Reinvestigation of the Phase Equilibria in the La2O3-P2O5 System

Abstract

The phase equilibria between the solid phases in the La 2 O 3-P 2 O 5 system were reinvestigated with solid state reaction method. The existence of La 3 PO 7 , La 7 P 3 O 18 , LaPO 4 , and LaP 3 O 9 was confirmed. La 7 P 3 O 18 can form only at $1200°C or higher possibly due to kinetic reasons, but it is stable at lower temperatures. On the other hand, three intermediate compounds proposed to exist, La 5 PO 10 , La 4 (P 2 O 7) 3 , and La 2 P 4 O 13 were not obtained in this study. Based on the literature, La 4 (P 2 O 7) 3 and La 2 P 4 O 13 are considered to be metastable phases, although thermodynamic evidence is still required.

Effect of Sr2+ doping on sintering behavior, microstructural development and electrical properties of LaPO4·nH2O nanorods prepared by dry mechanical milling

“…It is also in agreement with the phase diagrams in the system La 2 O 3 -P 2 O 5 established by Park and Kreidler [16], Kropiwincka and Znamierowska [17], and Hatada et al [18].…”

“…Consequently, due to its detrimental influence on sintering process, more particularly on the microstructural design of sintered ceramics, La(PO 3 ) 3 must be eliminated or at least minimized. However, La(PO 3 ) 3 is thermodynamically stable according to the La 2 O 3 -P 2 O 5 phase diagrams [16][17][18]; for its removal Bregiroux et al [15] proposed to heat the raw powders of LaPO 4 at 1400ºC for 1h. However, such process can provoke the formation of hard agglomerates that hinder the sintering process.…”

Mechanical and dielectric properties of porous lanthanum orthophosphate materials with TiO2 addition via foam-gelcasting

“…The XRD patterns of lanthanum phosphate powders calcined at 1500°C with various mass ratios of H 3 PO 4 are shown in Figure 1. The monoclinic LaPO 4 (JCPDS # 32-0493) [6] is the dominant phase in all sample powders, while traces of La 3 PO 7 (JCPDS # 49-1023) [19] for a mass ratio of 10:10:3 and La(PO 3 ) 3 (JCPDS file # 33-0718) [20] for 10:10:5 and 10:10:6 are also observed. Relatively pure monoclinic LaPO 4 phase was obtained only for a mass ratio of 10:10:4 ( Figure 1(b)), so powder under this processing condition was used subsequently.…”

“…The XRD pattern for powder samples calcined at 1200°C is similar to that of 1000°C. According to Figure 1(b), after calcination at 1500°C, the phase of La(PO 3 ) 3 disappears [19,22]:…”

Microwave Dielectric Properties of LaPO$lt;inf$gt;4$lt;/inf$gt; Ceramics Synthesized by a Hydrothermal Method

“…The crystallite size was calculated from the XRD line broadening using Scherrer relationship, D hkl = 0.89λ/ (β hkl •cosθ), where hkl was the index of the diffracting plane, D hkl was the average thickness of the crystal in a direction normal to the diffracting plane hkl in nm, β hkl was the crystallite size contribution to the peak width (full width at half maximum) in radians, λ was the wavelength of X-rays. residual species adsorbed at the particle surface, which decomposed by incongruent melting in the 1050-1235℃ temperature range [28][29] . Curve 2c-d showed the XRD patterns of the H-LaPO 4 ceramics at 1260℃ and SSR-LaPO 4 ceramics at 1300℃.…”