Melilite LaSrGa_3−<i>x</i>Al_<i>x</i>O₇ Series: A Combined Solid-State NMR and Neutron Diffraction Study

Abstract

Oxides characterized by a layered melilite structure, with general formula ABT¹₍₁₎T²₍₂₎O₇, find applications in many different technological fields due to their relevant magnetic, optical, and electrical properties. These functional properties are, in turn, related to local features such as structural defects and cation substitutions. Therefore, a complete structural characterization of these complex anisotropic compounds is mandatory, and the combined use of long-range (X-ray and neutron diffraction) and short-range (solid state NMR) techniques is a key approach to this aim. In this work, we present the full structural characterization of the series LaSrGa_3–<i>x</i>Al_<i>x</i>O₇ (<i>x</i> = 0, 1, 1.5, 2, and 3), which was obtained for the first time by means of a new sol–gel approach. Analysis of neutron diffraction data revealed that the distribution of La/Sr and Ga/Al on the respective sites is random. ²⁷Al and ⁷¹Ga solid state NMR enabled us to rationalize the local structure of the T sites in terms of nearest and next-nearest neighbors. This study provides a deep structural insight that can be helpful for the understanding of the functional properties and is a powerful strategy for the analysis of complex oxide systems