On the High‐temperature Crystal Structure of Sr/Mg‐doped Lanthanum Gallate. Evidence for the First Perovskite‐type Structure with R3¯m Symmetry

The high temperature structure above 700 °C of the oxygen superionic conductor La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 has been analyzed by means of a combined neutron and high resolution synchrotron powder study. The splitting of reflections and the absence of any superstructure reflections leads to the conclusion that the correct space group is R3¯m. This is the first example of this space group appearing within the subgroup family of the ideal parent perovskite structure with Pm3¯m symmetry.