0.5KBT-(0.5-x) BF-xLMN with [Formula: see text], 0.04, 0.06, 0.08 and 0.10 ceramics were fabricated using a conventional solid-state reaction method. All samples exhibited a single pseudocubic perovskite phase with minor levels of Bi4Ti3O[Formula: see text] as a secondary phase. The average grain size decreased slightly with x from [Formula: see text] to 1.8[Formula: see text] [Formula: see text]m and Impedance Spectroscopy at elevated temperatures showed the ceramics to be electrically homogeneous with the insulation resistance of [Formula: see text] all exceeding [Formula: see text] with [Formula: see text] displaying the highest activation energy for conduction at [Formula: see text] [Formula: see text]eV. The permittivity ([Formula: see text] at 100∘C) was frequency-dependent, implying relaxor behavior, and exhibited a temperature-stable plateau between [Formula: see text]–250∘C. 0.5KBT-0.46BF-0.04LMN had the highest [Formula: see text] and recoverable energy density, [Formula: see text] of 130[Formula: see text]kV[Formula: see text]cm[Formula: see text] and 1.14[Formula: see text] [Formula: see text]J[Formula: see text]cm[Formula: see text], respectively, accompanied by low strain ([Formula: see text]%). The combination of high [Formula: see text], a temperature-stable plateau in permittivity, exceptionally low strain and large [Formula: see text], suggests these compositions have potential for use in multilayer ceramic capacitors (MLCCs) for high voltage/temperature applications in power electronics.

X7R rated dielectrics with room temperature relative permittivity (epsilon(r)) of similar to 2000 are produced as ceramic-ceramic composites based on a ferroelectric BaTiO3 matrix (BT, Curie Temperature, T-c = 122 degrees C) and a relaxor-ferroelectric Na0.6Ba0.4Nb0.6Ti0.4O3 filler (T-max = -135 degrees C at 250 kHz) in a respective 80:20 wt. % mass fraction. X8R rating is achieved when the composite is formed with a Ba0.93Ca0.07TiO3 (BCT, T-c = 129 degrees C) matrix phase instead of BT. The enhancement from X7R to X8R performance is attributed to creating a broader epsilon(r) peak at similar to 121 degrees C due to a wider distribution of A-site cations in the composite, as opposed to an increase in T-c of monolithic BCT.

0.5KBT-(0.5-x) BF-xLMN with x=0, 0.04, 0.06, 0.08 and 0.10 ceramics were fabricated using a conventional solid-state reaction method. All samples exhibited a single pseudocubic perovskite phase with minor levels of Bi4Ti3O12 as a secondary phase. The average grain size decreased slightly with x from similar to 2.2 to 1.8 mu m and Impedance Spectroscopy at elevated temperatures showed the ceramics to be electrically homogeneous with the insulation resistance of x > 0 all exceeding x = 0 with x = 0.04 displaying the highest activation energy for conduction at similar to 1.1 eV. The permittivity (similar to 1500 at 100 degrees C) was frequency-dependent, implying relaxor behavior, and exhibited a temperature-stable plateau between similar to 100-250 degrees C. 0.5KBT-0.46BF-0.04LMN had the highest E-pulse and recoverable energy density, W-rec of 130kVcm(-1) and 1.14 Jcm(-3), respectively, accompanied by low strain (<0.1%). The combination of high E-pulse, a temperature-stable plateau in permittivity, exceptionally low strain and large Wrec, suggests these compositions have potential for use in multilayer ceramic capacitors (MLCCs) for high voltage/temperature applications in power electronics.

The thermal instability of SNN across different temperatures has been investigated, revealing that both the end-member structures (NN and SN2) and the presence of A-site vacancies play significant roles.

Power modules in electric vehicles (EVs) are essential electronic components that manage and convert electrical power between the battery and other vehicle systems, such as the motor. The electronics are required to operate at higher temperatures (>200 o C) and fields (>0.5 MV/cm) than in conventional consumer goods such as phones and tablets. This requires the use of, e.g., SiC based semiconductor technology, along with associated filters/capacitors that can withstand high temperature/fields. Such capacitors have a large energy density arising from the ability of the dielectric to withstand repeated application of high fields (>0.5 MV/cm) without breakdown. This article reviews examples and presents new data and concepts on high energy density dielectrics intended for use in power electronic. In particular, the article focuses on a new class of dielectrics which have high permittivity (>1000) but do not saturate at high field and exhibit a quasi-linear polarisation-field response. The roles of chemical, polar and octahedral tilt disorder are assessed and a new mechanism proposed by which tilt disorder restricts strain coupling and therefore polar coupling, leading to a quasi-linear response in polarisation-field (P-E) loops. The influences of local variations in stoichiometry and multi-valent and multi-sized substituents in these polar lattices to attain enhanced resistivity are also discussed. The article therefore illustrates how a combination of high resistivity and tilt disorder are pivotal in the design of a new generation of high energy density capacitors for power electronics.

