Bond valences and anharmonicity in vacancy-ordered double perovskite halides

Maughan, Annalise E.; Paecklar, Arnold A.; Neilson, James R.

doi:10.1039/c8tc03527j

Cited by 34 publications

(36 citation statements)

References 52 publications

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“…Recently, X-ray pair distribution function analysis on Cs2SnI6 has revealed asymmetry in the interoctahedral I−I distance, which can be correlated with rotational disorder for the isolated SnI6 octahedral units, but the technique does not provide information about the activation energy associated with this rotation. 81,82 Therefore, variable-temperature 119 Sn NMR measurements were carried out on a solvent-synthesized Cs2SnI6 sample to probe specifically the anharmonicity of the isolated octahedral SnI6 units to determine the associated activation energies needed for this unique property.…”

Section: Sni6 Octahedral Dynamics In Cs2sni6mentioning

confidence: 99%

Uncovering Halide Mixing and Octahedral Dynamics in Vacancy-Ordered Double Perovskites by Multinuclear Magnetic Resonance Spectroscopy

Karmakar¹,

Mukhopadhyay²,

Gachod³

et al. 2021

Preprint

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Vacancy-ordered double perovskites Cs2SnX6 (X = Cl, Br, I) have emerged as promising lead-free and ambient-stable materials for photovoltaic and optoelectronic applications. To advance these promising materials, it is crucial to determine the correlations between physical properties and their local structure and dynamics. Solid-state NMR spectroscopy of multiple NMR-active nuclei (133Cs, 119Sn and 35Cl) in these cesium tin(IV) halides has been used to decode the structure, which plays a key role in the materials’ optical properties. The 119Sn NMR chemical shifts span approximately 4000 ppm and the 119Sn spin-lattice relaxation times span three orders of magnitude when the halogen goes from chlorine to iodine in these diamagnetic compounds. Moreover, ultrawideline 35Cl NMR spectroscopy for Cs2SnCl6 indicates an axially symmetric chlorine electric field gradient tensor with a large quadrupolar coupling constant of ca. 32 MHz, suggesting a chlorine that is directly attached to Sn(IV) ions. Variable temperature 119Sn spin lattice relaxation time measurements uncover the presence of hidden dynamics of octahedral SnI6 units in Cs2SnI6 with a low activation energy barrier of 12.45 kJ/mol (0.129 eV). We further show that complete mixed-halide solid solutions of Cs2SnClxBr6−x and Cs2SnBrxI6−x (0 ≤ x ≤ 6) form at any halogen compositional ratio. 119Sn and 133Cs NMR spectroscopy resolve the unique local SnClnBr6−nand SnBrnI6−n (n = 0−6) octahedral and CsBrmI12−m (m = 0−12) cuboctahedral environments in the mixed-halide samples. The experimentally observed 119Sn NMR results are consistent with magnetic shielding parameters obtained by density functional theory computations to verify random halogen distribution in mixed-halide analogues. Finally, we demonstrate the difference in the local structures and optical absorption properties of Cs2SnI6 samples prepared by solvent-assisted and solvent-free synthesis routes.

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Section: Sni6 Octahedral Dynamics In Cs2sni6mentioning

confidence: 99%

Uncovering Halide Mixing and Octahedral Dynamics in Vacancy-Ordered Double Perovskites by Multinuclear Magnetic Resonance Spectroscopy

Karmakar¹,

Mukhopadhyay²,

Gachod³

et al. 2021

Preprint

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“…The structure is derived from conventional perovskites by doubling the ABX 3 unit cell along all three crystallographic axes and removing every other B-site cation to form a face-centered lattice of isolated BX 6 octahedral units bridged by A-site cations in the void (vacancy-ordered DHPs). [18,19] The absence of one B-site cation in the double perovskite A 2 B 2 X 6 yields the vacancy-ordered double perovskite structure, [20] as illustrated in the schematic diagram in Figure 2. The A 2 BX 6 structure shows similar features to ABX 3 perovskites, mostly of cubic structures.…”

Section: Introductionmentioning

confidence: 99%

Titanium‐Based Vacancy‐Ordered Double Halide Family in Perovskite Solar Cells

Aslam

Farooqi

Rahman

et al. 2022

Physica Status Solidi (a)

