. et al. (5 more authors) (2014) A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3. Nature Materials, 13 (1). 31 -35. ISSN 147631 -35. ISSN -1122 https://doi.org/10.1038/NMAT3782 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Introductory paragraphOxide ion conductors find important technical applications in electrochemical devices such as solid oxide fuel cells (SOFCs), oxygen separation membranes and sensors 1-9 . Na 1/2 Bi 1/2 TiO 3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity which is problematic for its piezoand ferroelectric applications 10-15 . 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 o 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 [10][11][12][13][14][15] . NBT exhibits maximum relative permittivity,  r ~ 3000 at ~ 320 o C (T max ) and possesses a distorted perovskite structure with extensive chemical, cationdisplacement and octahedral tilt disorder. 14 The resulting complex nanodomain structure is well known to facilitate high and temperature stable permittivity behaviour which is suitable for the fabrication of high temperature ceramic capacitors in addition to easy phase switching under the application of a large electric field which creates large strains suitable for actuator applications [10][11][12][13][14][15] . One drawback of NBT for piezoelectric and capacitor applications, however, is its high leakage conductivity 10,11 . The piezoelectric properties and room temperature dc conductivity depend on the nominal starting composition 10,11 , the origin of which has not been resolved. Here we report on the surprising and dramatic sensitivity of the ionic and electronic transport properties of NBT on low levels of A-site nonstoichiometry in the nominal starting composition. We demonstr...

The transport of oxygen in dense samples of yttria-stabilized zirconia (YSZ), of average grain size d approximately 50 nm, has been studied by means of 18O/16O exchange annealing and secondary ion mass spectrometry (SIMS). Oxygen diffusion coefficients (D*) and oxygen surface exchange coefficients (k*) were measured for temperatures 673

The conductivity of dense ceramics of nanocrystalline yttria-stabilized zirconia (nano-YSZ), with average grain sizes ranging from 13 nm to 100 nm, was measured in wet and dry air as a function of temperature between 30 C and 500 C. Under wet conditions (p H 2 O ¼ 2.3 Â 10 À2 atm) the measured conductivity at low temperatures (<150 C) was found to increase strongly with decreasing grain size, displaying a highly non-linear dependence on grain size. This is interpreted as evidence of the protonic conductivity of grain boundaries increasing with decreasing grain size.

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Oxygen isotope exchange experiments, H218O/H216O (”wet” anneals) and 18O2/16O2 (”dry” anneals), were performed on single crystal samples of yttria‐stabilized zirconia (YSZ) at a temperature of T = 1073 K with subsequent determination of the oxygen isotope profiles in the solid by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Such experiments yielded oxygen tracer diffusion coefficients (D*) and oxygen tracer surface exchange coefficients (k*), from both the polished (smooth) and unpolished (rough) sides of single crystal samples, as a function of water partial pressure pH2O and oxygen partial pressure pO2. Isothermal values of D* were found to depend on neither pO2 nor pH2O (nor surface roughness). Isothermal values of k*, in contrast, displayed a strong dependence on pO2 or pH2O; k*wet was, in addition, 2–3 orders of magnitude higher than k*dry. Surprisingly, surface roughness had little effect on k*wet, whereas rough surfaces exhibited much higher k*dry values than smooth surfaces. Data for k*wet obtained as a function of temperature at pH2O = 18 mbar show a change in activation enthalpy at T ≈ 973 K. The behavior of k* is discussed in terms of surface composition, surface area and surface reaction mechanisms.