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This paper combines experimental and modelling studies to provide a detailed examination of the influence of porosity volume fraction and morphology on the polarisation-electric field response of ferroelectric materials.The broadening of the electric field distribution and a decrease in the electric field experienced by the ferroelectric ceramic medium due to the presence of low-permittivity pores is examined and its implications on the shape of the hysteresis loop, remnant polarisation and coercive field is discussed. The variation of coercive field with porosity level is seen to be complex and is attributed to two competing mechanisms where at high porosity levels the influence of the broadening of the electric field distribution dominates, while at low porosity levels an increase in the compliance of the matrix is more important. This new approach to understanding these materials enables the seemingly conflicting observations in the existing literature to be clarified and provides an effective approach to interpret the influence of pore fraction and morphology on the polarisation behaviour of ferroelectrics. A new general rule to describe the relationship between the polarisation and porosity is also proposed. Such information provides new insights in the interpretation of the physical properties of porous ferroelectric materials to inform future effort in the design of ferroelectric materials for piezoelectric sensor, actuator, energy harvesting, and transducer applications.

This paper reports a new figure of merit for the selection of pyroelectric materials for thermal energy harvesting applications, for example, when the material is exposed to heat or radiation of a specified power density. The figure of merit put forward and developed is of interest to those selecting materials for the design of thermal harvesting devices or the development of novel ceramic, single-crystal and composite materials for pyroelectric harvesting applications.

Domain-engineered relaxor-ferroelectric single crystals with compositions near the morphotropic phase boundary are considered as a key component for modern high-performance piezo-active composites. The advantages of using the relaxor-ferroelectric single crystals of solid solutions of (1 − x)PbIJMg 1/3 Nb 2/3 )O 3 − xPbTiO 3 and (1 − y)Pb(Zn 1/3 Nb 2/3 )O 3 − yPbTiO 3 in piezo-active composites of 2-2 and 1-3 configurations are discussed by taking into account the complex relationships between the outstanding properties of the components and the effective parameters of the composite structure as a whole. Examples of their high piezoelectric activity, strong electromechanical coupling, large piezoelectric anisotropy, and large hydrostatic parameters of the composites demonstrate how the relaxor-ferroelectric single-crystal component improves the effective parameters and promotes the formation of non-monotonic volume-fraction dependences of particular effective parameters that are of interest for a variety of piezotechnical applications, such as transducers, sensors, hydrophones, and energy-harvesting devices. CrystEngCommThis journal is

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