Co-precipitation synthesis of Nd:YAG nano-powders: the effect of Nd dopant addition with thermal treatment

Nanopowders of Yttrium Aluminium Garnet doped with neodymium ions were obtained by the co-precipitation method from the reaction of aluminium, yttrium and neodymium nitrate with ammonia. The amount of neodymium was selected in order to produce samples of nominal stoichiometry NdXY (3-X)Al5O12 (where X = 0.006, 0.012, 0.024, 0.048, 0.081, 0.096, 0.17, 0.19, 0.38, 0.54, and 0.72, respectively). After washing and drying, the hydroxide precursors were subjected to Thermo-Gravimetry and Differential Thermal Analysis experiments from room temperature up to 1500 °C, which showed the presence of exothermal events accompanying phase transformation phenomena. X-ray diffraction investigations conducted with a high-resolution powder diffractometer on the specimens arrested at selected temperature of the thermograms, evidenced the amorphous-to-crystalline transformation phenomena leading to the garnet phase as the main product. On increasing the concentration of Nd, the presence of the monoclinic Y 4Al2O9 phase was also detected together with a variable amount of a metastable hexagonal YAlO3 phase. Precise determination of the cubic garnet lattice parameters as a function of the neodymium content according to the Rietveld method shows a change from the value of 12.016 (±2) Å when X = 0 up to 12.128 (±2) Å for X = 0.720 with two distinctive regimes of increase. The line broadening analysis of X-ray profiles after correction for instrumental factors indicates that the average crystallite size is in the range 50-80 nm. Field-Emission Gun-Scanning Electron Microscopy observations showed the presence of aggregation features in the powders with a rounded morphology and a relatively uniform and narrow particle size distribution, with the average size figures in substantial agreement with the diffraction analyses.