Glass‐ceramic composites as insulation material for thermoelectric oxide multilayer generators

Abstract

Thermoelectric generators can be used as energy harvesters for sensor applications. Adapting the ceramic multilayer technology, their production can be highly automated. In such multilayer thermoelectric generators, the electrical insulation material, which separates the thermoelectric legs, is crucial for the performance of the device. The insulation material should be adapted to the thermoelectric regarding its averaged coefficient of thermal expansion α and its sintering temperature while maintaining a high resistivity. In this study, starting from theoretical calculations, a glass-ceramic composite material adapted for multilayer generators from calcium manganate and calcium cobaltite is developed. The material is optimized towards an α of 11 × 10 −6 K −1 (20-500 • C), a sintering temperature of 900 • C, and a high resistivity up to 800 • C. Calculated and measured α are in good agreement. The chosen glass-ceramic composite with 45 vol.% quartz has a resistivity of 1 × 10 7 Ωcm and an open porosity of <3%. Sintered multilayer samples from tape-cast thermoelectric oxides and screen-printed insulation show only small reaction layers. It can be concluded that glass-ceramic composites are a well-suited material class for insulation layers as their physical properties can be tuned by varying glass composition or dispersion phases.

Effect of Reaction Layers on Internal Stresses in Co‐Fired Multilayers of Calcium Manganate and Calcium Cobaltite

“…[ 15 ] The sintered insulation material is composed of 13 wt% celsian, 36 wt% quartz, and 51 wt% residual glass according to quantitative Rietveld method, as published before. [ 14 ]…”

“…[ 13 ] A glass‐ceramic composite suitable as insulation layer between CCO and CMO has also been reported. [ 14 ]…”

Co‐Fired Multilayer Thermoelectric Generators Based on Textured Calcium Cobaltite

“…In multilayer generators in contrast, thin dielectric layers like tailored glasses [15] or glass-ceramics [26] are used to separate the legs. These layers can be as thin as electrically necessary.…”

“…The insulation paste contained a special glass-ceramic composite with high Si content. The coefficient of thermal expansion and the sintering profile of this composite were purposefully adapted to Ca 3 Co 4 O 9 [26] . Screen-printing in an 8fold panel is cost-effective as eight thermoelectric couples are fabricated in one step.…”

A Study on the Effects of La/Sm Codoping on the Structural and High Temperature Thermoelectric Properties of n‐Type CaMnO3−δ Perovskite

“…Recently, the fabrication of unileg n‐type prototype based on Sm‐doped CMO was studied in detail by researchers, [ 8 ] which generated 16 mW with a temperature difference of 360 K and a hot module temperature of 760 K. Based on valence equilibrium, an oxygen vacancy or substitution of RE 3+ ions on Ca 2+ sites will induce Mn 3+ ions and charge carriers, which is responsible for the increase in electrical conductivity through the hopping mechanism. [ 9,10 ] Trivalent doping:Y 3+ , Sm 3+ , [ 11 ] Gd 3+ , [ 12 ] Dy 3+ , La 3+ , Yb 3+ at the Ca site; pentavalent doping: Nb 5 + , V 5+ at the Mn site, hexavalent W 6+[ 13 ] doping at Mn site, and so on, were/are studied/ studying in order to enhance the electrical conductivity of CMO. Ca‐site co‐doping strategy with Dy/Yb, [ 14,15 ] Pr/Yb [ 16 ] Dy/Bi, [ 17 ] Dy/Y [ 18 ] were also tried for the improvement of thermoelectric properties of CMO.…”