“Next-Generation Electrocaloric and Pyrocaloric Materials for Solid-State Electrothermal Interconversion” To Be Featured in December 2014 MRS Bulletin
By Giorgina Paiella
a. Pyroelectric effect: a change in the temperature results in a variation in the polarization that generates a pyroelectric current; b. Electrocaloric effect: A change in the applied electric potential from Va to Vb generates an electric field change DE that results in an adiabatic temperature variation DT. c. Polarization (P) – applied electric field (E) response of a ferroelectric material above and below TC. Below TC, there is a hysteretic behavior associated with nucleation and growth of electrical domains. d. The variation of polarization with respect to an applied electric field E of a ferroelectric. The electric field destroys the phase transformation at TC. e. The change in the relative dielectric constant eR as a function of E. The lambda-type anomaly at TC is smeared with the application of theelectric field. f. The Heckmann diagram correlating applied stress s, applied electric field E, and temperature T in a ferroelectric material. D, S, e, eR, p, and CP are the dielectric displacement, entropy, strain, relative dielectric constant, pyroelectric coefficient, and heat capacity at constant pressure, respectively.
MSE Department Head Dr. S. Pamir Alpay, in conjunction with colleagues Dr. Joseph Mantese (MSE Industrial Advisory Board and United Technologies Research Fellow), Dr. Susan Trolier-McKinstry (Pennsylvania State University), Dr. Qiming Zhang (Pennsylvania State University), and Roger W. Whatmore (Imperial College London), has published an article in the forthcoming December 2014 issue of the Materials Research Society (MRS) Bulletin.
The paper, “Next-Generation Electrocaloric and Pyrocaloric Materials for Solid-State Electrothermal Interconversion,” details thin-film electrocaloric and pyroelectric electrothermal interconversion energy sources that have recently emerged as viable and promising for solid-state cooling and power generation. These newer materials are favorable in the conversion of thermal to electrical energy because they support larger electric fields and therefore allow for operation at higher voltages. The authors provide an overview of current state-of-the-art materials, thermodynamic cycles, and future directions for electrothermal interconversion research.
Crystal structures of four most common pyroelectric materials: a. PbTiO3, b. x·Pb(Mg1/3Nb2/3)O3-(1-x)·PbTiO3 (PMN-PT) in the rhombohedral phase, c. LiTaO3, and d. polyvinylidene difluoride(PVDF), -(C2H2F2)n-. The direction of the spontaneous polarization is also shown.