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Direct evidence of mixed-phase induced anomalous thermal transport in hybrid perovskite single crystals
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DOI：10.1016/j.mtphys.2026.102107.png)
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Abstract
En 中文
The thermal conductivity of crystalline semiconductors is critical for their optoelectronic performance and is commonly described by the classical phonon gas model. Here, we report a clear violation of this conventional behavior during the phase transition of methylammonium lead bromide (MAPbBr3) perovskite single crystals. Through transient frequency domain thermoreflectance experiments, an anomalous kink in thermal conductivity between 170-220 K is observed, disrupting the usual monotonic decrease with increasing temperature above the Debye temperature. Temperature-dependent X-ray diffraction (TDXRD) experiments reveal that a mixed orthorhombic-tetragonal phase exists in MAPbBr3 from 140 K to 210 K. By combining TDXRD with phonon Wigner transport equation calculations, the origin of this anomalous thermal conductivity kink is attributed to two causes: the differences in the phonon properties between the tetragonal and orthorhombic phases and an increasing proportion of the tetragonal phase at increasing temperature. The notable differences in the phonon properties between these two phases, coupled with the potential differences in the properties of the charge carriers, can dramatically impact the optoelectronic performance of hybrid perovskites. Importantly, a similar kink is also observed within methylammonium lead chloride, suggesting such mixed-phase-induced thermal transport properties may be applicable to a broader class of perovskite semiconductors.
Keywords:
thermal conductivity
perovskite single crystals
phase transition
phonon properties
mixed-phase effects
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