Significant Reduction in Thermal Conductivity and Improved Thermopower of Electron‐Doped Ba 1– x La x TiO 3 with Nanostructured Rectangular Pores

Electron-doped BaTiO is a less studied n-type metal oxide thermoelectric material. In this work, the electrical conductivity of BaTiO samples has been improved by introducing La to yield an n-type BaLaTiO semiconducting material. Density functional theory calculations show that the optimal electron-doping occurs at x = 0.2, and this is also confirmed experimentally. To improve the thermoelectric properties further, nanostructured cuboidal pores are introduced into the bulk BaLaTiO using F127 surfactant micelles for a chemical templating process, followed by spark plasma sintering. Interestingly, transmission electron microscopy images and X-ray powder diffraction analysis confirms that our fabricated samples are cubic BaTiO perovskite phase with the nanostructured rectangular-prism pores of >4 nm. Scanning electron microscopy images show that all the samples have similar grain boundaries and uniform La doping, which suggests that the large reduction in the lattice thermal conductivity in the F127-treated samples arises primarily from the pore distribution, which introduces anisotropic phonon scattering within the unique nanoarchitecture. The sample with 20 at% La doping and nanopores also shows a thermopower that is doubled compared to the related sample without porosity. Together with the lattice thermal conductivity, enables a significant improvement in figure of merit, zT compared to the other samples.