Preparation of high entropy ceramics with ultra-low lattice thermal conductivity using the high-pressure and high-temperature method

Ceramic materials with low thermal conductivity are critically important in applications such as thermoelectric conversion and thermal barrier coatings. Introducing the concept of entropy and its singular physical properties permits attainment of low thermal conductivity in ceramics, and the high-pressure synthesis conditions can also reduce the thermal conductivity of the synthesized samples by adjusting the micro-morphology. In this work, high-entropy (Sr0.2La0.2Nd0.2Sm0.2Eu0.2)TiO3 ceramics were synthesized by solid-state reaction at high temper-ature and high pressure, which significantly shortened the synthesis time. X-ray diffraction (XRD) results affirmed that high-entropy cubic perovskite ceramics can be synthesized using high temperature and high pressure. High-resolution transmission electron microscopy (HRTEM) results show that the multi-component cations are uniformly distributed at the A-site. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the pressure provided by the synthesis method can effectively adjust the microstructure of the synthesized samples. Ultra-low thermal conductivity was obtained by synthesizing high -entropy samples under high pressure; the lowest thermal conductivity of resulting high-entropy (Sr0.2La0.2Nd0.2Sm0.2Eu0.2)TiO3 perovskite ceramics was 0.82 Wm-1 K-1 at the test temperature of 973 K, which is the lower value of perovskite strontium-titanate-based ceramics reported in the literature at present. The high-entropy perovskite ceramics prepared by this new high-temperature and high-pressure method also have good mechanical properties, with Vickers hardness of 10.05 GPa. This study provides a new synthesis strategy for the rapid and effective synthesis of perovskite ceramics with low thermal conductivity, which is a new method for the synthesis of high-entropy materials.