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• This paper reviews both the phenomenological defect chemistry approaches and considers the importance of doping strategies in the formation of associated point defect complexes. • Modern first principle calculations enable the understanding of these complexes compared to isolated defect species. • Dopants and defects control the conduction mechanism, including Fermi level pinning. • Mixed conduction is considered for doped BaTiO 3 and the impact of different oxygen vacancy concentrations over a wide range of conditions. • The association and dissociation of kinetic oxygen vacancies in Fe and Mn acceptor doping are investigated via Electron Paramagnetic Resonance (EPR). • Additionally, co-doping amphoteric and acceptors are studied. Kinetic data obtained via Thermally Stimulated Depolarization Current (TSDC) measures different dissociation energies for oxygen vacancies associated with various amphoteric rare earths and Y+3. • The deleterious impact on time-dependent properties in ferroelectrics is reviewed, including time-dependent dielectric breakdown (TDDB), fatigue, and aging. • Additionally, film composition, processing, defect chemistry and dynamics are considered with respect to BaTiO 3 in MLCCs, thin film tunable, and integrated decoupling capacitors. • Finally, we consider future opportunities and challenges beyond the knowledge of the present day. The processing science and fundamental understanding of defect chemistry of BaTiO 3 is a model example of how material science is used to guide the materials engineering of capacitive devices. The fundamentals are discussed from the phase equilibria, defect chemistry, and the impact on intrinsic properties. We reviewed the phenomenological defect chemistry approaches and considered the importance of doping strategies and the formation of associated point defect complexes. First principles calculations have proven to be a most informative strategy towards understanding these complexes and implications conduction mechanism. The nature of mixed conduction is considered with various dopants in the BaTiO 3 and conditions that can arise with different oxygen vacancy concentrations over a wide range of conditions. Defect dynamics are considered experimentally in terms of associations and dissociations kinetics of oxygen vacancies from these various complexes. The deleterious impact on time-dependent properties is reviewed, including time-dependent dielectric breakdown, fatigue, and aging. [ABSTRACT FROM AUTHOR]

The rising cost of energy and concerns about the environmental impact of manufacturing processes have necessitated the need for more efficient and sustainable manufacturing. The ceramic industry is an energy intensive industrial sector and consequently the potential to improve energy efficiency is huge, particularly through the introduction of modern sintering technologies. Although several energy efficient sintering processes have been developed, there is no comprehensive techno-economic analysis which compares and contrasts these techniques. This paper presents a critical review and analysis of a number of sintering techniques and compares them with the recently developed cold sintering process (CSP), including mode of operation, sintering mechanism, typical heating rates, duration of sintering, energy consumption profile and energy saving potential, limitations, key challenges for further development and current research efforts. By using a figure of merit, pounds per tonne of CO 2 saved (£/tCO 2 -eq), which links initial capital investment with energy savings, within a framework derived from ranking principles such as marginal abatement cost curves and Pareto optimisation, we have demonstrated that under the scenarios considered for 3 separate functional oxides ZnO, PZT and BaTiO 3 , CSP is the most economically attractive sintering option, indicating lower capital costs and best return on investment as well as considerable energy and emission savings. Although the current work establishes the viability of CSP as a competitive and sustainable alternative to other sintering techniques, the transition from laboratory to industry of CSP will require hugely different facilities and instrumentation as well as relevant property/performance validation to realise its full potential. [ABSTRACT FROM AUTHOR]

Abstract: A compositional dependence on the ferroelastic phase transition in scheelite solid-solution [(Li0.5Bi0.5) x Bi1− x ][Mo x V1− x ]O4 ceramics was characterized by the microwave dielectric data over the temperature range 10–420K. As x values increased from 0.0 to 0.125, a dielectric temperature-dependent anomaly consistent with a phase transition decreased linearly from 528K for the pure BiVO4 end member to 264K for the solid-solution composition at x =0.125. With further increasing x, the transition temperature decreased sharply to approximately 45K and became stable for x ⩾0.52. The phase transition point for pure tetragonal (Li0.5Bi0.5)MoO4 ceramics is approximately 43K. As the x value increases, the Raman band of the [(Li0.5Bi0.5) x Bi1− x ][Mo x V1− x ]O4 ceramics at room temperature broadens and overlaps. Ferroelastic domain structures were observed as a function of composition with diffraction contrast imaging and high-resolution imaging with transmission electron microscopy. Structure–property relations are inferred from the microscopy observations and the Raman spectra. [ABSTRACT FROM AUTHOR]

The phase relations in the BaO–TiO2−δ system within the concentration range of 14–65 mol% BaO under reducing conditions were investigated using high temperature DTA and X-ray powder diffraction. The stable compounds under these conditions were determined, together with the temperatures of the invariant reactions and the liquidus boundaries. The phase relations in this BaO–TiO2–Ti2O3 system under elevated temperatures and reducing atmospheres are represented in the form of quasi-binary phase diagrams. [Copyright &y& Elsevier]

A series of barium titanium oxides with various Ba/Ti ratios having a hollandite structure were obtained by firing chemical synthesized oxide precursors under reducing atmosphere conditions (H2/N2 gas mixture flow) at temperatures of 1100°C and above. An oxygen nonstoichiometry was determined by a thermogravimetric analysis through oxidizing in air. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen-deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. The influence of oxygen nonstoichiometry on the hollandite monoclinic–tetragonal phase transition and a barium superstructure ordering was investigated and discussed. Distortion scaling rules are considered to compare this work with earlier investigations on hollandites. [Copyright &y& Elsevier]

