Lone‐Pair‐Induced Covalency as the Cause of Temperature‐ and Field‐Induced Instabilities in Bismuth Sodium Titanate

Schütz, Denis; Deluca, Marco; Krauss, W.; Feteira, Antônio; Jackson, Tim; Reichmann, Klaus

doi:10.1002/adfm.201102758

Cited by 454 publications

(232 citation statements)

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“…This study also confirms generally accepted knowledge that the 6s 2 lone pair electronic structure of Bi 3+ ions plays a crucial role in anion migration of many Bibased oxide ion conductors 22,23 and extends the class of close packed structures from fluorites such as -Bi 2 O 3 to A-site Bi-based perovskites. 10 By adding a small excess of Bi 2 O 3 to the starting composition, i.e.…”

Section: Introductory Paragraphsupporting

confidence: 74%

“…NBT has an ABO 3 perovskite-type structure but the crystal chemistry is complex with differences in the average and local structure being reported depending on the characterisation techniques used and whether the samples are ceramics or single crystals [12][13][14][15][16][17][18][19][20][21][22] . On an average scale, based on neutron powder diffraction studies 12 , NBT is reported to exhibit a sequence of phase transitions (on cooling) from a high temperature cubic (space group Pm m), to tetragonal (space group, Pb4m) and then to a room temperature (RT) rhombohedral (space group R3c) structure.…”

Section: Crystal Structure and Ferroelectric Domain Structuresmentioning

confidence: 99%

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A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

et al. 2013

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. 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...

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Section: Introductory Paragraphsupporting

confidence: 74%

Section: Crystal Structure and Ferroelectric Domain Structuresmentioning

confidence: 99%

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

et al. 2013

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“…At T d , the inter-atomic spring constant responsible for the total energy of the mode was lowered abruptly, accompanied by a rapid change in symmetry of the whole crystal system. 42) This is a hallmark of the breaking of a covalent bond.…”

Section: )41)mentioning

confidence: 99%

Complex bonding in perovskite ferroelectrics

Schütz

Reichmann

2014

J. Ceram. Soc. Japan

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Perovskite ferroelectrics are an important class of functional ceramics. For more than 60 years they are well established materials for charge storage devices and all kinds of piezoelectric components. Increasing demands still drive their development, e.g. currently the quest for lead-free piezoelectric ceramics. Properties of perovskite ferroelectrics can be tailored taking into account the atomic mass of its constituents, which influences the ferroelectric/paraelectric phase transition, and their ionic radii, which are responsible for the symmetry of the lattice. By proper choice of ionic radii advantage of a morphotropic phase boundary can be taken. Donor-or acceptor-doping influences the defect thermodynamics and decides over "hard" or "soft" ferroelectrics. For the further development of ferroelectric ceramics the bonding situation may gain increasing importance. In this paper concepts for covalent or better complex bonding in perovskites are introduced and their consequences for the stability of structures and other material properties are outlined.

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“…The defect chemistry of NBT is rather different from other well-known titanates such as (Ba,Sr,Ca)TiO 3 in that the electrical conductivity is dominated by oxide-ion conduction in NBT and NB 0.49 T rather than electronic conduction. We have attributed the differences in behaviour and the high oxide-ion conductivity in these compositions to high oxygen ion mobility associated with highly polarised Bi 3+ cations and weak Bi-O bonds 31 as well as oxygen vacancies generated through loss of a small amount of Bi 2 O 3 during ceramic processing according to the Kroger-Vink equation, and clarify the origin(s) of its effect on electrical properties. We also highlight the importance of drying Na 2 CO 3 prior to ceramic processing as small changes in the nominal starting stoichiometry of this hygroscopic reagent influences the electrical properties of NBT ceramics.…”

Section: Introductionmentioning

confidence: 99%

Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na_0.5Bi_0.5TiO₃

et al. 2015

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Recently, there has been considerable interest in the perovskite phase Na 0.5 Bi 0.5 TiO 3 (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 ( b ) and the conduction mechanism(s). Nominal starting compositions with Na-excess exhibit high levels of oxide-ion conduction with  b ~ 2.2 mScm -1 (at 600 °C) and an activation energy (E a ) < 1 eV whereas those with Na-deficiency are dielectrics based on intrinsic electronic conduction across the band gap with  b ~ 1.6 Scm -1 (at 600 °C) and E a ~ 1.7 eV.Drying of reagents especially Na 2 CO 3 changes the starting stoichiometry slightly due to 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 nonstoichiometry and reveals how to fine-tune the nominal starting composition of NBT ceramics to suppress leakage conductivity for piezoelectric and high temperature capacitor applications.

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Lone‐Pair‐Induced Covalency as the Cause of Temperature‐ and Field‐Induced Instabilities in Bismuth Sodium Titanate

Cited by 454 publications

References 59 publications

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Complex bonding in perovskite ferroelectrics

Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na_0.5Bi_0.5TiO₃

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Lone‐Pair‐Induced Covalency as the Cause of Temperature‐ and Field‐Induced Instabilities in Bismuth Sodium Titanate

Cited by 454 publications

References 59 publications

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Complex bonding in perovskite ferroelectrics

Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na0.5Bi0.5TiO3

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Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na_0.5Bi_0.5TiO₃