Phase equilibria in the ErPO4–K3PO4 system

Abstract

The phase equilibria occurring in the ErPO 4 -K 3 PO 4 system were investigated by the thermal analysis, FTIR, and X-ray powder diffraction methods. On the basis of obtained results, the related phase diagram is proposed. This system includes one intermediate compound, K 3 Er(PO 4 ) 2 ; the double phosphate melts incongruently at 1355°C and occurs in two polymorphic forms; transformation b/a-K 3 Er(PO 4 ) 2 proceeds at 420°C. The eutectic occurs at the composition of 58.5 wt% K 3 PO 4 , 41.5 wt% ErPO 4 at 1317°C.

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

“…In addition, in Refs. [38,45] it has been shown that the thermal effects connected to the formation/ decomposition of Me 3 RE(PO 4 ) 3 are characterized by a large thermal hysteresis. The difference between the onset temperatures of effects on heating and cooling DTA curves is connected to kinetic hindrances occurring by the decomposition/formation of new phases and is a sign of reconstructive-type transformations [45,46].…”

“…Phase diagrams of phosphate systems with rare earth elements have been studied by our group in last decades [34][35][36][37][38][39]. In the Ca 3 (PO 4 ) 2 -REPO 4 systems (RE = Y, La, Ce) form compounds with the formula Ca 3 RE(PO 4 ) 3 [34][35][36].…”

Phase equilibria in the ErPO4–KPO3 system

“…Their polymorphism has been investigated by plenty of authors (see, e.g. [28][29][30][31][32][33]). Erbium orthophosphate ErPO 4 , is related to the LnPO 4 group with xenotime structure, isostructural to zircon (ZrSiO 4 ) and it crystallizes in the tetragonal system [SG I41/amd, a = 6.8614(5), c = 6.0082(9) Å , Z = 4] [33].…”

“…Erbium orthophosphate ErPO 4 , is related to the LnPO 4 group with xenotime structure, isostructural to zircon (ZrSiO 4 ) and it crystallizes in the tetragonal system [SG I41/amd, a = 6.8614(5), c = 6.0082(9) Å , Z = 4] [33]. ErPO 4 exists in one polymorphic form [30].…”