Investigation of O/N Ordering in Perovskite-Type Oxynitrides La1−xYxTa(O,N)3 on Long Range and Short Scale

Oxynitrides such as LaTa(O,N)(3) are attractive materials as photoelectrodes for photoelectrocatalytic solar water splitting. The potential anionic ordering in their perovskite-type structure has been shown to impact the materials' properties. Given the importance attributed to it, the present study reports a detailed experimental analysis supported by simulations of the anionic ordering of La1-xYxTa(O,N)(3). The influence of O/N and yttrium content on the anionic order was assessed. Neutron diffraction analysis was performed on four different nominal compositions-LaTaON2, LaTaO2N, La0.9Y0.1TaON2, and La0.9Y0.1TaO2N-at 10 K and 300 K to study potential long-range ordering. Neutron pair distribution function (PDF) analysis was performed on all samples at 10 K and on non-Y-substituted samples at 300 K to evaluate short-range ordering. There was no evidence of long-range O/N order in any of the compounds. In contrast, at a short range (1.5 & Aring; <= r < 6 & Aring;), a Pnma (a(-)b(+)a(-)) tilting pattern and local cis-ordering of the anions were seen. The latter faded rapidly, leaving the Pnma tilting pattern in a 6 & Aring; <= r <= 11 & Aring; range. At higher distances, the PDF analysis agreed with the Imma (a(-)b(0)a(-)) O/N disordered long-range structure. As the O/N content changed, not much difference in behavior was observed. Yttrium substitution introduced some disorder in the structure; nonetheless, it showed marginal influence on octahedral tilting and anionic ordering.