Optical properties of (La,Sr)TiO2N series depending on non-stoichiometries and particle sizes varying in accordance with heat treatment conditions

The stoichiometric LaTiO2N and cation nonstoichiometric La1-xTi1+xO2N and La1-xSrxTiO2N compounds have been prepared in order to clarify the influence on body colors from the viewpoint of particle sizes by controlling the nitriding temperatures and the cation nonstoichiometries. In case of preparing the stoichiometric LaTiO2N at nitriding temperatures from 750 to 9500C, the reflectivity in the longer wavelength region after the absorption edge was lowered and the edge was red-shifted in proportion to the degree of nitridation. The spectra nitrided at above 10500C showed the deterioration in reflectivity compared with the spectrum at 9500C, which would result from grain growth of the well-crystallized oxynitride LaTiO2N. The increase in Ti/La ratios in La1-xTi1+xO2N brought the grain/particle growth resulted in deterioration of reflectivity. Strontium substitution for lanthanum in La1-xSrxTiO2N brought the fining in the primary particles and the surface segregation of strontium and oxygen rich species like SrTiO3 from the oxynitride particles, both of which resulted in enhancement of reflectivity.