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Solid Solutions and Thermal Transformations in Nanosized LaPO₄-YPO₄-H₂O and LaPO₄-LuPO₄-H₂O Systems

V. Popova, L. Mezentseva, A. Osipov, V. Ugolkov, I. Kruchinina, A. Yakovlev, T. Maslennikova

Journal of Ceramic Science and Technology, Vol. 5, No. 3 (2014), pp. 237-244

DOI: 10.4416/JCST2014-00013

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Abstract

Nanosized powders of orthophosphates in the LaPO4-YPO4(-H2O) and LaPO4-LuPO4-H2O systems are synthesized to increase the mutual solubility of LaPO4·nH2O, YPO4·nH2O and LuPO4·nH2O initial components and to investigate physicochemical properties of nanosized solid solutions and their mixtures. The temperature dependence of nanoparticle size is investigated in the 200 – 1100 °C temperature range. Formation of limited hexagonal, monoclinic or tetragonal solid solutions is revealed, and the limits of their concentration and thermal stability are determined. In the LaPO4-YPO4(-H2O) system a series of limited hexagonal LaPO4·nH2O-based solid solutions is observed up to 500 – 600 °C within the 0 ≤ x ≤ 0.5 concentration range; a monoclinic LaPO4-based form is observed up to at least 1000 °C within the 0 ≤ x ≤ 0.7 concentration range. Melting temperatures of La1-xYxPO4 samples are found to be in the 2010 – 1960 °C temperature range. In the LaPO4-LuPO4-H2O system corresponding hexagonal solid solutions are observed within the 0 ≤ x ≤ 0.4 concentration range; isomorphic capacity of the monoclinic form at 1100 °C is between 20 – 25 mol%. Solubility of LaPO4 in tetragonal YPO4 or LuPO4 in all cases is less than 10 mol%. The specific surface area of La1-xLuxPO4·nH2O powders is in the range of 46.7 – 90.3 m2/g depending on x.

Keywords

LaPO4-YPO4-H2O and LaPO4-LuPO4-H2O systems, nanopowders, thermal behavior

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