Transverse thermoelectric multilayer generator with bismuth-substituted calcium cobaltite: Design optimization through variation of tilt angle

Abstract Sintering of Ca 2.7 Bi 0.3 Co 4 O 9 pellets and multilayer laminates at 920 °C results in a ceramic microstructure with low density with a pronounced anisotropy. The electrical conductivity of multilayers is 56 S/cm at 400 K (perpendicular to pressing direction). The Seebeck coefficient is positive, and the power factor increases from 60 μW/(K²m) at 400 K to 200 μW/(K²m) at 900 K. The thermal conductivity (parallel to pressing direction) is 0.65 W/(mK). Transverse multilayer thermoelectric generators (TMLTEG) were fabricated by stacking layers of Ca 2.7 Bi 0.3 Co 4 O 9 green tapes, screen-printing of AgPd stripes at various tilt angle φ relative to the heat flux direction (20°, 45°, and 65°), and co-firing at 920 °C. For φ = 65° the power output is 8 mW at ΔT = 200 K with room temperature at the cold side. FEM modelling as well as analytical calculations agree well with measurements, and the optimum tilt angle is found to be φ = 58°.