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.

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.

The crystallographic, microstructural, and dielectric properties of Sr2.1Na0.8-xCaxNb5-xSnxO15 (x = 0.00, 0.01, 0.05, 0.10) polycrystalline ceramics have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), dielectric spectroscopy (DS) and impedance spectroscopy (IS). For x=0.00, 0.05, and 0.10, samples are single phase with P4bm phase at room temperature with x = 0.01 showing a small quantity of secondary phase(s). All compositions show typical ceramic microstructure and d50 grain sizes ranging from 5.1 to 26.6 μm. DS shows a clear trend in the high temperature ferroelectric-paraelectric transition with the Curie temperature, T0, decreasing from ~ 160 to ~ 110oC, and an additional relaxation at approximately 120oC with increasing CaSnO3. 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 CaSnO3 content from 1.27 to 1.38eV likely due to the expansion of the band gap.

The radio-frequency permittivity-temperature profiles of acceptor-donor codoped TiO2-based rutiles commonly produce higher than expected values (>10(3) at 300 K) often with conflicting interpretations. A combination of dielectric spectroscopy (DS) and impedance spectroscopy (IS) with different electrode materials is used to reinvestigate the electrical properties of Fe3+-Nb5+-doped rutile in the form of FeTiNbO6 ceramics that show permittivity-temperature characteristics that are consistent with relaxor ferroelectrics (RFE). IS results reveal semiconducting grains with an activation energy of similar to 0.16 eV, and relative permittivity of similar magnitude and temperature dependence to undoped TiO2(<250). Reducing the work function of the electrode material by replacing Au with InGa has a dramatic effect on the IS and DS data. We propose the apparent RFE behavior observed by DS and previously attributed to the formation of nanoclustering of the cations is an extrinsic effect primarily associated with the development of Schottky barriers between the semiconducting ceramics and Au contacts.

High relative permittivity, epsilon(r), over a very wide temperature range, -65 degrees C to 325 degrees C, is presented for ceramics designed to be compatible with base metal electrode multilayer capacitor manufacturing processes. We report a >= 300 degrees C potential Class II capacitor material, free from Bi or Pb ions, developed by doping Sr2NaNb5O15 with Ca2+, Y3+ and Zr4+ ions, according to the formulation Sr2-2zCazYzNaNb5-zZrzO15. For sample composition z = 0.025, epsilon(r) values are 1565 +/- 15 % (1 kHz) from -65 degrees C to 325 degrees C. At a slightly higher level of doping, z = 0.05, epsilon(r) values are 1310 +/- 10 % from -65 degrees C to 300 degrees C. Values of the dielectric loss tangent, tan delta are <= 0.025 from -60 degrees C to 290 degrees C, for z = 0.025, with tand increasing to 0.035 at 325 degrees C. Microstructural analyses exclude coreshell mechanisms being responsible for the flattening of the epsilon(r) -T response.

The piezoelectric dij coefficient is often regarded in materials science as the most important figure of merit of piezoelectric performance. For many applications, the piezoelectric gij coefficient which correlates to voltage output and sensitivity of a piezoelectric material can be considered of equal or increased importance, however is often an overlooked parameter in materials science literature. The aim of this review is to highlight the importance of this parameter and to provide insight into the mechanisms that drive a high piezoelectric voltage coefficient in single crystal, polycrystalline, and composite form. For bulk ceramics, special attention is given to tetragonal systems due to the availability of electrical and crystallographic data allowing for a clear structure-property relation. Orthorhombic and rhombohedral systems are mentioned and specific cases highlighted, however investigating structure-property relations is difficult due to the lack of crystallographic datasets. Composite materials have been the forefront of high gij piezoelectric materials over the decades and are therefore also considered in both ceramic-matrix and polymer-matrix form. An overview of applications in medical, energy, fishing and defence industries where a high gij is desirable are considered and the scientific and commercial considerations that must be made for the transition from laboratory to industry are discussed from the perspective of integrating new piezoelectric materials into sonar devices.

Since the construction of the first structural phase diagram of the BiFeO3–PbTiO3 solid solution, there has been ambiguity as to the true location of the morphotropic phase boundary (MPB). In this study, a Landau–Devonshire derived phase diagram has been constructed in order to provide a mathematically derived perspective. The compositional dependence on properties has been modeled as a linear dependence between the Landau coefficients of each end member. It is found that the only structural phases found below TC are rhombohedral and tetragonal, which at 25 °C shows an MPB at 0.696BiFeO3–0.304PbTiO3. The MPB also shows temperature dependence similar to other ferroelectric solid solutions in which the tetragonal–rhombohedral phase transition moves toward higher BiFeO3 contents at higher temperatures. Although the replication of the experimentally observed phase diagram can be constructed, this method is found to be insufficient for describing the spontaneous strain behavior.

Charged domain walls (DWs) in ferroelectric materials are an area of intense research. Microscale strain has been identified as a method of inducing arrays of twin walls to meet at right angles, forming needlepoint domains which exhibit novel material properties. Atomic scale characterisation of the features exhibiting these exciting behaviours was inaccessible with the piezoresponse force microscopy resolution of previous work. Here we use aberration corrected scanning transmission electron microscopy to observe short, stepped, highly charged DWs at the tip of the needle points in ferroelectric PbTiO 3 . Reverse Ti 4+ shift polarisation mapping confirms the head-to-head polarisation in adjacent domains. Strain mapping reveals large deviations from the bulk and a wider DW with a high Pb 2+ vacancy concentration. The extra screening charge is found to stabilise the DW perpendicular to the opposing polarisation vectors and thus constitutes the most highly charged DW possible in PbTiO 3 . This feature at the needle point junction is a 5 nm × 2 nm channel running through the sample and is likely to have useful conducting properties. We envisage that similar junctions can be formed in other ferroelastic materials and yield exciting phenomena for future research.

Previous work in ferromagnetic microwave amplification has followed a two-fold course of reducing the necessary pump power by 1) reducing the resonant absorption linewidth and 2) improving the filling factor of magnetic material to the resonant system. These developments have led to the Denton-type amplifier employing a parallel-pumped single crystal sphere of yttrium iron garnet operating in the ...