Crystal structure, spectroscopy and thermodynamic properties of M{sup I}VWO{sub 6}(M{sup I} - Li, Na)

• Published in: Journal of solid state chemistry Vol. 182; no. 11
• Main Authors: Knyazev, Aleksandr V., Maczka, Miroslaw, Smirnova, Nataliya N., Macalik, Lucyna, Kuznetsova, Nataliya Yu, Letyanina, Irene A.
• Format: Journal Article
• Language: English
• Published: United States 15-11-2009
• Subjects: ALKALI METAL COMPOUNDS; BRANNERITE; CALORIMETRY; CHALCOGENIDES; CHEMICAL REACTIONS; COHERENT SCATTERING; CRYSTAL LATTICES; CRYSTAL STRUCTURE; DECOMPOSITION; DIFFRACTION; ENERGY LEVELS; ENTHALPY; ENTROPY; EXCITED STATES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LASER SPECTROSCOPY; LITHIUM COMPOUNDS; MATERIALS; MATERIALS SCIENCE; MINERALS; MONOCLINIC LATTICES; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; RADIOACTIVE MATERIALS; RADIOACTIVE MINERALS; RAMAN SPECTROSCOPY; REFRACTORY METAL COMPOUNDS; SCATTERING; SODIUM COMPOUNDS; SPACE GROUPS; SPECIFIC HEAT; SPECTROSCOPY; SYMMETRY GROUPS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE; TEMPERATURE RANGE 0000-0013 K; TEMPERATURE RANGE 0013-0065 K; TEMPERATURE RANGE 0065-0273 K; TEMPERATURE RANGE 0273-0400 K; THERMODYNAMIC PROPERTIES; THORIUM MINERALS; TRANSITION ELEMENT COMPOUNDS; TUNGSTEN COMPOUNDS; TUNGSTEN OXIDES; URANIUM MINERALS; VANADIUM COMPOUNDS; VIBRATIONAL STATES; X-RAY DIFFRACTION
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2009.08.010

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 M{sup I}VWO{sub 6}(M{sup I} - 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 C{sub p}{sup o}(T), enthalpy H{sup o}(T)-H{sup o}(0), entropy S{sup o}(T)-S{sup o}(0) and Gibbs function G{sup o}(T)-H{sup o}(0), for the range from T->0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study. - Graphical abstract: Fragment of the structure of Li(Na)VWO{sub 6}.