IMF2017

Ferroelectric thin films have been the focus of significant research on understanding and improving their pyroelectric/electrocaloric performance. The standard characterization method for these materials is the isothermal hysteresis loop, from which the pyroelectric coefficient can be extracted. The electrothermal conversion performance is subsequently calculated using Maxwell’s relations. Using direct measurement of the pyroelectric response, we find the isothermal hysteresis loop to incorrectly predict the response of three ferroelectric materials systems: a standard ferroelectric lead zirconate titanate (PZT) thin film, an antiferroelectric (AFE) PZT thin film, and a PZT thin film with an interposed hafnia buffer layer. The pyroelectric coefficient is extracted by measuring the current response to pulsed laser heating at a frequency of 1 kHz superimposed over an applied triangle wave electrical bias at 1 Hz, creating a pyroelectric hysteresis loop. When this technique is applied to a standard PZT thin film, we find that the pyroelectric response to electric field is underestimated by the coefficient calculated from isothermal hysteresis loops. In the case of the AFE film, the inverse pyroelectric response at low fields is dramatically over-estimated by the isothermal method. These results are confirmed by energy conversion experiments at different fields. Finally, films with an interposed buffer layer have a unique charging method, which masks the real pyroelectric response of these films. We will discuss the implications of this work on electrothermal conversion performance and techniques for measuring the pyroelectric response moving forward.