Solid-state material has potential to replace greenhouse gas-powered systems in refrigeration and air conditioning.
Cooling systems, whether in food storage or air conditioning, are generally driven by compressing gases into a liquid state and allowing them to expand, which draws heat in from the environment. This has been a cause of environmental concern for decades: for many years, the working fluids were the cause of atmospheric ozone depletion, and the replacement of these fluids has tended to be low-mass alkanes such as butane and propane, which are flammable and powerful greenhouse gases. A team led by material scientist Xavier Moya of Cambridge University has been working on a replacement for such systems which works by passing an electric current through oxide multilayer capacitors.
In a paper in Nature, Moya and his colleagues describe how they built capacitors consisting of layers of oxides of lead, scandium and tantalum, and explain how these undergo a phase transition when exposed to electric field which draws in heat from the surroundings and causes the largest temperature drop yet observed in a body large enough for cooling applications. This represents an improvement on similar systems that had been investigated containing gadolinium which depends on magnetic fields to induce the phase transition – unlike these, the new material does not need bulky and expensive permanent magnets. “Replacing the heart of prototype magnetic fridges with a material that performs better, and does not require permanent magnets, could represent a game-changer for those currently trying to improve cooling technology,” said co-author Professor Neil Mathur, also of Cambridge.
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As well as eliminating potentially harmful refrigerants, the discovery may be important in reducing the energy requirements of cooling systems.
“When facing a challenge as big as climate change and reducing carbon emissions to net zero, we tend to focus on how we generate energy – and rightly so – but it’s critical that we’re also looking at the consumption of energy,” Moya said. Currently, refrigeration and air conditioning accounts for a fifth of all energy consumption.
The oxide multilayer capacitors are driven by voltage rather than magnetic fields, and this is advantageous in engineering terms, Moya explained.
“Using voltage instead of pressure to drive cooling is simpler from an engineering standpoint, and allows existing design principles to be repurposed without the need for magnets.”
Working with colleagues in Japan and Costa Rica, the Cambridge scientists devised capacitors consisting of layers of the metal oxides, known as PST, interspersed with metallic electrodes.
This helps the PST material withstand higher voltages and produce better cooling over a wider range of temperatures than previous types of oxide multilayer capacitors.
Team now intends to optimise the microstructure of the PST further so that it can withstand even higher voltages and generate better cooling effects.