Oxynitride perovskites were prepared by reacting Ta2La2/3O6 with NaNO3 or LiOH at 600 to 950C in NH3 gas, and were characterized by means of X-ray powder diffraction, thermogravimetry and impedance measurements. The incorporation of Na or Li into Ta2La2/3O6 resembled intercalation, and involved the simultaneous replacement of O2- by N3-. The compounds which were formed exhibited the same type of unit cell as that of Ta2La2/3O6 (P4/mmm, a = 0.392, c = 0.791nm). Rietveld refinement of the atom-site occupancy factors for Na-containing phases revealed a preferential occupancy of Na and La atoms in alternating layers perpendicular to the c-axis. The available data suggested that analogous phases with Li were formed. The latter were Li-ion conductors, with an activation energy of 0.8eV and a maximum conductivity of 1.3 x 10-4S/cm at 300C. A new oxynitride compound, Li2Ta2LaNO6, was prepared by reacting Li2CO3, La(OH)3 and Ta2O5 together in an NH3 atmosphere at 800 to 900C. Using powder diffraction data, the crystal structure was related to a member of the Ruddlesden-Popper series of perovskite-like phases, with space-group I4/mmm (a = 0.39506, c = 1.8456nm). The compound was a moderate Li-ion conductor, with a conductivity of 3.5 x 10-6S/cm at 300C and an activation energy of 0.66eV.

Synthesis and Ionic Conductivity Properties of Oxynitride Perovskites. S.Esmaeilzadeh, J.Grins, T.Hörlin: Materials Science Forum, 2000, 325-326, 11-6