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A new computational analysis of tilt behaviour in perovskites is presented. This includes the development of a computational program – PALAMEDES – to extract tilt angles and the tilt phase from molecular dynamics simulations. The results are used to generate simulated selected-area electron and neutron diffraction patterns which are compared with experimental patterns for CaTiO3. The simulations not only reproduced all symmetrically allowed superlattice reflections associated with tilt but also showed local correlations that give rise to symmetrically forbidden reflections and the kinematic origin of diffuse scattering.

The TiO2 polymorph has a dramatic impact on the electrical conductivity and conduction mechanisms of nominally stoichiometric NBT ceramics prepared by solid-state reaction.

Low levels of impurities can have a dramatic influence on the electrical properties of metal oxides. Here, we use a combination of impedance spectroscopy and Seebeck coefficient measurements to show the defect chemistry and p-type conduction mechanism in undoped LaFeO3(LF) ceramics is significantly influenced by impurities in Fe2O3 reagents. A low but significant concentration of impurities associated with 99.9 % Fe2O3 reagent is sufficient to compete against the intrinsic Schottky disorder responsible for the p-type behaviour normally observed for undoped LF ceramics. This produces electrically heterogeneous grain (bulk) responses that are strongly dependent on the processing conditions. To achieve electrically homogeneous bulk responses requires adjustment of the oxygen content by annealing in a reducing atmosphere (n-type) or via doping with a significant level of acceptors (mixed ionic/ p-type electronic). These results illustrate the importance of using high purity reagents when studying the electrical properties of ferrite-based perovskites.

Lead-free bismuth sodium titanate piezoceramics were processed by a solid-state route with a novel precursor approach. By carefully controlling the processing parameters and sintering atmospheres, translucent ceramics with pore-free, homogeneous microstructures with exceptionally low dielectric loss at elevated temperatures. The pore-free microstructure can influence the operating life of a dielectric device positively, since pores and other microstructural defects are usually responsible for material failures within devices. Synchrotron and surface X-ray diffraction experiments revealed a clear dependence of the crystal structure on sintering parameters and defect chemistry. Microstructural analysis showed a dependency of a secondary phase on the sintering atmosphere. The grain size could be adjusted using a shortened grinding process instead of using the common methods like increasing calcining or sintering temperature.

0.9Ba(Ti1−xMgx)O3−x-0.1NaNbO3 (BTNN-100xMg) solid solutions are investigated with a view to developing Bi, Pb, and rare earth free, high voltage multilayer ceramic capacitors. Mg doping on the B-site significantly reduced the electronic conductivity and resulted in ceramics that could withstand a pulsed unipolar field of >300 kV/cm (Emax) to give a recoverable energy density of 3.4 J/cm3 at 82.6% efficiency for x = 0.01. The high Emax is accompanied by a high dielectric permittivity (ε′ ∼ 1700 at room temperature) with temperature-stable dielectric permittivity of Δε/ε298K ≤ ±15% and loss tangent tan δ < 0.02 from 116 to 378 K, corresponding to an X6R designation in the Electronic Industry Alliance codes.

The compositional limits of a previously reported (J. Am. Ceram. Soc., 61, 5‐8. (1978)) but relatively unstudied sodium‐bismuth titanate pyrochlore solid solution are revised and their electrical properties presented. The pyrochlore solid solution we report forms via a different mechanism to that originally reported and occurs in a different location within the Na2O‐Bi2O3‐TiO2 ternary system. In both cases, relatively large amounts of vacancies are required on the A‐sites and on the oxygen sites, similar to that reported for undoped ‘Bi2Ti2O7’ pyrochlore. In contrast to ‘Bi2Ti2O7’, this ternary pyrochlore solid solution can be prepared and ceramics sintered using conventional solid‐state methods; however, the processing requires several challenges to be overcome to obtain dense ceramics. This cubic pyrochlore series has low electrical conductivity (and does not exhibit any evidence of oxide‐ion conduction) and exhibits relaxor ferroelectric behavior with a broad permittivity maximum of ~100 near room temperature. Variable temperature neutron diffraction data do not provide any conclusive evidence for a phase transition in the pyrochlore solid solution between ~4 and 873 K.

Existing equivalent circuit extraction techniques are inaccurate for piezoelectric transformers (PTs) with low-input capacitance or high damping. A new method is presented, offering improved accuracy in both damping resistance and resonant frequency extraction compared with state-of-the-art methods. Effectiveness is evaluated on two sample PTs, with the proposed method achieving up to 84% decrease in error compared with previous methods.

