Local structure, bonding, and asymmetry of $$\mathrm{((NH_2)_2CH)PbBr_3}$$, $$\mathrm{CsPbBr_3}$$, and $$\mathrm{(CH_3MH_3)PbBr_3}$$

Journal Article · Sun Dec 10 23:00:00 EST 2023 · Physical Review. B

DOI:https://doi.org/10.1103/physrevb.108.214102· OSTI ID:2328196

Bridges, F. ^[1]; Gruzdas, J. ^[2]; MacKeen, C. ^[2]; Mayford, K. ^[2]; Weadock, N. J. ^[3]; Baltazar, V. Urena ^[2]; Rakita, Y. ^[4]; Waquier, Louis ^[5]; Vigil, Julian A. ^[6]; Karunadasa, Hemamala I. ^[7]; Toney, M. F. ^[3]

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1. University of California, Santa Cruz, CA (United States); SLAC
2. University of California, Santa Cruz, CA (United States)
3. University of Colorado, Boulder, CO (United States)
4. Ben Gurion University of the Negev, Beer Sheva (Israel)
5. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
6. Stanford University, CA (United States)
7. Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Institute for Materials and Energy Science (SIMES)

Here we report local structure measurements for CsPbBr₃ and ((NH₂)₂CH)PbBr₃ (FAPbBr₃) and compare them with recent results for (CH₃NH₃)PbBr₃ (MAPbBr₃). The Pb-Br bonding is similar for all three systems; the effective spring constants, κ, are comparable (ranging from 1.20 to 1.95 eV/Ų), but small in magnitude indicating very soft materials. However, there are also important differences between the three systems. Static disorder is very small for CsPbBr3 but increases somewhat with the size of the organic molecular ions MA⁺ and FA⁺. At room temperature, dynamic disorder dominates in all compounds. The thermal disorder of the Pb-Br pair distribution function (PDF), i.e., the Debye-Waller factor σ² follows a correlated Debye or Einstein model up to 300 K in CsPbBr₃ (orthorhombic phase), but for FAPbBr₃ and MAPbBr₃, there is a break in the σ²(T) curve at the orthorhombic-tetragonal transition (o-t) near 150 K, indicating a small change in the spring constant κ. κ increases for MAPbBr₃ but decreases in FAPbBr₃ at this transition. These changes are attributed to changes in the H-bonding between Br^- and MA⁺ or FA⁺ at this transition, as a result of librations or rotations of these molecular cations. In addition, the Pb-Br PDF becomes asymmetric at a relatively low temperature for FAPbBr₃ and MAPbBr₃, while this effect is significantly smaller for CsPbBr₃. Finally, we address the question of a model to explain the asymmetric PDF. Two main models are discussed in the literature, an anharmonic pair potential and a split-pair distribution, possibly driven by the presence of a lone pair on the Pb ion. We show that the fourth cumulant C₄ can differentiate between these two models and other possible models. Experimentally C₄ is positive at 250 K and above, for all three systems and that is inconsistent with a split-peak model, for which C₄ is negative for splittings larger than 0.12 Å.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); National Science Foundation (NSF)
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 2328196
• Journal Information: Physical Review. B, Journal Name: Physical Review. B Journal Issue: 21 Vol. 108; ISSN 2469-9950
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
chemical bonding
lattice dynamics
structural properties
x-ray absorption spectroscopy
x-ray diffraction