arXiv subjects

Chongjia Lin

Publications and source records attributed to Chongjia Lin.

3 recordsLinked to original sources

arXiv2024

Ineffectiveness of Formamidine in Suppressing Ultralow Thermal Conductivity in Cubic Hybrid Perovskite FAPbI3

Fundamentally understanding the lattice dynamics and microscopic mechanisms of thermal transport in cubic hybrid organic-inorganic perovskites remains elusive, primarily due to their strong anharmonicity and frequent phase transitions. In this work, we comprehensively investigate the thermal transport behavior in cubic hybrid perovskite FAPbI3, integrating first principles-based anharmonic lattice dynamics with a linearized Wigner transport formula. The Temperature Dependent Effective Potential (TDEP) technique allows us to stabilize the negative soft modes, primarily dominated by organic cations, at finite temperatures in cubic FAPbI3. We then predict an ultra-low thermal conductivity of ~0.63 Wm^(-1) K^(-1) in cubic FAPbI3 at 300 K, with a temperature dependence of T^(-0.740), suggesting a good crystalline nature of phonon transport. Notably, the ultra-low thermal conductivity in cubic FAPbI3 is primarily attributed to the [PbI3]1- units, challenging the conventional focus on organic FA+ cations. This shift in focus is due to the presence of Pb(s)-I(p) anti-bonding sates within the [PbI3]1- units. Furthermore, thermal transport in cubic FAPbI3 is predominantly governed by the particle-like phonon propagation channel across the entire temperature range of 300-500 K, a result of diminished suppression of low-frequency phonons by FA+ cations and large inter-branch spacings. Finally, our findings underscore that the anharmonic force constants are highly temperature-sensitive, leading to underestimations of thermal conductivity when relying on 0-K anharmonic force constants. Our study not only elucidates the microscopic mechanisms of thermal transport in cubic FAPbI3 but also provides a crucial framework for the discovery, design, and understanding of hybrid organic-inorganic compounds with ultra-low thermal conductivity.

cond-mat.mtrl-sci↗

arXiv2023

Wave-like Tunneling of Phonons Dominates Glass-like Thermal Transport in Quasi-1D Copper Halide CsCu2I3

Fundamental understanding of thermal transport in compounds with ultra-low thermal conductivity remains challenging, primarily due to the limitations of conventional lattice dynamics and heat transport models. In this study, we investigate the thermal transport in quasi-one-dimensional (1D) copper halide CsCu2I3 by employing a combination of first principles-based self-consistent phonon calculations and a dual-channel thermal transport model. Our results show that the 0-K unstable soft modes, primarily dominated by Cs and I atoms in CsCu2I3, can be an-harmonically stabilized at ~ 75 K. Furthermore, we predict an ultra-low thermal conductivity of 0.362 Wm^(-1) K^(-1) along the chain axis and 0.201 Wm^(-1) K^(-1) along cross chain direction in CsCu2I3 at 300 K. Importantly, we find that an unexpected anomalous trend of increasing cross-chain thermal conductivity with increasing temperature for CsCu2I3, following a temperature dependence of ~T 0.106, which is atypical for a single crystal and classified as an abnormal glass-like behavior. The peculiar temperature-dependent behavior of thermal conductivity is elucidated by the dominant wave-like tunnelling of phonons in thermal transport of CsCu2I3 along cross-chain direction. In contrast, particle-like phonon propagation primarily contributes to the chain-axis thermal conductivity across the entire temperature range of 300-700 K. The sharp difference in the dominant thermal transport channels between the two crystallographic directions can be attributed to the unique chain-like quasi-1D structure of CsCu2I3. Our study not only illustrates the microscopic mechanisms of thermal transport in CsCu2I3 but also paves the way for searching for and designing materials with ultra-low thermal conductivity.

cond-mat.mtrl-sci↗

arXiv2023

Unravelling Ultralow Thermal Conductivity in Double Perovskite Cs2AgBiBr6: Dominant Wave-like Phonon Tunnelling, Strong Quartic Anharmonicity and Lattice Instability

In this work, we investigate the microscopic mechanisms of anharmonic lattice dynamics and thermal transport in lead-free halide double perovskite Cs2AgBiBr6 from first principles. We combine self-consistent phonon calculations with bubble diagram correction and a unified theory of lattice thermal transport that considers both the particle-like phonon propagation and wave-like tunnelling of phonons. An ultra-low thermal conductivity at room temperature (~0.21 Wm-1K-1) is predicted with weak temperature dependence(~T-0.45), in sharp contrast to the conventional ~T-1 dependence. Particularly, the vibrational properties of Cs2AgBiBr6 are featured by strong anharmonicity and wave-like tunnelling of phonons. Anharmonic phonon renormalization from both the cubic and quartic anharmonicities are found essential in precisely predicting the phase transition temperature in Cs2AgBiBr6 while the negative phonon energy shifts induced by cubic anharmonicity has a significant influence on particle-like phonon propagation. Further, the contribution of the wave-like tunnelling to the total thermal conductivity surpasses that of the particle-like propagation above around 340 K, indicating the breakdown of the phonon gas picture conventionally used in the Peierls-Boltzmann Transport Equation. Importantly, further including four-phonon scatterings is required in achieving the dominance of wave-like tunnelling, as compared to the dominant particle-like propagation channel when considering only three-phonon scatterings. Our work highlights the importance of lattice anharmonicity and wave-like tunnelling of phonons in the thermal transport in lead-free halide double perovskites.

cond-mat.mtrl-sci↗