Understanding size and interface dependent anisotropic thermal conduction in correlated multilayer structures

最近已经确定，提高热电效率的一种非常有效的方法是通过在纳米级结构中抑制热导率，例如在多层系统中。然而，这种效应的机制，即不同波长声子在界面上的散射和阻挡还不是很清楚。这个联合项目的目标是进一步发展对氧化物多层体系中各向异性和尺寸相关热传导的理解。我们优化了顶部和底部电极几何形状的3-omega方法，以可靠地测量导热系数κ。结合使用神经网络和详细的热和电耦合条件的有限元建模，将允许高精度地确定面内和跨面贡献，κ -和κ||。我们对声子色散的连续模型选择了有前途的多层热电氧化物体系，即掺杂SrTiO3和Pr1-xCaxMnO3以及失配层状化合物Ca3Co4O9，供我们进一步研究。通过仔细的实验研究，结合使用非平衡分子动力学和声子玻尔兹曼方程的热导率原子水平建模，将声阻抗失配的影响从界面、无序和掺杂剂的各种散射贡献中分离出来。

It has recently been established that a very effective method for enhancement of thermoelectric efficiency is through suppression of thermal conductivity by structuring at the nanoscale, such as in multilayer systems. However, the mechanisms of this effect, i.e. the scattering and blocking of phonons at various wavelengths by interfaces are not well understood. The objective of this proposed joint project is to further develop the understanding of anisotropic and size dependent thermal conduction in oxide multilayer systems. We have optimized the 3-omega method in top and bottom electrode geometries for reliable measurements of thermal conductivity κ. The use of neural networks in combination with detailed finite element modelling of the coupled thermal and electrical conditions will allow for high-precision determination of in-plane and cross-plane contributions, κ┴ and κ||. Our continuum modelling of phonon dispersion has led to the selection of promising thermoelectric oxide systems for multilayers, namely doped SrTiO3 and Pr1-xCaxMnO3 and the misfit layered compound Ca3Co4O9, for our further studies. Separating out the influence of acoustic impedance mismatch of layers from various scattering contributions of interfaces, disorder, and dopants will be performed by careful experimental studies combined with atomic level modelling of thermal conductivity using non-equilibrium molecular dynamics and the phonon Boltzmann equation.