Synthesis, Resistivity, and Thermal Properties of the Cubic Perovskite NH₂CH=NH₂SnI₃and Related Systems

Combining concentrated hydriodic acid solutions of tin(II) iodide and formamidine acetate in an inert atmosphere results in the precipitation of a new conducting organic-inorganic compound, NH2CH=NH2SnI3, which at room temperature adopts a cubic perovskite structure. The lattice constant for NH2CH=NH2SnI3is found to bea=6.316(1) Å, which is approximately 1.2% larger than that for the isostructural compound CH3NH3SnI3. The electrical resistivity of a pressed pellet of the new compound exhibits semimetallic temperature dependence from 10 to 300 K, with evidence of a structural transition at approximately 75 K. NH2CH=NH2SnI3begins to slowly decompose in an inert atmosphere at temperatures as low as 200°C, with bulk decomposition/melting occurring above 300°C. The properties of the formamidinium-based perovskite are compared with those of the related cubic (at room temperature) perovskite CH3NH3SnI3and the mixed-cation system (CH3NH3)1-x(NH2CH=NH 2)xSnI3. © 1997 Academic Press.