Raman study of copper and iron oxide particles embedded in an SiO2 matrix

The structure of heat-treated sol-gel-made SiO2 samples containing copper o r iron in various amounts was studied using Raman spectroscopy and x-ray di ffraction, The treatments were in air in the temperature range 200-800 degr ees C, Copper and iron concentrations were in the range 7-55 wt%, It was fo und that in the samples containing copper, the metal is mainly dissolved in the SiO2 network when the thermal treatment is at low temperatures. For hi gher annealing temperatures, first a copper silicate is formed and then mos t of the copper forms cupric oxide particles at temperatures of about 800 d egrees C. In samples containing iron, the formation of particles with nanom etric size of the gamma-Fe2O3 (maghemite) phase is observed after annealing at 500 degrees C. At 800 degrees C the maghemite phase is transformed into the stable hematite (alpha-Fe2O3) phase. Copyright (C) 1999 John Wiley & S ons, Ltd.