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Novel Ceramic/Metallic Materials October 2015 Viewpoints

Technology Analyst: Nick Evans

Room-Temperature Thermoelectric Record

By Alastair Cunningham
Cunningham is a specialist consultant in nanoelectronics and nanomaterials.

Why is this topic significant?

Thermoelectric materials can convert waste heat into electricity but suffer from issues related to efficiency. Recent research uncovers a novel technique to boost this efficiency significantly.

Description

In June 2015, researchers from the Lawrence Berkeley National Laboratory published the results of their research into a novel method to improve the performance of thermoelectric materials. Thermoelectric materials convert temperature gradients into electric energy or vice versa. The Berkeley Lab technique involved exposing thin films of bismuth telluride to a stream of alpha particles, removing atoms from their locations within the crystal lattice and introducing defects such as vacancies and interstitial atoms. These defects dramatically improve the thermoelectric performance of the material by simultaneously increasing its electrical conductivity by up to 200% and its thermopower (or the Seebeck coefficient) by up to 70%. Normally an improvement in one of these parameters comes at the expense of the other. However, in this case, the researchers were able to improve the overall thermoelectric performance of the material by up to a factor of ten. After undergoing the irradiation procedure, the material exhibited a "figure of merit" (or ZT) of 1.24—the highest rating ever recorded for bismuth telluride at room temperature. The researchers claim that the technique is applicable across a wide range of thermoelectric materials—potentially removing the need for alternative, and more expensive, processing steps.

Implications

Many researchers working in the field of thermoelectrics generally accept that a ZT value of approximately 3 is necessary for an application to be commercially viable. Therefore, the Berkeley Lab material, with a ZT of 1.24, will not immediately find widespread use in any commercial applications. However, this result remains particularly impressive. It signifies the highest achieved ZT for bismuth telluride at room temperature—potentially enabling the use of thermoelectrics in a range of applications in which high temperatures are not present. Perhaps more important, the research also represents a significant step forward in the fundamental understanding of how to optimize the properties of thermoelectric materials, using a single technique to improve two normally anticorrelated parameters. The researchers state that their results "establish the importance of understanding and controlling point defects in thermoelectric materials as an [opportunity] to much improve device performance."

Impacts/Disruptions

Waste heat remains a potentially huge source of untapped energy. The use of thermoelectric materials to exploit this source could have a major impact on the fossil-fuel industry and, indeed, on other energy-harvesting and renewable-energy technologies. A key opportunity area for thermoelectric materials lies in the recovery of waste heat from automotive exhaust systems. All major automotive manufacturers are investigating the implementation of this technology and are likely to bring systems online in the next five to ten years. Other potential applications include cooling devices for, for example, electronics, car seats, or the refrigeration of food. The July 2015 Viewpoints discusses other developments in the commercialization of thermoelectric materials.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: Medium

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 5 Years to 10 Years

Opportunitites in the following industry areas:

Automotive, aerospace, consumer electronics, industrial processing

Relevant to the following Explorer Technology Areas:

Material Advances: Flexible and Stretchable Ceramics

By Alastair Cunningham
Cunningham is a specialist consultant in nanoelectronics and nanomaterials.

Why is this topic significant?

Standard ceramic materials are generally highly brittle—rendering them unsuitable for a wide range of flexible applications. Recent research reveals an inexpensive method to prepare flexible and stretchable bulk ceramic materials that could find use across a range of industrial applications.

Description

In June 2015, researchers from Kiel University published the results of their research into flexible and stretchable ceramics. The scientists fashioned nanoscale ribbon-like tin-oxide-materials components into three-dimensional macroscopic materials that maintain the flexible properties of the original nanoceramics—rendering them of potential use across a wide range of industrial applications. The researchers employ a "flame-transport-synthesis" method to fabricate the bulk networks—essentially "baking" the ceramic precursors into a macroscopic material that is simultaneously electrically conductive and stable at high temperatures and that possesses a "very soft and stretchable architecture." The technique is simple and effective and does not require expensive equipment or high-tech laboratory conditions.

The researchers used a sample of flexible tin oxide to fabricate a portable electronic-sensing device and claim that the tin-oxide networks "show enormous potential for gas/UV sensing." The researchers assert that further applications—beyond sensing—could include "flexible and stretchable electronic devices, luminescent actuators, batteries, smart cloths or sacrificial templates for the growth of new materials."

Implications

Indium tin oxide (ITO) currently dominates the market for transparent conductive films—a necessary component of all touch-screen devices and many photovoltaic applications. However, ITO is expensive and brittle, which means that the material is starting to face stiff competition from flexible alternatives such as graphene, carbon-nanotube films, and conductive polymers. The advent of flexible ceramic networks could mean that yet another material will be vying for market share as flexible electronic applications grow in popularity and gradually become more commercially available. However, ceramic materials possess the additional advantage of being able to withstand high temperatures—making them of particular interest in applications in which high-temperature processing forms a critical step in the fabrication of electronic devices.

The extent to which the Kiel materials find use in commercial processes will largely depend on the overall demand for flexible ceramics and the economics of producing industrial volumes of these materials. However, at the very least, the techniques represent a fundamental breakthrough in materials science that could potentially be of interest across a wide range of industrial sectors.

Impacts/Disruptions

The Kiel University development contributes to a growing body of work that demonstrates that ceramics need not necessarily be brittle and inflexible. Indeed, the November 2014 Viewpoints also discusses research into flexible ceramics and the potential commercialization of these novel materials. Such research is causing a shift in the perception of what a ceramic material actually is and in what situations ceramic materials could potentially find use in commercial applications. However, this technology's achieving commercial maturity, coupled with a wholesale removal of all preconceptions, will probably take a considerable time.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 15 Years

Opportunitites in the following industry areas:

Sensor, display, consumer electronics, textile, portable power

Relevant to the following Explorer Technology Areas: