Sintering and crystallite growth of nanocrystalline copper doped tin oxide

The effect of Cu2+ contents and of firing temperature on sintering and crys tallite growth of nanocrystalline SnO2 xerogels was analyzed by thermoanaly sis (mass loss (TG), linear shrinkage, and differential thermal analysis (D TA)), X-ray powder diffraction (XRPD), and EXAFS (extended X-ray absorption fine structures) measurements. Samples were prepared by two methods: (a) c oprecipitation of a colloidal suspension from aqueous solution containing b oth Sn(IV) and Cu(II) ions and (b) grafting copper(II) species on the surfa ce of tin pride gel. The thermoanalysis has shown that the shrinkage associ ated with the mass loss decreases by increasing the amount of copper. The E XAFS measurements carried out at the Cu K edge have evidenced the presence of copper in substitutional solid solution for the dried xerogel prepared w ith 0.7 mol % of copper, while for higher concentration of doping, copper h as been observed also at the external surface of crystallites. The solid so lution is metastable and copper migrates toward the surface during firing. The XRPD and DTA results have shown a recrystallization process near 320 de grees C, which leads to crystallite growth. The presence of copper segregat ed near the crystallite surface controls its growth.