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Raman spectroscopy of ball milling of TiO2 and ZrO2 to nanometric sizes

High-energy ball milling of TiO2 and ZrO2 powders decrease particle sizes and induce changes of crystal structure. Structural changes during different milling condition and possible solid-state reaction were investigated by Raman spectroscopy. Raman spectroscopy has an advantage to resolve easily tetragonal and cubic structures of ZrO2. The appearance of low-frequency Raman mode indicated the diminution of oxide particles to nanometric sizes, which dimensions were determined by transmission electron microscopy (TEM). The kinetics of phase transition during the milling of both oxides was dependent on powder-to-ball weight ratio. The different milling times of TiO2 induced sequence of phase transitions, from anatase through high-pressure TiO2 II phase to rutil. Monoclinic ZrO2 was partially transformed to tetragonal phase during milling. The milling of the equimolar mixture of the oxides did not complete the solid-state reaction, so the subsequent heating was required. In both materials the low-frequency Raman band appeared after prolonged milling, which suggested the nanometric sizes of particles. The band was broad and its maximum was difficult to determine. TEM was used to determine particle sizes, which were even smaller than 10 nm in some samples. The milling induced phase transition for which otherwise high temperature or high pressure were necessary, and it was shown to be a simple method for preparation of nanoparticles.

Raman spectroscopy; nanoparticles; ball milling; TiO2; ZrO2

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