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Pyroelectric and electrocaloric characterization has been determined for 0.75Pb(Mg1∕3Nb2∕3)O3–0.25PbTiO3 relaxor based single crystal and ceramic. Differential scanning calorimetry was used for measuring the electrocaloric response for different electric fields in the vicinity of the Curie temperature. For both ceramic and crystals the maximum activity is found to be around the transition temperature. On the other hand hysteresis loops for different temperatures were used to predict the electrocaloric effect with very good qualitative agreements with direct measurements. Pyroelectric coefficient is found to be much larger for ⟨111⟩ single crystals reaching 1300×10−6Cm−2K−1 whereas the ceramic reaches only 750×10−6Cm−2K−1. Higher pyroelectric coefficient and lower dielectric permittivity lead to outstanding figures of merits for sensors and energy harvesting, with a gain of 260% for voltage responsivity and more than 500% for energy harvesting. Although having a much larger pyroelectric activity, the electrocaloric effect is about the same for crystals and ceramics—around 0.40J∕g for 2.5kV∕mm electric field step. This result is interpreted by the decrease of the pyroelectric coefficient for high electric field. The electrocaloric activity is in fact limited by the saturation polarization and difference between Curie transition temperature and the working temperature. Those two parameters are very similar for crystals and ceramics. Single crystals are consequently very interesting materials in the framework of energy harvesting and sensor applications whereas no real improvement of performances can be expected for electrocaloric refrigeration devices.

This article reviews the developments in electrostrictive polymers for energy harvesting. Electrostrictive polymers are a variety of electroactive polymers that deform due to the electrostatic and polarization interaction between two electrodes with opposite electric charge. Electrostrictive polymers have been the subject of much interest and research over the past decade. In earlier years, much of the focus was placed on actuator configurations, and in more recent years, the focus has turned to investigating material properties that may enhance electromechanical activities. Since the last 5 years and with the development of low-power electronics, the possibility of using these materials for energy harvesting has been investigated. This review outlines the operating principle in energy scavenging mode and conversion mechanisms behind this generator technology, highlights some of its advantages over existing actuator technologies, identifies some of the challenges associated with its development, and examines the main focus of research within this field, including some of the potential applications. KEYWORDS: actuators; dielectric properties; electrostrictive polymers; energy harvesting; ferroelectricity; nanoparticles INTRODUCTION The performance of energy harvesters is directly linked to the efficiency of the mechanical-electrical conversion within the active materials. For piezoelectric materials, the efficiency of the conversion can be estimated with the help of the coupling coefficient. For a given vibration mode, this coefficient expresses the ratio of the converted energy to the input one. Another key point for electroactive materials concerns the easiness of their integration within the whole structure.

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