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The toxicity and stability risk of perovskite structured materials have raised concerns in respective to utilization as a solar energy conversion material. The most common perovskite structured material is lead (Pb)-based, which is an element that is knowingly toxic to humans and the environment. Although the stability issue has been well allayed with several optimizations, the ruinous Pb remains a future challenge for perovskite solar cells. Compositional and structural derivatives of the perovskite family, specifically vacancy-ordered double halide perovskites (DHPs), have attracted the attention of researchers in terms of efficiency and toxicity issues subjugation. Although tin (Sn)-based vacancyordered DHPs have been widely explored, the intrinsic property conduces low performance output. Titanium (Ti) is a potential substituting candidate of Sn in a vacancy-ordered DHPs structure. It is an environment-friendly element ideal for sustainable perovskite structured compositions. Rudimentary studies of Ti-based vacancy-ordered DHPs emphasized its potential development as an eco-friendly and stable solar cell. In promoting the development of Ti-based vacancy-ordered DHPs as potential absorbers, we summarized herein the recent progress of experimental and theoretical studies of this perovskite material.

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“…The weak bonding allows the atoms to vibrate with a large frequency in the case of the Cs atom, whereas the vibrations in I and Sn occur with smaller frequencies due to the stronger bonding interaction. A neutron diffraction study conducted recently by Maughan et al, to investigate the anharmonicity in vacancy-ordered double perovskite halides (Cs 2 Sn 1– x Te x I 6 ), showed that, by increasing the temperature, atomic displacements of Cs atoms were higher than those of I and Sn, specifically when x = 0 . Accordingly, the Cs atoms act as scattering centers, which negatively influence the phonon propagation pathway, while the vibration of strongly bonded atoms (I and Sn) forms small ducts for phonon propagation.…”

Section: Resultsmentioning

confidence: 99%

Lattice Thermal Conductivity: An Accelerated Discovery Guided by Machine Learning

Jaafreh

Kang

Hamad

2021

ACS Appl. Mater. Interfaces

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In the present work, we used machine learning (ML) techniques to build a crystal-based model that can predict the lattice thermal conductivity (LTC) of crystalline materials. To achieve this, first, LTCs of 119 compounds at various temperatures (100− 1000 K) were obtained based on density functional theory (DFT) and phonon calculations, and then, these data were employed in the next learning process to build a predictive model using various ML algorithms. The ML results showed that the model built based on the random forest (RF) algorithm with an R 2 score of 0.957 was the most accurate compared with the models built using other algorithms. Additionally, the accuracy of this model was validated using new cases of four compounds, which was not seen for the model before, where a good matching between calculated and predicted LTCs of the new compounds was found. To find candidates with ultralow LTCs (<1 W m −1 K −1 ) at room temperature, the model was used to screen compounds (32116) in the Inorganic Crystal Structure Database. From the screened compounds, Cs 2 SnI 6 and SrS were selected to validate the ML prediction using the counterpart theoretical calculations (DFT and phonon), and it was found that the outcome behaviors by both methods (ML prediction and DFT/phonon calculations) are fairly consistent. Considering the type of employed feature, the prime novelty in this work is that the built model can credibly predict the LTC−temperature behaviors of new compounds that are constructed based on prototype structures and chemical compositions, without the use of any DFT-relaxed structure parameters. Accordingly, using the periodic table, prototype structures, and the RF-based model, the LTC−temperature behavior of a huge number of compounds can be predicated.

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Bond valences and anharmonicity in vacancy-ordered double perovskite halides

Abstract: Anharmonicity is observed in vacancy-ordered double perovskites when the A-site cation is not optimally coordinated by the octahedral framework.

Cited by 34 publications

References 52 publications

Uncovering Halide Mixing and Octahedral Dynamics in Vacancy-Ordered Double Perovskites by Multinuclear Magnetic Resonance Spectroscopy

Uncovering Halide Mixing and Octahedral Dynamics in Vacancy-Ordered Double Perovskites by Multinuclear Magnetic Resonance Spectroscopy

Titanium‐Based Vacancy‐Ordered Double Halide Family in Perovskite Solar Cells

Lattice Thermal Conductivity: An Accelerated Discovery Guided by Machine Learning

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