TY - JOUR
T1 - Thermochemistry of rare-earth orthophosphates
AU - Ushakov, S. V.
AU - Helean, K. B.
AU - Navrotsky, A.
AU - Boatner, L. A.
N1 - Funding Information:
This work was performed as part of the project supported by the United States Department of Energy through the Environmental Management Science Program, Grant DE-FG07-7ER45673 to University of California Davis. The authors thank Juraj Majzlan for help on the initial stage of the project and for editing the manuscript.
PY - 2001/9
Y1 - 2001/9
N2 - The enthalpies of formation for the compounds (RE3+)PO4, (where RE = Sc, Y. La-Nd, Sm-Lu) were determined by oxide-melt solution calorimetry. Calorimetric measurements were performed in a Calvet-type twin microcalorimeter in sodium molybdate (3Na2O · 4MoO3) and lead borate (2PbO · 2B2O3) solvents at 975 K. The experiments were carried out using both powdered single crystals grown by a flux technique and powders synthesized by precipitation. Formation enthalpies were derived from the drop-solution enthalpies for (RE)PO4, RE oxides, and P2O5. Enthalpies of formation for the (RE)PO4 compounds with respect to the oxides at 298 K become more negative with increasing RE3+ ionic radius; i.e., in going from ScPO4 (-209.8 ± 1.0 kJ/mol), to LuPO4 (-263.9 ± 1.9 kJ/mol), to LaPO4 (-321.4 ± 1.6 kJ/mol). From structural considerations, a similar trend is expected for the isostructural RE vanadates and arsenates, as well as for the tetravalent actinide orthosilicates.
AB - The enthalpies of formation for the compounds (RE3+)PO4, (where RE = Sc, Y. La-Nd, Sm-Lu) were determined by oxide-melt solution calorimetry. Calorimetric measurements were performed in a Calvet-type twin microcalorimeter in sodium molybdate (3Na2O · 4MoO3) and lead borate (2PbO · 2B2O3) solvents at 975 K. The experiments were carried out using both powdered single crystals grown by a flux technique and powders synthesized by precipitation. Formation enthalpies were derived from the drop-solution enthalpies for (RE)PO4, RE oxides, and P2O5. Enthalpies of formation for the (RE)PO4 compounds with respect to the oxides at 298 K become more negative with increasing RE3+ ionic radius; i.e., in going from ScPO4 (-209.8 ± 1.0 kJ/mol), to LuPO4 (-263.9 ± 1.9 kJ/mol), to LaPO4 (-321.4 ± 1.6 kJ/mol). From structural considerations, a similar trend is expected for the isostructural RE vanadates and arsenates, as well as for the tetravalent actinide orthosilicates.
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U2 - 10.1557/JMR.2001.0361
DO - 10.1557/JMR.2001.0361
M3 - Article
AN - SCOPUS:0000008954
SN - 0884-2914
VL - 16
SP - 2623
EP - 2633
JO - Journal of Materials Research
JF - Journal of Materials Research
IS - 9
ER -