Metrology of the electrocaloric effect based on an infrared imaging technique

Abstract

In recent years the electrocaloric effect has gained the substantial interest of researchers due to its potential applications in commercial cooling. The high theoretical effciency of electro-thermal conversion places this phenomenon as a potential alternative to commercial vapour-compression refrigerators. Success in such solid state cooling is anticipated to lead to global scale energy savings and reduction in the emission of greenhouse gases. Most of the focus has been directed towards the achievement of high values of the electrocaloric effect temperature change ∆T EC . High values of around 10 K and more have been reported. However little attention has been given to the methods of measurements and their uncertainties. This work aims to use a metrological approach to study the electrocaloric phenomenon, to compare certain methods and to explore these measurements and their uncertainties. There are various ways to quantify the electrocaloric effect and various parameters infuence the direct measurements of ∆T EC . Here a direct method using infrared imaging is employed for the spatial and time-resolved temperature measurements of electrocaloric bodies. A set of the parameters infuencing the∆T EC is determined. Based on these quantifed contributions, an uncertainty for such measurements is reported. The calibration of the imager is performed to validate the traceability of measurements, and a further set of characterisation apparatus was implemented to establish its performance. A bulk Ba 0.65 Sr 0.35 TiO 3 sample was employed as a cross reference specimen in an inter-laboratory comparison involving infrared imaging and two types of differential scanning calorimetry. Within the scope of this work, two commercial ceramic material compositions were characterised; a multilayer capacitor and a PMN-PT ceramic. First, BaTiO 3 in form of a multilayer ceramic capacitor was used to establish the optimal performance of such a structure and to investigate the in-situ measurements. In this measurement there were substantial differences in ∆T EC depending on where on the sample (surface vs. interior) the measurement was made and an explanation for this difference is suggested. Second, the polycrystalline Pb(Mg 1/3 Nb 2/3 )−PbTiO 3 ceramic sample was used investigate other sources of uncertainties arising from the mechanical coupling during electrocaloric measurements, estimated to account for up to 20% of the observed electrocaloric effect.