Vibrational spectra, particularly Raman spectra provide useful information on the internal structure, bonding, and state-oforder of materials ranging from bulk crystals to nanoscale particulates. Spectra of bulk crystals contain first order phonons excited at the center of the Brillouin zone. Disorder produces a broadening of Raman lines due to breakdown of strict translational symmetry. Structural disorder can be distinguished from dipolar disorder in strongly polar materials by the temperature dependence of the line shapes. At particle sizes in the nanoscale range, new phenomena appear due the effects of phonon confinement. These include mode wavenumber shifts and line broadening, the appearance of zone boundary phonons, the appearance of surface phonons, and the appearance of extremely low wavenumber bands due excitation of bulk resonances of the particle. One must distinguish between purely nanocrystal effects due to phonon confinement and the increased structural disorder that often accompanies extreme reduction in particle size. The present paper reviews these concepts and the underlying theory with the aim of making Raman spectroscopy a useful characterization tool for particulate ceramic materials.

Keywords: Raman Spectra, Particulates, Order/Disorder