Journal of Alloys and Compounds 475 (2009) 745–751 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Effect of BaO, SrO and MgO addition on microwave dielectric properties of (Zr 0.8 ,Sn 0.2 )TiO 4 ceramics D. Pamu, G. Lakshmi Narayana Rao, K.C. James Raju ∗ School of Physics, University of Hyderabad, Central University PO, Hyderabad 500046, Andhra Pradesh, India article info Article history: Received 27 May 2008 Received in revised form 30 July 2008 Accepted 31 July 2008 Available online 26 September 2008 Keywords: ZST ceramics Powder solid-state reaction method Microstructure Microwave dielectric properties abstract The effect of BaO, SrO or MgO on (Zr 0.8 ,Sn 0.2 )TiO 4 (ZST) ceramics has been investigated. It is found that the ZST ceramics densified at lower sintering temperatures of 1300 ◦ C, 1350 ◦ C and 1400 ◦ C for the samples added with BaO, SrO and MgO, respectively. The reduction in sintering temperature with the addition of BaO can be attributed to the liquid phase effect. The addition of BaO and SrO additives significantly improved the density, microstructure and the microwave dielectric properties of the ZST ceramics com- pared to MgO. No secondary phases were observed with the addition of BaO, SrO or MgO up to 1.5wt% of the additives. The dielectric constant (ε r ) and the temperature coefficient of the resonant frequency ( f ) of the ZST ceramics with these additives are not affected much where as the quality factors (Q × f 0 ) are affected. The maximum Q × f 0 of the ZST ceramics obtained are 60,300, 54,250 and 38,850 for the samples added with BaO, SrO and MgO, respectively. The increase in Q × f 0 is attributed to the uniform grain growth, increase in grain size and density. The effect of these additives on structure, microstructure densification and microwave dielectric properties are discussed. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Recent progress in mobile and satellite communications have increasing demands on the development of microwave compo- nents. The miniaturization of microwave circuits strongly requires high dielectric constant and low dielectric loss with good tem- perature stability. Several types of microwave dielectric materials have been investigated to meet the requirements of the microwave applications [1–3]. Zirconium tin titanate (ZST) has been devel- oped for microwave applications in communication networks due to its high dielectric constant, high quality factor and good temperature stability [4,5]. It is well known that ZST ceram- ics are difficult to densify without any sintering aid. To densify at low temperatures a combination of two or more oxides are used as sintering aids, i.e. ZnO, La 2 O 3 , CuO, NiO, Fe 2 O 3 , etc. [6–9]. Kim et al. [10] reported that all the alkaline earth metal oxides were effective for densification of ZST ceramics. Because these metal oxides have the ability to form eutectic liquids with TiO 2 at temperatures below 1400 ◦ C [11]. The present work reports the systemic study of BaO, SrO or MgO (0.5–1.5 wt%) addition on the sin- terabilty, densification, microstructure and on microwave dielectric properties of ZST. ∗ Corresponding author. Tel.: +91 40 23011205; fax: +91 40 23010227. E-mail address: kcjrsp@uohyd.ernet.in (K.C.J. Raju). 2. Experimental procedure Samples of (Zr0.8,Sn0.2)TiO4 were synthesized by conventional solid-state method from individual high-purity oxide powders ZrO2, SnO2 and TiO2 (99.9% pure) of Sigma–Aldrich, USA. The starting materials were mixed according to the desired stoichiometry of (Zr0.8,Sn0.2)TiO4 ceramics, with 1 wt% addition of ZnO as a sintering aid. A planetary ball mill (Retsch, PM100) was used to mix the powders with zirconia balls and deionized water as milling media. The powders were dried and calcined at 1300 ◦ C for 1min. To obtain BaO and SrO, BaCO3 and SrCO3 powders were cal- cined at 1200 ◦ C for 6 h. The calcined ZST powders were again ball milled at higher speeds for 15 h to reduce the particle size. The particle size of the milled powder was obtained using a particle size analyzer (Zeta Sizer 3000 HSA). These milled powders were mixed with different amounts (0.5–1.5 wt%) of BaO SrO or MgO for 1 h again using the ball mill. Pellets were formed and they were sintered at temperatures of 1300–1450 ◦ C for different durations. The heating and cooling rates were 15 ◦ C/min and 2 ◦ C/min, respectively. The phase purity of the calcined powders and the sintered pellets were identified by X-ray diffraction (Philips PW 1830). The microstructure of the sintered ZST ceram- ics was observed using scanning electron microscopy (Philips XL 30 ESEM). A vector network analyzer (Agilent 8722ES) was used to measure the microwave dielectric properties. Dielectric constant (εr ) and the quality factor values (Q) at microwave frequencies were measured using the Hakki–Coleman dielectric resonator method [12] as modified and improved by Courtney [13]. The temperature coefficient of res- onance frequency ( f ) was measured in the temperature range of 25–80 ◦ C using an invar cavity. 3. Experimental results and discussion 3.1. X-ray diffraction patterns Fig. 1(a–c) shows the XRD patterns of the samples sintered at 1300 ◦ C, 1350 ◦ C and 1400 ◦ C for 3 h with BaO (0.5–1.5 wt%), SrO 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.07.136