Micro‐contact impedance spectroscopy (MCIS) is potentially a powerful tool for the exploration of resistive surface layers on top of a conductive bulk or substrate material. MCIS employs micro‐contacts in contrast to conventional IS where macroscopic electrodes are used. To extract the conductivity of each region accurately using MCIS requires the data to be corrected for geometry. Using finite element modeling on a system where the resistivity of the surface layer is at least a factor of ten greater than the bulk/substrate, we show how current flows through the two layers using two typical micro‐contact configurations. This allows us to establish if and what is the most accurate and reliable method for extracting conductivity values for both regions. For a top circular micro‐contact and a full bottom counter electrode, the surface layer conductivity (σs) can be accurately extracted using a spreading resistance equation if the thickness is ~10 times the micro‐contact radius; however, bulk conductivity (σb) values can not be accurately determined. If the contact radius is 10 times the thickness of the resistive surface, a geometrical factor using the micro‐contact area provides accurate σs values. In this case, a spreading resistance equation also provides a good approximation for σb. For two top circular micro‐contacts on thin resistive surface layers, the MCIS response from the surface layer is independent of the contact separation; however, the bulk response is dependent on the contact separation and at small separations contact interference occurs. As a consequence, there is not a single ideal experimental setup that works; to obtain accurate σs and σb values the micro‐contact radius, surface layer thickness and the contact separation must all be considered together. Here we provide scenarios where accurate σs and σb values can be obtained that highlight the importance of experimental design and where appropriate equations can be employed for thin and thick resistive surface layers.

The influence of Ti-site acceptor-doping (Mg2+, Zn2+, Sc3+, Ga3+ and Al3+) on the electrical conductivity and conduction mechanism of a nominally Bi-excess sodium bismuth titanate perovskite, Na0.5Bi0.51TiO3.015 (NB0.51T), is reported. Low levels of acceptor-type dopants can introduce appreciable levels of oxide-ion conductivity into NB0.51T, i.e., 0.5% Mg-doping for Ti4+ can enhance the bulk conductivity of NB0.51T by more than 3 orders of magnitude with the oxide-ion transport number going from 0.9 at 600 °C. The intriguing electrical behaviour in acceptor-doped NB0.51T dielectrics is a synergistic effect based on the defect chemistry and ceramic microstructure in these materials. NB0.51T ceramics with extremely low levels of doping show an inhomogeneous microstructure with randomly distributed large grains embedded in a small grained matrix. This can be considered as a two-phase composite with large grains as a conductive phase and small grains as an insulating phase based on an empirical conductivity – grain size relationship. Variation in the fraction of the conductive, large grained phase with increasing doping levels agrees with the oxide-ion transport number. This electrical two-phase model is supported by finite element modelling. This study reveals the significance of ceramic microstructure on the electrical conduction behaviour of these materials and can provide a guideline for selecting suitable doping strategies to meet the electrical property requirements of NBT-based ceramics for different applications.

The critical role of electrical homogeneity in optimising electric-field breakdown strength (BDS) and energy storage in high energy density (0.7 − x)BiFeO3–0.3BaTiO3–xBi(Li0.5Nb0.5)O3 (BF–BT–xBLN) lead-free capacitors is demonstrated. The high BDS for bulk ceramics and multilayers (dielectric layer thickness ∼ 8 μm) of ∼260 and ∼950 kV cm−1, respectively, gives rise to record-performance of recoverable energy density, Wrec = 13.8 J cm−3 and efficiency, η = 81%. Under an electric field of 400 kV cm−1, multilayers are temperature stable up to 100 °C, frequency independent in the range 10−2 to 102 Hz, have low strain (

A nominal Bi-excess starting composition of sodium bismuth titanate, Na0.5Bi0.51TiO3.015 (NB0.51T) produces dielectric ceramics that exhibit mixed n-type and oxide-ion conductivity with an ionic transport number of ∼0.1 at ≥600 °C. The bulk electrical conductivity, σb, of NB0.51T ceramics under a dc bias field of ≤100 V cm−1 has been investigated by impedance spectroscopy. Over the temperature range ∼550 to 750 °C, σb increases by up to one order of magnitude under the dc bias and returns to its initial value on removal of the bias. The enhancement of conductivity is dependent on temperature, atmosphere, dc bias field and the electrode materials. A maximum conductivity enhancement of >2000% is achieved at 600 °C in nitrogen using Pt electrodes. This is in contrast to that observed for other n-type perovskite titanates and oxygen-deficient rutile where σb is suppressed under a dc bias. This ‘unusual’ non-ohmic behaviour is attributed mainly to the influence of highly mobile oxygen vacancies in NB0.51T. The field-enhanced σb is best described to be a consequence of increased pumping of oxygen from the cathode to the anode, in which the electrode reactions play an important role. In addition, dissociation of defect clusters may also contribute to the enhanced σb under a dc bias. The high, fast and reversible response to the dc bias voltage may expand the potential application of NBT-based materials to memory devices.

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 CO2 saved (£/tCO2-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 BaTiO3, 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.

