Ti Kβ and X-ray Raman spectra from BaTiO3 nano particles

Recently a research group led by Okayama University in Japan has reported the successful application of resonant X-ray emission spectroscopy (RXES) to BaTiO₃ nanoparticles of various sizes ranging from a bulk-like 200 nm to a paraelectric 50 nm. While it is well known that the crystal structure changes from tetragonal to cubic as the particle size decreases, some recent reports indicated that a very large enhancement of the dielectric constant was observed at a specific particle size of around 70 nm. The research was done to clarify the above problem. In the X-ray emission spectra measured with monochromatic excitation near the sharp peak of the Ti-K absorption edge, two small Raman peaks were observed between Kβ_2,5 (4962.6 eV) and elastic scattering of (for example, 4983.6 eV) peaks. It was found that the higher energy Raman peak (5.3 eV lower than incident X-ray energy) still exists at a size of 85 nm, even though the intensity basically diminishes for the small particle size BaTiO₃, which corresponds to the extraordinary large crystal structure change. The results suggest that Raman peak intensity is correlated to the large enhancement of the dielectric constant. For more information, see the paper, "Enhancement of dielectric constant of BaTiO₃ nanoparticles studied by resonant x-ray emission spectroscopy", N. Nakajima et al., Phy. Rev. B86, 224114 (2012).