Thermal decomposition of lanthanide orthophosphates synthesized through crystallisation from phosphoric acid solution

• Published in: Thermochimica acta 2003-09, Vol.404 (1), p.81-88
• Main Author: Kijkowska, Regina
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Inorganic chemistry and origins of life; Lanthanide phosphates; Polymorphic transformation; Preparations and properties; Salts; Thermal dehydration
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/S0040-6031(03)00085-6

Thermal decomposition characteristics of lanthanide phosphates LnPO 4·H 2O (Ln: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) prepared by crystallisation from boiling phosphoric acid solution has been presented. On the basis of the effects observed on DTA and DTG curves, while heated up to 1000 °C, the phosphates can be divided into two groups: (a) the first group includes hexagonal (La→Tb), and orthorhombic Dy phosphates, (b) the second group consists of tetragonal (Ho→Lu) and Y phosphates. The group (a) is characterised by two endotherms below 300 °C, associated with dehydration, and one exotherm above 700 °C, associated with transformation of the hexagonal/orthorhombic into monoclinic modification. The temperature of the polymorphic transformation is increasing with the increase of the atomic number of the lanthanide from 900 °C (Tb, Dy). The group (b) dehydrates within a wide temperature range (100–600 °C) and maintains the tetragonal crystal structure even after heating at 950 °C. However, an increased crystallinity, contraction of the a- and c-axes, and difference in IR spectra suggests topotactical structural changes in (Ho→Lu) and Y phosphates.