PZT: electric cooling
A new material has been developed by a team of Cambridge scientists that turns cold at the press of a button. They have found a ceramic material that has a giant electrocaloric effect; 100 times larger than that seen in the 1960s when this principle was first discovered. The material is a variant of lead zirconate titanate or PZT. It is a hard, crystalline piezoelectric solid which when squeezed, creates an electric field within. In order to obtain an electrocaloric effect, a material that undergoes an abrupt change of its crystal structure at a particular temperature, i.e. a phase change, is needed. In PZT, the temperature of this phase change can be altered by an electric field. This means that close to the phase change, an electric field can pull the atoms in the crystal lattice into a low-energy state, allowing them to suck energy into the lattice and in doing so produce cooling. The electrocaloric effect is very similar to the pyroelectric effect where warming is used to create an electric field. The scientists found that by applying 25 volts to a film of zirconium-rich PZT a third of a micrometer thick, they could reduce its temperature by 12°C. This effect could be used to make a heat pump for refrigeration. Further research is required however given that the strongest electrocaloric effect only occurs at temperatures around 220°C. Scientists are now looking for alternatives that work well closer to room temperature.