Atomic-scale imaging of CH3NH3PbI3 structure and its decomposition pathway

AbstractUnderstanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA+ followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold doses also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH3 and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategies into material optimization.

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Quasiperiodic interfaces: HREM observations of grain and phase boundaries

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174795 ◽

1990 ◽

Vol 48 (4) ◽

pp. 332-333

Author(s):

K. L. Merkle

Keyword(s):

Atomic Structure ◽

Direct Determination ◽

Lattice Parameter ◽

Atomic Scale ◽

Misfit Dislocations ◽

Oxide Systems ◽

Atomic Structures ◽

Periodic Arrays ◽

Parameter Ratio ◽

Metal Metal

The atomic structures of internal interfaces have recently received considerable attention, not only because of their importance in determining many materials properties, but also because the atomic structure of many interfaces has become accessible to direct atomic-scale observation by modem HREM instruments. In this communication, several interface structures are examined by HREM in terms of their structural periodicities along the interface.It is well known that heterophase boundaries are generally formed by two low-index planes. Often, as is the case in many fcc metal/metal and metal/metal-oxide systems, low energy boundaries form in the cube-on-cube orientation on (111). Since the lattice parameter ratio between the two materials generally is not a rational number, such boundaries are incommensurate. Therefore, even though periodic arrays of misfit dislocations have been observed by TEM techniques for numerous heterophase systems, such interfaces are quasiperiodic on an atomic scale. Interfaces with misfit dislocations are semicoherent, where atomically well-matched regions alternate with regions of misfit. When the misfit is large, misfit localization is often difficult to detect, and direct determination of the atomic structure of the interface from HREM alone, may not be possible.

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Correlation Between Plasticity and Atomic Structure Evolution of a Rejuvenated Bulk Metallic Glass

Metallurgical and Materials Transactions A ◽

10.1007/s11661-019-05391-x ◽

2019 ◽

Vol 50 (10) ◽

pp. 4743-4749 ◽

Cited By ~ 5

Author(s):

Majid Samavatian ◽

Reza Gholamipour ◽

Ahmad Ali Amadeh ◽

Shamsoddin Mirdamadi

Keyword(s):

Metallic Glass ◽

Bulk Metallic Glass ◽

Atomic Structure ◽

Structure Evolution

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Atomic-scale structure and chemistry of ceramic/metal interfaces—I. Atomic structure of {222} MgO/Cu (Ag) interfaces

Acta Materialia ◽

10.1016/s1359-6454(99)00255-4 ◽

1999 ◽

Vol 47 (15-16) ◽

pp. 3939-3951 ◽

Cited By ~ 28

Author(s):

D.A Shashkov ◽

M.F Chisholm ◽

D.N Seidman

Keyword(s):

Atomic Structure ◽

Scale Structure ◽

Atomic Scale ◽

Metal Interfaces ◽

Atomic Scale Structure

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Atomic Structure of PbZrO3 Determined by Pulsed Neutron Diffraction

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768198003802 ◽

1998 ◽

Vol 54 (6) ◽

pp. 750-765 ◽

Cited By ~ 88

Author(s):

S. Teslic ◽

T. Egami

Keyword(s):

Atomic Structure ◽

Intermediate Phase ◽

Function Analysis ◽

Lead Zirconate ◽

Neutron Powder Diffraction Data ◽

Antiferroelectric Phase ◽

Atomic Pair Distribution Function ◽

Atomic Pair ◽

Increasing Temperature ◽

Pulsed Neutron

The atomic structure of lead zirconate, PbZrO3 (PZ), was studied using Rietveld refinement and atomic pair distribution function analysis of pulsed neutron powder diffraction data for the antiferroelectric, intermediate and paraelectric phases. The symmetry of PZ at T = 20 K in the antiferroelectric phase was determined to be Pbam. The structure was characterized by distortions of the ZrO6 octahedra which are smaller than in previous studies. Locally correlated displacements of Pb in the c direction develop with increasing temperature. The average magnitude was 0.06 Å at room temperature, 0.14 Å at T = 473 K and 0.20 Å in the intermediate phase at T = 508 K. The intermediate phase was characterized by in-plane antiferroelectric Pb displacements which produce 1\over 2{110} superlattice diffraction peaks. Above 473 K the local structure of PZ remains largely unchanged, in spite of the transitions in the long-range order from the antiferroelectric to the intermediate and to the paraelectric phases.

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Atomic Structure Evolution of Pt–Co Binary Catalysts: Single Metal Sites versus Intermetallic Nanocrystals

Advanced Materials ◽

10.1002/adma.202106371 ◽

2021 ◽

pp. 2106371

Author(s):

Xing Li ◽

Yanghua He ◽

Shaobo Cheng ◽

Boyang Li ◽

Yachao Zeng ◽

...