The effect of calcining in either air (VSTO-A) or 5% H2/N2 (VSTO-H) on the thermoelectric performance of La and Sm co-doped A-site-deficient Sr1-3x/2Lax/2Smx/2TiO3-δ ceramics is reported. All calcined powders were sintered 6 h in 5% H2/N2 at 1773 K to ≥96% relative density. All peaks in X-ray diffraction patterns indexed as a cubic perovskite phase. Scanning electron microscopy revealed grain sizes ~14 and ~10 μm for VSTO-A and VSTO-H ceramics, respectively. x = 0.30 showed the lowest k (2.99 W/m.K at 973 K) for VSTO-A, whereas x = 0.20 had the lowest (2.67 W/m.K at 973 K) for the VSTO-H ceramics. x = 0.30 VSTO-A showed a thermoelectric figure of merit, ZT = 0.25 (at 973 K), whereas the maximum ZT = 0.30 (at 973 K) was achieved for x = 0.20 VSTO-H ceramics, demonstrating that thermoelectric properties are optimized when all processing is carried out in 5% H2/N2.

The electrical behaviour of the interface between the ceramic and electrode layers in multi layer ceramic capacitors has been studied using finite element modelling. Interface models were produced with varying amplitudes of roughness based upon analysis of micrographs both captured in-house and from the literature. The impedance responses, direct current electric field and current density distributions of the different interfaces were compared. Increasing the root-mean-squared amplitude roughness from 0 to 0.16 μm increased the maximum field strength by over a factor of four. The electric field distribution showed that fluctuations in the increase of field strength were due to local interface morphology. Sharp intrusions of the electrode into the ceramic layer resulted in particularly large field enhancements and should be avoided to reduce the likelihood of device breakdown.

Ceramics-ceramic composites in series (1-x)Li2MoO4-xBaFe12O19 (LMO-BF12, 0.00 ≤ x ≤ 0.15) have been cold sintered at 120 °C and their structure and properties characterized. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that compositions were dual phase and had a dense microstructure. Composites in the xBF12-(1-x)LMO (0.0 ≤ x ≤ 0.15) series resonated at MW frequencies (∼6 GHz) with 5.6≤er ≤ 5.8 and Qf = 16,000–22,000 GHz, despite the black colour of compositions with x > 0. The permeability of the composites was measured in the X band (∼8 GHz) and showed an increase from 0.94 (x = 0.05) to 1.02 (x = 0.15). Finite element modelling revealed that the volume fraction of BF12 dictates the conductivity of the material, with a percolation threshold at 10 vol% BF12 but changes in er as a function of x were readily explained using a series mixing model. In summary, these composites are considered suitable for the fabrication of dual mode or enhanced bandwidth microstrip patch antennas.

Globally, the issue of climate change due to greenhouse gas (GHG) emissions is now broadly acknowledged as one of the major challenges facing humankind that requires urgent attention. Accordingly, considerable efforts on clean energy technologies and policy recommendations have been developed to address this challenge. Solid oxide fuel cells (SOFCs) have been touted to play a role in achieving a reduction in global GHG emissions, offering numerous advantages including higher efficiencies and reduced emissions, over other conventional methods of energy generation. The increasing recognition and emphasis on fuel cells as a representative power generation system of the future has raised concerns over their environmental profile. Extensive research regarding the environmental profile of current structures of SOFCs can be found in the literature, but none consider the use of new materials to achieve lower environmental impacts. This research fills the gap and presents a comparison of the environmental profile of three SOFC structures: a commercially available structure, and two intermediate temperature structures, one using erbia-stabilised bismuth oxide electrolytes and a proposed structure using strontium-doped sodium bismuth titanate electrolytes. Using a functional unit of kg/100 kW of power output for each of the SOFC structures (excluding the interconnects), within a hybrid life cycle analysis framework, the environmental hotspots across the supply chains of each SOFC type are identified, quantified and ranked. The results show the use of these novel material combinations leads to a reduction in embodied materials and toxicological impact but higher electrical energy consumption during fabrication, in comparison to commercial SOFCs. The findings support the move to reduce the operating temperatures of SOFCs using these novel material architectures, which leads to an overall reduction in environmental impact due to the lower operational energy requirement of the chosen material constituents.

