Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na) |
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Authors: | Aleksandr V Knyazev Miroslaw Mczka Nataliya N Smirnova Lucyna Macalik Nataliya Yu Kuznetsova Irene A Letyanina |
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Institution: | aNizhny Novgorod State University, Gagarin Prospekt 23/2, 603950 Nizhny Novgorod, Russia;bInstitute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw, Poland |
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Abstract: | In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for MIVWO6(MI – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity Cpo(T), enthalpy Ho(T)−Ho(0), entropy So(T)−So(0) and Gibbs function Go(T)−Ho(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study. |
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Keywords: | Brannerite Heat capacity Thermodynamic functions IR and Raman spectroscopy Absorbance X-ray diffraction |
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