A new barium polytitanate Ba1.054Ti0.946O2.946 was synthesized by a citrate chemical route. The X-ray powder pattern of this compound was indexed to a hexagonal system, with space group P63/mmc and lattice parameters a=5.722(4) and c=13.996(8) A˚. Prolonged annealing of the Ba1.054Ti0.946O2.946 in air at temperatures above 1150°C leads to a peritectoid decomposition reaction yielding Ba2TiO4 and cubic-BaTiO3, consistent with the known phase diagram. A thermal stability study of this compound demonstrates it to be a stable phase under ambient conditions and metastable under low oxygen partial pressures. [ABSTRACT FROM AUTHOR]

The prohibition of lead in many electronic components and devices due to its toxicity has reinvigorated the race to develop substitutes for lead zirconate titanate (PZT) based mainly on the potassium sodium niobate (KNN) and sodium bismuth titanate (NBT). However, before successful transition from laboratory to market, critical environmental assessment of all aspects of their fabrication and development must be carried out in comparison with PZT. Given the recent findings that KNN is not intrinsically ‘greener’ than PZT, there is a tendency to see NBT as the solution to achieving environmentally lead-free piezoelectrics competitive with PZT. The lower energy consumed by NBT during synthesis results in a lower overall environmental profile compared to both PZT and KNN. However, bismuth and its oxide are mainly the by-product of lead smelting and comparison between NBT and PZT indicates that the environmental profile of bismuth oxide surpasses that of lead oxide across several key indicators, especially climate change, due to additional processing and refining steps which pose extra challenges in metallurgical recovery. Furthermore, bismuth compares unfavourably with lead due to its higher energy cost of recycling. The fact that roughly 90–95% of bismuth is derived as a by-product of lead smelting also constitutes a major concern for future upscaling. As such, NBT and KNN do not offer absolute competitive edge from an environmental perspective in comparison to PZT. The findings in this work have global practical implications for future Restriction of Hazardous Substances (RoHS) legislation for piezoelectric materials and demonstrate the need for a holistic approach to the development of sustainable functional materials. [ABSTRACT FROM AUTHOR]

Piezoelectric transformers (PT's) offer high efficiency in compact volumes compared to their electromagnetic counterparts. In particular, multilayer PT's can deliver both efficiency and higher power when they are made of hard-piezoceramics. However, hard-piezoceramics usually have high sintering temperatures (~ 1200 °C), which limit the inner electrode of the multilayer structure to precious metals such as silver‑palladium (Ag/Pd) with high Pd content or platinum (Pt). High Pd content or Pt increases device price dramatically and their electrical/thermal performances are not satisfactory for high power multilayer applications. Therefore, two compositions were developed by utilizing a commercially available hard-piezoelectric ceramic (APC 841) and sintering temperature was brought down to 1000 °C or below by keeping essential high power properties at satisfactory levels (mechanical quality factor ~ 1000, planar coupling coefficient > 0.5, and dielectric loss < 0.02). Then, ring-dot step-down multilayer PT's were prototyped and co-fired with Ag/Pd:90/10 electrodes accordingly. PT's were able to reach an output power density level of 30 W cm − 3 (P output /Volume) with > 96% efficiency (P output /P input ) and a 20 °C temperature rise. In addition, PT's were tested at higher output power levels and were able to generate 45 W cm − 3 and 60 W cm − 3 with a temperature rise of 40 °C and 80 °C, respectively. [ABSTRACT FROM AUTHOR]

We have investigated the spatial distribution of non-centrosymmetric defects in the electrocolored bulks of oxidized and reduced Fe -doped SrTiO 3 (Fe:STO) single crystals by optical second harmonic generation (SHG) spectroscopy in the transmission geometry. Transmitted SHG intensities were examined across the anodic, mixed, and cathodic bulk regions of both Fe:STO crystals. The obtained nonlinear susceptibility ratios show that the structural distortions in the anodic and cathodic bulks of the electrocolored crystals are dominated by Fe:Ti O bond bending around Fe 4+ defect centers and Fe:Ti O bond stretching around Fe 3+ defect centers, respectively. Moreover, we identified a stronger local strain field at the color front of the oxidized crystal over the reduced one. This is attributed to more efficient strain relaxation during oxygen vacancy demixing in the reduced crystal. [ABSTRACT FROM AUTHOR]

Abstract: This investigation discovers a discrete metallic alloy layer containing Ni, Ti, and Ba between Ni and BaTiO3 co-fired in reducing atmospheres at ∼1300°C along with an oxygen-depleted zone in BaTiO3 adjacent to the metallic layer. Using high-resolution transmission electron microscopy and electron energy-loss spectroscopy, detailed structural and chemical analyses of the metallic layer are carried out. With complementary thermodynamic approximations, these observations render an assessment of the local effective oxygen partial pressure, which is considerably lower than the external, ambient processing environment. Through a set of model experiments on Ni–BaTiO3–carbon composites, we illustrate that the presence of carbon is sufficient to reduce locally BaTiO3 and form the observed metallic layer at ∼1300°C. A phase stability analysis indicates that the formation of the Ba and Ni–Ti liquid phases provides a kinetic path for the interfacial reaction. [Copyright &y& Elsevier]