Ultrahigh discharge energy density (Wdis = 10.5 J cm−3) and efficiency (η = 87%) have been obtained in doped BiFeO3–BaTiO3 ceramic multilayers by achieving an electrically rather than chemically homogeneous microstructure. Back scattered scanning and transmission electron microscopy combined with energy dispersive X-ray spectroscopy mapping of (0.7 − x)BiFeO3–0.3BaTiO3–xNd(Zn0.5Zr0.5)O3 (0.05 ≤ x ≤ 0.10) ceramics revealed a core–shell grain structure which switched from a bright to dark contrast as x increased. Compositions with x = 0.08 were at the point of cross over between these two manifestations of core–shell contrast. Dielectric measurements together with the absence of macrodomains in diffraction contrast TEM images suggested that compositions with x = 0.08 exhibited relaxor behaviour within both the core and shell regions. Impedance spectroscopy demonstrated that, despite being chemical dissimilar, the grains were electrically homogeneous and insulating with little evidence of conductive cores. Multilayers of x = 0.08 had enhanced breakdown strength, EBDS > 700 kV cm−1 and a slim hysteresis loop which resulted in large Wdis and high η which were temperature stable to

Various two terminal electrode geometry configurations are commonly employed to probe the electrical properties of materials with the key consideration being how current flows through the sample. Here, finite element modeling is used to simulate the dc electrical response of an electrically homogeneous sample (based on single crystal SrTiO3) using two terminal electrode geometries based on full surface, top‐bottom macro‐contacts as is commonly used when characterizing bulk ceramics or large single crystals and top‐bottom and top‐top micro‐contacts that are used to characterize thin films and local intra‐ and inter‐granular regions in ceramics. Well‐known equations for macro‐ and micro‐contacts are used to calculate the conductivity of the sample and are compared to the intrinsic values to determine their accuracy. A geometric factor returns accurate bulk conductivity values when there is homogeneous current flow whereas the spreading resistance equation gives the most accurate conductivity values for heterogeneous current flow. When micro‐contacts are used, the response is dominated by a small region of high current density in the vicinity of the contact, providing local electrical properties. Interference can occur when regions of high current density overlap, providing a less resistive route for current flow, thus reducing the applicability of the spreading resistance equation. For top‐top micro‐contacts at small separations, the conductivity is overestimated. The accuracy of the spreading resistance equation increases as the contact separation increases and is within 10% error when they are separated by eight times the micro‐contact radius. Convergence of the error to values lower than 10% becomes increasingly difficult and requires excessively large (and experimentally challenging) separation distances. For example, to obtain a result with an error below 5% requires separations in excess of 28 times the micro‐contact radius. Confinement occurs when the sample size limits the ability of the current to spread out from a micro‐contact, thus increasing the resistance. As the sample shape and dimensions can limit current flow, a geometric factor can sometimes be used to determine accurate conductivity values. In some cases, interference can counter‐balance confinement to yield fortuitously accurate conductivity values.

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.

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

The activation energy associated with bulk electrical conduction in functional materials is an important quantity which is often determined by impedance spectroscopy using an Arrhenius-type equation. This is achieved by linear fitting of bulk conductivity obtained from complex (Z*) impedance plots versus T−1 which gives an activation energy Ea(σ) or by linear fitting of the characteristic frequency fmax obtained from the large Debye peak in M′′–log f spectroscopic plots against T−1 which gives an activation energy Ea(fmax). We report an analysis of Ea(σ) and Ea(fmax) values for some typical non-ferroelectric and ferroelectric materials and employ numerical simulations to investigate combinations of different conductivity–temperature and permittivity–temperature profiles on the log fmax–T−1 relationship and Ea(fmax). Results show the log fmax–T−1 relationship and Ea(fmax) are strongly dependent on the permittivity–temperature profile and the temperature range measured relative to Tm (temperature of the permittivity maximum). Ferroelectric materials with a sharp permittivity peak can result in non-linear log fmax–T−1 plots in the vicinity of Tm. In cases where data are obtained either well above or below Tm, linear log fmax–T−1 plots can be obtained but overestimate or underestimate the activation energy for conduction, respectively. It is therefore not recommended to use Ea(fmax) to obtain the activation energy for bulk conduction in ferroelectric materials, instead Ea(σ) should be used.

The electrical properties of (Na0.5Bi0.5TiO3)1−x(BiScO3)x (NBT-BS, 0.00 ≤ x ≤ 0.25) solid solutions are established by ac impedance spectroscopy and electromotive force transport number measurements. The bulk conductivity decreases with increasing BS incorporation but the oxide-ion transport number remains high (>0.85) over a wide compositional range 0.00 ≤ x ≤ 0.15 and drops to ∼0.7 for x ≥ 0.20. NBT-BS solid solutions can only present either predominant oxide-ion conduction or mixed ionic-electronic conduction behaviour, indicating that oxide-ion conduction cannot be fully eliminated by incorporation of BS. This is in contrast from our previous study where incorporation of ∼7% BiAlO3 (BA) can fully suppress the oxide-ion conduction in NBT. The conductivity–composition relationships of NBT-BS solid solutions are attributed to a competing effect from lattice expansion, which enlarges the channel for oxygen ion migration, with trapping between B-site acceptor ions, , and oxygen vacancies, , which decreases oxygen ion migration. Comparisons between NBT-BS, NBT-BA and NBT-BiGaO3 (BG) solid solutions suggest that small acceptor ions on the B-site are more effective in trapping oxygen vacancies and consequently more effective to suppress the oxide-ion conduction and thus reduce dielectric loss at elevated temperatures.