Keyword(s):

Atomic Structure ◽

Structure Evolution ◽

Binary Catalysts

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Crystal Structure Evolution of La2Ni7 during Hydrogenation

MRS Proceedings ◽

10.1557/opl.2013.188 ◽

2013 ◽

Vol 1516 ◽

pp. 183-188 ◽

Cited By ~ 2

Author(s):

Yuki Iwatake ◽

Kyosuke Kishida ◽

Haruyuki Inui

Keyword(s):

Hydrogen Absorption ◽

Dark Field ◽

Atomic Scale ◽

Structure Evolution ◽

Desorption Process ◽

Atomic Arrangement ◽

Anisotropic Expansion ◽

Scanning Transmission ◽

Annular Dark Field ◽

Scale Characterization

ABSTRACTAtomic scale characterization of the La2Ni7 hydrides by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that not only the anisotropic expansion of the La2Ni4 unit layer previously reported but also the shearing on the basal plane of the La2Ni4 unit layers occur during one-cycle of hydrogen absorption/desorption process. Two different types of orthorhombic La2Ni7 hydrides with the same atomic arrangement of La and different atomic arrangement of Ni were observed depending on the maximum hydrogen concentration achieved during one hydrogen absorption/desorption cycle.

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Phenomena And Mechanism On Phase Transformation Twinning In Nanocrystalline BaTiO3

MRS Proceedings ◽

10.1557/proc-1256-n06-49 ◽

2010 ◽

Vol 1256 ◽

Author(s):

Sujata Mazumder ◽

Jiten Ghosh

Keyword(s):

Phase Transition ◽

Phase Transformation ◽

High Temperature ◽

Intermediate Phase ◽

High Vacuum ◽

Point Group ◽

Atomic Scale ◽

Twin Structure ◽

High Temperature Xrd ◽

Low Symmetry

AbstractThe detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.

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An independent derivation and verification of the voids nucleation failure mechanism: significance for materials failure

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2018.0755 ◽

2019 ◽

Vol 475 (2222) ◽

pp. 20180755 ◽

Cited By ~ 4

Author(s):

Richard Christensen ◽

Zhi Li ◽

Huajian Gao

Keyword(s):

Stress State ◽

Failure Mechanism ◽

Density Functional ◽

Failure Modes ◽

Shear Bands ◽

Failure Criteria ◽

Atomic Scale ◽

Ideal Strength ◽

Failure Theory ◽

The Ideal

Independent derivations are given for the failure criteria of the purely dilatational stress state involving voids nucleation failure as well as for the purely distortional stress state involving shear bands failure. The results are consistent with those from a recently derived failure theory and they further substantiate the failure theory. The voids nucleation mechanism is compared with the ideal theoretical strength of isotropic materials as derived by density functional theory and two other atomic-scale methods. It is found that a cross-over occurs from the voids nucleation failure mechanism to the ideal strength limitation as the tensile to compressive strengths ratio, T / C , increases toward a value of unity. All the results are consistent with the failure modes transition results from the general failure theory.

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A New Hierarchical Technique for the Multiscale Modeling of Carbon Nanostructures

Microelectromechanical Systems ◽

10.1115/imece2005-82988 ◽

2005 ◽

Author(s):

Arash Mahdavi ◽

Eric Mockensturm

Keyword(s):

Finite Element ◽

Atomic Structure ◽

Carbon Nanostructures ◽

Degrees Of Freedom ◽

Finite Size ◽

Multiscale Methods ◽

Atomic Scale ◽

Modeling Technique ◽

Element Formulation ◽

Kinematic Constraints

We present a new hierarchical modeling technique called the Consistent Atomic-scale Finite Element (CAFE´) method [1]. Unlike traditional approaches for linking the atomic structure to its equivalent continuum [2-7], this method directly connects the atomic degrees of freedom to a reduced set of finite element degrees of freedom without passing through an intermediate homogenized continuum. As a result, there is no need to introduce stress and strain measures at the atomic level. This technique partitions atoms to masters and salves and reduces the total number of degrees of freedom by establishing kinematic constraints between them [5-6]. The Tersoff-Brenner interatomic potential [8] is used to calculate the consistent tangent stiffness matrix of the structure. In this finite element formulation, all local and non-local interactions between carbon atoms are taken into account using overlapping finite elements (Figure 1b). In addition, a consistent hierarchical finite element modeling technique is developed for adaptively coarsening and refining the mesh over different parts of the model (Figure 2a, 2b). The stiffness of higher-rank elements is approximated using the stiffness of lower-rank elements and kinematic constraints. This process is consistent with the underlying atomic structure and, by refining the mesh, molecular dynamic results will be recovered. This method is valid across the scales and can be used to concurrently model atomistic and continuum phenomena so, in contrast with most other multiscale methods [4-7], there is no need to introduce artificial boundaries for coupling atomistic and continuum regions. Effect of the length scale of the nanostructure is also included in the model by building the hierarchy of elements from bottom up using a finite size atom cluster as the building block (Figures 2a, 2b). In this method by introducing two independent field variables, the so-called inner displacement is taken into account (Fig. 3b). Applicability of the method is shown with several examples of deformation of carbon nanostructures such as graphene sheet, nanotube, and nanocone, subjected to different loads and boundary conditions.

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