Thermodynamic functions and fractal dimensions of samariumcalcium tungstate based on low-temperature calorimetry
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BISSENGALIYEVA, Mira, ZHAKUPOV, Ramazan, GOGOL, Daniil, TAIMASSOVA, Shynar. Thermodynamic functions and fractal dimensions of samariumcalcium tungstate based on low-temperature calorimetry. In: Central and Eastern European Conference on Thermal Analysis and Calorimetry, Ed. 4, 28-31 august 2017, Chişinău. Germany: Academica Greifswald, 2017, Editia 4, p. 258. ISBN 978-3-940237-47-7.
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Central and Eastern European Conference on Thermal Analysis and Calorimetry
Editia 4, 2017
Conferința "Central and Eastern European Conference"
4, Chişinău, Moldova, 28-31 august 2017

Thermodynamic functions and fractal dimensions of samariumcalcium tungstate based on low-temperature calorimetry


Pag. 258-258

Bissengaliyeva Mira1, Zhakupov Ramazan21, Gogol Daniil1, Taimassova Shynar1
 
1 Institute of Problems of Complex Development of Mineral Resources,
2 Lobachevsky State University of Nizhni Novgorod
 
Disponibil în IBN: 3 octombrie 2019


Rezumat

Compounds in the triple oxide systems based on rare earth elements, alkaline earth and transition metals constantly attract the attention of researchers. The presence of lanthanide atoms in their structure gives these compounds a variety of magnetic and electrical properties, often unique. This paper presents the results of the synthesis and study of the calorimetric properties of the compound based on calcium, tungsten, and samarium. The compound under study was synthesized from oxides of the corresponding elements of CaO, Sm2O3, and WO3 taken in the stoichiometric ratio 1: 1: 1. The purity of the starting materials corresponded to the qualification "chemically pure" ("Ch.P"), in this case they were additionally purified by recrystallization or reprecipitation followed by thermal decomposition down to oxides. The synthesis was carried out by one of the variants of the "sol-gel" method using polyvinyl alcohol. The resulting solution of the organic precursor was evaporated to form a solid product, which was then annealed in several stages at gradually increasing temperatures up to 1150 ° C at the final stage. The product obtained is a powder of a light brown colour. Based on the results of the microprobe analysis, the sample is characterized by a sufficiently high homogeneity and constancy of the composition. On the basis of the X-ray diffraction data, the synthesized substance was indexed in the orthorhombic system with the unit-cell parameters a=13.49 Å, b=8.177 Å, c=7.417 Å. The heat capacity of the sample was measured on a low temperature thermophysical installation of the firm "Thermax" (Moscow) starting from a temperature of 12 K. Over the temperature range from 12 to 320 K no significant deviations from the normal course of the heat capacity curve are observed. On the basis of the measurements we obtained the values of the thermodynamic functions of the sample, taking into account extrapolation to absolute zero by the power function equation: Cp (298.15) = 227.8 J/mol • K, S°(298.15) = 255.2 J/mol • K, H°(298.15) - H°(0) = 40.50 kJ/mol. In the process of distinguishing the lattice component of the heat capacity in the coordinates ln(Cp/T 3) vs. ln(1Cp/3Rn) [1,2], we discovered a deviation of the dependence from the linear course, that can indicate the presence of a phase transition below 12 K. The fractal dimensions were also calculated for the sample over the range of characteristic temperatures from 100 to 1000 K on the basis of the experimental values of the heat capacity. These dependences at the values of the heat capacity above 200 K show an increased scatter of the points, what may indicate a structural imperfection of the obtained sample.