THERMODYNAMIC PROPERTIES AND THERMAL EXPANSION OF “HEAVY” RARE-EARTH DITITANATES AT HIGH TEMPERATURES
Gavrichev K.S., Gagarin P.G., Guskov V.N., Guskov A.V., Betenev G.I.
Kurnakov Institute of General and Inorganic Chemistry RAS
119991, Moscow, Leninsky prospect, 31
Rare-earth dititanates, RE2Ti2O7, with a cubic structure are promising components in the design of catalysts, solid-state fuel cells, optical and laser materials, protective coatings and matrices for the disposal of radioactive waste.
Previously, the heat capacity of RE2Ti2O7 was measured systematically in the low-temperature region, and the results obtained are in satisfactory agreement (e.g., [1, 2]), while the measurements in the high-temperature region were carried out fragmentarily. Data on the enthalpies of formation of rare-earth dititanates of the yttrium subgroup are presented in [3].
In this study, RE2Ti2O7 titanates (RE=Tb-Lu) were synthesized by reverse precipitation followed by stepwise calcination to 1500°C. The samples were characterized by X-ray diffraction (phase composition and lattice parameters) and SEM with EDX spectroscopy (particle size, element composition).
The heat capacity of rare-earth dititanates was determined in the temperature range of 300–1850 K by differential scanning calorimetry using the ratio method. Based on the obtained values and literature data, Gibbs energies were calculated to assess the stability of rare-earth dititanates towards action of high temperature and of CMAS oxides.
Crystallographic parameters of RE dititanates were studied by X-ray diffraction at high temperatures and thermal expansion coefficients were calculated.
1. Bissengalieva M.R., Knyazev A.V., Bespyatov M.A., et al. // J. Chem. Thermodyn. 2022. V. 165. P. 106646. https://doi.org/10.1016/j.jct.2021.103346
2. P.G. Gagarin, A.V. Guskov, V.N. Guskov, et al. // Russ. J. Inorg. Chem. 2024. V. 69. P. 1438–1449. https://doi.org/10.1134/S0036023624602046
3. K.B. Helean, S.V. Ushakov, C.E. Brown, et al. // J. Solid State Chem. 2004. V. 177. P. 1858–1866. https://doi.org/10.1016/j.jssc.2004.01.009
This work was performed under the State Assignment of Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences.