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Complex Rare-Earth Tantalates with Pyrochlore-Like Structure: Synthesis, Structure, and Thermal Properties.
- Source :
- Russian Journal of Inorganic Chemistry; Nov2019, Vol. 64 Issue 11, p1342-1353, 12p
- Publication Year :
- 2019
-
Abstract
- The existence of a wide range of pyrochlore-like (PL) Ln<subscript>2</subscript>FeTaO<subscript>7</subscript> compounds (Ln = Pr–Yb, including Y) with a hexagonal structure (space group R ) was shown. Two new low-temperature methods for the synthesis of Ln<subscript>2</subscript>FeTaO<subscript>7</subscript> were developed to reduce the production temperature and time, namely, coprecipitation followed by annealing and synthesis in molten salts NaCl/KCl. The synthesis of PL phases was found to involve the formation of a nanocrystalline metastable fluorite phase, the fluorite irreversibly transforming to a PL phase as the crystallization time or temperature increases. No other transitions in Ln<subscript>2</subscript>FeTaO<subscript>7</subscript> were recorded by DSC up to the melting point of 1320–1450°C (depending on the composition of the Ln<subscript>2</subscript>FeTaO<subscript>7</subscript> compound). The isobaric heat capacity C<subscript>p</subscript>(T) was measured and the thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) were calculated in the temperature range 5–1300 K for Y<subscript>2</subscript>FeTaO<subscript>7</subscript> by the way of example. In the low-temperature region of 2–25 K, an abnormal behavior of Cp(T), apparently related to the Y<subscript>2</subscript>FeTaO<subscript>7</subscript> magnetic transition, was detected. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00360236
- Volume :
- 64
- Issue :
- 11
- Database :
- Complementary Index
- Journal :
- Russian Journal of Inorganic Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 140314206
- Full Text :
- https://doi.org/10.1134/S0036023619110056