| Initial crystal system | tetragonal |
| Final crystal system | cubic |
| Initial space group | I4/mcm |
| Final space group | Pm3-m |
| Direction | Heating |
| Phase transition temperature | 339.0 K |
Hysteresis: 9
Starting materials: Lead(II) acetate (Chemical Reagents, Sigma), aqueous HI, CH3NH2 (40% soluble in water, Merck)
Product: Black MAPbI3 Polycrystals
Description: Following method by [1], dissolve 2.5 g of lead(II) acetate in 10 ml of concentrated (57% by weight) aqueous HI contained in a pyrex test tube and heat in a water bath. Add an additional 2 ml of HI solution with 0.597 g of CH3NH2 to the solution. Filter the black precipitate upon cooling from 100 °C to 46 °C over 6 hours and dry (100 °C/10 hours). Maintain solution temperature above 40 °C. Black crystals up to 2 mm long were obtained by cooling the solution over 4 days. Crystallization proceeded most rapidly at approximately 70 °C.
Comment: Synthesis references: [1] A. Poglitsch and D. Weber, J. Chem. Phys., 1987, 87, 6373–6378. [2] J. H. Im, C. R. Lee, J. W. Lee, S. W. Park and N. G. Park, Nanoscale, 2011, 3, 4088–4093.
Method: Powder X-ray diffraction
Description: Tetragonal/cubic phase transition was investigated using variable temperature powder X-ray diffraction. In situ XRD data were collected in asymmetric reflection mode under a static helium atmosphere on an INEL Equinox 3000 (Inel, Artenay, France) equipped with an XRK-900 reactor chamber (Anton-Paar, Graz, Austria), a curved position sensitive detector (Ine, Artenay, France), a copper Ka source and a Ge-(111) focussing mirror. Two different heating experiments were conducted. In the first, MAPbI3 was heated to 85 °C in five degree steps starting from 25 °C, with data collected for 5 minutes at each holding temperature. The second experiment employed a continuous heating ramp at a rate of 1° min^-1 during which 30 measurements of 120 seconds were performed. Each measurement corresponds to a temperature span of 2 °C; the final temperature of each measurement was recorded in the measurement file. Five empty sample holder measurements were conducted at room temperature in order to establish the chamber background. Refer to Page 5633 Results and discussion; Page 5634 Figure 4 and Figure 5.
Comment: Transition approximately from (327 - 330 K, 54 - 57 °C), large change in diffraction intensity at 57 °C weak scattering persists up to 75 °C on heating collected at 2 °C intervals.