Domain variance and superstructure across the antiferroelectric/ferroelectric phase boundary in Pb1−1.5xLax(Zr0.9TiM0.1)O3

Transmission electron microscopy, x-ray diffraction, relative permittivity as a function of temperature, and polarization versus field loops were used to study the antiferroelectric/ferroelectric (AFE/FE) phase boundary in Pb1−1.5xLaxZr0.9Ti0.1O3 (PLZT, 100x/90/10) ceramics. X-ray diffraction and electrical measurements indicated a FE rhombohedral (R) to AFE tetragonal (T) phase transition between PLZT 2/90/10 and 4/90/10. Both phases exhibited superstructure reflections in electron-diffraction patterns at 1⁄2{hkl} positions consistent with rotations of the octahedra in antiphase. Previously, neutron diffraction suggested that the FER has an a−a−a− tilt system (Glazer notation), in agreement with its macroscopic symmetry. By analogy, it is proposed that the AFET phase has an a0a0c− tilt system. The AFE phase was also characterized by incommensurate superstructure along pseudocubic 〈110〉p directions, whereas the FE phase had extra commensurate superlattice reflections at 1⁄2{hk0}p positions. 1⁄2{hk0}p reflections are forbidden in both tilt systems, but their presence is explained by Pb ion displacements averaged along 〈111〉 but with short coherence antiparallel components along 〈110〉 directions. The antiparallel Pb displacements are coupled to an a−b−b− (a ≈ b) monoclinic tilt system in the vicinity of the AFE/FE boundary

Cold sintered ceramic composites for microwave applications

Cold sintering is a revolutionary processing technology that permits the densification of ceramics using a pressure mediated liquid phase at sintering temperatures \u3c200 oC. This contribution explores the potential of cold sintering for the fabrication of microwave (MW) materials and devices. We will demonstrate how cold sintering can be used to fabricate temperature stable ceramic composites suitable for dielectric substrates and RF components, resulting in properties either equivalent to, or superior than, conventionally sintered compositions. In addition, we will illustrate how cold sintering can be utilised to fabricate composites impossible by conventional processing. Finally, we demonstrate devices such as multilayer ceramic capacitors, graded index lenses and microstrip patch antennas fabricated using cold sintered ceramic composites

Substitution and sustainability in functional materials and devices

Functional Materials and Devices (FMD) is a rapidly evolving subject which underpins many aspects of modern life such as antennas, energy storage devices, multicomponent sensors and smart materials. At a segment size of ~£3Bn p.a., the UK represents ~25% of the total EU production. However, the FMD sector in the EU and UK relies heavily on raw materials which have geopolitical, geological and environmental constraints. The response to materials scarcity and environmental restrictions depends on the industry, but companies indicate that resource efficiency, R&D, and innovations for substitution are necessary. Our vision is to utilise materials engineering, multiscale modeling, advanced manufacturing, supply chain/life cycle analysis and industrial partnerships to establish an holistic response to substitution and sustainability within the UK FMD sector. The talk will focus on: i) Elimination of expensive RE-oxides from the fabrication of multilayer ceramics capacitors (MLCC): Currently, the lifetime of an MLCC is enhanced by the use of ~2wt% of RE-oxide (RE = Dy, Ho). Dy is the number one most endangered element according to the US government. Eradicating Dy and Ho from the fabrication MLCC is thus an urgent priority ii) Manufacture of actuators using PbO-free piezoelectric oxides: Environmentally friendly, PbO-free piezoelectrics) have been developed over the last decade as potential replacements for Pb(Zr,Ti)O3 (PZT). Device fabrication and characterization will be studied along with an investigation of critical issues concerning direct integration into end-user applications. iii) Replacing exotic compounds with robust oxide ceramics in thermoelectric generators: Currently, the best thermoelectric materials (Figure of Merit, ZT \u3e 1) for waste heat harvesting are based on tellurides, antimonides and germanides. Not only are these compounds toxic and in short supply but they are also unstable at the proposed operating temperatures. Thermoelectric generators based on equally performant, more abundant and less toxic oxide materials will be developed iv) Replacing expensive Si based PV cells with efficient inorganic/organic perovskite hybrid cells: the next generation of PV cells are envisaged to be based on methyl ammonium lead iodide (MALI) which has been reported to have \u3e20% efficiency and is vastly cheaper the Si based technology. However, there are major concerns about its long term stability during cell lifetime. Here, we will present initial data relating to thermal stability of MALI fabricated using two different routes

The atomic structure and chemistry of Fe-rich steps on antiphase boundaries in Ti-doped Bi_0.9Nd_0.15FeO3

Stepped antiphase boundaries are frequently observed in Ti-doped Bi<sub>0.85</sub>Nd<sub>0.15</sub>FeO<sub>3</sub>, related to the novel planar antiphase boundaries reported recently. The atomic structure and chemistry of these steps are determined by a combination of high angle annular dark field and bright field scanning transmission electron microscopy imaging, together with electron energy loss spectroscopy. The core of these steps is found to consist of 4 edge-sharing FeO<sub>6</sub> octahedra. The structure is confirmed by image simulations using a frozen phonon multislice approach. The steps are also found to be negatively charged and, like the planar boundaries studied previously, result in polarisation of the surrounding perovskite matrix

