Fapbi3: Cif File
Unraveling the Mystery of "fapbi3": CIF Files, Perovskites, and Database Accuracy
In the world of materials science and crystallography, the CIF (Crystallographic Information File) is the gold standard for data exchange. Researchers frequently search for specific structural files using shorthand or chemical formulas. One such query that occasionally arises is "fapbi3 cif file."
If you are looking for this specific file, it is highly likely that you are encountering a data entry error, a typo, or a confusion of chemical nomenclature. There is currently no standard, peer-reviewed material in the Inorganic Crystal Structure Database (ICSD) or the Cambridge Structural Database (CSD) listed simply as "fapbi3."
This article breaks down the likely intended material behind this search, the chemistry involved, and how to find the correct structural data.
1. The Crystallography Open Database (COD)
- URL: crystallography.net
- Search: "FAPbI3" or "formamidinium lead iodide"
- Reliability: High. Look for entries with a DOI linking to published, peer-reviewed papers.
- Recommended COD ID: Check the latest records. As of 2025, entry #9000000 (hypothetical) derived from Weller et al. (2013) is a reference.
Further reading
- Structural studies and phase behavior of FAPbI3 in peer-reviewed crystallography and materials journals.
- CIF dictionary and guidelines from the International Union of Crystallography (IUCr) for proper CIF formatting.
Related search suggestions: FAPbI3 CIF, formamidinium lead iodide crystal structure, FAPbI3 alpha phase CIF. fapbi3 cif file
Problem 1: The Wrong Lattice Constant
- Issue: A CIF from 2013 gives
a = 6.36 Ã…. A CIF from 2024, after strain engineering, gives a = 6.34 Ã….
- Solution: For DFT bandgap calculation, use experimental lattice parameters from the specific paper you are benchmarking against (e.g., 6.362 Ã… at 293K). Do not mix-and-match.
2.2 The Space Group Controversy ($Pm\bar3m$ vs. $Fm\bar3m$)
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:
- Pb resides at the corner (1a) site: $(0, 0, 0)$.
- I resides at the face-center (3d) site: $(0.5, 0, 0)$.
- FA resides at the body-center (1b) site: $(0.5, 0.5, 0.5)$.
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. Unraveling the Mystery of "fapbi3": CIF Files, Perovskites,
B. The $Fm\bar3m$ Model (Disordered Model):
Recent high-resolution synchrotron studies suggest that the cubic phase is better described by space group $Fm\bar3m$.
- Pb site: $4a$ $(0, 0, 0)$.
- I site: $8c$ $(0.25, 0.25, 0.25)$ equivalent to face centers in a doubled lattice, or refined as split positions.
- FA Disorder: In this model, the FA molecule is disordered over multiple orientations, reducing the symmetry from primitive to face-centered.
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):
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
URL: crystallography
Note: The high $U_iso$ values for N and C in the primitive model necessitate advanced modeling techniques.
The δ-Phase (Yellow, Non-Photoactive)
- Space Group: P6₃mc – Hexagonal.
- Lattice Parameters:
a ≈ 8.98 Å, c ≈ 11.41 Å.
- Note: If you accidentally use the δ-phase CIF file for a simulation of an efficient solar cell, your bandgap calculation will be wrong. Always verify the phase.
Defects and Vacancies
A pristine CIF lacks defects. To study iodine vacancies (V_I), open the CIF in VESTA, delete an iodine atom, and save a new CIF (now with partial occupancy). Warning: Charge neutrality must be maintained in DFT.
Part 2: What is a CIF File?
A CIF file is a plain-text (.cif) format standardized by the International Union of Crystallography (IUCr). It is the universal currency of crystallography.
Method C: Literature Extraction
The most accurate structural parameters often come directly from the seminal papers. The definitive structure was elucidated by researchers like M. Grätzel and colleagues.
- Key Reference: W. S. Yang et al., "High-performance photovoltaic perovskite layers fabricated through intramolecular exchange", Science (2015).
- Supplementary Materials: Always check the Supplementary Information (SI) of high-impact papers. They almost always contain the experimental CIF as a downloadable attachment.
