Electrocaloric effects in multilayer capacitors of stoichiometric lead scandium tantalate with varying B‑site cation order

Multilayer capacitors (MLCs) of stoichiometric lead scandium tantalate (PbSc0.5Ta0.5O3 or PST) have been shown to generate large thermal changes (known as electrocaloric, or EC, effects) in response to large changes in applied electric fields sustained without breakdown. These MLCs represent a solid‑state, more efficient and eco‑friendly alternative to fluid refrigerants used in vapour‑compression coolers currently employed to satisfy the vast majority of the world’s demands for small‑ and large‑scale cooling. The discussion begins with the origins of EC effects, their practical use and a brief history of research into EC materials, followed by the introduction of MLCs as macroscopic EC bodies, and a summary of the effects of B‑site cation ordering on EC effects in PST. Basic heat flow dynamics and concomitant thermal boundary conditions are then summarised in the context of experimental techniques that can be employed for the evaluation of EC effects in bulk and MLC bodies. This dissertation covers EC effects in MLCs of stoichiometric PST with various degrees of B‑site cation ordering measured via direct, quasi‑direct and indirect methods under (highly) isothermal and (highly) adiabatic conditions. For annealed MLCs of 0.9PST, in which large temperature changes have been previously driven over a wide range of temperatures using supercritical fields, EC effects are measured by direct isothermal calorimetry. MLCs of 0.6PST are then shown to have qualitatively similar first‑order phase transitions without significant loss of EC performance, and without the energetically expensive anneal required to achieve high B‑site ordering. For 0.4PST and 0.5PST with even less order, it is shown that large EC effects can also be driven over wide temperature ranges without the need for supercritical fields. Additionally, it is demonstrated that the order parameter for PST can be internally inhomogeneous, with implications for measured EC effects.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Farenkov, Vladimir

Advisor dc:contributor.advisor

• Mathur, Neil

• calorimetry
• electrocaloric
• lead scandium tantalate
• multilayer capacitors
• thermometry

Licence

• https://www.repository.cam.ac.uk/bitstreams/f9d063b2-07c7-4a8f-a3af-2160cafbb23a/download
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

eng

Author Identifier

0000-0003-3234-3457

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/393176