Organometallic perovskite materials based on MAPbI3 achieve photovoltaic efficiencies as high as 22% for solar cells; however, the long-term stability of these perovskite materials is still a hurdle for applications. Here, we report the air and charge induced instabilities of MAPbI3 perovskite materials with different local stoichiometry using Secondary Electron Hyperspectral Imaging (SEHI). We find that individual grains which do not have the ideal ABX3 stoichiometry degrade faster than stoichiometric grains. We also observe that the degradation pathways depend on the local stoichiometry. Non-stoichiometric grains (with excess MAI) degrade from the centre of the grain and further degradation moves towards the grain boundary, whereas in stoichiometric grains degradation sets in at the grain boundary. We further use deliberately high doses of electron beam exposure to highlight the presence of local non-stoichiometry in device cross-sections of bias degraded devices which pinpoints different onset locations of degradation, depending on the local stoichiometry. These results, therefore, show that precise control of local stoichiometry is required to improve the stability of MAPbI3 and thus the lifetime of perovskite solar cells.

The thermoelectric properties of Sr1-xLax/2Smx/2TiO3-δ (0.05 ≤ x ≤ 0.30) ceramics have been investigated with compositions batched, synthesised by solid state reaction and sintered in 5% H2/N2 at 1500 °C for 6 hrs. All X-ray diffraction patterns were fully indexed according to a cubic perovskite phase. Scanning electron microscopy revealed homogeneous grain structure in the ceramics and confirmed relative density ≥ 89%. The electrical conductivity (σ) of x ≤ 0.15 displayed metallic behaviour with σ < 1000 S/cm, whereas x ≥ 0.20 were semiconducting with σ < 250 S/cm. The Seebeck coefficient of all compositions was negative indicating n-type behaviour. Within this series, x = 0.20 displayed the lowest thermal conductivity of ∼ 3 W/m.K (at 973 K), x = 0.10 displayed the highest power factor of 1400 μW/K2.m (at 573 K) and overall x = 0.15 had the highest dimensionless figure of merit (ZT) of 0.24 (at 875 K).

Novel synthetic routes to prepare functional oxides at lower temperatures are an increasingly important area of research. Many of these synthetic routes, however, use water as the solvent and rely on dissolution of the precursors, precluding their use with, for example, titanates. Here we present a low-cost solvent system as a means to rapidly create phase-pure ferroelectric barium titanate using a choline chloride-malonic acid deep eutectic solvent. This solvent is compatible with alkoxide precursors and allows for the rapid synthesis of nanoscale barium titanate powders at 950 °C. The phase and morphology were determined, along with investigation of the synthetic pathway, with the reaction proceeding via BaCl2 and TiO2 intermediates. The powders were also used to create sintered ceramics, which exhibit a permittivity maximum corresponding to a tetragonal-cubic transition at 112 °C, as opposed to the more conventional temperature of ∼120 °C. The lower-than-expected value for the ferro- to para-electric phase transition is likely due to undetectable levels of contaminants.

We present an aberration corrected scanning transmission electron microscopy (ac-STEM) analysis of the perovskite (LaFeO3) and pyrochlore (Yb2Ti2O7 and Pr2Zr2O7) oxides and demonstrate that both the shape and contrast of visible atomic columns in annular dark-field (ADF) images are sensitive to the presence of nearby atoms of low atomic number (e.g. oxygen). We show that point defects (e.g. oxygen vacancies), which are invisible - or difficult to observe due to limited sensitivity - in X-ray and neutron diffraction measurements, are the origin of the complex magnetic ground state of pyrochlore oxides. In addition, we present, for the first time, a method by which light atoms can be resolved in quantitative ADF-STEM images. Using this method, we resolved oxygen atoms in perovskite and pyrochlore oxides., Comment: 18 pages and 7 figures plus supplementary information

We demonstrate a fast, efficient combinatorial method for the optimisation of materials for multi-layer ceramic capacitors (MLCCs). Experimentally gathered permittivity-temperature profiles for nine compositions spanning a solid solution are used as input, and with series mixing rules, binary and ternary permittivity contour maps are calculated based on individual layer thicknesses. These are converted into Temperature Coefficient of Capacitance (TCC) contour maps and an algorithm is then used to identify material combinations and individual thicknesses suitable for various MLCC classifications. These facilitate targeted experimentation and allowed experimental verification of the methodology. The approach highlights that binary systems can achieve X9 (R, S T and U). classification but the addition of a third complimentary material can facilitate a tighter TCC classification (X9P) with a wider tolerance in layer thicknesses, providing a better strategy for mass production of MLCCs. The room temperature permittivity (ƐRT) for combinations with similar TCC values can also be evaluated to ensure adequate ƐRT is achieved for commercial applications.

