Tilted inverse-perovskites, new class of three-dimensional Dirac electron systems

The inverse-perovskites M₃TtO (M = Ca, Sr, Ba, Eu; Tt = tetrel element: Si, Ge,Sn, Pb) have  been proposed as new candidates for 3D Dirac electron systems. We synthesized the series and characterization by crystal structure analysis was performed in the temperature range of 500–50 K. Physical property measurements on Sr₃PbO confirm the existence of Dirac electrons. Furthermore for different variations of M and Tt, temperature driven phase transitions are observed. A structure field map, based on the ionic radii of the constituent elements, shows the stability regions of different distortion variants.