From heat to electrical energy thanks to perovskites

Scientists from Tokyo Institute of Technology Reversible perovskites, which are environmentally friendly and have high energy conversion efficiency, have the potential for practical application as thermoelectric materials (TEMs), a new study reported. Then perovskite, which is typically used to produce photovoltaic films. It can also be used, in some forms, to generate electricity from thermal energy.

Such a material would allow thermal energy to be used to produce electricity without going through complex conversion systems such as steam turbines. Waste heat from thermal heating systems, even domestic ones, can easily be converted into electricity.

In a recent study published in AAdvanced scienceThe researchers presented “reversible” high-ZT perovskite-based GSTs with the chemical formula Ba3BO, where B stands for silicon (Si) and germanium (Ge).
By addressing the typical limitations of TSOs, such as insufficient energy conversion efficiency and environmental toxicity due to heavy elements, the new TSOs represent a suitable alternative to TSOs based on toxic elements with better thermoelectric properties than traditional green TSOs.

Thermoelectric materials (GSTs) that can convert thermal energy into electrical energy and vice versa have become an essential part of our world, which needs better systems for collecting waste energy and cooling systems for electronic gadgets.

The power conversion efficiency of TSGs depends on the dimensionless figure of merit (ZT), which is the product of two different factors: the inverse of the thermal conductivity (k) and the power factor (PF).

A high-performance GST has a high ZT if it has low k and high PF. Over the years, scientists have developed several high-performance GSTs based on heavy metal chalcogenides, such as Bi2Te3 and PbTe, that meet these criteria.

Although ideal for energy conversion, these materials were toxic to the environment and to the health of living organisms: they contained heavy toxic elements, such as lead (Pb) and tellurium (Te), which limited their practical applications.

On the other hand, although oxide-based GSTs, such as SrTiO3, have many advantages, such as non-toxicity and abundant natural resources, their ZT was limited by the high k.

To solve this problem, a research team led by Associate Professor Takayoshi Katase from Tokyo Institute of Technology explored effective TSGs that are free of toxic elements and can therefore be used in daily life without particular problems.

Explaining the properties of the materials, Dr. Katasi explained: “Unlike ordinary perovskites, such as SrTiO3, the positions of the cation and anion sites are reversed in the reversed perovskite Ba3BO. Therefore, it contains a large amount of the heavy element Ba, and its crystal structure consists of a smooth flame consisting of weak O-Ba bonds. These properties realize the low k of inverse perovskite“.

The research team demonstrated that the synthesized bulk Ba3BO crystals possess an extremely low k of 1.0-0.4 W/m K at T 300-600 K, lower than Bi2Te3 and PbTe LEDs.
As a result, the Ba3BO LEDs showed a fairly high ZT of 0.16-0.84 at T = 300-623 K. In addition to the promising experimental results, the team performed theoretical calculations that predicted a possible maximum ZT of 2.14 for Ba3SiO and 1.21 for Ba3GeO at T = 600 K by improving hole focusing.

The maximum ZT of this non-toxic GST is much higher than that of other environmentally friendly GST and is comparable to that of toxic GST with heavy elements in the same temperature range.

Furthermore, the team showed that the higher ZT of Ba3BO is due not only to lower k but also to higher PF: the B ion, which normally behaves as a positively charged cation, in Ba3BO is a negatively charged anion. B anions are responsible for carrier transport, which achieves high PF.

In summary, this study investigates the potential of the newly developed Ba3BO as a high-performance, environmentally friendly alternative to toxic and heavy traditional GST. The results demonstrate that reversible perovskite is a promising option for developing advanced environmentally friendly GST.

In this regard, Dr. Katasi concluded: “We believe that our unique vision in designing high-ZT materials without the use of toxic elements has a strong impact on the materials science and chemistry communities, as well as innovators who seek to expand the horizon of applications of thermoelectric materials beyond laboratories to everyday life.”