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Title: Octahedral tilting instabilities in inorganic halide perovskites

Authors:
;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1419096
Grant/Contract Number:
AC02-05CH11231
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 2; Journal Issue: 2; Related Information: CHORUS Timestamp: 2018-02-01 10:04:52; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Bechtel, Jonathon S., and Van der Ven, Anton. Octahedral tilting instabilities in inorganic halide perovskites. United States: N. p., 2018. Web. doi:10.1103/PhysRevMaterials.2.025401.
Bechtel, Jonathon S., & Van der Ven, Anton. Octahedral tilting instabilities in inorganic halide perovskites. United States. doi:10.1103/PhysRevMaterials.2.025401.
Bechtel, Jonathon S., and Van der Ven, Anton. 2018. "Octahedral tilting instabilities in inorganic halide perovskites". United States. doi:10.1103/PhysRevMaterials.2.025401.
@article{osti_1419096,
title = {Octahedral tilting instabilities in inorganic halide perovskites},
author = {Bechtel, Jonathon S. and Van der Ven, Anton},
abstractNote = {},
doi = {10.1103/PhysRevMaterials.2.025401},
journal = {Physical Review Materials},
number = 2,
volume = 2,
place = {United States},
year = 2018,
month = 2
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on February 1, 2019
Publisher's Accepted Manuscript

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  • The structures of the lead halide perovskites CsPbCl3 and CsPbBr3 have been determined from X-ray powder diffraction data to be orthorhombic with Pnma space group symmetry. Their structures are distorted from the cubic structure of their hybrid analogs, CH3NH3PbX3 (X = Cl, Br), by tilts of the octahedra (Glazer tilt system a–b+a–). Substitution of the smaller Rb+ for Cs+ increases the octahedral tilting distortion and eventually destabilizes the perovskite structure altogether. To understand this behavior, bond valence parameters appropriate for use in chloride and bromide perovskites have been determined for Cs+, Rb+, and Pb2+. As the tolerance factor decreases, themore » band gap increases, by 0.15 eV in Cs1–xRbxPbCl3 and 0.20 eV in Cs1–xRbxPbBr3, upon going from x = 0 to x = 0.6. The band gap shows a linear dependence on tolerance factor, particularly for the Cs1–xRbxPbBr3 system. Comparison with the cubic perovskites CH3NH3PbCl3 and CH3NH3PbBr3 shows that the band gaps of the methylammonium perovskites are anomalously large for APbX3 perovskites with a cubic structure. This comparison suggests that the local symmetry of CH3NH3PbCl3 and CH3NH3PbBr3 deviate significantly from the cubic symmetry of the average structure.« less
  • The room-temperature crystal structures of six A{sub 2}M{sup 3+}M{sup 5+}O{sub 6} ordered perovskites have been determined from neutron and X-ray powder diffraction data. Ba{sub 2}YNbO{sub 6} adopts the aristotype high-symmetry cubic structure (space group Fm{bar 3}m, Z = 4). The symmetries of the remaining five compounds were lowered by octahedral tilting distortions. Out-of-phase rotations of the octahedra about the c axis were observed in Sr{sub 2}CrTaO{sub 6} and Sr{sub 2}GaTaO{sub 6} which lowers the symmetry to tetragonal (space group = I4/m, Z = 2, Glazer tilt system = a{sup 0}a{sup 0}c{sup -}). Octahedral tilting analogous to that seen in GdFeO{submore » 3} occurs in Sr{sub 2}ScNbO{sub 6}, Ca{sub 2}AlNbO{sub 6} and Ca{sub 2}CrTaO{sub 6}, which lowers the symmetry to monoclinic (space group P2{sub 1}/n, Z = 2, Glazer tilt system = a{sup -}a{sup -}c{sup +}). The Sr{sub 2}MTaO{sub 6} (M = Cr, Ga, Sc) compounds have unit-cell dimensions that are highly pseudo-cubic. Ca{sub 2}AlNbO{sub 6} and Ca{sub 2}CrTaO{sub 6} have unit-cell dimensions that are strongly pseudo-orthorhombic. This high degree of pseudosymmetry complicates the space-group assignment and structure determination. The space-group symmetries, unit-cell dimensions and cation ordering characteristics of an additional 13 compositions, as determined from X-ray powder diffraction data, are also reported. An analysis of the crystal structures of 32 A{sub 2}MTaO{sub 6} and A{sub 2}MNbO{sub 6} perovskites shows that in general the octahedral tilt system strongly correlates with the tolerance factor.« less
