Photoacoustic spectra studies of nanometer BaTiO₃

Photoacoustic spectroscopy has been used to study nanoscaled BaTiO₃ powder with different annealing temperatures. The photoacoustic spectra show that the absorption edge of nanoscaled BaTiO₃ powder appears red shift with the increase of annealing temperature, which demonstrates that the energy gap becomes narrow. The decrease of energy gap is related to the growth of grains and the reduction of lattice parameters. In addition, an absorption band with several fine structures appear around 700 nm which is induced by the additional energy levels of oxygen vacancies and the transition of the captured electrons in the additional energy levels. Thus it is illustrated that the variation of the photoacoustic spectra strongly depends upon the grain sizes.