Low temperature structural phase transition of Ba3NaIr2O9

Structural representation of Ba3NaIr2O9 with hexagonal (P63/mmc, top) and monoclinic (C2/c, bottom) symmetry. The structures on the left show a view looking down the a axis while those on the right show the view looking down the c axis. The yellow prism shows the unit cell in each case. The blue polyhedra represent [Ir2O9], the orange octahedra [NaO6] and the green spheres represent Ba2+ ions (for interpretation of the references to colour in this figure, the reader is referred to the web version of this article).