Metal cation s lone-pairs increase octahedral tilting instabilities in halide perovskites

Gao, Lingyuan; Yadgarov, Lena; Sharma, Rituraj; Korobko, Roman; McCall, Kyle M.; Fabini, Douglas H.; Stoumpos, Constantinos C.; Kanatzidis, Mercouri G.; Rappe, Andrew M.; Yaffe, Omer

doi:10.1039/d1ma00288k

Cited by 31 publications

(49 citation statements)

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“…Its minima correspond to a variety of configurations involving octahedral tilting coupled to Cs distortions. [7,[59][60][61][62][63] As temperature increases, hopping between the wells (i.e., large amplitude octahedral tilting and deformations) becomes possible [21,60,64] and phase transitions take place.…”

Section: Comparison Of Anharmonic Expressions In Cs 2 Agbibr 6 and Cs...mentioning

confidence: 99%

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Diverging Expressions of Anharmonicity in Halide Perovskites

et al. 2022

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Lead‐based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead‐free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead‐based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead‐based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead‐based analog, CsPbBr3. Using temperature‐dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well‐defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal‐mode picture above 200 K. It is suggested that the breakdown of the normal‐mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below ≈37 K.

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Section: Comparison Of Anharmonic Expressions In Cs 2 Agbibr 6 and Cs...mentioning

confidence: 99%

“…This type of behavior has also been observed for hybrid lead-based halide perovskites [6,7] as well as for tin-and germanium-based perovskites which also contain divalent group 14 metal cations with lone pair electron configurations. [63]…”

Section: Comparison Of Anharmonic Expressions In Cs 2 Agbibr 6 and Cs...mentioning

confidence: 99%

Diverging Expressions of Anharmonicity in Halide Perovskites

et al. 2022

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“…These features in the Cs and Br displacement distributions are yet another manifestation of the known effect of anharmonicity in the vibrations of this and other HaP systems. [19,[24][25][26][48][49][50][51] We can further support this rationale by examining Br displacements occurring in par- allel to the Pb-Br-Pb bonding axis (the y-direction in Fig. 1c, bottom panel), which are known to be involved in vibrations that are far less anharmonic: [19,23] the distribution of these Br displacements shows that they are much smaller in magnitude, peak at approximately a zero displacement, and follow a Gaussian function (see SI).…”

Section: Resultsmentioning

confidence: 99%

“…Along with related effects, such as the stereochemically activite lonepair that is described in, e.g., Ref. [24], this motivates a departure from simplified descriptions based purely on geometric factors of the idealized average structure, [57] as discussed in recent articles. [58,59]…”

Section: Resultsmentioning

confidence: 99%

“…[23] Concurrent with these local, dynamic fluctuations in the structure are octahedral tilting instabilities occurring in various relevant candidate materials of this class. [24][25][26][27] Therefore, the appearance of a finite-temperature atomic structure that is locally and dynamically disordered, while being long-ranged ordered at the same time, represents a generic feature of a wide range of HaP materials. The local fluctuations in the atomic structure are important because they impact the optoelectronic properties of HaPs at finite temperature and, by extension, the characteristics of devices made from them.…”

Section: Introductionmentioning

confidence: 99%

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Probing the Disorder inside the Cubic Unit Cell of Halide Perovskites from First-Principles

Zhu¹,

Caicedo‐Dávila²,

Gehrmann³

et al. 2021

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Strong deviations in the finite temperature atomic structure of halide perovskites from their average geometry can have profound impacts on optoelectronic and other device-relevant properties. Detailed mechanistic understandings of these structural fluctuations and their consequences remain, however, limited by the experimental and theoretical challenges involved in characterizing strongly anharmonic vibrational characteristics and their impact on other properties. We overcome some of these challenges by a theoretical characterization of the vibrational interactions that occur among the atoms in the prototypical cubic CsPbBr 3 . Our investigation based on first-principles molecular dynamics calculations finds that the motions of neighboring Cs-Br atoms interlock, which appears as the most likely Cs-Br distance being significantly shorter than what is inferred from an ideal cubic structure. This form of dynamic Cs-Br coupling coincides with very shallow dynamic potential wells for Br motions that occur across a locally and dynamically disordered energy landscape. We reveal an interesting dynamic coupling mechanism among the atoms within the nominal unit cell of cubic CsPbBr 3 and quantify the important local structural fluctuations on an atomic scale.

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Nonequilibrium Lattice Dynamics in Photoexcited 2D Perovskites

et al. 2022

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Metal cation s lone-pairs increase octahedral tilting instabilities in halide perovskites

Abstract: Lone-pair covalency can faciliate dynamic tilting of MBr6 octahedra and increase dynamic structural instabilities.

Cited by 31 publications

References 76 publications

Diverging Expressions of Anharmonicity in Halide Perovskites

Diverging Expressions of Anharmonicity in Halide Perovskites

Probing the Disorder inside the Cubic Unit Cell of Halide Perovskites from First-Principles

Nonequilibrium Lattice Dynamics in Photoexcited 2D Perovskites

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