Dielectric and electrical properties of gadolinium-modified lead-zirconate-titanate system S.C. Panigrahi a,b , Piyush R. Das a,⇑ , B.N. Parida a , R. Padhee a , R.N.P. Choudhary a a Department of Physics, Institute of Technical Education & Research, Siksha ‘O’ Anusandhan University, Jagmohan Nagar, Jagamara, Khandagiri, Bhubaneswar 751030, Odisha, India b Tihidi College, Tihidi, Bhadrak 75612830, Odisha, India article info Article history: Received 1 January 2014 Received in revised form 12 March 2014 Accepted 13 March 2014 Available online 22 March 2014 Keywords: Ceramics XRD Microstructure Dielectric studies CIS abstract The gadolinium (Gd) modified lead zirconate titanate (PbZr,TiO 3 ) ceramics with Zr/Ti = 48/52 (i.e., near morphotropic phase boundary (MPB)) in a general chemical formula Pb 1x Gd x (Zr 0.48 Ti 0.52 ) 1x/4 O 3 (PGZT; x = 0, 0.07, 0.10 and 0.12) have been synthesized using a high-temperature solid-state reaction method. Preliminary structural analysis using X-ray powder diffraction (XRD) shows the formation of a single-phase tetragonal structure of the compounds. Detailed studies of dielectric parameters of PGZT exhibit the diffuse phase transition but non-relaxor characteristics in the material for the higher concentration of gadolinium. The ac conductivity spectra of PGZT are found to obey Jonscher’s universal power law. The electrical impedance parameters of PGZT (near MPB) were obtained in a wide range of temperature (25–500 °C) and frequency (1–1000 kHz) using complex impedance spectroscopy (CIS) technique. Detailed analysis of these parameters shows that bulk (grain) and grain boundary resistance have significant effect on the total impedance of the materials. Temperature dependence of hysteresis characteristics of PGZT confirms that the phase transition parameter of the material is strongly affected by the substitution of Gd at the Pb-sites. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Among all the ferroelectric oxides known today, lead zirconate tiatanate (PZT) ceramics with different Zr/Ti ratios has unique position for device applications because of its high piezoelectric constant, dielectric permittivity, pyroelectric coefficients and elec- tromechanical coupling coefficients. The higher value of these parameters are very much required for actuators and sensors [1], capacitors, nonvolatile memories [2], pyroelectric devices [3] and micro-electro-mechanical (MEM) systems [4]. The distinctive fea- tures of PZT are high-sensitivity, non-hydroscopicity, mechanical strength, simplicity of preparation and ease in poling. Lead zircon- ate titanate Pb(Zr,Ti)O 3 (PZT) is a solid-solution of ferroelectric PbTiO 3 (Curie temperature (T c ) = 490 °C) and antiferroelectric PbZrO 3 (T c = 230 °C). It has a general formula of ABO 3 (A = mono/ divalent; B = tri/hexavalent) type. It is a well-established fact that various types and amount of modifications [5–8] can be made in this material at the A and/or B sites for desired devices. In this pro- cess, a large number of additions/substitutions of rare-earth ions have been made in PZT. Out of all the rare-earth element substi- tuted gadolinium (Gd) is found to be most effective and attractive. It has been found that soft dopants enhance piezoelectric coupling co-efficient, relative permittivity and other properties including lowering the Curie temperature. Most of the work has been reported on lanthanum-modified PZT with different Zr/Ti ratios. Detailed literature survey shows that not much work on Gd- modified PZT (Zr/Ti ratio such as 48:52) has been done on its impedance) spectroscopy. Therefore, we have synthesized and studied the effect of Gd on structural, electrical, dielectric and impedance properties of in PZT near morphotropic phase boundary (MPB). 2. Experimental 2.1. Sample preparation Lead monoxide (99% Loba Chemie Pvt. Ltd., India), titanium dioxide (99.5% Loba Chemie Pvt. Ltd., India), gadolinium trioxide (99.9% Loba Chemie Pvt. Ltd., India) and zirconium oxide (99%, Himedia Chemie Pvt. Ltd., India) were used to synthesize the required materials. The polycrystalline samples of Gd-modified lead zirconate titanate with a general formula Pb 1x Gd x (Zr 0.48 Ti 0.52 ) 1x/4 O 3 (PGZT) (x = 0, 0.07, 0.10 and 0.12) were prepared using a high-temperature solid-state reaction tech- nique with the above oxides. Two-mole% of excess PbO was taken to compensate for Pb loss during high-temperature calcination and sintering. The ingredient (oxi- des) were mixed thoroughly; first in an air atmosphere for 1 h and then in wet (i.e., methanol) atmosphere for 2 h in agate mortar. The calcination temperature of the mixed samples was optimized (1100 °C) based on repeated firing/mixing for 4 h http://dx.doi.org/10.1016/j.jallcom.2014.03.078 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 9438047597; fax: +91 6742351217. E-mail address: prdas63@gmail.com (P.R. Das). Journal of Alloys and Compounds 604 (2014) 73–82 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom