Thermoelectric generators (TEGs) based on oxide materials are non-toxic, cost-efficient devices that convert thermal energy directly into electrical energy employing the Seebeck effect. In this work, two different p-type oxide thermoelectric (TE) materials were prepared by solid state reaction (SSR) for building transverse thermoelectric devices with enhanced output power for low-power applications. These TE materials are lanthanum copper oxide La₂CuO₄ (LCO) which is suitable for energy harvesting in the low temperature regime, and calcium cobalt oxide Ca₃Co₄O₉ (CCO), which is suitable for applications at elevated temperatures up to 800°C.
For the optimization of the thermoelectric properties of LCO, strontium doping La_1.99Sr_0.01CuO₄ (LSCO) increased the electrical conductivity from 1440 S/m to 2960 S/m compared to undoped LCO, leading to a power factor of PF=305 µW/(m.K²) at 100°C. On the other hand, the synthesis protocol of CCO was optimized by controlling the average particle size of the fine-milled powder. The electrical conductivity of CCO pellets sintered at 920°C for 24h increased from 6500 S/m for a powder of an aggregate particle size d(50) of 4.5µm to 12390S/m at 800°C for a powder of d(50) of 0.95 µm, respectively. Consequently, the power factor (PF) and zT reach 380 µW/(m.K²) and 0.17, respectively, for sintered pellets of the latter powder.
A transverse thermoelectric generator (TTEG) consists of alternating layers of a thermoelectric material and a metal tilted at an angle ? relative to the heat flux direction. For building a TTEG, analytical calculations of the maximum figure-of-merit ( ) and the maximum PF as a function of TTEG tilt angle ? and the metal-to-ceramic thickness ratio () were accomplished. From these quick analytical calculations, the optimal values of  and ? for TTEGs with optimal efficiency and output power can be predicted. In addition, 3D FEM simulations of TTEGs and transverse multilayer TEGs (TMLTEGs) were carried out via COMSOL-Multiphysics software to overcome the limitations of the analytical calculations.  In order to verify these analytical calculations and COMSOL simulations, TTEGs of LSCO pellets with screen-printed silver (Ag) layers, and TMLTEGs based on LSCO or CCO green tapes with screen-printed Ag stripes tilted at angle ?, and cofired at 900°C or 920°C, respectively, were fabricated and their thermoelectric performance was measured. Preliminary results of a 5-pellet TTEG with dimensions of 16.4*10.3*3.6 mm³, LSCO thickness of 1.4 mm, Ag layer-thickness of 58 µm, hence =3%, and ?=66°, show an output power of 2.1mW at ΔT=150°C. Moreover, for a TTEG with Ag layer-thickness of 144µm, and =8%, the output power is 3.3mW at ΔT=150°C. Other TTEGs with different LSCO thickness and number of layers are fabricated and tested. Alternatively, a TMLTEG with dimensions of 36.5*3.3*6.3 mm³ based on LSCO tapes with screen-printed Ag stripes tilted at 60° measures an output power of 9.3mW at ΔT=250°C.  These experimentally measured results verify the analytical calculations and COMSOL simulations. This demonstrates that a generator design using the transverse thermoelectric effect and low-performance, but inexpensive thermoelectric oxide materials might prove useful for harvesting electric power in the mW range from temperature gradients.