Simultaneous manipulations of thermal expansion and conductivity in symbiotic ScTaO4/SmTaO4 composites via multiscale effects

Effective manipulations of thermal expansion and conductivity are significant for improving operational performances of protective coatings, thermoelectric, and radiators. This work uncovers determinant mechanisms of the thermal expansion and conductivity of symbiotic ScTaO4/SmTaO4 composites as thermal/environmental barrier coatings (T/EBCs), and we consider the effects of interface stress and thermal resistance. The weak bonding and interface stress among composite grains manipulate coefficient of thermal expansion (CTE) stretching from 6.4x10-6 to 10.7x10-6 K-1 at 1300., which gets close to that of substrates in T/EBC systems. The multiscale effects, including phonon scattering at the interface, mitigation of the phonon speed (vp), and lattice point defects, synergistically depress phonon thermal transports, and we estimate the proportions of different parts. The interface thermal resistance (R) reduces the thermal conductivity (k) by depressing phonon speed and scattering phonons because of different acoustic properties and weak bonding between symbiotic ScTaO4 and SmTaO4 ceramics in the composites. This study proves that CTE of tantalates can be artificially regulated to match those of different substrates to expand their applications, and the uncovered multiscale effects can be used to manipulate thermal transports of various materials.