Defect-dominated phonon scattering processes and thermal transports of ferroelastic (Sm1-XYbX)TaO4 solid solutions

Thermal transport management is of great significance for materials such as thermal barrier coatings, photovoltaics, and thermoelectrics. In particular, tremendous efforts have been made to tailor phonon thermal transport to improve performance. This work elucidated origins of low thermal conductivity of ferroelastic (Sm1-XYbX)TaO4 solid solutions from defect-dominated phonon scattering processes. We estimated the influences of point defects (misfits in atomic weight and ionic radius, and oxygen vacancies), ferroelastic domains, and the Umklapp process on thermal transports via the corresponding phonon relaxation time (τ). The phonon relaxation time caused by point defects (τD), ferroelastic domains (τF), and the Umklapp process (τU) exhibited a trend of τD−1>τU−1>τF−1, indicating that point defects dominated the thermal transports. The effects of ferroelastic domains on thermal conductivity were estimated according to domain widths and space mismatches between neighboring domains. The approximately parallel relationship between the neighboring domains was beneficial for reducing ferroelastic t-m transition energy. Furthermore, a model was developed to derive the high-temperature thermal conductivity, and the contributions of radiative thermal conductivity were separated from the total thermal conductivity. The analysis of thermal transports can be used in other materials to estimate the contributions of different thermal transport mechanisms to the total thermal conductivity at both low and high temperatures, and to effectively tailor thermal transports according to specific applications.