An overview is given of the literature on current approaches to the measurement, analysis and interpretation of broadband impedance data and examples of its application to Na materials, cells and batteries. Standard 2-terminal measurements on full cells are often complemented by both 2- and 3-terminal measurements on a range of materials and cell configurations; this should enable identification of the different impedance contributions that control full cell operation. Data analysis usually revolves around equivalent circuit modelling; strategies to identify the most appropriate circuits are reviewed, including increasing use of the distribution of relaxation times methodology. Interfacial phenomena are fundamental components of solid electrolyte interfaces and composite electrodes in operational batteries; these are reviewed for Na-based materials and systems.

The properties of the hexagonal P2 sodium cobaltate, Na0.7CoO2 (NCO) phase densified using the conventional and cold sintering methods were investigated, and we demonstrated that the cold sintering method yields NCO with a relative density of over 98 % (compared to 90 % attained after conventional sintering) while maintaining high room temperature conductivity (10(-2) Scm(-1)). In X-ray diffraction, the original P2-phase framework is retained regardless of the sintering process, and the magnetic properties of NCO strongly depend on the densification route. Cold-sintered samples showed a classic paramagnetic response down to 2 K, while conventionally sintered samples developed a spin-glass behaviour below 6 K. The emergence of the spin-glass state on conventionally sintered ceramics was attributed to the enhanced disorder of Co3+ and Co4+ ions. A multitude of complex superstructures associated with Na ordering was identified for both cold and conventionally sintered NCO in electron diffraction.

The crystallographic, microstructural, and dielectric properties of Sr 2.1 Na 0.8-x Ca x Nb 5-x Sn x O 15 (x = 0.00, 0.01, 0.05, 0.10) polycrystalline ceramics have been studied by X-ray diffraction, scanning electron microscopy, dielectric spectroscopy (DS) and impedance spectroscopy (IS). For x = 0.00, 0.05, and 0.10, samples are single phase with P 4 bm symmetry at room temperature with x = 0.01 showing a small quantity of secondary phase(s). All compositions show typical ceramic microstructures and d 50 grain sizes ranging from 5.1 to 26.6 mu m. DS shows a clear trend in the high temperature ferroelectric-paraelectric transition with the Curie temperature, T 0 , decreasing from - 160 to - 110 degrees C, and an additional relaxation at approximately 120 degrees C with increasing CaSnO 3 . 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 CaSnO 3 content from 1.27 to 1.38 eV likely due to the expansion of the band gap.

The structural and electrical properties of A-site deficient Sr x Na 1−2 x NbO 3 (0 ≤ x ≤ 0.25) ceramics have been studied by X-ray diffraction, electron microscopy, dielectric spectroscopy, impedance spectroscopy and polarisation against electric field.

Electrostatic energy storage capacitors are essential passive components for power electronics and prioritize dielectric ceramics over polymer counterparts due to their potential to operate more reliably at > 100 & ring;C. Most work has focused on non-linear dielectrics compositions in which polarization (P)/electric displacement (D) and maximum field (E-max) are optimized to give values of energy density, 6 <= U <= 21 J cm(-3). In each case however, either saturation (dP/dE = 0, AFE) or "partial" saturation (dP/dE -> 0, RFE) of P limits the value of U which can be achieved before breakdown. It is proposed that U can be further improved with respect to relaxors (RFEs) and anti-ferroelectrics (AFEs) by designing high permittivity quasi-linear dielectric (QLD) behaviour in which dP/dE remains constant up to ultrahigh E-max. QLD multilayer capacitor prototypes with dielectric layers composed of 0.88NaNb(0.9)Ta(0.1)O(3)-0.10SrTiO(3)-0.02La(Mg1/2Ti1/2)O-3 deliver room temperature U approximate to 43.5 J cm(-3), supporting an extremely-large E-max approximate to 280 MV m(-1), both of which exceed current state-of-art by a factor of two for devices based on powder, tape-cast technology. Importantly QLD capacitors exhibit scant variation in U (approximate to 15 J cm(-3)) up to > 200 & ring;C and robust resistance to cyclic degradation, offering a promising new approach for the development of sustainable technology.

Micro-contact impedance spectroscopy (mcIS) is a powerful tool that can allow local features such as grain boundaries and surfaces in electro-ceramics to be directly interrogated. Typical macroscopic electrodes fully cover the specimen surfaces and data are converted from resistance into conductivity using a geometric correction factor based on the surface area of the electrodes and thickness of the sample. For mcIS measurements this requires a different approach. The conversion factor required in this case is that for a spreading resistance and the correction factor depends on the radius (r) and separation of the micro-contacts. When dealing with conversions for samples with a resistive surface layer, two extreme scenarios exist depending on the thickness of the surface layer (T) and the arrangement and size of the contacts. When the resistive layer is thin (T/r < 10) the geometric correction factor provides accurate conductivities but for thick layers (T/r > 10) the spreading resistance correction equation is required. When the surface layer is an intermediate thickness however neither provides a good estimate for conductivity. Using finite element modelling we simulate resistive surface layer systems using a top-top micro-contact arrangement and show that instead of using either of the two separate correction equations, a single modified spreading resistance equation can be used on the resulting impedance data to provide greater accuracy and simplicity in the extraction of conductivity. With this modified correction factor, when the ratio of bulk material conductivity versus surface layer conductivity (sigma(b)/sigma(s)) is >= 100, sigma(s) can be calculated for any surface layer thickness. When the ratio is < 100, only when (T/r) is > 3 can sigma(s) be accurately estimated.

