Heat Capacity of Pb10 –xPrx(GeO4)2 +x(VO4)4– x (x = 0, 1, 2, 3) Apatites in the Range 350–1050 K

• Published in: Inorganic materials Vol. 56; no. 10; pp. 1027 - 1032
• Main Authors: Denisova, L. T., Kargin, Yu. F., Golubeva, E. O., Zeer, G. M., Abkaryan, A. K., Denisov, V. M.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 2020; Springer Nature B.V
• Subjects: Apatite; Chemistry; Chemistry and Materials Science; Germanium oxides; Heat; High temperature; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Mathematical analysis; Mixed oxides; Phase transitions; Praseodymium oxide; Specific heat; Synthesis; Thermal expansion; Unit cell; X-ray diffraction; lead praseodymium germanatovanadates; high-temperature heat capacity; thermal expansion; apatites; unit-cell parameters
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168520100039

Pb 10 – x Pr x (GeO 4 ) 2 + x (VO 4 ) 4 – x ( x = 0, 1, 2, 3) apatites have been prepared by solid-state reactions via sequential firing of appropriate oxide mixtures (PbO, Pr 2 O 3 , GeO 2 , and V 2 O 5 ) in air in the temperature range 773–1073 K. Their unit-cell parameters have been determined as functions of temperature by high-temperature X-ray diffraction measurements, and the linear and volume expansion coefficients of Pb 7 Pr 3 (GeO 4 ) 5 (VO 4 ) have been calculated. The heat capacity of the synthesized Pb 10 – x Pr x (GeO 4 ) 2 + x (VO 4 ) 4 – x ( x = 0, 1, 2, 3) compounds with the apatite structure has been determined by differential scanning calorimetry in the temperature range 350–1050 K. The c p ( T ) curves of the samples with x = 1, 2, and 3 have been shown to have extrema (in particular, peaks at 701, 917, and 1018 K for the x = 3 sample) due to phase transitions. The experimental C p ( T ) heat capacity data have been used to evaluate the thermodynamic functions of the synthesized apatites.