Observation of grey cesium tin bromide with unusual phase transition


 A new grey colour polymorph of CsSnBr3 with non-cubic phase at 295(±1) K is observed. Contrary to Black and Yellow polymorphs, it seems not only the α-β transition at 292 K shift to 304 K but also the presence of new β3-phase with second order phase transition (β2-β3) can be seen in this new Grey polymorph. The structural refinement shows the monoclinic C2h5-P21/c phase with holohedry for the β3-CsSnBr3 against the group-subgroup theory. However, the parameters c/a~1.492 and b/c~1.004 are suggesting pseudo-tetragonality for β3-CsSnBr3.