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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.

The title compound, C24H19NO, was obtained via the reaction of (1E,2E)-3-(3-methoxyphenyl)-1-phenylprop-2-en-1-one with ethyl 2-oxopropanoate, using NH4I as a catalyst. The compound crystallizes in the monoclinic space group I2/a. In the molecule, the four rings are not in the same plane, the pyridine ring being inclined to the benzene rings by 17.26 (6), 56.16 (3) and 24.50 (6)°. In the crystal, molecules are linked by C—H...π interactions into a three-dimensional network. To further analyse the intermolecular interactions, a Hirshfeld surface analysis was performed. Hirshfeld surface analysis indicates that the most abundant contributions to the crystal packing are from H...H (50.4%), C...H/H...C (37.9%) and O...H/H...O (5.1%) interactions.