Suppression of Nb reduction in high-κ perovskite oxynitrides, BaMxNb1−xO2+4xN1−4x (M = Li, Na; x ≤ 0.15)

Abstract

Dielectric polarization of the Nb-containing perovskite oxynitrides was realized through the controls of the electronic and geometric environments of Nb. To suppress the Nb reduction which is detrimental to the dielectric polarization, two different approaches were employed, particularly in the preparation of BaNbO2N. First, the starting reactants were provided with an excess of Ba, to avoid the possibility of surplus Nb. Second, part of Nb was replaced with low-valence cations, to form BaMxNb1−xO2+4xN1−4x (M = Li, Na; x ≤ 0.15). Diffuse-reflectance spectroscopy and X-ray photoelectron spectroscopy indicated that the introduction of M+ is effective in preserving the Nb5+ state. As revealed by the Fourier-transform infrared spectroscopy, the octahedral frameworks of BaNbO2N and BaMxNb1−xO2+4xN1−4x were substantially distorted, to form readily polarizable lattices. The dielectric constant (κ) of BaNa0.11Nb0.89O2.44N0.56 was evaluated to be as high as 15,000 at 300 K.