Research On Thermal Transport Properties Of Three-Dimensional Carbon Allotropes And Cubic Anti-Perovskite A₃XB

Thermal conductivity,heat conduction under a finite-temperature gradient,is of vital importance in various modern technologies,including transistors,photovoltaics,and thermoelectric devices.In particular,increasing power density in microprocessors demands high thermal conductivity materials remove heat away.On the other hand,thermal conductivity needs to be minimized in order to achieve optimal energy conversion efficiency in the application of thermoelectric materials.Therefore,semiconducting materials of particular interest are those exhibiting extreme thermal conductivities,with either very high or very low lattice thermal conductivities.Here,using first-principles calculation method combined with Boltzmann transport equation（BTE）,compressive sensing techniques and self-consistent phonon（SCP）theory,we investigate the heat transport properties of carbon allotropes,five hydrogen-based cubic perovskite A₃HB materials（A=Li,Na;B=S,Se,Te）and four fluorine-based cubic perovskite A₃FB materials（A=Li,Na;B=Se,Te）.To date,many carbon allotropes have been proposed theoretically or experimentally,and a variety of attractive physical and chemical characters have been uncovered in these materials simultaneously.Although these researches have been abundant,there is still a lack of systematic studies on thermal transport properties of various carbon allotropes.Therefore,the lattice thermal conductivity（_）of all common carbon allotropes with different crystal systems,such as diamond,bct-C₄,bct-C₈,hex-C,kagome,m-carbon,pentadiamond,t-carbon and w-carbon has been investigated systematically.The results indicate that all these materials have high_,mainly due to their high phonon group velocity,weak anharmonicity and long phonon lifetime.Besides,the mechanical properties of these carbon are also calculated,indicating that the_are proportional to bulk modulus in these carbon allotropes with different crystal structures,which can be used to estimate_of carbon allotropes effectively.Given the considerable anharmonicity in the hydride-based cubic antiperovskites A₃HB（A=Li,Na;B=S,Se,Te）,higher order anharmonicity is of vital significance in accurately determining_.In this paper,we investigate the heat transport properties of these material with the inclusion of quartic anharmonicity,which do not contain orthorhombic Na₃HS.It is worth noting that only the values of_obtained by SCP theory are valid for Li₃HS and Na₃HS,because there is imaginary frequency in harmonic approximation（HA）phonon mode,which makes the conventional calculation of BTE invalid.The results indicate that the full quartic anharmonicity is important to capture the reasonable temperature dependence of the_,while only taking phonon frequency shifts（4 phonon scattering processes）into account will result in weaker（stronger）temperature dependence.Next,we aim at the structural stability,lattice thermal conductivity,transport properties of four cubic antiperovskites A₃FB（A=Li,Na;B=Se,Te）.The results indicate that the strong quartic anharmonicity of alkali-metal atoms harden low-frequency phonon branch to ensure dynamic stability of the material.In addition,we analyze the impact of phonon group velocities,the scattering rate and scattering phase space of three-phonon and four-phonon on phonon transport,revealing that Na₃FTe own the low_of 0.51W/m K,mainly due to the strong four-phonon scattering rates which is dominated by redistribution and Umklapp processes.Our studies provide the microscopic understanding of the quartic anharmonicity together with their impact on lattice dynamics and phonon transport is essential to design and explore materials with ultralow thermal conductivity.