Precise control of electronic and/or ionic conductivity in electroceramics is crucial to achieve the desired functional properties as well as to improve manufacturing practices. We recently reported the conventional piezoelectric material Na1/2Bi1/2TiO3 (NBT) can be tuned into a novel oxide-ion conductor with an oxide-ion transport number (tion) > 0.9 by creating bismuth and oxygen vacancies. A small Bi-excess in the nominal starting composition (Na0.50Bi0.50+xTiO3+3x/2, x = 0.01) or Nb-donor doping (Na0.50Bi0.50Ti1−yNbyO3+y/2, 0.005 ≤ y ≤ 0.030) can reduce significantly the electrical conductivity to create dielectric behaviour by filling oxygen vacancies and suppressing oxide ion conduction (tion ≤ 0.10). Here we show a further increase in the starting Bi-excess content (0.02 ≤ x ≤ 0.10) reintroduces significant levels of oxide-ion conductivity and increases tion ∼ 0.4–0.6 to create mixed ionic/electronic behaviour. The switch from insulating to mixed conducting behaviour for x > 0.01 is linked to the presence of Bi-rich secondary phases and we discuss possible explanations for this effect. Mixed conducting behaviour with tion ∼ 0.5–0.6 can also be achieved with lower levels of Nb-doping (y ∼ 0.003) due to incomplete filling of oxygen vacancies without the presence of secondary phases. NBT can now be compositionally tailored to exhibit three types of electrical behaviour; Type I (oxide-ion conductor); Type II (mixed ionic-electronic conductor); Type III (insulator) and these results reveal an approach to fine-tune tion in NBT from near unity to zero. In addition to developing new oxide-ion and now mixed ionic/electronic NBT-based conductors, this flexibility in control of oxygen vacancies allows fine-tuning of both the dielectric/piezoelectric properties and design manufacturing practices for NBT-based multilayer piezoelectric devices.

Barium titanate is the dielectric material of choice in most multilayer ceramic capacitors (MLCCs) and thus in the production of ≈3 trillion devices every year, with an estimated global market of ≈$8330 million per year. Rare earth dopants are regularly used to reduce leakage currents and improve the MLCC lifetime. Simulations are used to investigate the ability of yttrium, dysprosium, and gadolinium to reduce leakage currents by trapping mobile oxygen defects. All the rare earths investigated trap oxygen vacancies, however, dopant pairs are more effective traps than isolated dopants. The number of trapping sites increases with the ion size of the dopant, suggesting that gadolinium should be more effective than dysprosium, which contradicts experimental data. Additional simulations on diffusion of rare earths through the lattice during sintering show that dysprosium diffuses significantly faster than the other rare earths considered. As a consequence, its greater ability to reduce oxygen migration is a combination of thermodynamics (a strong ability to trap oxygen vacancies) and kinetics (sufficient distribution of the rare earth in the lattice to intercept the migrating defects).

La-doping mechanisms and thermoelectric properties of Sr3Ti2O7 Ruddlesden-Popper (RP) ceramics sintered under air and flowing 5% H2 at 1773 K for 6 hours have been investigated. Changes in lattice parameters and conductivity revealed a limited interstitial anion mechanism (~1 at.%) based on La3+ + ½O2- → Sr2+ which resulted in insulating samples when processed in air. In contrast, electronic donor-doping (La3+ + e- → Sr2+) and oxygen loss [O2- → ½ O2 (g) + 2 e-] are the dominant mechanism(s) in 5% H2- sintered ceramics with a solution limit of ~5 at.%. The increased solubility limit is attributed to the formation of Ti3+ during reduction which compensates for the extra positive charge associated with La on the A-site and also to the occurrence of oxygen loss due to the reducing conditions. For 5% H2-sintered samples, an insulating surface layer formed associated with SrO volatilisation and oxygen up-take (during cooling) from the sintering. Unless removed, the insulating layer masked the conductive nature of the ceramics. In the bulk, significantly higher power factors were obtained for ceramics that 2 were phase mixtures containing highly conductive perovskite-based (Sr,La)TiO3- (ST). This highlights the superior power factor properties of reduced perovskite-type ST phases compared to reduced RP-type Sr3Ti2O7 and serves as a precaution for the need to identify low levels of highly conducting perovskite phases when exploring rare-earth doping mechanisms in RP-type phases.

In this work, American Iron and Steel Institute (AISI) O1 steel was pack borided in the temperature range of 1123–1273 K for treatment times between 2 and 8 hours. A kinetic model was proposed for estimating the boron diffusion coefficients through the Fe2B layers. As a result, the boron activation energy for the AISI O1 steel was estimated as 197·2 kJ mol− 1. This value of energy was compared to the literature data. In addtion, to extend the validity of the present model, two additional boriding conditions were done. The Fe2B layers grown on AISI O1 steel were characterised by use of the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and Daimler-Benz Rockwell-C indentation technique. Finally, the scratch and pin on disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions.

