Microstructure development and piezoelectric properties of highly textured CuO-doped KNN by templated grain growth
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ephen F. Poterala Department of Materials Science and Engineering, and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802
Zupei Yang School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an, 710062 Shaanxi, People’s Republic of China
Susan Trolier-McKinstry and Gary L. Messinga) Department of Materials Science and Engineering, and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802 (Received 18 October 2009; accepted 22 December 2009)
This paper demonstrates the production of h00li-oriented CuO-doped (K0.476Na0.524)NbO3 (KNN) piezoelectric ceramics with a polymorphic phase transition (PPT) temperature greater than 180 C by templated grain growth (TGG) using high aspect ratio NaNbO3 template particles. A novel (to the KNN system) two-step sintering and annealing process combined with CuO doping is demonstrated to improve density and maximize texture quality (F00l = 99% and rocking curve FWHM = 6.9 ) in textured KNN ceramics. The best electromechanical properties (kp 0.58, k31 0.33, d33 146 pC/N, To-t 183 C, Tc 415 C, er = 202, and tan d = 0.016) are achieved in 1 mol% CuO-doped KNN with F00l = 99% and a relative density of 96.3%. The values of d33, kp, and k31 are 70–90% higher than randomly oriented ceramics and are obtained without a significant reduction in the PPT temperature, resulting in stable piezoelectric performance over a wide temperature range (50 to 180 C). These results show that high-quality textured KNN can be obtained by TGG and that a reactive matrix is unnecessary. I. INTRODUCTION
Lead-based perovskites like Pb(ZrxTi1x)O3 (PZT) ceramics dominate the commercial piezoelectric market for sensors, actuators, and transducers, because they have excellent dielectric and piezoelectric properties near the morphotropic phase boundary (MPB) and can operate from 50 to 150 C.1 However, the toxicity of lead has raised environmental and health concerns and prompted extensive research worldwide to develop lead-free piezoelectric materials.2 Pure (K,Na)NbO3 has a rhombohedral-orthorhombic phase transition temperature of about 160 C, an orthoa)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2010.0084 J. Mater. Res., Vol. 25, No. 4, Apr 2010
rhombic-tetragonal polymorphic phase transition (PPT) temperature of 200 C and a Curie temperature of 400 C, resulting in a wide operating temperature range.1–3 However, pure (K,Na)NbO3 is difficult to sinter to high density and has relatively low room-temperature electromechanical properties.3,4 Modified (K,Na)NbO3 systems can partially overcome these problems and have attracted attention following the report of textured (K,Na,Li)(Nb,Ta,Sb)O3 ceramics with a piezoelectric coefficient d33 o
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