2011/07/21 by James R. Rustad, Rustad, James R.
Chemistry · Environmental Science · Materials Science · #Chemical Synthesis and Characterization #Crystal Structures and Properties #FOS: Physical sciences #Luminescence Properties of Advanced Materials #Materials Science (cond-mat.mtrl-sci) #Zeolite Catalysis and Synthesis
paper · pdf · doi:10.48550/arxiv.1107.4261
openalex publication_date 2011/07/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Electronic structure calculations are carried out to estimate the heats of\nformation of rare-earth orthophosphates from their oxides. The calculated heats\nof formation are systematically about 40 kJ/mol less exothermic than the\nmeasured values. Based on estimated corrections for zero-point energies and\nH(298.15)-H(0), the discrepancy is almost entirely electronic in origin. The\ndecreasingly exothermic \ΔHfox with decreasing ionic radius (i.e. LaPO4\nmore exothermic than ScPO4) results from the higher charge localization on the\noxide anion (O2-) relative to the phosphate anion (PO43-). The lattice energy,\nof course, becomes more negative with decreasing ionic radius for both oxide\nand phosphate phases, but does so more rapidly for the oxide, making the\nreaction less exothermic as ionic radius becomes smaller. This effect should\ncarry over to \ΔHfox other oxyacids, such as silicates and sulfates.\n