Chemical nature of giant strain in Mn-doped 0.94(Na0.5Bi0.5)

Chemical nature of giant strain in Mn-doped 0.94(Na 0.5Bi 0.5)TiO 3–0.06BaTiO 3lead-free ferroelectric single crystals

Haiwu Zhang,a ,b ,⇑Hao Deng,a ,b Chao Chen,a ,b Long Li,a ,b Di Lin,a Xiaobing Li,a

Xiangyong Zhao,a Haosu Luo a ,⇑and Jun Yan c

a

Key Laboratory of Inorganic Functional Materials and Devices,

Shanghai Institute of Ceramics,Chinese Academy of Sciences,215Chengbei Road,Jiading,Shanghai 201800,China

b

Graduate University of Chinese Academy of Sciences,Beijing 100049,China

c

Shibei Power Supply Branch,Shanghai Municipal Electric Power Company,Shanghai 200072,China

Received 25October 2013;accepted 15November 2013

Available online 22November 2013

Giant bipolar and unipolar strains i.e.S max >0.5%,e max /E max >1000pm V –1have been observed in Mn-doped Na 0.5Bi 0.5TiO 3–6BaTiO 3single crystals after being annealed.Temperature-dependent impedance spectra were studied and activation energies of oxygen vacancies were calculated accordingly.The two different binding energies present in X-ray photoelectron spectra for Na and Bi were assigned to different coordinate environments.However,titanium exhibits only one oxidation state (e.g.Ti 4+).The site occupation and valence fluctuation of Mn were characterized by electric paramagnetic resonance spectra.Ó2013Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved.

Keywords:Ferroelectric;Single crystals;Annealing;Electrical properties

Colossal effects,such as giant dielectric and elec-tromechanical responses,make relaxor ferroelectrics suitable for use in advanced devices such as high-perfor-mance super capacitors and high-power transducers.Recently,large electric-field-induced strains have been found in Na 1/2Bi 1/2TiO 3-based materials,which were considered promising environmental friendly alterna-tives to the toxic Pb-based counterparts [1–4].Around the morphotropic phase boundary (MPB),the average structure of Na 1/2Bi 1/2TiO 3–BaTiO 3(NBBT)as well as

Na 1/2Bi 1/2TiO 3–BaTiO 3–K 1/2Na 1/2NbO 3

(NBT–BT–KNN)is pesudocubic [5–7].However,short-range anti-phase (a Àa Àa À)and in-phase (a 0a 0c +)oxygen octa-hedral tilted polar nanoregions (PNRs)coexist in the point view of local structure [8].These PNRs will pro-mote the development of long-range ferroelectric order under the application of an electric field (E):when E is applied along the <001>crystallographic direction,the coherent length of the anti-phase (a Àa Àa À)tilted re-

gions increases and phase transition from pseudocubic to tetragonal structures occurs;along the <111>direc-tion,the in-phase (a 0a 0c +)oxygen octahedral tilted re-gions expand,resulting in an induced transition from pseudocubic to rhombodedral structures [9].Therefore,polarization extension was proposed to explain the large strain in NBT-based ferroelectrics [4,9,10].This is quite different from the Pb-based ferroelectrics,where polari-zation rotation via the bridging phases determines the electromechanical properties [11–13].

The electrical properties of perovskite ferroelectrics are typically tailored by doping with different elements,especially in the case of acceptor doping [14–16].Models such as “volume effect ”,“domain-wall effect ”and “grain boundary effect ”have been proposed to explain the con-figuration of defect dipoles and their interaction with domain walls [17–19].In particular,the defect dipoles align preferentially and generate a restoring force for domain switching during aging [20–22].However,the ef-fects of chemical defects on electrical properties in NBBT have not been systematically studied.Besides,the defect structures in NBBT are sensitive to processing parameters.Noguchi et al.[23]found that the concen-tration of Bi and oxygen vacancies depends on the O 2flow rate during crystal growth processing.A slight

1359-6462/$-see front matter Ó2013Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved./10.1016/j.scriptamat.2013.11.017

⇑Corresponding author at:Key Laboratory of Inorganic Functional

Materials and Devices,Shanghai Institute of Ceramics,Chinese Academy of Sciences,215Chengbei Road,Jiading,Shanghai 201800,China.Tel.:+862169987759;fax:+862159927184;e-mail addresses:zhw3789@ ;hsluo@

Available online at

ScienceDirect

Scripta Materialia 75(2014)

50–53

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