Ultralow thermal conductivity and enhanced thermoelectric properties in a textured (Ca0.35Sr0.2Ba0.15Na0.2Bi0.1)3Co4O9 high-entropy ceramic

A novel layered (Ca0.35Sr0.2Ba0.15Na0.2Bi0.1)3Co4O9 high-entropy ceramic is prepared for the first time by the traditional solid-state reaction. The XRD, SEM-EDS and TEM data exhibit that the multi-component cations can be introduced into the Ca site to form a single-phase and homogeneous solid solution with highly preferential crystal orientation and multi-scale structural defects. The textured high-entropy ceramic, compared to the pristine Ca3Co4O9 sample, shows a significantly increased electrical conductivity due to the higher carrier mobility derived from the c-axis selective orientation, and obtains an enhanced power factor of 0.27 mW·m−1·K−2. Besides, high entropy induced multi-dimensional lattice defects can act as the phonon scattering centers to effectively suppress the lattice thermal conductivity, and achieves an ultralow thermal conductivity of 0.87 W·m−1·K−1 as well as a peak figure-of-merit of 0.3 at 973 K, which is about 2.5 times larger than that of Ca3Co4O9. Our work deeply reveals the impact of the microstructure on thermoelectric properties in a high-entropy ceramic, which may help to advance the understanding and design of high-entropy thermoelectric materials.