The volume fraction of core- and shell-regions is an important parameter in the control of temperature-dependent electrical properties of core–shell-microstructured electroceramics such as BaTiO3. Here, we highlight the potential unreliability of using capacitance ratios, obtained by simulating impedance spectra, to extract accurate volume fractions of the two regions. Two microstructures were simulated using a finite element approach: an approximation to a core–shell structure (the encased model) and a series-layer model (SLM). The impedance response of the microstructures was simulated for a range of input volume fractions. The volume fractions obtained from the simulation agreed with the input values for the SLM microstructure but differed for the encased model. Current density and electric field plots revealed that this discrepancy was caused by differences between the physical and electrical microstructures of the encased model. A stream trace analysis of current density demonstrated that the current follows the path of least resistance through the core, leaving regions of shell with lower current density. These differences are important when attempting to extract volume fractions from encased microstructures with small cores. In the present case, core volume fractions less than 0.7 produce differences in excess of 25%.

Recently, there has been considerable interest in the perovskite phase Na0.5Bi0.5TiO3 (NBT) as a promising lead-free piezoelectric material. Here we report low levels of Na nonstoichiometry (±2 atom % on the A-site) in the nominal starting composition of NBT ceramics can lead to dramatic changes in the magnitude of the bulk (grain) conductivity (σb) and the conduction mechanism(s). Nominal starting compositions with Na excess exhibit high levels of oxide-ion conduction with σb ∼ 2.2 mS cm–1 at 600 °C and an activation energy (Ea) < 1 eV whereas those with Na deficiency are dielectrics based on intrinsic electronic conduction across the band gap with σb ∼ 1.6 μS cm–1 at 600 °C and Ea ∼ 1.7 eV. Drying of reagents, especially Na2CO3, changes the starting stoichiometry slightly due to a small amount of adsorbed moisture in the raw materials but influences significantly the electrical properties. This demonstrates the bulk electrical properties of NBT to be highly sensitive to low levels of A-site nonstoichiom...

A solid solution forms for Sr3NdNb(3-x)Ti(x)O(12-δ) with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R3, as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550-800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550-700 °C, as confirmed by the H(+)/D(+) isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10(-6) S cm(-1) for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a -¼ slope for both doped and undoped samples in the range 10(-19) ≤ pO2 ≤ 10(-8) atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of pO2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron-hole contribution. The dielectric constant at RT of nominally stoichiometric Sr3NdNb3O12 is εr ∼ 37, with a moderately high quality factor of Q × f ∼ 16,400 GHz at fr ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τf ∼ 12 ppm °C(-1), which lowers to -3 ppm °C(-1) for the Ti-doped phase x = 0.06.

Mixed halide (I/Br) complex organic/inorganic hybrid perovskite materials have attracted much attention recently because of their excellent photovoltaic properties. Although it has been proposed that their stability is linked to the chemical inhomogeneity of I/Br, no direct proof has been offered to date. Here, we report a new method, secondary electron hyperspectral imaging (SEHI), which allows direct imaging of the local variation in Br concentration in mixed halide (I/Br) organic/inorganic hybrid perovskites on a nanometric scale. We confirm the presence of a nonuniform Br distribution with variation in concentration within the grain interiors and boundaries and demonstrate how SEHI in conjunction with low-voltage scanning electron microscopy can enhance the understanding of the fundamental physics and materials science of organic/inorganic hybrid photovoltaics, illustrating its potential for research and development in “real-world” applications.

Classical computer simulations are performed on the whole solid solution range of Ba1–xCaxTiO3 (BCT) and Ba1–xSrxTiO3 (BST). The enthalpies and volumes of mixing are produced, and a full local structural analysis is performed. The simulations demonstrate that large degrees of disorder form in the BCT solid solution which leads to distortions in the TiO6 octahedra. Comparing the positions of Sr in BST and Ca in BCT, the position of the Sr cation is largely central within the dodecahedra while the position of the Ca is significantly off-center in many configurations. The relaxation is associated with a shift toward an eight coordinate site compared to a 12 coordinate cation. An empirical model is fitted for predicting the Curie Temperature of the solid solution based on the local structure which shows excellent agreement with experimental values.

The dielectric properties of CaZrO3 (CZ) modified 0.94Bi1/2Na1/2TiO3 (BNT)–0.06BaTiO3 (BT) and 0.82(0.94BNT–0.06BT)–0.18(K1/2Na1/2)NbO3 have been investigated by impedance spectroscopy over a wide temperature range. The presence of a highly polarizable phase in addition to a bulk response is revealed by electric modulus (M″) spectra in both systems. The relaxation frequency of the polar phase follows the Vogel–Fulcher law below the Burns temperature which decreases with increasing CZ content. The dc conductivity of the ceramics is dominated by the bulk response which follows the Arrhenius law with an activation energy ranging from 1.4 to 1.7 eV and has an oxygen partial pressure dependence consistent with n-type semiconductivity. This information is pertinent to on-going compositional development of relaxor-based high-temperature dielectrics.

