Tokyo Institute of Technology scientists report in a new study environmentally benign inverse-perovskites with high energy conversion efficiency have potential for practical application as thermoelectric materials (TEMs).
The recent study published in Advanced Science, the researchers presented “inverse”-perovskite-based high ZT TEMs with the chemical formula Ba3BO, where B refers to silicon (Si) and germanium (Ge).
Addressing the limitations typically faced with TEMs, such as insufficient energy conversion efficiency and environmental toxicity due to heavy elements, the new TEMs provide a suitable alternative to TEMs based on toxic elements with better thermoelectric properties than conventional eco-friendly TEMs.
Thermoelectric materials (TEMs) capable of converting thermal energy to electrical energy and vice versa have become an essential part of our world, which needs better waste-energy harvesting systems and cooling systems for electronic gadgets.
The energy conversion efficiency of TEMs depends on a dimensionless figure of merit (ZT), which is a product of two different factors: the inverse of thermal conductivity (k) and the power factor (PF).
A high-performance TEM exhibits a high ZT if it possesses low k and high PF. Over the years, scientists developed several high-performance heavy metal chalcogenide-based TEMs, such as Bi2Te3 and PbTe, that fulfill these criteria.
While these materials were ideal for energy conversion, they were toxic to the environment and the health of living organisms – they contained toxic heavy elements, such as lead (Pb) and tellurium (Te), which limited their practical applications.
On the other hand, although oxide-based TEMs, such as SrTiO3, have several advantages of non-toxicity and abundant natural resources, their ZT has been limited due to their high k.
To address this, a research team led by Associate Professor Takayoshi Katase from Tokyo Institute of Technology explored efficient yet environmentally benign toxic-element-free TEMs.
Dr. Katase, elaborating on the standout properties of the materials explained, “Unlike normal perovskites, such as SrTiO3, the positions of cation and anion sites are inverted in inverse-perovskites Ba3BO. So, they contain a large amount of the heavy element, Ba, and their crystal structure is formed by a soft flamework made up of weak O-Ba bonds. These characteristics realize the low k in inverse-perovskites.”
The research team clarified the synthesized bulk polycrystals of Ba3BO possess extremely low k of 1.0-0.4 W/mK at a T of 300-600 K, which is lower than those of Bi2Te3 and PbTe bulks.
As a result, the Ba3BO bulks exhibit rather high ZT of 0.16-0.84 at T = 300-623 K. Additionally to the promising experimental results, the team carried out theoretical calculations which predicted a potential maximum ZT of 2.14 for Ba3SiO and 1.21 for Ba3GeO at T = 600 K by optimizing hole concentration.
The maximum ZT of these non-toxic TEMs is much higher than that of other eco-friendly TEMs and comparable to the toxic heavy element ones in the same temperature range.
In addition, the team clarified that the high ZT of Ba3BO is due not only to its low k but also its high PF: B ion, which usually behaves as a positively charged cation but as a negatively charged anion in Ba3BO. The B anions are responsible for the carrier transport, which achieves high PF.
In summary, this study validates the potential of the newly designed Ba3BO as a high-performing and eco-friendly alternative to conventional toxic, heavy element-based TEMs. The results establish inverse-perovskites as a promising option for developing advanced environmentally benign TEMs.
In that regard, Dr. Katase concluded, “We believe that our unique insight into designing high ZT materials without using toxic elements would have a strong impact on the materials science and chemistry communities as well as among innovators looking to expand the horizon of thermoelectric material applications beyond laboratories into our everyday life.”
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That’s a pretty technical press release. But even a newbie can get through it with quite a knowledge gain by just treading slowly and keeping track of the terms.
One might also begin to suspect, as others following this study find similar or perhaps better innovative results, that this team might have hit a breakthrough.
For thermoelectric and heat harvesting a breakthrough would surely be welcome news. Lets hope others follow on with this work with even more insight, intellect, and creativity.
By Brian Westenhaus via New Energy and Fuel
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