PMN-8PT device structures for electrocaloric cooling applications

Abstract

Based on fundamental research carried out on PMN-8PT bulk ceramics, screen-printed thick films and multilayer ceramic (MLC) structures have been developed. The influence of device design on the microstructural, dielectric, ferroelectric and electrocaloric properties has been investigated in detail. MLC structures turned out to be promising candidates for implementation into electrocaloric cooling systems providing large refrigerant volume and low single layer thickness. The latter allows for the application of high electric fields under low operation voltages. An electrocaloric temperature change of DT = 0.21 K was measured directly, by application/withdrawal of an electric field ofDE = 2.1 kVmm-1

Effect of inactive volume on thermocouple measurements of electrocaloric temperature change in multilayer capacitors of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3

“…Using the heat capacity and density values that we reported previously [25], the maximum value of |ΔT j | ~ 2.7 K corresponds to an isothermal heat of ~0.19 J, or 918 J kg −1 when normalized by the mass of the active region. The EC properties of our MLCs compare favourably with respect to the EC properties of PMN-PT layers of similar or greater thickness, as found in MLCs [18,19] and bulk samples [4], respectively (table 2). Detailed comparison with these other MLCs is not straightforward due to differences in MLC structure, but our maximum values of |ΔT j | ~ 2.7 K and |ΔE| = 28.8 V µm −1 exceed the values recorded for these other MLCs.…”

“…Table 2. EC temperature change |ΔT | for MLCs and bulk samples of 0.9PMN-0.1PT (0.92PMN-0.08PT in [18] a Denotes data obtained after multiplying the measured temperature change by a 'correction' factor of 2.86.…”

“…Here we investigate how thermocouple measurements of EC temperature change are influenced by the active/total volume ratio, using MLCs of (1 − x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT, x ~ 0.1), which is known to be a good EC material based on studies of thin films [11], bulk samples [21][22][23] and MLCs [17][18][19]. We find that rapidly driven EC effects are highly adiabatic if measured near MLC face centres that lie sufficiently far from the inactive EC material.…”

Direct Measurement of the Electrocaloric Temperature Change in Multilayer Ceramic Components using Resistance‐Welded Thermocouple Wires

“…However, while the first two require expensive technical equipment and meticulous calibration, the latter is accompanied with high preparation efforts of each specimen. Other methods using thermo‐electrical transducers such as thermistors, sheath thermocouples, or unhoused thermocouples are easy to apply, but are not fast enough with respect to heat exchange towards the inactive regions or absorb to much heat themselves and lead thus to erroneous results. Furthermore, heat transfer into the temperature sensing element might be critical due to an undefined thermal contact to the specimen when the temperature sensor, for instance, is simply taped onto the MLC .…”

“…measured on MLC with 39 μm and 2 μm ceramic layer and electrode thickness, respectively, published by Molin et al . For the latter, MLC design presented by Molin and Gebhardt with outer lateral dimension 17.8 mm×8.1 mm and active region of 14.6 mm×7.4 mm are used.…”