Crystal Structure and Photoconductivity of Cæsium Plumbohalides

WELLS1 and his collaborators have shown that crystals of the general compositions CsPbX 3 with X = Cl, Br or I, and Cs4PbX 6 with X = Cl or Br, may be prepared from aqueous solutions. I have investigated the structures of these crystals and also prepared a few more. I have found2 that CsPbCl3 and CsPbBr3 have the perovskite structure. At room temperature they are tetragonally or monoclinically distorted. Both of them, however, show transition to pure cubic perovskite structure, at 47° C. and 130° C. respectively and with cell dimensions a = 5.605 A. for CsPbCl3, a = 5.874 A. for CsPbBr3. Whereas no extra or forbidden X-ray reflexions can be observed above these transition temperatures, CsPbBr3 below 130° C.—and presumably also CsPbCl3 below 47° C.—exhibit a new structure corresponding to a doubling of the cell dimensions. The transitions are likely to be of second order as ΔV = 0 within the limits of accuracy of my measurements.