Ba_1/3CoO₂: A Thermoelectric Oxide Showing a Reliable ZT of ∼0.55 at 600 °C in Air

Abstract

Thermoelectric energy conversion technology has attracted attention as an energy harvesting technology that converts waste heat into electricity by means of the Seebeck effect. Oxide-based thermoelectric materials that show a high figure of merit are promising because of their good chemical and thermal stability as well as their harmless nature compared to chalcogenide-based state-of-the-art thermoelectric materials. Although several high-ZT thermoelectric oxides (ZT > 1) have been reported thus far, the reliability is low due to a lack of careful observation of their stability at elevated temperatures. Here, we show a reliable high-ZT thermoelectric oxide, Ba1/3CoO2. We fabricated Ba1/3CoO2 epitaxial films by the reactive solid-phase epitaxy method (Na3/4CoO2) followed by ion exchange (Na+ → Ba2+) treatment and performed thermal annealing of the film at high temperatures and structural and electrical measurements. The crystal structure and electrical resistivity of the Ba1/3CoO2 epitaxial films were found to be maintained up to 600 °C. The power factor gradually increased to ∼1.2 mW m–1 K–2 and the thermal conductivity gradually decreased to ∼1.9 W m–1 K–1 with increasing temperature up to 600 °C. Consequently, the ZT reached ∼0.55 at 600 °C in air.

Fabrication and Thermoelectric Properties of Freestanding Ba1/3CoO2 Single-Crystalline Films

“…Because Ba 1/3 CoO 2 epitaxial films exhibit good electron transport properties in the in-plane direction, κ must be measured in the in-plane direction to extract ZT . Previously, we used the TDTR method to measure the out-of-plane κ of the Ba 1/3 CoO 2 epitaxial films with two different crystallographic orientations: a c -axis orientation and a 55°-inclined c -axis. , Using these two out-of-plane κ data, we extracted the in-plane κ theoretically . It is very important that the κ value of the freestanding Ba 1/3 CoO 2 single-crystalline film measured using the AC calorimetric method agrees well with the κ value of the Ba 1/3 CoO 2 epitaxial film measured using the TDTR method.…”

“…Ba 1/3 CoO 2 exhibited metallic p-type conductivity up to 600 °C in air. Recently, we found that Ba 1/3 CoO 2 epitaxial films exhibit a large ZT of 0.11 at room temperature and 0.55 at 600 °C . These values are the highest among reliable oxide thermoelectric materials and are comparable to those of commercially available p-type PbTe and SiGe .…”

Boosted Output Voltage of BiSbTe‐Based Thermoelectric Generators via Coupled Effect between Thermoelectric Carriers and Triboelectric Charges

“…[12,13] For sustainable generation of the power required in practical environments, hybrid and multisource energy-harvesting technologies have attracted substantial attention for their ability to continuously harvest energy and increase power output. [14][15][16][17] Among the energy harvesting technologies that have been reported thus far, TEGs have a number of advantagesincluding simplicity, [18,19] minimal maintenance requirements, [20,21] low cost, [22,23] and reliability, [24,25] that make them a good solution for sustainable power supply from waste heat sources. [26,27] From micro-electronics to industrial furnaces, numerous types of waste heats ranging from room temperature to high temperature (>600 °C) can be recovered into electricity by thermoelectric power generators depending on the materials.…”

“…Among the energy harvesting technologies that have been reported thus far, TEGs have a number of advantages—including simplicity, [ 18,19 ] minimal maintenance requirements, [ 20,21 ] low cost, [ 22,23 ] and reliability, [ 24,25 ] that make them a good solution for sustainable power supply from waste heat sources. [ 26,27 ] From micro‐electronics to industrial furnaces, numerous types of waste heats ranging from room temperature to high temperature (>600 °C) can be recovered into electricity by thermoelectric power generators depending on the materials.…”

Contact/Noncontact‐Mode Thermoelectric Characteristics of Polytriarylamine/Lewis Acid Complex Films in Horizontal Device Geometry

“…[5][6][7][8] Such inorganic thermoelectric materials need a high-temperature process (≥600 °C) and basically possess rigid and hard characteristics leading to very limited flexibility even in thin films. [8][9][10][11] To apply TEDs for various heat sources with curved surfaces including human skins, pipes, vehicles, etc., thermoelectric materials should have high flexibility and can be processed at low temperatures. [12,13] Although conventional inorganic materials can be formed on a flexible substrate or elastomeric frame, the resulting bulky TED modules have a restriction in practical uses.…”