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Abstract: The occurrence of the inverse (or negative) electrocaloric effect, where the isothermal application of an electric field leads to an increase in entropy and the removal of the field decreases the entropy of the system under consideration, is discussed and analyzed. Inverse electrocaloric effects have been reported to occur in several cases, for example, at transitions between ferroelectric phases with different polarization directions, in materials with certain polar defect configurations, and in antiferroelectrics. This counterintuitive relationship between entropy and applied field is intriguing and thus of general scientific interest. The combined application of normal and inverse effects has also been suggested as a means to achieve larger temperature differences between hot and cold reservoirs in future cooling devices. A good general understanding and the possibility to engineer inverse caloric effects in terms of temperature spans, required fields, and operating temperatures are thus of fundamental as well as technological importance. Here, the known cases of inverse electrocaloric effects are reviewed, their physical origins are discussed, and the different cases are compared to identify common aspects as well as potential differences. In all cases the inverse electrocaloric effect is related to the presence of competing phases or states that are close in energy and can easily be transformed with the applied field. [ABSTRACT FROM AUTHOR]

Abstract: The impact of charged point defects on the electrocaloric response of morphotropic Pb(Zr,Ti)O3 (PZT) ceramics is investigated using direct electrocaloric and polarization hysteresis measurements. The electrocaloric response determined for undoped, hard‐, and soft‐doped PZT is rationalized by considering the dipolar entropy change over polarization change and hysteresis losses. The highest electrocaloric effect is observed in poled hard PZT with the field applied along the poling direction, which is related to the reduced hysteresis losses caused by internal electric fields associated with defect complexes. The weak hysteretic dependency of polarization as function of the electric field in hard PZT also allows inducing an inverse electrocaloric effect. The experimental results are compared with model calculations that provide a physical interpretation. The results reveal how the electrocaloric response of ferroelectrics can be optimized by defect engineering. [ABSTRACT FROM AUTHOR]

Dynamic modeling of all-solid-state batteries (SSBs) has gained strong research interest in recent years. However, the intrinsic equilibrium state, important for the exchange current calculation and the interface resistance analysis is hardly addressed. For the first time, we introduce an advanced MPNP-FBV model which takes the electrical double layer (EDL) structure and the unoccupied regular lattice sites (vacancies) into account to illustrate the fundamental phenomena at the equilibrium state. This general model is verified from the chemical perspective and the interface experimental results in our previous investigations, which indicates that the model is able to calculate the exchange current and the charge transfer resistance from fundamental material properties. The influence on concentration and electrostatic potential by the different EDL structures, the state of charge (SOC) and the diffusivity are also investigated. Results show that the total electrostatic potential drop at the equilibrium state is related to the free enthalpy difference between the two materials. Furthermore, the charge transfer resistance with the diffuse double layer structure is higher than that with the compact double layer. • An advanced general model for all-solid-state batteries is introduced. • The vacancy effect in solid material and kinetic reaction is presented. • Different electrical double layer structures are analyzed. • The free enthalpy difference of materials is discussed. [ABSTRACT FROM AUTHOR]

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