Effect of Tb3+ doping and self-generated pressure on the crystallographic/morphological features and thermal stability of LaPO4·nH2O single-crystal nanorods obtained by microwave-assisted hydrothermal synthesis

The effect of Tb3+-doping content (in the range 0-20 mol%) and autogeneous/self-generated pressure (in the range 2.3-3.4±0.1 bar) on the crystallographic/morphological features and thermal stability of single-crystal nanorods of LaPO4·nH2O obtained by a simple and fast microwave-assisted hydrothermal synthesis was investigated. It is shown that high-quality (that is, well-shaped and linear/planar defect free) rhabdophane-type single-crystal La1-xTbxPO4·nH2O (x=0-0.20) nanorods, with a high morphological uniformity, are obtained in all cases. In addition, it is shown that the Tb3+ solutes are incorporated into the LaPO4·nH2O host, forming substitutional solid solutions (i.e., partial substitution of La3+ by Tb3+) with progressively smaller unit-cell volume but with identical thermal stability. Morphologically Tb3+ doping however results in the formation of nanorods with lower aspect ratio. With respect to the self-generated pressure during the microwave synthesis, it is shown that its increase does not affect to crystallographic aspects, but however results again in nanorods with lower aspect ratio. It is also demonstrated that monazite-type single-crystal La1-xTbxPO4 nanorods can be obtained by calcining their rhabdophane-type La1-xTbxPO4·nH2O counterparts at ~700 °C in air. Consequently, in the present study important guidelines have been identified for the controlled synthesis of functional La1-xTbxPO4·nH2O nanorods with tailored morphology.