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      Scanning X-ray nanodiffraction from ferroelectric domains in strained K 0.75Na 0.25NbO 3 epitaxial films grown on (110) TbScO 3 1

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          Abstract

          Scanning X-ray nanodiffraction with 100 nm spatial resolution has been applied to investigate the ferroelectric domain structure of K 0.75Na 0.25NbO 3 epitaxial layers grown on a (110) TbScO 3 substrate using metal–organic chemical vapour deposition. Two variants differing in domain wall alignment and vertical lattice parameters have been identified and independently analysed.

          Abstract

          Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K 0.75Na 0.25NbO 3 epitaxial layer has been performed by using a focused X-ray beam of about 100 nm probe size. A 90°-rotated domain variant which is aligned along [1 2] TSO has been found in addition to the predominant domain variant where the domains are aligned along the [ 12] TSO direction of the underlying (110) TbScO 3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K 0.75Na 0.25NbO 3 epitaxial layer.

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          Most cited references14

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          Lead-free piezoceramics.

          Lead has recently been expelled from many commercial applications and materials (for example, from solder, glass and pottery glaze) owing to concerns regarding its toxicity. Lead zirconium titanate (PZT) ceramics are high-performance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices; they contain more than 60 weight per cent lead. Although there has been a concerted effort to develop lead-free piezoelectric ceramics, no effective alternative to PZT has yet been found. Here we report a lead-free piezoelectric ceramic with an electric-field-induced strain comparable to typical actuator-grade PZT. We achieved this through the combination of the discovery of a morphotropic phase boundary in an alkaline niobate-based perovskite solid solution, and the development of a processing route leading to highly textured polycrystals. The ceramic exhibits a piezoelectric constant d33 (the induced charge per unit force applied in the same direction) of above 300 picocoulombs per newton (pC N(-1)), and texturing the material leads to a peak d33 of 416 pC N(-1). The textured material also exhibits temperature-independent field-induced strain characteristics.
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            Monoclinic and triclinic phases in higher-order Devonshire theory

            Devonshire theory provides a successful phenomenological description of many cubic perovskite ferroelectrics such as BaTiO3 via a sixth-order expansion of the free energy in the polar order parameter. However, the recent discovery of a novel monoclinic ferroelectric phase in the PZT system by Noheda et al. (Appl. Phys. Lett. 74, 2059 (1999)) poses a challenge to this theory. Here, we confirm that the sixth-order Devonshire theory cannot support a monoclinic phase, and consider extensions of the theory to higher orders. We show that an eighth-order theory allows for three kinds of equilibrium phases in which the polarization is confined not to a symmetry axis but to a symmetry plane. One of these phases provides a natural description of the newly observed monoclinic phase. Moreover, the theory makes testable predictions about the nature of the phase boundaries between monoclinic, tetragonal, and rhombohedral phases. A ferroelectric phase of the lowest (triclinic) symmetry type, in which the polarization is not constrained by symmetry, does not emerge until the Devonshire theory is carried to twelfth order. A topological analysis of the critical points of the free-energy surface facilitates the discussion of the phase transition sequences.
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              Giant piezoelectricity in potassium-sodium niobate lead-free ceramics.

              Environment protection and human health concern is the driving force to eliminate the lead from commercial piezoelectric materials. In 2004, Saito et al. [ Saito et al., Nature , 2004 , 432 , 84 . ] developed an alkali niobate-based perovskite solid solution with a peak piezoelectric constant d33 of 416 pC/N when prepared in the textured polycrystalline form, intriguing the enthusiasm of developing high-performance lead-free piezoceramics. Although much attention has been paid on the alkali niobate-based system in the past ten years, no significant breakthrough in its d33 has yet been attained. Here, we report an alkali niobate-based lead-free piezoceramic with the largest d33 of ∼490 pC/N ever reported so far using conventional solid-state method. In addition, this material system also exhibits excellent integrated performance with d33∼390-490 pC/N and TC∼217-304 °C by optimizing the compositions. This giant d33 of the alkali niobate-based lead-free piezoceramics is ascribed to not only the construction of a new rhombohedral-tetragonal phase boundary but also enhanced dielectric and ferroelectric properties. Our finding may pave the way for "lead-free at last".
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                Author and article information

                Journal
                J Appl Crystallogr
                J Appl Crystallogr
                J. Appl. Cryst.
                Journal of Applied Crystallography
                International Union of Crystallography
                0021-8898
                1600-5767
                01 April 2017
                17 February 2017
                17 February 2017
                : 50
                : Pt 2 ( publisher-idID: j170200 )
                : 519-524
                Affiliations
                [a ]Leibniz-Institut für Kristallzüchtung, Max-Born-Strasse 2, Berlin 12489, Germany
                [b ]Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin, Hausvogteiplatz 5–7, Berlin 10117, Germany
                [c ]ESRF – The European Synchrotron, 71 Avenue des Martyrs, Grenoble Cedex 9, CS-40220, 38043, France
                Author notes
                Author information
                https://orcid.org/0000-0001-6398-6370
                https://orcid.org/0000-0002-8919-3608
                Article
                vh5071 JACGAR S1600576717000905
                10.1107/S1600576717000905
                5377345
                87653e94-0fdb-4eec-a868-e1cd21410687
                © Martin Schmidbauer et al. 2017

                This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

                History
                : 01 December 2016
                : 18 January 2017
                Categories
                Research Papers

                Analytical chemistry
                x-ray nanodiffraction,ferroelectric domains,kxna1−xnbo3,strained epitaxial films

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