Simultaneous manipulations of thermal expansion and conductivity in symbiotic ScTaO <sub>4</sub>/SmTaO <sub>4</sub> composites via multiscale effects
Lin Chen, Jiankun Wang, Baihui Li, Keren Luo, Jing Feng
Abstract
Effective manipulations of thermal expansion and conductivity are significant for improving operational performances of protective coatings, thermoeletrics, and radiators. This work uncovers determinant mechanisms of thermal expansion and conductivity of symbiotic ScTaO<sub>4</sub>/SmTaO<sub>4</sub> composites as thermal/environmental barrier coatings (T/EBCs), and we consider effects of interface stress and thermal resistance. The weak bonding and interface stress among composites grains manipulate coefficient of thermal expansion (CTE) stretching from 6.4 to 10.7×10<sup>-6</sup> K<sup>-1</sup> at 1300 ºC, which gets close to that of substrates in T/EBC systems. The multiscale effects, including phonon scattering at interface, mitigation of phonon speed, and lattice point defects, synergistically depress phonon thermal transports, and we estimate the proportions of different parts. The interface thermal resistance reduces thermal conductivity by depressing phonon speed and scattering phonons because of differential acoustic properties and weak bonding between the symbiotic ScTaO<sub>4</sub> and SmTaO<sub>4</sub> ceramics in composites. This study proves that CTE of tantalates can be artificially regulated to match that of different substrates to expand their applications, and the uncovered multiscale effects can be used to manipulate thermal transports of various materials.