Crystal structures/Geometric properties: Previous reports indicated that ABX 3 type compounds show various phases under different temperatures, but in the high temperature phase, all adopt a cubic perovskites structure , with a three-dimensional framework of corner-sharing BX 6 octahedron. Figure shows the crystal structure for cubic CuPbI 3 perovskites. The primitive cell of this perovskites is consisting of cornerlinked PbI 6 octahedral of the iodine atoms, with the Pb cation at their center and the Cu cation between them. The structure of CuPbI 3 was relaxed first and the obtained lattice constant for this cubic material is 6.405Å after optimization with α = γ = β = 90.0° for the unit cell shown in Figure . Volume of the cell is 6.405 ^3 Å ^3. The bond lengths obtained from the relaxed structure are: Pb -I: 3.21, Pb -Pb: 6.42, Pb -Cu: 5.55, Cu -I: 4.53, Cu -Cu: 6.41, I -I: 4.53 Å as well as the effective coordination number is 6.00. The obtained space group was also determined to be Pm-3m. The calculated crystal structure parameters are presented in Table Summary of crystal structure parameters The tolerance factor is invented by Goldschmidt to describe the perovskites structure by taking three types of spheres in a perovskites-structure into account. Since the ionic radii are generally known, a tolerance factor can be calculated, that indicates the degree of compatibility of a given set of ions with the ideal, cubic perovskites structure. This relationship was first explored by Goldschmidt, in 1926 , who suggested that it could be used to predict the likelihood that a pair of ions would form a perovskites structure phase.