The interpretation of the FAPbI$_3$ CIF is non-trivial due to the "orbits" of the FA cation.
A. The $Pm\bar3m$ Model (Aristotype): In the ideal perovskite structure:
While chemically intuitive, this model assumes the FA cation is spherical and statically centered. In reality, FA is a planar molecule. Fitting diffraction data to $Pm\bar3m$ often results in anomalously high thermal parameters ($B_iso$ or $U_iso$) for the nitrogen and carbon atoms, indicating static disorder rather than true vibration. fapbi3 cif file
B. The $Fm\bar3m$ Model (Disordered Model): Recent high-resolution synchrotron studies suggest that the cubic phase is better described by space group $Fm\bar3m$.
Refined CIF Representation (Cubic Phase): Below is a representation of the structural data typically found in a refined FAPbI$_3$ CIF for the cubic phase ($T=360$ K): The interpretation of the FAPbI$_3$ CIF is non-trivial
data_FAPbI3_Cubic _audit_creation_method 'Rietveld Refinement' _chemical_name_common 'Formamidinium Lead Iodide' _cell_length_a 6.359 _cell_angle_alpha 90 _cell_angle_beta 90 _cell_angle_gamma 90 _symmetry_space_group_name_H-M 'P m -3 m' _symmetry_Int_Tables_number 221
loop_ _atom_site_label _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_occupancy _atom_site_U_iso_or_equiv Pb1 0.00000 0.00000 0.00000 1.0 0.023 I1 0.50000 0.00000 0.00000 1.0 0.035 N1 0.50000 0.50000 0.50000 0.5 0.080 ! Disordered C1 0.50000 0.50000 0.50000 0.5 0.090 ! Disordered
Note: The high $U_iso$ values for N and C in the primitive model necessitate advanced modeling techniques.
The most accurate structural parameters often come directly from the seminal papers. The definitive structure was elucidated by researchers like M. Grätzel and colleagues. While chemically intuitive, this model assumes the FA
If you are searching for this CIF file, you are likely working on perovskite solar cells. FAPbI$_3$ is prized for its ideal bandgap (~1.48 eV), making it more efficient for solar absorption than its cousin, MAPbI$_3$ (Methylammonium Lead Iodide).
This is the highest symmetry cubic space group. It implies that the PbI₆ octahedra are perfectly aligned with no tilting. The CIF includes a loop_ of symmetry operations that generate the entire crystal from the asymmetric unit.