Study of the relaxor behavior in BaTi 1x Hf x O 3 (0.20  x  0.30) ceramics Shahid Anwar * , P.R. Sagdeo, N.P. Lalla UGC-DAE Consortium for Scientific research, University campus, Khandwa road, Indore 452001, M.P., India Received 5 March 2007; received in revised form 3 July 2007; accepted 8 July 2007 Available online 29 July 2007 Abstract The influence of Hf doping on the structure and dielectric properties of BaTiO 3 has been studied. For this purpose Ba(Ti 1x Hf x )O 3 ceramics were prepared through solid-state reaction route at close compositions, having x ¼ 0.20, 0.22, 0.23 and 0.30. The study was aimed to locate the exact hafnium concentration for normal to relaxor crossover in these ceramics. X-ray diffraction followed by Rietveld refinement, reveals the formation of single phase with Pm3m cubic structure. Temperature and frequency dependence of real (3 0 ) and imaginary (3 00 ) parts of the dielectric permittivity have been studied in the temperature range of 90e350 K, at frequencies between 0.1 kHz and 100 kHz. The dielectric permittivity variations with temperature show deviation from CurieeWeiss behavior and strong frequency dispersion. The deviation from CurieeWeiss behavior, discontin- uous jump along with the change in the slope of T m vs Hf concentration plot, and the degree of relaxation (g) approaching w2, indicate a crossover from normal to relaxor ferroelectrics. Substitution of Hf 4þ for Ti 4þ in BaTiO 3 introduces structural disorder, causing perturbations like local electric and strain fields. These perturbations reduce the long-range polar order resulting in relaxor behavior. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Ferroelectric; Structural; X-ray diffraction (XRD) 1. Introduction Ever since the discovery of BaTiO 3 as a high permittivity fer- roelectric ceramic in 1943, pure and doped BaTiO 3 have been widely studied for its use as passive components in electronic industries, e.g. as capacitors. Since BaTiO 3 has characteristic anomalies in the dielectric constant near the ferroelectrice paraelectric transition temperature (w393 K), to make it suit- able for low-temperature applications, several homovalent and hetrovalent substitutions have been tried [1,2]. The dielectric response of relaxors is quite different than that of the normal ferroelectrics. Relaxors show the occurrence of strong frequency dispersion in its dielectric permittivities, ab- sence of macroscopic polarization and anisotropy at tempera- tures much below T m (the temperature at which the dielectric permittivity shows a maximum). The high dielectric permittiv- ity in the vicinity of phase transition makes relaxors an excellent candidate for multi-layered ceramic capacitors and other piezo- electric and ferroelectric devices [1,2]. To extend their applica- bility to modern electronics, detailed information of their physical properties are always required [3e5]. The relaxor behavior is correlated with the cationic disorder at the same crystallographic site and has been extensively studied in lead- containing compound and solid solutions, such as PMN, PLZT, etc. [3,6,7]. However, due to the toxicity of lead, these com- pounds bear a possible hazard, which has recently stimulated the development of lead-free ceramics exhibiting relaxor prop- erties [5,8]. Doped BaTiO 3 is found to be a good replacement for the lead-based relaxor systems. Doping in ceramics is a common way to modify and improve the material performance. Several dopants like Ca, Zr, Ce, etc, have been tried and enhanced ferro- electric properties have been obtained [4,5,9]. Among these Ba(Ti 1x Zr x )O 3 has received renewed attention due to its enhanced properties both in single crystals and ceramics [5]. Hafnium doped BaTiO 3 has recently come up as a new lead- free relaxor ceramic [8,10]. * Corresponding author. Tel.: þ91 9993125744; fax: þ91 7312462294. E-mail addresses: shahidanwr@gmail.com (S. Anwar), nplalla@csr.ernet. in (N.P. Lalla). 1293-2558/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2007.07.023 Available online at www.sciencedirect.com Solid State Sciences 9 (2007) 1054e1060 www.elsevier.com/locate/ssscie