Available online at www.sciencedirect.com Journal of the European Ceramic Society 31 (2011) 1861–1864 Short communication Ferroelectric domain structure of lead-free potassium-sodium niobate ceramics Rigoberto López-Juárez a,∗ , Omar Novelo-Peralta a , Federico González-García b , Fernando Rubio-Marcos c,d , María-Elena Villafuerte-Castrejón a a Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior S/N, A.P. 70-360, México, D.F., Mexico b Departamento de Ingeniería de Procesos e Hidráulica, Universidad Autónoma Metropolitana-Iztapalapa, A.P. 55-534, 09340 México, D.F., Mexico c Laboratoire de Science des Procédés Céramiques et de Traitements de Surface, UMR 6638 CNRS, Université de Limoges, Centre Européen de la Céramique, 12 rue Atlantis, 87068 Limoges Cedex, France d Electroceramic Department, Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049 Madrid, Spain Received 26 August 2010; received in revised form 11 February 2011; accepted 22 February 2011 Available online 3 April 2011 Abstract The complex domain structure of orthorhombic (K 0.5 Na 0.5 )NbO 3 (KNN) piezoelectric ceramics has been studied by SEM. The study was performed in samples prepared by microwave-hydrothermal synthesis. The identification of the domain structure has been afforded in KNN ceramics. Abnormal grain growth was observed in the microstructure of KNN ceramics, with an average grain size of 63 m. Most of the ferroelectric domains were 90 ◦ type with square-net and herringbone structures alternating a–a and a–c configurations. In addition, 180 ◦ domains were also identified arranged in the common watermark pattern. © 2011 Elsevier Ltd. All rights reserved. Keywords: Grain growth; Electron microscopy; Ferroelectric properties; Niobates 1. Introduction Lead zirconate-titanate ceramics (PZT) are the most widely used piezoelectric materials until now, because of their high piezoelectric response, large scale production capability and the tailoring of their properties through composition. Recently, the European Union has published a health normative (ROH) 1 avoiding the use of lead (toxicity and environmental risks). Nev- ertheless, PZT ceramics are temporarily tolerated because of the lack of an adequate alternative. The search for alternative lead-free piezoelectric materials is now being focused on sys- tems in which a morphotropic phase boundary (MPB) occurs. One promising alternative is based on potassium sodium nio- bate solid solution (KNN), due to their good electromechanical properties (k p ∼ 0.36, d 33 ∼ 80 pC/N) and Curie temperature (T C ∼ 420 ◦ C). 2 The crystalline symmetry and point group ∗ Corresponding author. Tel.: +52 55 56 22 46 41x24646; fax: +52 55 56 16 13 71. E-mail address: rigobertolj@yahoo.com.mx (R. López-Juárez). of KNN at room temperature are orthorhombic and mm2, respectively, which allow to establish all possible domain wall orientations. On the other hand, piezoelectricity appears on ferroelectric ceramics when the random ferroelectric domains are aligned through the poling process. 3 So, the study of ferroelectric domains in piezoelectric materials is necessary for a better understanding of their properties. In order to investigate the structure and distribution of ferroelectric domains, a num- ber of techniques have been applied, among them, scanning probe microscopy, 4 environmental scanning microscopy, 5 opti- cal microscopy, 6 transmission electron microscopy, 7 scanning force microscopy 8 and lately, scanning electron microscopy in the backscattered mode. 9,10 There are several methods for reveling domains 10 depending upon the particular composition. For example, it is possible to study ferroelectric domains in backscattered mode by scanning electron microscopy with an appropriate sample preparation. 9 The ferroelectric domain pattern is generated by the interac- tion between the electron beam and electric dipoles inside the domains. However, it is crucial to avoid surface charge accumu- 0955-2219/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2011.02.031