Extended solubility of Sr in LaPO4 monazite

Abstract

Monazite-type LnPO4 is a stable phase for many of the larger rare earths. The 9-fold coordinated La 3+ sites can be substituted by other large ions including aliovalent ions such as Sr 2+.

Structure and Dynamics Investigations of Sr/Ca-Doped LaPO4 Proton Conductors

“…A very weak secondary phase is detected above the 8% Sr-LaPO 4 doping level, which is found to hinder the proton conductivity. This weak peak probably may be related to amorphous phase or to poorly crystalline Sr­(PO 3 ) 2 secondary phase . Given our synthesis method, the solubility limit of Sr into LaPO 4 is around 8%, and the sintering temperature should not exceed 1200 °C.…”

“…This weak peak probably may be related to amorphous phase or to poorly crystalline Sr(PO 3 ) 2 secondary phase. 22 Given our synthesis method, the solubility limit of Sr into LaPO 4 is around 8%, and the sintering temperature should not exceed 1200 °C.…”

“…Acceptor-doped lanthanum orthophosphates LaPO 4 have been reported to be promising candidates for intermediate-temperature fuel cell electrolytes − due to good conductivity, thermal stability, and thermal expansion properties. However, their proton conductivity remains lower than ideal, on the order of 10 –4 S cm –1 . ,,− A number of syntheses and crystal growth conditions have been considered such as identifying the optimal heat treatment conditions. ,,− However, the synthesis of the acceptor-doped lanthanum orthophosphates is challenging due to the typical presence of a secondary phase, the limited dopant solubility, and the segregation of Sr which restricts the proton conductivity in the orthophosphates. , …”

“…9,10,18−22 However, the synthesis of the acceptor-doped lanthanum orthophosphates is challenging due to the typical presence of a secondary phase, the limited dopant solubility, and the segregation of Sr which restricts the proton conductivity in the orthophosphates. 22,23 In order to create charge-compensating oxygen vacancies, a fraction of the trivalent rare earth replaced with a divalent ion such as Sr or Ca. 18 These oxygen vacancies condense into pyrophosphate groups and formed by two tetrahedra sharing an oxygen ion.…”

Formation of nanocrystals based on equimolar mixture of lanthanum and yttrium orthophosphates under microwave-assisted hydrothermal synthesis

“…Among the numerous REE orthophosphates, two-and multicomponent phases [9,10] are of considerable interest. They have applicability as structural [11] and luminescent materials [12,13], thermal barrier coatings [14], as proton-conducting electrolyte [15][16][17][18]. Lanthanum orthophosphate is used as component of two-phase mixtures with refractory oxides to produce reinforced high-temperature ceramics [19].…”