The electrical and dielectric properties of (1 − x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) with x = 0, 0.03, 0.09, 0.18 have been investigated by impedance spectroscopy over a wide temperature range. The dc conductivity of the ceramics follows the Arrhenius law with an activation energy ranging from ~1.20 to 1.50 eV. Measurements under different atmospheres show the materials exhibit n-type semiconducting behavior at elevated temperatures. The presence of a highly polarizable phase for all compositions is revealed by electric modulus (M″) spectra. The Burns temperature decreases with increasing KNN content. The change in temperature-dependent permittivity with composition is explained by the difference in thermal evolution of polar nanoregions induced by the addition of KNN.

The electrical properties of Sr1−3xLa2xTiO3 ceramics (x = 0.05, LST) change dramatically with sintering temperature and atmosphere. Ceramics sintered at 1200 °C in both O2 and N2 exhibit near intrinsic band-type conduction with bulk conductivity ∼10−7 S cm−1 at 500 °C and activation energy for conduction, Ea of ∼1.6–1.8 eV. LST ceramics sintered at 1450 °C in O2 exhibit much higher bulk conductivity (>10−4 S cm−1 at −50 °C) with an Ea ∼ 0.16 eV. For LST ceramics sintered at 1450 °C in N2, the bulk conductivity was too high to be measured by impedance spectroscopy even at 10 K. In addition, electrical heterogeneity is observed in LST pellets sintered at 1450 °C under both O2 and N2 where pellet outer surfaces are more resistive than the inner regions of the ceramic. The defect chemistry of Sr0.85La0.10TiO3 perovskite is discussed based on chemical doping and oxygen-loss mechanisms and we highlight the importance of A-site vacancies on the oxygen-loss mechanism in La-doped ST-based ceramics.

Guest Editors Caroline Kirk, Finlay Morrison, Jan Skakle, Derek Sinclair and John Irvine introduce this Journal of Materials Chemistry A themed issue on advances in solid state chemistry and its applications, in celebration of Professor Tony West’s 70th birthday.

The impedance response of a core–shell microstructure with 80% core volume fraction has been simulated using finite‐element modeling and compared to two equivalent circuits for a wide range of shell permittivity and conductivity values. Different equivalent circuits, corresponding to different variants of the well‐known brick layer model, are applicable for different combinations of material properties in the microstructure. When the shell has a similar conductivity or permittivity to the core, adding a parallel pathway increases the accuracy of the fit by ≈±10%. When both the conductivity and permittivity values of the core and shell regions are different the series circuit is a better fit. This is confirmed by multiformalism impedance analysis, which reveals features in the data that are not apparent using a single formalism. Finally, the conductivity and permittivity values for both the shell and core are extracted from the simulated spectra using all formalisms and compared to the original input values. The accuracy of the extracted values often depends on the impedance formalism used. It is concluded that impedance spectroscopy data must be analyzed using multiple formalisms when considering core–shell microstructures.

In high-energy density pulsed power capacitors, high permittivity particles are dispersed within a high breakdown strength polymer matrix. In theory, such composites should be able to achieve higher volumetric energy densities than is possible with either of the individual constituents. CH3NH3PbI3 (MALI) has a perovskite structure and may be fabricated at room temperature using a mechanosynthesis route in ethanol. In this study, MALI is used to form a dielectric composite with poly(methyl methacrylate) (PMMA) used as the matrix. Theoretical models are used to predict composite permittivity values that are compared to experimental values. Finite element modeling is used to simulate their effective permittivity and, beyond what the theoretical models can achieve, predicts their energy storage capabilities by analyzing electric field intensification. The simulations show increasing energy storage capability with penetration of MALI, but this is limited experimentally by their mixing capability.

A method of characterizing electrically heterogeneous electroceramics for a full three-dimensional collection of randomly shaped grains is presented. Finite element modeling, solving Maxwell's equations in space and time is used to simulate impedance spectroscopy (IS) data. This technique overcomes several deficiencies associated with previous methods used to simulate IS data and allows comprehensive treatment of a full three-dimensional granular representation of ceramic microstructure without the requirement for equivalent circuits based on the Brickwork layer model (BLM) or the introduction of constant phase elements to describe any nonideality of the IS response. This is applied to a full three-dimensional ceramic microstructure with varying grain size and electrical properties to generate IS plots that highlight limitations of the BLM in data analysis. © 2013 The American Ceramic Society.

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.