Multiple lattice instabilities and complex ground state in Cs$_2$AgBiBr$_6$
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| Autori principali: | , , , , , , , , , , , , , |
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| Natura: | Preprint |
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2021
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| _version_ | 1866913299799474176 |
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| author | He, Xing Krogstad, Matthew Gupta, Mayanak K Lanigan-Atkins, Tyson Mao, Chengjie Ye, Feng Liu, Yaohua Hong, Tao Chi, Songxue Wei, Haotong Huang, Jinsong Rosenkranz, Stephan Osborn, Raymond Delaire, Olivier |
| author_facet | He, Xing Krogstad, Matthew Gupta, Mayanak K Lanigan-Atkins, Tyson Mao, Chengjie Ye, Feng Liu, Yaohua Hong, Tao Chi, Songxue Wei, Haotong Huang, Jinsong Rosenkranz, Stephan Osborn, Raymond Delaire, Olivier |
| contents | Metal halides perovskites (MHPs) are attracting considerable interest for optoelectronic applications, with Cs$_2$AgBiBr$_6$ one of the main contenders among lead-free systems. Cs$_2$AgBiBr$_6$ crystallizes in a nominally double-perovskite structure, but exhibits a soft lattice with large atomic fluctuations characteristic of MHPs. While crucial to understand electron-phonon and phonon-phonon couplings, the spatio-temporal correlations of these fluctuations remain largely unknown. Here, we reveal these correlations using comprehensive neutron and x-ray scattering measurements on Cs$_2$AgBiBr$_6$ single-crystals, complemented with first-principles simulations augmented with machine-learned neural-network potentials. We report the discovery of an unexpected complex modulated ground state structure containing several hundred atoms, arising from a soft-phonon instability of the low-temperature tetragonal phase. Further, our experiments and simulations both reveal extensive correlated 2D fluctuations of Br octahedra at finite temperature, arising from soft anharmonic optic phonons, reflecting very shallow potential wells. These results provide new insights into the atomic structure and fluctuations in MHPs, critical to understand and control their thermal and optoelectronic properties. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2112_04717 |
| institution | arXiv |
| publishDate | 2021 |
| record_format | arxiv |
| spellingShingle | Multiple lattice instabilities and complex ground state in Cs$_2$AgBiBr$_6$ He, Xing Krogstad, Matthew Gupta, Mayanak K Lanigan-Atkins, Tyson Mao, Chengjie Ye, Feng Liu, Yaohua Hong, Tao Chi, Songxue Wei, Haotong Huang, Jinsong Rosenkranz, Stephan Osborn, Raymond Delaire, Olivier Materials Science Metal halides perovskites (MHPs) are attracting considerable interest for optoelectronic applications, with Cs$_2$AgBiBr$_6$ one of the main contenders among lead-free systems. Cs$_2$AgBiBr$_6$ crystallizes in a nominally double-perovskite structure, but exhibits a soft lattice with large atomic fluctuations characteristic of MHPs. While crucial to understand electron-phonon and phonon-phonon couplings, the spatio-temporal correlations of these fluctuations remain largely unknown. Here, we reveal these correlations using comprehensive neutron and x-ray scattering measurements on Cs$_2$AgBiBr$_6$ single-crystals, complemented with first-principles simulations augmented with machine-learned neural-network potentials. We report the discovery of an unexpected complex modulated ground state structure containing several hundred atoms, arising from a soft-phonon instability of the low-temperature tetragonal phase. Further, our experiments and simulations both reveal extensive correlated 2D fluctuations of Br octahedra at finite temperature, arising from soft anharmonic optic phonons, reflecting very shallow potential wells. These results provide new insights into the atomic structure and fluctuations in MHPs, critical to understand and control their thermal and optoelectronic properties. |
| title | Multiple lattice instabilities and complex ground state in Cs$_2$AgBiBr$_6$ |
| topic | Materials Science |
| url | https://arxiv.org/abs/2112.04717 |