Characterization of A-site deficient samarium doped barium titanate M. Ganguly a , S.K. Rout a,n , W.S. Woo b , C.W. Ahn b , I.W. Kim b a Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi 835215, India b Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, Republic of Korea article info Article history: Received 14 September 2012 Received in revised form 4 November 2012 Accepted 7 November 2012 Available online 17 November 2012 Keywords: Samarium Doping Barium titanate Rietveld Raman Dielectric Photoluminescence abstract Ba 1 x Sm 2x/3 TiO 3 (0.00 rx r0.10, in a step of 0.02) ceramics have been prepared through solid state reaction route. Structural studies (XRD, FTIR, Raman) suggested a tetragonal symmetry of all the prepared ceramics and a decrease in tetragonality with increase in Sm content. Rietveld refinement technique has been employed to investigate the details of crystal structure and was found to be tetragonal at room temperature with space group P4mm. Photoluminescence study confirmed formation of shallow defects. The prepared materials are found to show photoemission in the violet, blue and green zone. Optical band gap values calculated from UV-visual diffuse reflectance spectra showed a decreasing trend in band gap values with increase in samarium concentration. Disk shaped pellets were prepared using PVA as binder. Scanning electron microscopy showed a drastic decrease in grain size on doping than undoped barium titanate. A regular increase in the grain size with increase in Sm content in the doped compositions is observed. Dielectric studies were performed over a wide temperature range from 15 K to 600 K at different frequencies. Normal ferroelectric character was obtained for all the compositions. A gradual decrease in the Curie temperature was noticed with increase in samarium content. P E hysteresis loops showed a domain pinning effect which increased successively resulting in a decrease in the values of remnant polarization and coercive fields. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Substitution of rare earth elements to barium titanate (BT) has gained importance in many aspects particularly in electronic device industry. Cations like samarium (Sm) is highly soluble in BT and is hence used variedly to modify its various properties. The largest applications are as PTCR material [1,2] and dielectric material in MLCC [3,4], though pure BT is an insulator and no PTC effect can be observed. It has also got wide application in electro mechanical systems, electro optical systems, pyroelectric detectors, piezoelectric actuators, MEMS, FeRAM, in microwave devices, especially in the areas of telecommunications and satel- lite broadcasting systems [4–10]. It is already established that the electrical resistance, dielectric constant, transition temperature etc can be effectively controlled by doping with proper donor impurity ions [11–15]. With increase in concentration of Sm in BT, Thakur et al. [16] have observed an increase in the room temperature value of dielectric constant and a decrease in the transition temperature while Jo et al. [17] have found a strong dependency of the Curie temperature on the unit cell volume. Dongsheng et al. have reported that the penetration of Sm decreases the resistivity of BT powders with increase in penetra- tion temperature [18]. BT has a perovskite structure (ABO 3 ) where Ba occupies the A site and Ti the B site. Sm is incorporated at the A site where it behaves as a donor according to equation: Ba 2 þ -Sm 3 þ þ e ð1Þ Creation of oxygen vacancies is also responsible for semicon- ductive behavior, according to equation: O 2 -½O 2 þ 2e ð2Þ The effect of Ln-substitution for Ba-ion can be expressed by Kr¨ oger–Vink notation as: BaO þ Ln 2 O 3 -Ba Ba þ 2Ln Ba þ V* Ba þ 4O O ð3Þ Eq. (3) implies that for every two rare earth cation substitution at the A-site, three alkaline cations gets replaced creating one positively double charge vacancy, provided the charges are to be taken to the perfect lattice. The number of vacancy increases with increase in doping concentration [19]. Sm doped BT ceramics were prepared according to equation: 1x ð ÞBaCO 3 þ TiO 2 þ x=3   Sm 2 O 3 -Ba 1x Sm 2x=3 TiO 3 þ CO 2 , 0:00 rx r0:10 ð Þ ð4Þ Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physb.2012.11.006 n Corresponding author. Tel.: þ91 9471555277. E-mail addresses: skrout@bitmesra.ac.in, drskrout@gmail.com (S.K. Rout). Physica B 411 (2013) 26–34