Physical Mechanism and Chemical Trends in the Thermal Expansion of Inorganic Halide Perovskites

Abstract

The considerable thermal expansion of halide perovskites is one of the challenges to device stability, yet the physical origin and modulation strategy remain unclear. Herein, we report first-principles calculations of the thermal properties of halide perovskites at 300 K using oxides as a reference. We found that the large thermal expansion of halide perovskites can mainly be attributed to their low bulk modulus and volumetric heat capacity because of the soft crystal lattice, whereas composition-dependent anharmonicity emerges as the most important factor in determining thermal expansion with the same structure. We discovered that thermal expansion of halide perovskites can be decreased by weakening the B−X bond to promote the octahedral anharmonicity. We further proposed an effective thermal expansion coefficient descriptor of halide perovskites with a Pearson correlation coefficient of nearly −80%. Our findings provide insights into the underlying mechanisms and chemical trends in the thermal expansion behavior of halide perovskites.

Which Ion Dominates the Temperature and Pressure Response of Halide Perovskites and Elpasolites?

“…This observation is consistent with their larger bulk moduli, showing that the elpasolite structure is more resistant to changes in both temperature and pressure. Furthermore, the absolute values are close to recent theoretical predictions . Note that previous studies of Cs 2 AgBiBr 6 thin films have reported a cubic-to-tetragonal phase transition at 122 K .…”

Low-Temperature Heat Capacity of CsPbI3, Cs4PbI6, and Cs3Bi2I9

“…For δ-CsPbI 3 , a correction using the Grüneisen parameter and thermal expansion coefficient (eq ) is able to reproduce the heat capacity beyond Dulong-Petit fairly well. The Grüneisen parameter for this compound is reported to be 0.86 and 1.03 . Volumetric thermal expansion coefficients for δ-CsPbI 3 of (132 × 10 –6 K –1 ) and (118 × 10 –6 K –1 ) have been determined based on cell parameters in the temperature region 298–609 K as determined using synchrotron-based powder diffraction.…”

Strong Anharmonicity at the Origin of Anomalous Thermal Conductivity in Double Perovskite Cs2NaYbCl6

“…To this aim the Birch-Murnaghan equation of state [33,34] was used, and a value of 16.28˜GPa was obtained, in line with the typical values of this class of perovskites. [35,36] In the framework of quasi-harmonic approximation, [37] we also calculated the thermal expansion coefficient by performing 16 phonon dispersions calculations, each one with a different volume in the range 1225-1420 Å 3 . As reported in Table 2, we found a fair agreement with the experimental data here taken 𝛼 DFT (• 10 −5 K −1 ) 1.8± 0.2 1.9 ± 0.1 1.88 ± 0.17 1.54 ± 0.17 As a final test for the accuracy of calculated IFCs, the results for heat capacity calculation  v (T) as a function of temperature T provided the data shown in Figure 2b.…”