Co-precipitation synthesis of Nd:YAG nano-powders: the effect of Nd dopant addition with thermal treatment
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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 Y4Al2O9 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.
KeywordsNeodymium Yttrium Aluminium Garnet YAlO3 Isothermal Treatment Garnet Phase
This work is carried out within two collaborative Projects, entitled “Nanostructured Luminescent Oxides”, and “Synthesis of nanopowders assisted by microwaves” respectively, funded by the Italian Ministry for Education, University and Science (PRIN call 2003).
We acknowledge useful discussions with prof. G. Cocco, L. Schiffini (Univ. of Sassari, Italy) and prof. M. Baricco (Univ. of Torino, Italy) on the phase metastability.
We thank Dr. G. M. Ingo and Tilde De Caro (ISMN-CNR Montelibretti, Roma, Italy) for FEG-SEM micrographs, Dr. P. Guerra (Dipartimento di Ingegneria Chimica dei Processi e dei Materiali—Univ. of Palermo, Italy) for EDX analysis and Dr. Luca Lutterotti for making available a copy of the programme MAUD running in a personal computer. (http://www.ing.unitn.it/∼luttero/).
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