Mechanical properties of APbX3 (A = Cs or CH3NH3; X= I or Br) perovskite single crystals

Rakita, Yevgeny; Cohen, Sidney R.; Kedem, Nir; Hodes, Gary; Cahen, David

doi:10.1557/mrc.2015.69

Cited by 309 publications

(325 citation statements)

References 47 publications

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“…Our parameterisation provides good qualitative fits to the experimentally derived DOS, with key peaks reproduced 22 . The bulk modulus has an average value of 13.62 GPa, which is comparable to the value of 13.9 GPa as determined by Rakita et al 54 The Sheer Modulus was also determined by Rakita et al to be 5.4 GPa, compared to our calculated value of 7.28 GPa.…”

Section: Resultssupporting

confidence: 89%

A new potential for methylammonium lead iodide

Handley

Freeman

2017

Phys. Chem. Chem. Phys.

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We present a new set of interatomic potentials for modelling Methylammonium Lead Iodide. The potential model uses existing potentials for lead iodide and methylammonium, and new functions are fitted to enable these pre-exisiting potentials to be used together, while still be capable of modelling lead iodide and methylammonium iodide as spearate materials. Fitting was performed using a combination of ab initio, and experimental reference data. The model is tested by simulating methylammonium lead iodide at a range of temperatures. Our simulaltions are in agreement with experiment and reveal the short and long range ordering of the molecular cations and lead iodide octahedra.

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Section: Resultssupporting

confidence: 89%

A new potential for methylammonium lead iodide

Handley

Freeman

2017

Phys. Chem. Chem. Phys.

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“…The increased values of the U┴ ADPs on cooling to the γ-phase suggest disorder that is not fully captured by this crystallographic model. [19,20] CsSnI3 γ (solid) 298 126 [21] Ag3[Co(CN)6] Solid 276 121 [22] Hg Liquid 293 182 [21] The unit cell volume per formula unit, V, is given in Figure 4(a). A comparison of the volumetric thermal expansion coefficient, αV, with those of other main-group halides and selected framework materials and liquids is given in Table 1.…”

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confidence: 99%

Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide

et al. 2016

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Abstract:The structure of the hybrid perovskite HC(NH2)2PbI3 (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb 2+ lone pair to express its stereochemistry. High-resolution synchrotron X-ray powder diffraction reveals a continuous transition from the cubic α-phase (Pm 3 m, #221) to a tetragonal β-phase (P4/mbm, #127) at around 285 K, followed by a first-order transition to a tetragonal γ-phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β-to-γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid.Photovoltaic absorbers based on the hybrid perovskite HC(NH2)2PbI3 (formamidinium lead iodide) and its alloys exhibit impressive performance, [1] but the description of the crystal structure of this material is incomplete. In addition to this technological motivation, [2] dense hybrid materials with 3-D inorganic connectivity and isolated organic molecular ions combine features of traditional inorganic solids and open framework materials, and their composition-structure relations are of fundamental interest.The initial report of the preparation and characterization of HC(NH2)2PbI3 proposed perovskite structures of trigonal symmetry for the α-and β-phases on the basis of laboratory single crystal X-ray diffraction, [3] while a subsequent report assigned the structure of the cubic perovskite aristotype for the α-phase from neutron powder diffraction. [4] The structure of the γ-phase has not been reported. Figure 1. X-ray scattering intensity from HC(NH2)2PbI3 around selected lowangle Bragg peaks between 90 K and 490 K, normalized to maximum peak intensity. (a) The 211t tetragonal Bragg peak emerges upon cooling through a continuous phase transition around 285 K from the cubic α-phase to the tetragonal β-phase. (b) The 200c cubic Bragg peak splits continuously on cooling due to the emergent tetragonality. A first order transition to the pseudocubic γ-phase with tetragonal symmetry occurs at 140 K. [5] The 002t and 220t tetragonal peaks "fuse" across the β-γ transition while the 211t tetragonal peak remains.The disordered molecular cation, challenges associated with twinning in single crystals, and issues of pseudosymmetry led us to employ high-resolution synchrotron X-ray powder diffraction to follow the structure evolution of HC(NH2)2PbI3 between 90 K and 490 K. The temperature-dependent scattering intensity around instructive low-angle Bragg peaks is given in Figure 1. The continuous α-β phase transition around 285 K is evident in the emergence of the 211 tetragonal peak and the splitting of the 200 cubic peak into the 002 and 220 tetragonal peaks on cooling. The first-order β-γ transition can be seen in the abrupt change in intensities and peak positions at 140 K (transition temperature fro...

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“…In this paper, we present an investigation of the mechanical characteristics of MAPbI 3 -to which relatively limited attention has so far been paid [25][26][27] -and, in particular, to their variation under exposure to humid environments. Indeed, given that future devices will be exposed to diverse external mechanical forces (shocks, bending), characterization of the mechanical properties is undoubtedly crucial, especially to move from prototype to real large-scale applications.…”

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confidence: 99%

“…27, are 16.7 GPa for E and 1.0 GPa for H. Beyond computational details, an important difference between the two calculations lies in the pseudopotentials, which include only scalar relativistic effects in Ref. 26 and also spin-orbit coupling in our scheme. 36 When exposed to humid environment, we observed a gradual color change with time: from grayish/black-typical of the fresh crystal-to colorful interference patterns showing up after a few days in visible light, and eventually, after one or more months yellowish areas became clearly visible, indicating the presence of PbI 2 .…”

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confidence: 99%

Mechanical signatures of degradation of the photovoltaic perovskite CH3NH3PbI3 upon water vapor exposure

Spina

Karimi

Andreoni

et al. 2017

Applied Physics Letters

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We report on the mechanical properties of CH3NH3PbI3 photovoltaic perovskite measured by nanoindentation. The Young's modulus (E) of the pristine sample is 20.0 ± 1.5 GPa, while the hardness (H) is 1.0 ± 0.1 GPa. Upon extended exposure to water vapor, both quantities decrease dramatically and the sample changes color from silver-black to yellow. Calculations based on density functional theory support this trend in the mechanical response. Chemical treatment of the degraded crystal in methylammonium iodide solution recovers the color of the pristine sample and the values of E and H within 50%.

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Mechanical properties of APbX3 (A = Cs or CH3NH3; X= I or Br) perovskite single crystals

Cited by 309 publications

References 47 publications

A new potential for methylammonium lead iodide

A new potential for methylammonium lead iodide

Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide

Mechanical signatures of degradation of the photovoltaic perovskite CH3NH3PbI3 upon water vapor exposure

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