Synthesis and characterisation of perovskite-type oxynitrides

Rare earth and alkaline earth tantalum oxynitride perovskite-type systems of the stoichiometry A((1-x))Ln(x)TaO((2-x))N((1+x)), where A is an-alkaline earth metal (Ca, Sr and Ba) and Ln, a lanthanide, have been synthesised and characterised using powder X-ray and neutron diffraction. The samples formed were orthorhombically distorted perovskites and crystallised in the space group Pnma. Further analysis of the diffraction data has highlighted the influences that the nature of the cations incorporated and the distribution of the anions have on crystal structure and lattice size. Thermogravimetric analyses have been performed in air and show the onset of decomposition at ca. 400degreesC for all materials. UV-Vis spectroscopic measurements show that these compounds exhibit absorption bands in the visible region, due to inter-band transitions, with positions that can be correlated with structure and composition.