Variation of fundamental and higher-order Raman spectra of ZrO2 nanograins with annealing temperature

ZrO2 nanograins annealed at different temperatures are systematically investigated using x-ray diffraction ~XRD! and Raman spectroscopy. Our results show that bulk properties of nano-ZrO2 diminish but the defect-, surface-, and size-related features display as grain size decreases. A critical size that divides respective predominance is determined to be about 15 nm. Both XRD and Raman spectra of nano-ZrO2 of size above 15 nm are similar to bulk ones. On the contrary, those of nano-ZrO2 of size below 15 nm are deteriorated bulk spectra with spectroscopic line broadening and merging, line intensity reducing, and position shifting. Deteriorated XRD spectra are essentially associated with increasing defects in small nanograins. General mode softening, a surface mode around 1040 cm and 14 weak second-order ~overtone and combination! modes are characteristics of Raman spectra of nano-ZrO2 below 15 nm. They are associated with microstructure change of nanograins, i.e., they reflect the effects of grain size, surface, and the interaction between nanograins. @S0163-1829~99!02803-9#