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Consecutive stochastic 90° polarization switching events, clearly resolved in recent experiments, are described by a new nucleation and growth multi-step model. It extends the classical Kolmogorov-Avrami-Ishibashi approach and includes possible consecutive 90°-and parallel 180°-switching events. The model predicts the results of simultaneous time-resolved macroscopic measurements of polarization and strain, performed on a tetragonal Pb(Zr,Ti)O3 ceramic in a wide range of electric fields over a time domain of five orders of the magnitude. It allows the determination of the fractions of individual switching processes, their characteristic switching times, activation fields, and respective Avrami indices.

Domain wall motion in ferroics, similar to dislocation motion in metals, can be tuned by well‐concepted microstructural elements. In demanding high‐power applications of piezoelectric materials, the domain wall motion is considered as a lossy hysteretic mechanism that should be restricted. Current applications for so‐called hard piezoelectrics are abundant and hinge on the use of an acceptor‐doping scheme. However, this mechanism features severe limitations due to enhanced mobility of oxygen vacancies at moderate temperatures. By analogy with metal technology, the authors present here a new solution for electroceramics, where precipitates are utilized to pin domain walls and improve piezoelectric properties. Through a sequence of sintering, nucleation, and precipitate growth, intragranular precipitates leading to a fine domain structure are developed as shown by transmission electron microscopy, piezoresponse force microscopy, and phase‐field simulation. This structure impedes the domain wall motion as elucidated by electromechanical characterization. As a result, the mechanical quality factor is increased by ≈50% and the hysteresis in electrostrain is suppressed considerably. This is even achieved with slightly increased piezoelectric coefficient and electromechanical coupling factor. This novel process can be smoothly implemented in industrial production processes and is accessible to simple laboratory experimentation for microstructure optimization and implementation in various ferroelectric systems.

Ferroelectrics are a technologically important class of materials, used in actuators, sensors, transducers, and memory devices. Introducing porosity into these materials offers a method of tuning functional properties for certain applications, such as piezoand pyroelectric sensors and energy harvesters. However, the effect of porosity on the polarization switching behaviour of ferroelectrics, which is the fundamental physical process determining their functional properties, remains poorly understood. In part, this is due to the complex effects of porous structure on the local electric field distributions within these materials. To this end, freeze cast porous lead zirconate titanate ceramics were fabricated with highly oriented, anisometric pores and an overall porosity of 34 vol.%. Samples were sectioned at different angles relative to the freezing direction and the effect of pore angle on the switching behaviour was tracked by simultaneously measuring the temporal polarization and strain responses of the materials to high voltage pulses. Finite element modelling was used to assess the effect of the pore structure on the local electric field distributions within the material, providing insight into the experimental observations. It is shown that increasing the pore angle relative to the applied electric field direction decreases the local electric field, resulting in a reduced domain wall dynamic and a broadening of the distribution of switching times. Excellent longitudinal piezoelectric (d33 = 630 pm/V) and strain responses (Sbip = 0.25% and Sneg = 0.13%, respectively), comparable to the dense material (d33 = 648 pm/V, Sbip = 0.31% and Sneg = 0.16%), were found in the PZT with anisometric pores aligned with the poling axis. Orienting the pores perpendicular to the poling axis resulted in the largest reductions in the 2 effective permittivity (𝜀 33 𝜎 = 200 compared to 𝜀 33 𝜎 = 4100 for the dense at 1 kHz), yielding the highest piezoelectric voltage coefficient (g33 = 216 x 10 -3 Vm/N) and energy harvesting figure of merit (d33g33 = 73 x 10 -12 m 2 /N). These results demonstrate that a wide range of application-specific properties can be achieved by careful control of the porous microstructure. This work provides a new understanding of the interplay between the local electric field distribution and polarization reversal in porous ferroelectrics, which is an important step towards further improving the properties of this promising class of materials for sensing, energy harvesting, and low-force actuators.

Highly (100),(001)-oriented (Ba0.85Ca0.15)TiO3 (BCT) lead-free piezoelectric ceramics were fabricated by the reactive templated grain growth method using a mixture of plate-like CaTiO3 and BaTiO3 particles. Piezoelectric properties of the ceramics with a high degree of texture were found to be considerably enhanced compared with the BCT ceramics with a low degree of texture. With increasing the Lotgering factor from 26% up to 94%, the piezoelectric properties develop towards the properties of a single crystal. The dynamics of polarization switching was studied over a broad time domain of 8 orders of magnitude and was found to strongly depend on the degree of orientation of the ceramics. Samples with a high degree of texture exhibited 2–3 orders of magnitude faster polarization switching, as compared with the ones with a low degree of texture. This was rationalized by means of the Inhomogeneous Field Mechanism model as a result of the narrower statistical distribution of the local electric field values in textured media, which promotes a more coherent switching process. The extracted microscopic parameters of switching revealed a decrease of the critical nucleus energy in systems with a high degree of texture providing more favorable switching conditions related to the enhanced ferroelectric properties of the textured material.

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Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used to investigate the electric conduction at nominally neutral domain walls in hexagonal manganites. The EFM measurements reveal a propensity of mobile charge carriers to accumulate at the nominally neutral domain walls in ErMnO3, which is corroborated by cAFM scans showing locally enhanced d.c. conductance. Our findings are explained based on established segregation enthalpy profiles for oxygen vacancies and interstitials, providing a microscopic model for previous, seemingly disconnected observations ranging from insulating to conducting domain wall behavior. In addition, we observe variations in conductance between different nominally neutral walls that we attribute to deviations from the ideal charge-neutral structure within the bulk, leading to a superposition of extrinsic and intrinsic contributions. Our study clarifies the complex transport properties at nominally neutral domain walls in hexagonal manganites and establishes new possibilities for tuning their electronic response based on oxidation conditions, opening the door for domain-wall based sensor technology.