Ferroelectric Property Measurements
Ferroelectric properties such as polarization and dielectric response as function of temperature and electric field are critical parameters for discovery of new electrocaloric materials.
Ferroelectrics is a core area of expertise at Penn State, which is critical to the discovery and development of advanced electrocaloric materials. The electrocaloric effect takes advantage of characteristic electrical behaviors. In order to make electrocaloric refrigeration attractive, consortium researchers identify ferroelectric polymers and ceramics that show the highest possible rates of change of polarization with temperature and that retain these high rates in strong electric fields at or near the temperature of interest. Strong electrocaloric effects occur when a ferroelectric material is toggled between a state with low polarization in a zero electric field and another state where the polarization is drastically and rapidly increased by the action of the field. The low polarization state can be either a disordered one (aka paraelectric) or another ordered state, for example, anti-ferroelectric. The high polarization state is usually ferroelectric, where the majority, if not all, individual ferroelectric moments are oriented in nearly the same direction inside tiny regions called ferroelectric domains.
Measurements of polarization as a function of temperature and/or electric field are relatively fast and highly accurate. Sets of data, which are essentially electrical fingerprints of a material, are then converted into reliable electrocaloric effect data, namely the entropy change. This serves as the first indication of whether or not the material has a potential for future use in an electrocaloric cooling or heat pumping device.
The PE system is intended to measure the polarization of materials induced by an electric field. The typical covered ranges are, frequency from 1 mHz to 1 kHz, charge from ~10 pc to 100 µc, and voltage from 0 to ± 30 kV. In most cases the PE measurements can be made over a temperature range of -100°C to +180°C.
Dielectric constant is another important parameter for electrocaloric material. Multiple system configurations exist to measure dielectric constant at discrete or swept frequency ranges with or without temperature and/or large AC/DC voltages. Covered ranges include 1mHz to 10s of MHz, <1V AC to 1kV AC, +/- 4kV DC, and -180°C to +750°C.
Bret Neese, Baojin Chu, Sheng-Guo Lu, Yong Wang, E. Furman, and Q. M. Zhang, "Large Electrocaloric Effect in Ferroelectric Polymers Near Room Temperature," Science, 321, 821-823 (2008). http://science.sciencemag.org/content/321/5890/821
Xiaoshi Qian, Shan Wu, Eugene Furman, Ji Su, and Q. M. Zhang, "Ferroelectric polymers as multi-functional electroactive materials: Recent advances, Potentials, and Challenges," MRS Communications, 5, 115 (2015). https://www.cambridge.org/core/journals/mrs-communications/article/ferroelectric-polymers-as-multifunctional-electroactive-materials-recent-advances-potential-and-challenges/B74884637DF5C8E986C32ECADC8275BD