Progress in Bioactive Metal and, Ceramic Implants for Load- Bearing Application

The field of biomaterials is an exuberant and enticing field, attracting interest across a number of scientific disciplines. Synthetic materials such as metals and ceramics have helped civilisation accomplish many feats, and this can also be said for the achievements in orthopaedic applications. Metals and ceramics have achieved success in non-load-bearing applications and attempts are made to translate the accomplishments into weight-bearing applications. For this, a material needs to be porous but with sufficient strength to withstand daily loading; however, both properties are mutually exclusive. The implant must also avoid causing adverse reactions and toxicity and, preferably, bond to the surrounding tissues. Metals such as stainless steels and chromium-cobalt alloys have been used due to their excellent mechanical properties that can withstand daily activities, but retrospective studies have alluded to the possibilities of significant adverse reaction when implanted within the human body, caused by the elution of metal ions. Lessons from metals have also demonstrated that materials with significantly higher mechanical properties will not necessarily enhance the longevity of the implant—such is the complexity of the human body. Ceramics, on the other hand, exhibit excellent biocompatibility, but their mechanical properties are a significant hindrance for load-bearing use. Thus, the chapter herein provides a select overview of contemporary research undertaken to address the aforementioned drawbacks for both metals and ceramics. Furthermore, the chapter includes a section of how metals and ceramics can be combined in a multi-material approach to bring together their respective properties to achieve a desirable characteristics

Temperature Dependent Piezoelectric Properties of Lead-Free (1-x)K0.6Na0.4NbO3–xBiFeO3 Ceramics

(1-x)K0.4Na0.6NbO3–xBiFeO3 lead-free piezoelectric ceramics were successfully prepared in a single perovskite phase using the conventional solid-state synthesis. Relative permittivity (εr) as a function of temperature indicated that small additions of BiFeO3 not only broadened and lowered the cubic to tetragonal phase transition (TC) but also shifted the tetragonal to orthorhombic phase transition (TO–T) toward room temperature (RT). Ceramics with x = 1 mol.% showed optimum properties with small and large signal piezoelectric coefficient, d33 = 182 pC/N and d∗33 = 250 pm/V, respectively, electromechanical coupling coefficient, kp = 50%, and TC = 355°C. kp varied by ∼5% from RT to 90°C, while d∗33 showed a variation of ∼15% from RT to 75°C, indicating that piezoelectric properties were stable with temperature in the orthorhombic phase field. However, above the onset of TO–T, the properties monotonically degraded in the tetragonal phase field as TC was approached

Phase transitions, domain structure, and pseudosymmetry in La- and Ti-doped BiFeO3

The phase transitions and domain structure of the promising PbO-free solid solution series, (0.95-x)BiFeO3-xLaFeO3-0.05La2/3TiO3, were investigated. X ray diffraction(XRD) revealed a transition from a ferroelectricR3c to a PbZrO3-like (Pbam) antiferroelectric (AFE) structure at x = 0.15 followed by a transition to a paraelectric (PE, Pnma) phase at x > 0.30. The ferroelastic/ferroelectric twin domain width decreased to 10–20 nm with increasing x as the AFE phase boundary was approached but coherent antiphase tilted domains were an order of magnitude greater. This domain structure suggested the local symmetry (20 nm) is lower than the average structure (R3c, a−a−a−) of the tilted regions. The PE phase (x = 0.35) exhibited a dominant a−a−c+ tilt system with Pnma symmetry but diffuse reflections at ∼1/4{ooe} positions suggest that short range antipolar order is residual in the PE phase. The complex domain structure and phase assemblage of this system challenge the conventional interpretation of phase transitions based on macroscopic symmetry. Instead, it supports the notion that frustration driven by chemical distributions at the nanometric level influences the local or pseudo-symmetry as well as the domain structure, with XRD giving only the average macroscopic structure

Optimising dopants and properties in BiMeO3 (Me = Al, Ga, Sc, Y, Mg2/3Nb1/3, Zn2/3Nb1/3, Zn1/2Ti1/2) lead-free BaTiO3-BiFeO3 based ceramics for actuator applications

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

p-type/n-type behaviour and functional properties of KxNa (1-x)NbO3 (0.49 <= x <= 0.51) sintered in air and N2

Abstract Potassium sodium niobate (KNN) is a potential candidate to replace lead zirconate titanate in sensor and actuator applications but there are many fundamental science and materials processing issues to be understood before it can be used commercially, including the influence of composition and processing atmosphere on the conduction mechanisms and functional properties. Consequently, KNN pellets with different K/Na ratios were sintered to 95% relative density in air and N2 using a conventional mixed oxide route. Oxygen vacancies (VO..) played a major role in the semi-conduction mechanism in low p(O2) for all compositions. Impedance spectroscopy and thermo-power data confirmed KNN to be n-type in low p(O2) in contradiction to previous reports of p-type behaviour. The best piezoelectric properties were observed for air- rather than N2-sintered samples with d33=125 pC/N and kp=0.38 obtained for K0.51Na0.49NbO3

Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallizatio