Ferroelectric relaxor behavior in hafnium doped barium-titanate ceramic Shahid Anwar, P.R. Sagdeo, N.P. Lalla * UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017, India Received 22 June 2005; received in revised form 7 March 2006; accepted 18 March 2006 by B.-F. Zhu Available online 4 April 2006 Abstract Temperature and frequency dependence of the real (3 0 ) and imaginary (3 00 ) parts of the dielectric permitivity of cubic Ba(Ti 0.7 Hf 0.3 )O 3 ceramic has been studied in the temperature range of 100 K to 350 K at the frequencies 0.1 kHz, 1 kHz, 10 kHz, 100 kHz for the first time. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behavior. The observed relaxor behavior has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO 3 has also been presented. For Hf doped samples transmission electron microscopy (TEM) characterization do show the presence of highly disordered microstructure at length scales of few tens of nano-meters. q 2006 Elsevier Ltd. All rights reserved. PACS: 77.; 77,22.Ch Keywords: A. Ferroelectric; C. Structure; D. Dielectric 1. Introduction Perovskite-based ferroelectrics materials attract consider- able interest owing to rich diversity of their physical properties and possible applications in various technologies like memory storage devices [1], micro-electromechanical systems [2], multilayer ceramic capacitors [3], and recently in the area of opto-electronic devices [4]. These useful properties have most often been observed in lead based perovskite compounds, such as PMN, PST, PLZT [5–7]. The enhanced properties of these compounds are attributed to their relaxor behavior, observed in doped (mixed) perovskites. However these compositions have obvious disadvantages of volatility and toxicity of PbO. Therefore much effort has been carried out towards investi- gating environmental friendly ‘Pb-free’ ceramic materials. Specifically, BaTiO 3 and its isovalent substituted materials are the promising candidates for microwave and opto-electronic applications. The effect of substitution on dielectric relaxation, ferro- electric phase transition and electrical properties of BaTiO 3 has been extensively studied [8,9]. On partial substitution of dopants like Ca, Sr, Zr [10–12], the variation of 3 0 around T c gets broadened out in ceramics and single crystal samples both. Broadening increases with increasing concentration of the dopant, as also does the deviation from Curie–Weiss behavior at temperatures above the peak temperature (T m ) of the 3 0 KT variation. The observed broadening in 3 0 KT variation has generally been attributed to the presence of nano-regions resulting from local composition variation over length scale of 100–1000 A ˚ . Different nano-regions in a macroscopic sample transform at different temperatures giving rise a range of transformation temperatures, the so-called ‘Curie range’. Thus the compositional fluctuation [6,11] in an otherwise composi- tionally homogenous system leads to diffuse phase transition (DPT). In compositionally homogenous systems quenched random disorder breaks the long range polar order at unit cell level, leading to broad 3 0 KT response [7]. Such materials exhibit slow enough relaxation dynamics and hence have been termed as ferroelectric relaxors [5–7]. A series of impurity doped BaTiO 3 system such as Sn, Ce, Zr etc have shown ferroelectric relaxor behavior. Among these the Zr-substituted BaTiO 3 ceramics have received renewed attention due to its enhanced properties both in single crystals and ceramics [12]. In the present investigation, we have studied the ferro- electric relaxor behavior in high concentration Hf substituted BaTiO 3 , i.e. Ba(Ti 0.7 Hf 0.3 )O 3 ceramics, by monitoring the variation of its dielectric permittivity with temperature in the range of 90–350 K and in the frequency range of 0.1–100 KHz. Till date only limited amount of work has been carried out for Hf doping on Ti site in BaTiO 3 [13,14] ceramics like its effect Solid State Communications 138 (2006) 331–336 www.elsevier.com/locate/ssc 0038-1098/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2006.03.018 * Corresponding author. Tel.: C91 731 2463913; fax: C91 731 2462294. E-mail address: nplalla@csr.ernet.in (N.P. Lalla).