independent susceptibility. Both compounds appear to have semiconducting properties, but the strontium analog is a better conductor. Both compounds are unstable when heated in air above 400°C. They are readily decomposed by chemical oxidizing agents.

Structural studies of Li0.7VO2 in the temperature range 20–300°C

The ordered rock-salt type compound Li/sub 0.7/VO/sub 2/ has recently been found to exhibit some unusually large hysteresis effects in its magnetic and thermal properties between 150 and 280/sup 0/C, related to the magnetic transition known to occur at about 190/sup 0/C in LiVO/sub 2/. X-ray and neutron powder diffraction measurements have been made on samples of Li/sub 0.7/VO/sub 2/ in an effort to classify structural changes believed to accompany this transition but not hitherto reported in any detail. The unit cell parameters were found to change from a = 2.837, c = 14.775 A at 24/sup 0/C to a = 2.913, c = 14.640 A at 263/sup 0/C, with a large discontinuity in the transition region. Rietveld refinement was carried out on X-ray data collected at these temperatures and on neutron data collected at 35/sup 0/C, the main change being an increase in the V-O and V-V distances from 1.98 and 2.84 A at 24/sup 0/C to 2.02 and 2.91 A at 263/sup 0/C, respectively. The only indication of any departure from R3m symmetry in the low-temperature phase was the presence of two extremely weak superlattice peaks in the 24/sup 0/C X-ray data which can be indexed in termsmorexa0» of an enlarged cell with a = a ..sqrt.. 3,c = c. Above 250/sup 0/C, the gradual development of a second phase was noted, identified as the cubic spinel LiV/sub 2/O/sub 4/ resulting from the disproportionation of Li/sub 0.7/VO/sub 2/ into LiVO/sub 2/ and the spinel. Hysteresis effects were observed in the X-ray data which closely parallel those previously reported for the magnetic and thermal properties and which can be attributed to the disproportionation reaction.«xa0less

Preparation of LiVo2 crystals

Abstract The synthesis of LiVO2 crystals exhibiting two different morphologies is reported. Black hexagonal platelet-type and octahedral-like dendritic crystals were obtained using a fused-salt electrolytic method. DSC, TGA, magnetic susceptibility, and X-ray diffraction data are presented. Weak reflections observed in X-ray precession photographs of the platelets indicate a hexagonal superstructure with a unit cell a = 9.838(4) A = 2√3a′, where a′ = 2.84A, and c = 14.755(6) A. Observed systematic absences are consistent with the space groups P6222 and P6422. The dendrites appear to be a pseudocubic phase with a face-centered unit cell, a = 8.31(1) A.

The preparation and crystal structure of a BaRhO3 polytype

Abstract Barium rhodium oxide, BaRhO 3 , was prepared at 1175°C and 60–65 kbar by the reaction of BaO 2 and RhO 2 . A hexagonal black platelet obtained in the reaction product was found to possess a four-layer stacking sequence in space group P6 3 mmc having hexagonal unit cell parameters a = 5.744(1), c = 9.642(1) A. The structure was detemined from 707 independent reflections of which 224 were considered observed. Averaging equivalent reflections yielded 132 unique observed reflections. Refinement of the structure by least-squares methods gave a conventional R value of 4.4%. The structure consists of a four-layer stacking sequence of close-packed BaO 3 layers containing tetravalent rhodium in all the octahedral oxygen interstices. The compound was found to be isostructural with previously reported Ba M O 3 phases. This is the first single-crystal refinement of the 4 H polytype using a four-circle diffractometer.

A single crystal study of eight-layer barium managanese oxide, BaMnO3

Abstract A single crystal study of hydrothermally prepared eight-layer BaMnO3 has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO3 layers. The MnO6 octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 A, probable space group P6 3 mmc , Z = 8 . Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079.

A study on the NiVO3 system

Abstract The reaction of NiO and VO 2 at high pressure yielded a distorted ilmenite phase, NiVO 3 (I). The black crystalline product was characterized by crystallographic, electrical, and magnetic properties. This new phase was found to be a semiconductor and possess antiferromagnetic properties. The Neel temperature is 153°K and the moment corresponds to the valence states Ni 2+ V 4+ O 3 . The properties of NiVO 3 are quite similar to those reported for the isostructural CoVO 3 . A model is proposed which is consistent with the structural and magnetic properties.