Structure of 18R shifted hexagonal perovskite La6MgTi4O18 revisited by neutron diffraction

•Neutron diffraction reveals an octahedra-tilted structure in R3̄ for La6MgTi4O18.•Mg/Ti distribution in La6MgTi4O18 is partially ordered in the perovskite blocks.•Instability of La6MgTi4O18 on alumina ceramic at high temperature is demonstrated.

The structure of 18-layer shifted B-site deficient hexagonal perovskite La6MgTi4O18 compound has been re-examined by neutron powder diffraction. Structural analysis reveals that La6MgTi4O18 compound adopts a 18R octahedral-tilted structure with LaO3 layer stacking sequence of (hhcccc)3 in space group R3̄, in contrast with the previously proposed R3m. La6MgTi4O18 demonstrates partially ordered Mg cation distribution with a preference on the central octahedral sites over the outer octahedral sites in the cubic perovskite blocks isolated by the single vacant octahedral layers between the two consecutive hexagonal layers. The instability of the La6MgTi4O18 on alumina ceramic substrate at high temperature and its dependencies of cell parameters and permittivity were characterized as well.

Graphical abstract18-layer shifted hexagonal perovskite La6MgTi4O18 adopts octahedral-tilted structure in R3̄ and demonstrates partially ordered Mg distribution in the cubic perovskite blocks isolated by the vacant octahedral layers.Figure optionsDownload full-size imageDownload as PowerPoint slide