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- Tyutyunnik, A P, et al.
(author)
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Synthesis, superconducting properties and structural (including electron diffraction) studies of Na chi NbO2 and Li chi NbO2
- 1996
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In: European Journal of Solid State and Inorganic Chemistry. - : Wiley. - 0992-4361 .- 1873-3751. ; 33, s. 53-65
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Journal article (peer-reviewed)abstract
- Monophasic NaxNbO2 (x = 0.5 - 0.6), T-c approximate to 4.1 K was prepared by solid state reaction between Na3NbO4 and Nb. X-ray powder diffraction data from a monophasic sample were used for a refinement of the structure of Na0.5NbO2 (R(p) = 7.4 % and R(I) = 5.3 %), using the Rietveld method. At low x-values a closely related second phase can occur. Rietveld refinement using X-ray powder diffraction data showed this phase to be isostructural with NaNbO2 but with the chemical formula Na0.1NbO2. Transmission electron microscopy studies of NaxNbO2 and LixNbO2 revealed the presence of superstructures in some crystallites. The electron diffraction patterns resemble to some extent those reported for transformations among tantalum chalcogenides.
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| 2. |
- Zubkov, V G, et al.
(author)
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Condensed cluster phases in reduced oxoniobates: synthesis and studies of Sr4−xNb17O26 (x=0.0(1), 0.3(1)) and Eu4−xNb17O26 (x=0.3(1)) :
- 1997
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In: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 256, s. 129-139
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Journal article (peer-reviewed)abstract
- Sr4−xNb17O26 (x=0.0, 0.3) and Eu4−xNb17O26 (x = 0.3) were synthesised from SrCO3/Eu2O3 and Nb2O5 in a vacuum furnace at temperatures up to 1600°C (1500°C for Eu) using acetylene soot or Nb as reducing agents. The synthetic studies show that these phases are only formed via an intermediate disordered ‘phase’ (or phasoid). Sr4−xNb17O26 and Eu4−xNb17O26 are isostructural with Ba4Nb17O26 and crystallise in space group P 4/m (83) with the unit cell parameters for and and , respectively. The crystal structure can be described as an intergrowth between ANbO3 and NbO. Characteristic building blocks are quadruple chains of corner-sharing Nb6-octahedra. ?The structures of Sr4−xNb17O26 and Eu4−xNb17O26 were refined using X-ray powder diffraction and neutron diffraction data (only Sr4−xNb17O26). The Rietveld refiniments and microanalyses showed x in Eu4−xNb17O26 to be 0.3(l) while the Sr analogue both x= 0.0(1) and 0.3(1) were found. High resolution electron microscopy studies showed that the compounds frequently contained structural defects. The magnetic susceptibility of Eu4−xNb17O26 (x=0.3) shows a Curie-Weiss behaviour, with a magnetic moment in good agreement with the expected μeff=7.9 μB for Eu2+/ The Sr analogie is temperature-independent paramagnetic at room temperature, Sr4−xNb17O26 (x=0.3) and Eu4−xNb17O26 (x=0.3) are metallic, with a resistivity increasing with temperature.
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