考虑小尺度效应的纳米材料与结构的热释电性能研究

Owing to the influence of the small-scale effect, the classical pyroelectric theory is not applicable at the nanoscale. Such limitation of classical pyroelectric theory at the nanoscale will make the theoretical study of pyroelectric nanogenerators more difficult and thus may delay their further development. In this project, based on the multi-scale modelling technique we will give a comprehensive study of the pyroelectric properties of nanomaterials and nanostructures for the first time. Firstly, using molecular dynamics (MD) simulations we will conduct a calculation of the material properties related to the pyroelectric performance of nanostructures. The influence of the size effect and the environmental factors will be discussed. The obtained results will also be qualitatively validated by some experimental studies. Then, the results obtained from MD studies together with some certain continuum mechanics theories at the nanoscale will be used to introduce a two-dimensional surface element into the classical finite element method (FEM), which will make the small-scale effect incorporated in the FEM. After this, the modified FEM will be used to calculate the voltage output of pyroelectric nanostructures when subjected to heating. The influence of various internal and external factors on the voltage output will be also discussed. Finally, by analyzing the results obtained from nanostructures under different internal and external factors we will optimize the design and the working environment of pyroelectric nanogenerators. The present project will not only fulfill the theory gap of the study of the pyroelectricity at the nanoscale, but also provide constructive insights for the design of pyroelectric nanogenerators.

小尺度效应的影响使经典热释电理论在纳米尺寸下的适用性受到限制，这加大了热释电纳米发电机理论研究的难度从而滞后了其进一步的发展。本项目基于多尺度研究方法将首次对纳米材料及结构的热释电性能进行全面研究。首先，采用分子动力学方法对与纳米结构热释电性能相关的材料参数进行计算，讨论尺寸效应及外界环境因素的影响，并通过实验手段对计算结果予以定性验证。然后，根据所得结果结合纳米尺度下相关连续介质理论在传统有限元方法中引入一类二维表面单元，使其可有效地考虑小尺度效应的影响。通过改进后的有限元方法计算热释电纳米结构受热时的电压输出，讨论内外多种因素对结果的影响。最后，分析结果数据，从纳米结构自身及外界环境两个方面对热释电纳米发电机的结构设计及工作环境进行优化，使其输出电压达到较大值。本项目的研究成果将填补纳米材料热释电理论研究上的空缺，同时也为热释电纳米发电机的设计提供指导性的优化意见。

本项目在纳米热释电材料与结构的多尺度模拟及多物理场耦合研究方面取得重要进展。通过分子动力学方法计算，发现由于纳米尺度下表面热弹性、压电及介电层的存在，氮化镓纳米线的热释电参数随其尺寸的减小而增大。结合分子动力学计算结果，采用理论分析讨论了尺度效应对氮化镓纳米线热释电电压输出的影响，发现小尺度效应的存在可将氮化镓纳米线热释电电压输出提高一个量级。结合第一性原理计算、分子动力学模拟及有限元等跨尺度方法从原子尺度探讨了潮湿环境对氧化锌纳米线力电耦合行为的影响机理，为后续研究环境因素对其热释电性能的影响打下理论基础。采用第一性原理及分子动力学模拟方法，研究了新型二维材料（单层硫化锗）的电热效应，证明了电热效应与其材料手性的相关性，同时采用热力学理论对上述模拟所得结果进行了系统分析。此外，在项目进行期间受邀撰写关于二维材料力电耦合行为的综述文章，从表征、性能及应用三个层面对相关领域目前研究进展进行了系统的总结。结合本项目，目前课题组发表SCI论文28篇，培养硕士研究生5名。本项目的研究成果填补纳米材料力-热-电耦合理论研究上的某些空缺，同时也为新型热释电纳米发电机的设计提供指导性的优化意见。