Materials Chemistry and Physics 112 (2008) 858–862 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys A comparative study of Ba 0.95 Ca 0.05 Zr 0.25 Ti 0.75 O 3 relaxor ceramics prepared by conventional and microwave sintering techniques Sandeep Mahajan a , O.P. Thakur a,∗ , D.K. Bhattacharya a , K. Sreenivas b a Electroceramics Group, Solid State Physics Laboratory, Timarpur, Delhi 110054, India b Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India article info Article history: Received 7 February 2008 Received in revised form 3 June 2008 Accepted 21 June 2008 Keywords: BZT Ceramics Microwave sintering Dielectric Relaxors abstract A comparative study on the dielectric properties of (Ba 0.95 Ca 0.05 Zr 0.25 Ti 0.75 O 3 (BCZT) ) bulk ceramics pre- pared by conventional and microwave sintering (MWS) has been done. High-density ceramic materials were obtained in 4h of cycle time for microwave sintered sample whereas it took 22h for conventional method. Samples prepared by both sintering techniques showed single-phase formation in XRD with cubic structure. The dielectric properties of the samples were measured as a function of temperature in the frequency range of 100Hz–100kHz. Relaxor behaviour was observed in both types of samples. It was observed that the peak value of dielectric constant was higher for microwave sintered sample compared to conventional one and also the dielectric loss was lower. The value of activation energy was found to be ∼0.53 eV and 0.29 eV for microwave sintered and conventional sintered samples, respectively. © 2008 Published by Elsevier B.V. 1. Introduction Barium titanate is widely used as dielectrics because of its high dielectric constant and low loss [1,2]. It is well known that semi-conducting BaTiO 3 ceramics are also used for grain boundary barrier layer (GBBL) capacitors [3,4]. Substitution of both isovalent and aliovalent cation for the host ones in perovskite lattice plays a very important role. Ba(Zr x Ti 1-x )O 3 ceramics are generally used for making capacitors, and thus most studies are focused on the temperature dependence of the dielectric constant, the nature of phase transitions and the relaxor behaviour of this material [5–9]. Detailed ferroelectric and piezoelectric properties were less studied for this system [8]. On the other hand, the high piezoelectric and electrostrictive properties were found only in lead based ferroelectric relaxors, such as Pb(Mg 1/3 Nb 2/3 )O 3 (PMN), Pb(Zn 1/3 Nb 2/3 )O 3 (PZN) and (Pb, La) (Zr, Ti)O 3 (PLZT) ceramics [10–13]. The relaxor materials have found wide applications in electronics industries. Very high strain level and piezoelectric activity have been reported in these solid solu- tions. This leads to extensive interest in the possible correlation of ferroelectric relaxor behaviour and high piezoelectric performance. However, lead is toxic element, and with increasing demand of environmental protection, lead-free materials are highly desirable. BaTiO 3 is a well-known lead-free material. The strain is as high as ∗ Corresponding author. Tel.: +91 11 23903433; fax: +91 11 23913609. E-mail address: omprakasht@hotmail.com (O.P. Thakur). ∼1% in the form of single crystals, but the hysteresis is quite large, which blocks practical application of this material [14–17]. It is well known that the doping is an effective way to improve the materials performance for electro-ceramics. Zirconium-doped BaTiO 3 single crystal were recently grown and showed promising piezoelectric/electrostrictive properties [18–21]. At the same time, calcium substituted BZT ceramics is reported to exhibit a broad dielectric constant-temperature curve near T c with high value of dielectric constant [22]. It was reported that microwave technique is superior to conventional sintering (CS) due to its unique char- acteristics, such as rapid heating, enhanced densification rate and improved microstructure [23–28]. Microwave heating is funda- mentally different from conventional heating. In the microwave process, the heat is generated internally within the material instead of originating from external sources, and hence there is an inverse heating profile. The heating is very rapid as the material is heated by energy conversion rather than by energy transfer, which occurs in conventional techniques. Surprisingly, not much work has been performed on the piezoelectric and dielectric properties of BCZT ceramic prepared by microwave sintering (MWS) despite of the promising characteristics of the material and the preparation tech- nique. This has been our motivation for the study, which is reported here. 2. Experimental The starting materials BaCO 3 (Aldrich, 99+%), CaCO 3 (Aldrich 99.9%), TiO 2 (Aldrich 99.9+%) and ZrO 2 (Aldrich, 99.9%) were weighed according to the stoichio- metric composition Ba 0.95 Ca 0.05 Zr 0.25 Ti 0.75 O 3 (BCZT). The weighed powders were 0254-0584/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.matchemphys.2008.06.054