探究分子旋转对声子与传热的影响规律及其在声子调控器件的应用

The central government of China has identified and undertaken a major effort to optimize the use of the limited energy resources in the country. Understanding the transport of phonons, one of the principal thermal energy carriers in solid-state materials, will have a direct influence on the success of this goal. This proposal will investigate the inherent heat transfer mechanisms as well as how to control such mechanisms with external stimuli in large-unit cell systems containing freely rotating discrete molecular units. In a recent study published in Nature Materials, the applicant demonstrated that the rotation of such molecules in superatom crystals modulates thermal conductivity. Investigations into such rotation-phonon interactions are limited due to the novelty of such systems. With the emerging ubiquitousness of these systems in clean energy research, it is imperative to understand the governing rules behind these interactions to effectively mitigate the accompanying thermal related problems. Through systematic experimental and simulation investigations, these governing rules can be uncovered. We hypothesize that such molecular motions can be actively manipulated using external stimuli to control phonon properties and, hence, thermal transport. Rapidly acting physical stimuli such as electric and magnetic fields can couple with certain molecules to constrain their natural rotations while pressure and temperature can drive phase transitions that will also restrict such rotations. Through these external stimuli, in-depth knowledge for harnessing and controlling such interactions can be used to create hitherto elusive actively controlled phononic devices.

国家高度重视能源的优化利用。声子作为固体中能量的载体之一，对其传输和调控机理的探究是能源优化利用中一个关键的科学问题。本课题拟针对具有分子旋转的大晶胞系统，开展其传热机理和外场调控机制的研究。最近，申请者在Nature Materials发表的文章报道了超晶体内的分子旋转可调控其传热过程。由于这类系统较新颖，目前对分子旋转与声子相互作用的研究还处于起步阶段,但随着其在清洁能源领域的应用日益增加，理解这类相互作用的机理将有效解决其中涉及的传热问题。本课题拟采用系统性的实验和模拟来深入研究该类系统中传热的机理。因分子旋转的存在，我们可用外场来主动调控声子属性，从而达到控制热导率的目的。该研究旨在探索以施加快速变换的外场（如电场和磁场）来激发某类分子，以及通过调制压力和温度来引起系统相变，影响分子旋转，从而调控热导率。通过研究外场对分子旋转以及其热导率的影响，我们将能够开发主动式的声子调控器件。

本课题拟针对具有分子旋转的大晶胞体系，开展其传热机理和外场调控机制的研究。由于这类系统较新颖，目前对分子旋转与声子相互作用的研究还处于起步阶段,但随着其在清洁能源领域的应用日益增加，理解这类相互作用的机理将有效解决其中涉及的传热问题。本课题拟采用系统性的实验和模拟来深入研究该类系统中传热的机理。因分子旋转的存在，我们可用外场来主动调控声子属性，从而达到控制热导率的目的。本研究结合实验测量和模拟计算，以含有小分子的有机无机钙钛矿体系为研究对象，解开分子旋转对热导率的影响。基于频域热反射法，为该方法同时测量多参数的可行性创造了评估方法。借助实验平台开展对有机无机钙钛矿薄膜和单晶的热导率，推断出薄膜和单晶的热导率趋势的差异原因。利用分子动力学模拟优化MAPbI3的结构，并首次获得无虚频的声子谱。基于此声子谱，以晶格动力学计算解开MAPbI3 单晶的实验和之前的理论计算的热导率值的差异，意外发现在室温下分子旋转对热导率只有微弱的影响，但分子本身以声子的波动性贡献了大于50%的热导率。加上外部压力场的模拟，探究其对分子旋转和热传输的影响与机理，发现声子的波动性使体系的热导率在高达2GPa的压力范围内无敏感度，阐明了压力场对其的影响规律。.