Fapbi3 Cif File

Formamidinium lead iodide ( FAPbI3cap F cap A cap P b cap I sub 3

) is a premier hybrid organic-inorganic perovskite (HOIP) favored for high-efficiency solar cells due to its near-ideal band gap of approximately

. Crystallographic Information Files (CIF) are the standard for modeling its structure, essential for both theoretical simulations and experimental X-ray diffraction (XRD) analysis. Structural Phases and Crystallography FAPbI3cap F cap A cap P b cap I sub 3

primarily exists in two major polymorphs at room temperature: the photoactive -phase (black) and the non-perovskite -phase (yellow).

-Phase (Cubic Perovskite): This is the desired phase for photovoltaics. It typically crystallizes in the fapbi3 cif file

space group (No. 221). The structure consists of a corner-sharing PbI6cap P b cap I sub 6 octahedral framework with formamidinium ( FA+cap F cap A raised to the positive power

) cations occupying the 12-fold coordinated cuboctahedral cavities. -Phase (Hexagonal): At room temperature, the -phase is metastable and often transitions into the yellow

-phase, which features face-sharing octahedra and is unsuitable for solar applications due to its wide band gap (~ Key CIF Parameters for FAPbI3cap F cap A cap P b cap I sub 3 Standard CIF data for the cubic phase at approximately typically includes: Lattice Constant ( ): Roughly Cell Volume: ~ FA+cap F cap A raised to the positive power Cation Orientation: The organic FA+cap F cap A raised to the positive power

) is dynamically disordered within the inorganic cage. CIF models often represent this via multiple occupancy sites or specific orientation minimizations, such as the fragment lying in the CIF Data Sources and Tools High-quality CIF files for FAPbI3cap F cap A cap P b cap I sub 3 Formamidinium lead iodide ( FAPbI3cap F cap A

can be accessed through academic repositories and open databases: Description Crystallography Open Database (COD) A standard repository for experimental crystal structures. Materials Project

Provides DFT-relaxed structures and computational CIFs for perovskite materials. GitHub (WMD-group)

Hosts specific FAPbI3 CIF files used in prominent hybrid perovskite research. Cambridge Structural Database (CSD) Essential for verified experimental single-crystal data. Visualization and Analysis To utilize a CIF file: FAPbI3.cif - WMD-group/hybrid-perovskites - GitHub

hybrid-perovskites/2014_cubic_halides_PBEsol/FAPbI3. cif at master · WMD-group/hybrid-perovskites · GitHub. FAPbI3_tetragonal&cubic - 科学数据银行 _cell_length_a/b/c = 6

Title: Structural Elucidation and Symmetry-Composition Relations in Formamidinium Lead Triiodide (FAPbI$_3$): A Deep Dive into the $Fm\bar3m$ to $Pm\bar3m$ Transition via Powder Diffraction Analysis

Abstract

Formamidinium lead triiodide (HC(NH$_2$)$_2$PbI$_3$ or FAPbI$_3$) represents the forefront of next-generation photovoltaic materials, offering a reduced bandgap closer to the Shockley-Queisser optimum compared to its methylammonium counterpart. However, the structural instability of the photoactive perovskite phase ($\alpha$-phase) remains a critical bottleneck. This paper provides a comprehensive crystallographic analysis of the FAPbI$_3$ Crystallographic Information File (CIF), focusing on the temperature-dependent phase transitions from the cubic $Fm\bar3m$ (or pseudo-cubic $Pm\bar3m$) structure to the non-perovskite hexagonal $P6_3mc$ phase. Through simulated Rietveld refinement and group-subgroup analysis, we deconvolute the orientational disorder of the formamidinium cation and its impact on the lattice parameters, offering a definitive guide for interpreting experimental diffraction data.

3.1 Unit Cell Parameters

• _cell_length_a/b/c = 6.362 Å : This is the lattice constant. FAPbI₃ has a larger cell than MAPbI₃ (~6.29 Å) due to the larger formamidinium cation (HC(NH₂)₂⁺).
• Cubic Symmetry: All angles are 90°, and all sides are equal. This high symmetry simplifies quantum mechanical calculations (DFT).

Step 2: Use cif2cell (Command Line)

• Convert CIF to input for DFT codes. This script flags incomplete occupancy or symmetry errors.
• Command: cif2cell fapbi3.cif -p vasp

Crystal structure and phases

• Perovskite framework: FAPbI3 adopts the ABX3 perovskite structure where A = formamidinium (FA+, HC(NH2)2+), B = Pb2+, X = I−. The inorganic PbI6 octahedra form a 3D network with FA+ occupying the cuboctahedral A-site cavities.
• Phases: FAPbI3 exhibits several polymorphs depending on temperature and processing:
  • α-phase (black, cubic/tetragonal): The photoactive perovskite phase with corner-sharing PbI6 octahedra; desirable for solar cells.
  • δ-phase (yellow, non-perovskite): A hexagonal/vacancy-ordered polymorph that is optically inactive and often forms at room temperature in pure FAPbI3 without stabilization.
  • Intermediate phases: Lower-symmetry distortions (orthorhombic, tetragonal) can occur due to tilting of octahedra or FA orientation ordering.
• Typical lattice parameters: For the α-phase at room/near-room conditions, reported unit cells are pseudo-cubic with lattice constants around 6.3–6.4 Å (pseudo-cubic a ≈ 6.35 Å), but values vary with temperature, composition, and measurement method.