N.V. Stus

Crystal structure of a novel cubic pyrophosphate WP2O7

Abstract The crystal structure of a novel pyrophosphate WP 2 O 7 has been studied by X-ray powder diffraction. It was found that the crystal structure of WP 2 O 7 belongs to the well-known MoP 2 O 7 structure type ( a =7.9502 A). The tetravalent state of tungsten in the pyrophosphate has been confirmed by magnetic susceptibility measurements.

Synthesis and transport properties of prospective photovoltaic systems related to CuInSe2 and CuGaSe2

Abstract Solid solutions in CuGaSe2–ZnSe and CuInSe2–ZnSe systems have been obtained by radio frequency heating. In order to prepare n-type phases based on CuGaSe2, p-type (CuGa)1−xZn2xSe4 and (CuIn)1−xZn2xSe4 (0.05⩽x⩽0.1) single crystals were doped by Ag, Hg, Cd, Zn implantation. The crystal structure of the solid solutions was studied by X-ray diffraction; the substitutors as well as the implantant valence states were analyzed using X-ray photoelectron spectroscopy. Hall effect, electrical conductivity, and the charge carrier mobility of an n-type zinc-implantated solid solution (CuGa)1−xZn2xSe4 and (CuIn)1−xZn2xSe4 (0.05⩽x⩽0.1) were studied.

New high-temperature–high-pressure synthetic route: from crystalline hydrates to molybdenum bronzes NaxMoO3

Abstract A new method for preparation of alkaline molybdenum bronzes using molybdate crystalline hydrate precursor was elaborated. The reaction products contain sodium hydroxide and sodium molybdenum oxide bronzes Na x MoO 3 . The bronzes were characterized by X-ray diffraction and electron microscopy. The dimensions of Na x MoO 3 are non-uniform: nanosized Na x MoO 3 ( x =0.03–0.08, MoO 3 structure type) and micrometer sized cubic Na x MoO 3 ( x =0.33–0.92) particles were obtained.

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

Abstract A novel molybdenum diphosphate, Mo 1.3 O(P 2 O 7 ), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I 2/ a with the lattice parameters a =22.88(1), b =22.94(2), c =4.832(1) A, γ =90.36°, Z =8. Its original framework is built up from MoO 6 octahedra, P 2 O 7 groups and also from MoO 4 , Mo 2 O 4 and Mo 3 O 8 units containing Mo 2 and Mo 3 clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c , in which the inserted cations may be located.

Electrochemical Performance of Ni-CGO Nano-Grained Thin Film Anodes for Micro SOFCs

NiO-Ce0.8Gd0.2O1.9-x (CGO) thin film anodes with thicknesses around 400 nm were prepared by air blast spray pyrolysis. The film composition was 60/40 vol% Ni/CGO in the reduced state. The films were deposited on tape-cast YSZ electrolytes. The material was amorphous after deposition and was crystallized by sintering in air between 650 and 1200°C. The temperature treatment resulted in films with average grain sizes of the NiO and CGO grains between 5 and 250 nm. The area specific resistance of the thin film anodes was measured in a humidified 1:4 H2:N2 atmosphere as a function of grain size within the temperature interval of 400-600°C. The area specific resistance (ASR) was predominantly depending on the grain size of the films. At 550°C, an ASR of 0.5 Ωcm 2 was found for the 5 nm grain size anode. The value increased to 30 Ωcm 2 for the 250 nm grain size anode.

Crystal structure of a new monophosphate tungsten(V) bronze with hexagonal tunnels Na4(WO3)8(PO2)4

Abstract A new monophosphate tungsten(V) bronze Na 4 (WO 3 ) 8 (PO 2 ) 4 has been isolated in melted Na–W–P–O system by sealed tube reaction. Its structure has been determined by single crystal X-ray diffraction in the centrosymmetric space group P 2 1 / m with parameters a =6.6065(2), b =5.2711(2), c =8.8898(2) A, β =99.5898(2)°, Z =2, R =0.055, R W =0.065. The obtained Na 4 (WO 3 ) 8 (PO 2 ) 4 is related to the series of monophosphate tungsten bronzes with hexagonal tunnels A x (WO 3 ) 2 m (PO 2 ) 4 with A=Na, K. The framework {(WO 3 ) 8 (PO 2 ) 4 4− } 3∞ consists of ReO 3 type staircase-like layers built up of WO 6 octahedra interlinked by PO 4 tetrahedra and contains hexagonal tunnels running along [010] where the sodium atoms are located. The edge-sharing distorted pentagonal pyramids NaO 6 form infinite zigzag chains along the channels. A comparison of the Na 4 (WO 3 ) 8 (PO 2 ) 4 structure with that of sodium and potassium monophosphate tungsten bronzes is carried out.

Surface Tension of KPO3-WO3 Melts

The temperatures Tliq of molten xWO3-(1−x)KPO3 mixtures with a molar content between x = 0 and x=0.60 have been determined by differential thermal analysis. The surface tension of the xWO3- (1−x)KPO3 melts in the interval from x = 0 to x = 0.5 has been measured by ring tensiometry for temperatures 10 K- 20 K above the melting points, up to 1373 K. The data obtained for KPO3 were fitted by a linear dependence on the temperature and compared with data available in the literature. The surface tension of the xWO3-(1−x)KPO3 melts was found to decrease non-monotonously with x. Three bends at x ~ 0.15, 0.30, and 0.45 were observed in the surface tension vs. molar fraction curve. The first and the third bends correspond to eutectic compositions; the second one is related to the formation of congruently melting K2WO2P2O7. Equations describing the temperature and concentration dependences of the surface tension are proposed.

A Low-Temperature Route for ReP2O7 Synthesis

A low-temperature route for the synthesis of the Re(IV) diphosphate starting from ReO4 − is presented. The ReP2O7 polycrystals have been prepared in 63% yield by an interaction of NH4ReO4 with molten phosphoric acid at 673 K with subsequent cooling down to 298 K. The synthesized ReP2O7 was characterized by X-ray powder diffraction (XRPD) and DRIFT spectroscopy.