Na3Zr2Si2P2O12 (NZSP) has potential use as a solid electrolyte in Na-ion solid-state batteries due to its high ionic conductivity (10- 3-10-4 Scm- 1) at room temperature. It is established that all previous preparations involving the solid-state method for NZSP compositions contain m-ZrO2 as a secondary phase. Here, the solid-state method is used to prepare single-phase NZSP by modifying the mole fractions of the ZrO2 reactant. Reducing ZrO2 concentration may also create Zr and O vacancies and potentially increase the hopping sites for Na-ion conduction. X-ray diffraction, scanning electron microscopy, Raman and Fourier Transform Infrared spectroscopy, dilatometry and impedance spectroscopy were used to characterise the structure, morphology and electrical properties of single-phase NZSP, and the results were compared with samples that have m-ZrO2 secondary phase (Na3Zr2Si2PO12). The role of m-ZrO2 impurities on the conductivity of NZSP is investigated and compared with available literature.

Solid solutions of Na0.5Bi0.5TiO3 (NBT) and BiNi0.5Ti0.5O3 (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+ (NiNix) and Ni3+ (NiNi·), 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.

Johnson's approximation is implemented in a finite element code to simulate the electric field dependence of a core-shell microstructure material. We show how the microstructure, based here on a 50:50 volume fraction, influences the measured effective permittivity as a function of applied voltage. Using a Johnson's parameter of beta = 1.0 x 1010 Vm5/C3, verified from commercial BaTiO3-based multilayer ceramic capacitors (MLCC), we show how the microstructure and the difference in core and shell conductivities alter the local fields generated and how this influences the voltage dependence of the effective permittivity. Systems that comprise a conductive core-like material surrounded by a resistive shell experience little or modest voltage dependence due to the shell material providing shielding to large electric fields within the cores. Conversely, if the core material is more resistive than the shell material, substantial voltage dependence occurs with simulations showing over a 50% decrease in the effective permittivity. These simulations give improved understanding of voltage dependence and provide a method to help guide the design of future materials for MLCCs with improved performance.

For the first time, the origin of large electrostrain in pseudocubic BiFeO_{3}-based ceramics is verified with direct structural evidence backed by appropriate simulations. We employ advanced structural and microstructural characterizations of BiFeO_{3}-based ceramics that exhibit large electrostrain (>0.4%) to reveal the existence of multiple, nanoscale local symmetries, dominantly tetragonal or orthorhombic, which have a common, averaged direction of polarization over larger, meso- or microscale regions. Phase-field simulations confirm the existence of local nanoscale symmetries, thereby providing a new vision for designing high-performance lead-free ceramics for high-strain actuators.

Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO3-Bi(Mg0.5Ti0.5)O3 relaxor dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High-resolution, synchrotron X-ray diffraction indicated a globally cubic structure (Pm3̅m), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.

SiC and GaN devices are gaining in popularity in both research and commercial applications. One of the many benefits of these devices is the possibility of power converter operation at temperatures in excess of that possible with Si-based devices (>200°C). A bismuth scandium lead titanate (BSPT) piezoelectric transformer is analysed for use in high temperature (up to 250°C), resonant converters using impedance spectroscopy and power converter measurements. The PT shows declining losses with temperatures during testing, translating into an improvement of 15% points in efficiency whilst more than doubling the output power across the temperature range. A peak performance of 0.7W output power and 53% efficiency at 225°C was achieved, giving comparable performance to previous work but at higher temperatures.

Incorporation of BiCoO 3 induces n-type electronic conduction into NBT to make it a mixed ionic-electronic conductor with high conductivity.

Micro-contact impedance spectroscopy (MCIS) is a powerful tool to analyse local features of interest in electroceramics. The surface condition of the measured area of interest however may not always be ideal. Surface defects such as cracks may be present and therefore influence the measured MCIS data, especially for a top-top electrode configuration. Here we develop a finite element model on a system where a crack of various dimensions exists on the top surface between two surface micro-contact electrodes. We show how a crack can influence the current distribution within the sample and its effect in evaluating the MCIS data and associated extracted conductivity values. When the micro-contact separation is low, the hindrance effect forming from a crack acts to counterbalance the strong current interference effect that originates from closely placed top-top electrodes. The crack depth and length prove to be more effective than crack width in terms of counterbalancing interference. As the micro-contact separation increases, both current interference and crack hindrance decreases. Cracks in a specimen may therefore fortuitously assist in offsetting significant current interference effects, especially at the micro-contact separations used in many experimental set-ups.