Size–strain line broadening analysis of high-permittivity oxynitrides BaTaO2N and BaNbO2N

X-ray line broadening analysis of polycrystalline BaTaO2N and BaNbO2N was performed to extract microstructural information beyond the average structural descriptions. Both BaTaO2N and BaNbO2N display markedly broader diffraction peak profiles than observed from an oxide analogue KTaO3. Examination of the angular dependence of the integral peak breadth shows that the line broadening of BaTaO2N is caused by both finite crystallite size (Dv = 117 nm) and micro-strain (ɛ = 0.038%), whereas the latter effect dominates in the case of BaNbO2N (Dv = 574 nm, ɛ = 0.11%). The above results indicate that the temperature-independent high-permittivity behavior of BaTaO2N arises due to local atomic displacements, and further imply that even stronger dielectric polarizations could be generated in BaNbO2N.