New crystal-structure phase in oxygen-nonstoichiometric double-layered perovskite NdBaCo2O5.72

The crystal structure of an NdBaCo2O5+δ(δ=0.72) solid solution with a layered perovskite structure is studied by neutron diffraction. It is found that a new crystal-structure phase with the cation-anion ratio 1: 1: 2: 5.75 forms in this solid solution. At the same time, oxygen vacancy ordering occurs in the plane of the rare-earth ion in the crystallographic position \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$1c\left( {00\frac{1}{2}} \right)$$ \end{document} of the Pmmm space group. Oxygen vacancy diffusion along the crystallographic axes in the pane of the rare-earth element is also proposed as a mechanism for the formation of other crystal-structure phases found in double-layered cobaltites.