Materials Chemistry and Physics 130 (2011) 191–195 Contents lists available at ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Structural, dielectric and ferroelectric study of microwave sintered lanthanum substituted BaTiO 3 ceramics Sonia Sharma a , R.K. Patel a , C. Prakash b , P. Kumar c,∗ a Department of Chemistry, National Institute of Technology, Rourkela 769008, India b DRDO Bhawan, Rajaji Marg, New Delhi 110011, India c Department of Physics, National Institute of Technology, Rourkela 769008, India a r t i c l e i n f o Article history: Received 22 August 2010 Received in revised form 23 May 2011 Accepted 17 June 2011 Keywords: Oxides Sintering SEM Dielectric properties Ferroelectricity a b s t r a c t Lanthanum substituted barium titanate (BT), Ba (1-x) La x Ti (1-x/4) O 3 (where x = 0.02,0.04,0.06 and 0.08)/BLT1, BLT2, BLT3 and BLT4 ferroelectric ceramic samples were synthesized in single perovskite phase by microwave (MW) processing technique. Dense packing of grains with higher density at lower sintering temperature (1100 ◦ C) signifies the importance of MW process over conventional process. The structure changes from tetragonal to cubic and grain size gradually decreases with the increase in La 3+ ions substitution concentration in BT ceramic samples. Presence of pore free uniform grains suggested the advantage of using microwave sintering process. Transition temperature (T c ) decreases with the increase in La 3+ ions substitution concentration in BT system and for BLT3 and BLT4 systems T c is below room temperature (RT). Temperature coefficient of capacitance is negligible from RT temperature to 75 ◦ C and 50 ◦ C for BLT1 and BLT2 ceramic samples, respectively. Ferroelectric study confirms the transformation of structure from tetragonal to cubic with the increase of La 3+ ion substitution concentration in BT system. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Barium titanate (BT) is the most common ferroelectric oxide in the perovskite ABO 3 phase and often used in multilayer ceramic capacitors due to high dielectric constant (ε r ) and low dielectric loss (tanı) characteristics [1]. Many efforts have been tried to mod- ify this compound by different means in order to achieve stable capacitors with satisfactory operational capacity. Earlier reports show that substitution of host lattice cation significantly changes the dielectric properties. An excellent example is La 3+ ions substi- tuted BT system; it has both an exceptionally high (ε r ) for selected composition and temperature [2,3]. However, the performance of BT ceramic samples significantly depends on the microstructure and sintered body. The microwave (MW) processing of ceramics can be utilised as an alternative approach for conventional sintering of ceramics because of potential advantages such as rapid heat- ing, penetrating radiation, more uniform microstructure and hence higher density [4–10]. The literature data mainly reports the prepa- ration of La 3+ ions substituted BT system by conventional route [3,11–13]. Microwave sintering of ceramics offers several poten- tial advantages over conventional sintering. Microwave heating also has the potential for energy and cost savings when compared ∗ Corresponding author. Fax: +91 0661 2462999. E-mail address: pvn77@rediffmail.com (P. Kumar). with conventional heating. Besides that nearly theoretical density and uniform grains, which in turn improves the ceramics physi- cal properties, can be achieved in microwave processed ceramics. Many researchers have reported the enhancement in the solid state reaction rate or the solid state diffusion rate in a microwave dielec- tric field [14,15]. Ceramic in conventional furnace require generally rather long time owing to inertia of furnaces and much energy is lost by radiation. These disadvantages could be avoided by using microwave pro- cessing of ceramics. It is also worth pointing out that the use of microwave allows heating to be started at the core of ceramics con- trary to conventional heating which starts at the surface; this could change the microstructure and dielectric properties [16]. Therefore, substitution of La 3+ ions in BT system and its microwave processing can modify the structure and dielectric properties. In the present work, Ba 2+ and Ti 4+ ions in BT system are sub- stituted by La 3+ ions at A site (off-valent substitution) and B site (to maintain charge neutrality). Here, we report the dielectric, microstructure and ferroelectric studies of La 3+ ions substituted BT system sintered by microwave technique. 2. Experimental The polycrystalline ceramic samples of Ba (1-x) LaxTi (1-x/4) O3 (where x = 0.02,0.04,0.06,0.08))/BLT1, BLT2, BLT3 and BLT4 compositions were syn- thesized using grade reagents BaCO3, TiO2, and La2O3 powders (all Aldrich with 99.8% purity). These starting precursors were taken in stoichiometric ratio as the initial raw material. Stoichiometric weights of all the powders were mixed, 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.06.028