The high-temperature heat capacity of LnPO4 (Ln=La, Ce, Gd) by drop calorimetry

Evidence for Lattice Strain and Non-ideal Behavior in the (La1−xEux)PO4 Solid Solution from X-ray Diffraction and Vibrational Spectroscopy

“…The end members as well as nine compositions of the solid solution were prepared by sol-gel reaction (Popa and Konings, 2006;Popa et al, 2006b = 1-1.2) was added dropwise under continuous heating (70 • C) and stirring; this initiated the precipitation of a white gel. After 1 h a concentrated ammonia solution was added till pH = 5, at which point (La 1−x Eu x ) PO 4 formed.…”

“…Only gadolinium would have had a larger effects, but during several synthesis trials we observed that traces of a xenotime phase, typical for the heavy rare-earth orthophosphates, are always present in samples of that compound, making its study difficult. We therefore concentrated our investigations in the beginning on the (La 1−x Eu x ) PO 4 solid solution series for which thermodynamic data, indicating an excess energy of mixing, are already available (Popa et al, 2006b). …”

The heat capacity of NdPO4

“…We have started a systematic study of the heat capacity of the monazite-type lanthanide orthophosphates and have reported measurements in the (1.8 to 1600) K temperature range for LaPO 4 , CePO 4 , and GdPO 4 [2][3][4][5]. For CePO 4 and GdPO 4 , we observed cooperative anomalies close to T = 0 K, related to the removal of the ground state degeneracy.…”

High-temperature calorimetry of (La1−xLnx)PO4 solid solutions

“…In a series of recent publications we have presented heat capacity and enthalpy increment measurements for the monazite-type LnPO 4 compounds up to T = 1600 K [1][2][3][4][5][6]. The results were interpreted to be the sum of a lattice and an excess component:…”