Ultimate electromechanical energy conversion performance and energy storage capacity of ferroelectric materials under high excitation levels

Abstract

In the framework of piezoelectric energy harvesting, this work focused on the quantification of the ultimate energy conversion capability of various ferroelectric ceramics and single crystals. Energy conversion was achieved by the application of Ericsson cycles under high electric field and mechanical stress. The main aim of this approach was to experimentally apply the electromechanical Ericsson cycles on several key materials. This process was decomposed into four steps, which consisted of applying and removing an electric field under constant stress and stress application/removal under a constant electric field. In this work, ferroelectric ceramics—hard PZT C203, medium PZT C6, soft PZT C9, and single crystal PMN-25PT and PZN-8PT—and paraelectric ceramic PMN 15 were tested. The PMN-25PT and PZN-8PT ferroelectric single crystals exhibited higher energy conversion potential than the ceramics in the ferroelectric and paraelectric phases. However, the soft PZT C9 ceramic (107.6 mJ/cm3) was comparable to single crystal PMN-25PT (118.7 mJ/cm3). Considering the cost and fabrication process, PZT C9 is an excellent candidate for practical applications. A simple yet accurate experimental estimation of the energy density of the materials based on the bipolar hysteresis curves under compressive stresses of 1 and 100 MPa was also proposed. The estimated energy densities were similar to the real Ericsson cycles. The energy storage capacity of these materials was also analyzed. The PMN 15 ceramic in the paraelectric phase had the highest stored energy, and in the paraelectric phase, PMN 15 had a maximum stored electrical energy of 87 mJ/cm3 under a static stress value of 1 MPa, which was increased to 105 mJ/cm3 under a static stress value of 100 MPa. Ultimately, this study allowed for the evaluation of the maximal energy conversion capabilities of several classes of electroactive materials, highlighting their potential in terms of their target applications and operative environments (such as the maximal stress or electric field).