  • The advantageous performance of hybrid organic-inorganic perovskite halide semiconduc- tors in optoelectronic applications motivates studies of their fundamental crystal-chemistry. In particular, recent studies have sought to understand how dipolar, dynamic, and organic cations, such as methylammonium (CH 3 NH 3 + ) and formamidinium (CH(NH 2 ) 2 + ) affect physical properties such as light absorption and charge transport. Here, to probe the influence of organic- inorganic coupling on charge transport, we have prepared the series of vacancy-ordered double perovskite derivatives, A 2SnI 6, where A = Cs +, CH 3NH 3 +, and CH(NH 2) 2 +. Despitemore » nearly identical cubic structures by powder X-ray diffraction, replacement of Cs + with CH 3NH 3 + or CH(NH 2) 2 + reduces conductivity through a reduction in both carrier concentration and carrier mobility. We attribute the trends in electronic behavior to anharmonic lattice dynamics from the formation of hydrogen bonds that yield coupled organic-inorganic dynamics. This anharmonicity manifests as asymmetry of the inter-octahedral I-I pair correlations in the X-ray pair distribution function of the hybrid compounds, which can be modeled by large atomistic ensembles with random rotations of rigid [SnI 6] octahedral units. The presence of soft, anharmonic lattice dynamics holds implications for electron-phonon interactions, as supported by calculation of electron-phonon coupling strength that indicates the formation of more tightly-bound polarons and reduced electron mobilities with increasing cation size. Finally, by exploiting the relatively decoupled nature of the octahedral units in these defect-ordered perovskite variants, we can interrogate the impact of organic-inorganic coupling and lattice anharmonicity on the charge transport behavior of hybrid perovskite halide semiconductors.« less
  • The advantageous performance of hybrid organic-inorganic perovskite halide semiconduc- tors in optoelectronic applications motivates studies of their fundamental crystal-chemistry. In particular, recent studies have sought to understand how dipolar, dynamic, and organic cations, such as methylammonium (CH 3 NH 3 + ) and formamidinium (CH(NH 2 ) 2 + ) affect physical properties such as light absorption and charge transport. Here, to probe the influence of organic- inorganic coupling on charge transport, we have prepared the series of vacancy-ordered double perovskite derivatives, A 2SnI 6, where A = Cs +, CH 3NH 3 +, and CH(NH 2) 2 +. Despitemore » nearly identical cubic structures by powder X-ray diffraction, replacement of Cs + with CH 3NH 3 + or CH(NH 2) 2 + reduces conductivity through a reduction in both carrier concentration and carrier mobility. We attribute the trends in electronic behavior to anharmonic lattice dynamics from the formation of hydrogen bonds that yield coupled organic-inorganic dynamics. This anharmonicity manifests as asymmetry of the inter-octahedral I-I pair correlations in the X-ray pair distribution function of the hybrid compounds, which can be modeled by large atomistic ensembles with random rotations of rigid [SnI 6] octahedral units. The presence of soft, anharmonic lattice dynamics holds implications for electron-phonon interactions, as supported by calculation of electron-phonon coupling strength that indicates the formation of more tightly-bound polarons and reduced electron mobilities with increasing cation size. Finally, by exploiting the relatively decoupled nature of the octahedral units in these defect-ordered perovskite variants, we can interrogate the impact of organic-inorganic coupling and lattice anharmonicity on the charge transport behavior of hybrid perovskite halide semiconductors.« less