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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 PbTiO3. Reverse Ti4+ 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 Pb2+ 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 PbTiO3. 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.

High relative permittivity, εr, over a very wide temperature range, -65 ⁰C to 325 ⁰C, is presented for ceramics designed to be compatible with base metal electrode multilayer capacitor manufacturing processes. We report a ≥ 300 ⁰C 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, εr values are 1565 ± 15 % (1 kHz) from -65 °C to 325 °C. At a slightly higher level of doping, z = 0.05, εr values are 1310 ± 10 % from -65 °C to 300 °C. Values of the dielectric loss tangent, tanδ are ≤ 0.025 from -60 °C to 290 °C, for z = 0.025, with tanδ increasing to 0.035 at 325 ⁰C. Microstructural analyses exclude coreshell mechanisms being responsible for the flattening of the εr -T response.

This is a repository copy of Landau-Devonshire derived phase diagram of the BiFeO3-PbTiO3 solid solution.

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