A range of partial top full bottom electrodes are used to explore the use of bi-polar Polarisation-Electric field (P–E) measurements to quantify recoverable energy (Wrec), energy loss (Wloss) and the efficiency (η) of ferroelectric BaTiO3 ceramics. The values obtained are dependent on the ratio of sample thickness (S) and top contact radius (r). With increasing S/r from 0.17 to 1.96 the P–E responses become increasingly distorted and broader. Measurements show Wrec increases by a factor of ∼ 1.4 but Wloss increases by a factor of ∼7 with η decreasing from ∼ 29% to 8%. Finite element modelling was used to simulate the experimental set-up of the sample/electrode arrangements using the Jiles-Atherton model to replicate the ferroelectric behaviour of BaTiO3. These models demonstrate the experimentally applied electric field using a simple geometric correction for sample thickness is an underestimation of the actual field experienced by the material under the top contact at high S/r values. We stress the importance of reporting the contact sizes and thicknesses of samples when using P–E measurements to assess Wrec, Wloss and η in non-linear dielectric materials. This will allow a fairer comparison of performances between various types of materials being considered for high-energy-density ceramic capacitors.

Solid solutions of Na0.5 Bi0.5 TiO3 (NBT) and BiNi0.5 Ti0.5 O3 (BNiT) were prepared by a solid-state reaction route, and their electrical properties investigated by a combination of impedance spectroscopy and electromotive force measurements to explore the possibility of developing mixed ionic-electronic conductors based on NBT. Phase analysis showed that BNiT has a large solid solution limit in NBT (60 mol% based on X-ray diffraction), and the room temperature crystal structure changes from rhombohedral to pseudo-cubic with increasing BNiT content. Neutron diffraction revealed the coexistence of rhombohedral and tetragonal phases when the BNiT content >= 40 mol%. Electrically, incorporation of BNiT induces p -type electronic conduction into NBT by hopping of holes between Ni2 + (Ni xNi ) and Ni3 + (Ni Ni ), and therefore changes the electrical conduction mechanism systematically from predominant oxide-ion conduction to mixed ionic-electronic conduction and then to predominant p -type electronic conduction. The total conductivity of the solid solutions showed a "V-shape" variation with increasing BNiT content. Possible mechanisms for the phase evolution and the conductivity-composition relationships are discussed. Achieving high levels of ionic and electronic conductivity simultaneously in NBT by introducing elements with variable oxidation states remains challenging due to the competition between an enhanced electronic component and a suppressed ionic component. Low levels of BNiT incorporation are, however, beneficial to reducing the dielectric loss of NBT for dielectric applications. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The crystallographic, microstructural, and dielectric properties of Sr2.1Na0.8-xCaxNb5-xSnxO15 (x = 0.00, 0.01, 0.05, 0.10) polycrystalline ceramics have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), dielectric spectroscopy (DS) and impedance spectroscopy (IS). For x=0.00, 0.05, and 0.10, samples are single phase with P4bm phase at room temperature with x = 0.01 showing a small quantity of secondary phase(s). All compositions show typical ceramic microstructure and d50 grain sizes ranging from 5.1 to 26.6 μm. DS shows a clear trend in the high temperature ferroelectric-paraelectric transition with the Curie temperature, T0, decreasing from ~ 160 to ~ 110oC, and an additional relaxation at approximately 120oC with increasing CaSnO3. IS reveals all samples have a homogeneous electrical microstructure with predominantly electronic conduction. The activation energy of conduction calculated from Arrhenius plots of the conductivity increases with CaSnO3 content from 1.27 to 1.38eV likely due to the expansion of the band gap.

A combination of X-ray diffraction, analytical-electron microscopy, differential scanning calorimetry, impedance spectroscopy and electromotive force measurements (for oxide-ion transport number measurements, tion) are used to report on the influence of a small amount of a continuous Bi2O3-rich phase along the grain boundaries in sample composition x = 0.4 (BS0.4BT) of the high temperature dielectric solid solution series, x(BiScO3)-(1-x)(BaTiO3). Its presence produces a dramatic change in conductivity of similar to two orders of magnitude and a switch in tion over the range similar to 600 - 800 degrees C that is not observed for other ceramics with lower BiScO3 content. Below similar to 700 degrees C the grain boundaries in BS0.4BT act as electrically blocking layers and dominate the impedance of the ceramics. In contrast, at > 800 degrees C the grain boundaries become highly conductive due to a polymorphic phase transition to, and melting of delta-Bi2O3 which results in the current percolating along the grain boundaries and therefore avoiding the grains. The value of tion increases from similar to 0.13 at similar to 600 degrees C to near unity at similar to 800 degrees C for BS0.4BT, consistent with oxide ion conduction due to the presence of liquid Bi2O3 at grain boundary regions. This behaviour was reproduced by adding a small excess of 3 wt% Bi2O3 into x = 0.3 (BS0.3BT) samples to induce a Bi2O3-rich grain boundary phase, not otherwise present in this composition. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tailored dopant strategies are proposed to optimise the energy density of BiFeO3–SrTiO3, which can be adapted for other high polarisability oxide-based systems.

I am pleased to introduce this themed set of ten papers on microstructure–property– processing relationships in electroceramics. The contributions, which are based on presentations made at the Basic Science Symposium of the Electroceramics XI international conference, have been subject to MST’s standard refereeing procedure. Held in Manchester, UK on 31 August to 4 September 2008, Electroceramics XI featured a technical programme of 800 oral and poster presentations and attracted over 750 delegates from more than 35 countries.