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A crystallochemical framework is proposed based on electronegativity difference (en) and\ud tolerance factor (t) to optimise the BiMeO3 dopants and therefore the piezoelectric and\ud electrostrictive response in BaTiO3-BiFeO3 based ceramics. Compositions in the series\ud 0.05Bi(Me)O3-0.25BaTiO3-0.7BiFeO3 (BMe-BT-BF, Me: Y, Sc1/2Y1/2, Mg2/3Nb1/3, Sc,\ud Zn2/3Nb1/3, Zn1/2Ti1/2, Ga, and Al) were fabricated using solid state synthesis and furnace\ud cooled. Scanning electron microscopy and X-ray diffraction revealed that only\ud Bi(Mg2/3Nb1/3)O3 and BiScO3 dopants, which lie in a narrow range of en vs. t, form\ud homogeneous ceramics, free from secondary phases reflected in their superior\ud piezoelectric coefficients (d33 ~145 pC/N). All other BiMeO3 additions exhibited either\ud secondary phases (Y) and/or promoted a two-phase perovskite matrix (Zn, Ga and Al).\ud The promising initial properties of BiScO3 doped compositions prompted further studies\ud on 0.05BiScO3-(0.95-x)BaTiO3-(x)BiFeO3 (BS-BT-BF, x = 0.55, 0.60, 0.625, 0.65, and\ud 0.70) ceramics. As x increased the structure changed from predominantly pseudocubic to\ud rhombohedral, resulting in a transition from a relaxor-like to ferroelectric response. The\ud largest d33\ud * (465 pm/V) was achieved for x = 0.625 under 5 kV/mm at the crossover from\ud relaxor to ferroelectric behaviour. BS-BT-BF with x = 0.625 showed >0.3% strain under\ud 6 kV/mm up to 175ºC, demonstrating its potential for actuator applications.

High recoverable energy density (Wrec ∼ 2.1 J/cm3) was obtained in (0.7 – x)BiFeO3-0.3BaTiO3-xBi(Zn2/3Nb1/3)O3 + 0.1 wt % Mn2O3 (BF-BT-xBZN, x = 0.05) lead-free ceramics at

The relationship between the piezoelectric properties and the structure/microstructure for 0.05Bi(Mg2/3Nb1/3)O3-(0.95-x)BaTiO3-xBiFeO3 (BBFT, x = 0.55, 0.60, 0.63, 0.65, 0.70, and 0.75) ceramics has been investigated. Scanning electron microscopy revealed a homogeneous microstructure for x < 0.75 but there was evidence of a core-shell cation distribution for x = 0.75 which could be suppressed in part through quenching from the sintering temperature. X-ray diffraction (XRD) suggested a gradual structural transition from pseudocubic to rhombohedral for 0.63

Lead-free ceramics with high recoverable energy density (Wrec) and energy storage efficiency (η) are attractive for advanced pulsed power capacitors to enable greater miniaturization and integration. In this work, dense bismuth ferrite (BF)-based, lead-free 0.75(Bi1−xNdx)FeO3-0.25BaTiO3 (BNxF-BT) ceramics and multilayers were fabricated. A transition from a mixed pseudocubic and R3c to a purely pseudocubic structure was observed as x increased with the optimum properties obtained for mixed compositions. The highest energy densities, W ∼ 4.1 J cm−3 and Wrec ∼ 1.82 J cm−3, were achieved for BN15F-BT, due to the enhanced breakdown field strength (BDS ∼ 180 kV cm−1) and large maximum polarization (Pmax ∼ 40 μC cm−2). The multilayers of this composition possessed both a high Wrec of 6.74 J cm−3 and η of 77% and were stable up to 125 °C. Nd doped BF-based ceramics with enhanced BDS and large Wrec are therefore considered promising candidates for lead-free energy storage applications.

© 2019 The Royal Society of Chemistry. High electrostrain and breakdown strength (1 - x)BiFeO3-0.3BaTiO3-xNd(Li0.5Nb0.5)O3 (BF-BT-xNLN) ceramics were studied by in situ synchrotron X-ray diffraction (XRD) in combination with Rietveld refinement and conventional transmission electron microscopy. At zero field, compositions transformed from majority ferroelectric rhombohedral to pseudocubic as the NLN concentration increased, with 0.27% strain achieved at 60 kV cm-1 for x = 0.01. The large measured macroscopic strain was commensurate with peak shifting in XRD peak profiles, yielding 0.6% total strain at 150 kV cm-1. Strain anisotropy of ϵ200 > ϵ220 > ϵ111 was observed but despite the large applied field, no peak splitting was detected. We therefore concluded that the large electrostrain is not achieved through a conventional relaxor to field induced long-range ferroelectric transition. Instead, the data supports a model where local polar regions distort in the direction of the applied field within multiple local symmetries (pseudosymmetry) without long range correlation. We proposed that pseudosymmetry is maintained in BF-BT-xNLN even at high field (150 kV cm-1) due to the large ion radii mismatch and competing ionic/covalent bonding between Ba2+ and Bi3+ ions.

Lead-based electroceramics such as Pb(Zr.Ti)O3 (PZT) and its derivatives have excellent piezoelectric, pyroelectric and energy storage properties and can be used in a wide range of applications. Potential lead-free replacements for PZT such as potassium sodium niobate (KNN) and sodium bismuth titanate (NBT) have a much more limited range of useful properties and have been optimized primarily for piezoelectric applications. Here, we review the initial results on a new generation of lead-free electroceramics based on BiFeO3-BaTiO3 (BF-BT) highlighting the essential crystal chemistry that permits a wide range of functional properties. We demonstrate that with the appropriate dopants and heat treatment, BF-BT can be used to fabricate commercially viable ceramics for applications, ranging from sensors, multilayer actuators, capacitors and high-density energy storage devices. We also assess the potential of BF-BT-based ceramics for electrocaloric and pyroelectric applications.

Dense Bi 0.487 Na 0.427 K 0.06 Ba 0.026 TiO 3 (BNKBT) and Nb-doped Bi 0.487 Na 0.427 K 0.06 Ba 0.026 Ti 0.98 Nb 0.02 O 3 (Nb-BNKBT) ceramics were prepared by the solid state reaction route. BNKBT is a non-ergodic relaxor and exhibits a piezoelectric response typical for a ferroelectric, whereas Nb-BNKBT is an ergodic relaxor and exhibits an electromechanical response typical for an incipient ferroelectric. The incorporation of 2 mol% of Nb into the BNKBT lattice is accompanied by an enhancement of the room-temperature unipolar field-induced strain from 0.19% to 0.43% at 75 kV/cm. BNKBT shows a depolarisation temperature of ∼90 °C, above which an electrostrictive response is observed, whereas Nb-BNKBT shows an electrostrictive response in the entire temperature range studied. At 40 kV/cm, Nb-BNKBT exhibits a temperature stable electromechanical response in comparison with undoped BNKBT, but it worsens under higher electric fields. These results may motivate further investigations on the impact of minor doping and driving electric fields on the electromechanical response of Bi 0.5 Na 0.5 TiO 3 –Bi 0.5 K 0.5 TiO 3 –BaTiO 3 -based ceramics.