Preparation of Cerium Orthophosphate Nanosphere by Coprecipitation Route and Its Structural, Thermal, Optical, and Electrical Characterization

Cerium orthophosphate (CePO4) nanoparticles were synthesized via wet chemical coprecipitation technique using cerium nitrate hexahydrate for Ce3+ ion and ammonium dihydrogen phosphate for ion source. X-ray diffraction (XRD) analysis suggests that the material belongs to monoclinic crystal system with crystallite size of 49.3？nm. Scanning electron microscope (SEM) and transmission electron microscope (TEM) reveal the surface morphology of the prepared nanoparticles as nanospheres having grain size in the range of 30–50？nm. The energy dispersive X-ray analysis (EDAX) gives elemental composition present in the grown nanomaterial. Thermogravimetric analysis suggests that the structural phase transition is above 800°C. The optical properties include UV-VIS-NIR absorption and the photoluminescence spectrum shows the absorption and emission peaks in the ultraviolet region. The dielectric constant and ac conductivity properties were investigated with regard to change in temperature (40 to 500°C) and frequency (5？kHz to 1？MHz). The dielectric measurement indicates that the transition is diffused and the activation energy values decrease suggesting that the conduction mechanism is due to hopping of the charge carriers from one site to another. 1. Introduction Rare earth elements (REEs) known as lithophile are the elements enriched in the earth crust which occur naturally because all are trivalent and form a special group of transition elements in the periodic table. Among these REEs, cerium (Ce) is found in abundance which makes it one of the cheapest rare earth metals. However, cerium is found in several minerals like monazite (Ce, La, Nd, Th) PO4, xenotime (Y, Ce) PO4, bastnasite (Ce, La) CO3 (F, OH), and cerite (Ce, La)9(Mg, Fe)Si7(O, OH, F)28. Orthophosphates are substances that are composed of isolated PO4 tetrahedra analogous to “orthosilicates.” The most common naturally occurring orthophosphates are apatite [Ca3(PO4)3F, Cl, OH] and monazite (LnPO4) where “Ln” refers to rare earth elements. Rare earth orthophosphates with the general formula RXO4 (where R = rare earth and X = P, As, or V) belong to a family that crystallizes in different structural types like hexagonal, tetragonal, and monoclinic depending on the radius of ions and temperature. The rare earths compounds with large ionic radii, namely, RPO4 with R = La, Ce, Pr, Nd, Sm, Eu, and Gd, crystallize in the monoclinic monazite structure, whereas rare earth compounds with small ionic radii, namely, RPO4 (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc), crystallize in the tetragonal zircon (or