Enhanced ferromagnetic properties and high temperature dielectric anomalies in Bi 0.9 Ca 0.05 Sm 0.05 FeO 3 prepared by hydrothermal method K. Kamala Bharathi a, *, G. Ramesh b , L.N. Patro c , N. Ravi Chandra Raju d , Do Kyung Kim a, * a Department of Materials Science and Engineering, KAIST (Korea Advanced Institute of Science and Technology), Daejeon 305-701, Republic of Korea b Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India c Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea d School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia A R T I C L E I N F O Article history: Received 5 April 2014 Received in revised form 11 September 2014 Accepted 4 November 2014 Available online 7 November 2014 Keywords: Bismuth ferrite Oxygen vacancy Ferromagnetism X-ray photoelectron spectroscopy Raman spectroscopy Dielectric anomaly A B S T R A C T Enhanced ferromagnetic properties and high temperature dielectric anomalies in the temperature range of 300–873 K in Bi 0.9 Ca 0.05 Sm 0.05 FeO 3 (BCSFO) prepared by hydrothermal method are reported. BiFeO 3 is seen to crystallize in rhombohedrally distorted perovskite structure without any impurity phase. Substitution of small amount of Ca and Sm (Bi 0.9 Ca 0.05 Sm 0.05 FeO 3 ) leads to increase in the lattice constant values and formation of small amount of secondary phase. Magnetization curve of pure BFO indicates very weak ferromagnetism combined with antiferromagnetic nature of the samples. Whereas, BCSFO sample shows very clear and enhanced ferromagnetic nature. Saturation magnetization and Neel’s temperature values are found to be 4.36 emu/g and 664 K, respectively. X-ray photoelectron spectroscopy indicates the creation of oxygen vacancies upon Ca substitution in Bi site. Dielectric anomalies at 420 and 540 K were observed for Bi 0.9 Ca 0.05 Sm 0.05 FeO 3 from the temperature variation of dielectric constant and specific heat capacity measurements. Observation of dielectric anomalies in pure BiFeO 3 sample reveals that the origin of dielectric peaks is purely from the primary phase. Raman spectroscopy study indicates a clear shift and broadening of A modes (between 100 and 200 cm 1 ) at the dielectric anomaly temperatures supporting the observed dielectric anomalies. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Bismuth ferrite BiFeO 3 (BFO) is a multifunctional material, which simultaneously shows magnetic, ferroelastic and ferroelec- tric (FE) characteristics at room temperature (RT) [1–5]. Its antiferromagnetic Neel temperature (T N ) is 643 K and ferroelectric Curie temperature (T c ) is 1103 K [6]. In addition to the promising magnetoelectric applications, BFO finds applications as photovol- taic and photocatalytic materials due to its narrow bandgap of 2.67 eV [7–10]. Partial substitution of Bi 3+ ions by rare earth ions (R 3+ ) has been reported to enhance the ferroelectricity and saturation magneti- zation [11–14]. Structural changes, elimination of impurity phases and enhanced magnetization by destroying the cycloidal spin structure have been achieved by substitution of Sm, Nd, La and Gd ions on Bi site [11–14]. Oxygen vacancy [V   O ] concentration and its distribution play an important role in determining the ferroelectric properties of BFO material and its applications [15,16]. Amount of leakage current and strain relaxation in BFO thin films are mainly affected by oxygen vacancy concentration [15,16]. Recently, we have demonstrated that the substitution of calcium ions (Ca 2+ ) into Bi site causes the spontaneous formation of highly concentrated oxygen vacancies that compensate the Ca acceptors and maintain a stable Fe valence state in BFO thin film [17]. With the application of electric field, positively charged oxygen vacancies can be migrated and accumulated near the negatively biased electrode and subsequently the opposite side becomes p type, leading to the formation of a n–p junction across the film surface. C. H. Yang et al. [18], have demonstrated that the conductor–insulator transition takes place in a Ca doped BFO through band filling upon the application of electric field [18]. In the present work, we demonstrate a pathway to enhance the magnetic properties and the effect of oxygen vacancies on dielectric properties by substitution of Ca and Sm simultaneously at Bi site in BFO bulk material. The present work was performed on the controlled growth with faceted morphology and manipulation of structural changes, enhanced magnetic and dielectric properties of BFO and Bi 0.9 Ca 0.05 Sm 0.05 FeO 3 (BCSFO) bulk material prepared by hydrothermal method. Interestingly, we found dielectric anomalies * Corresponding authors. Tel.: +82 10 4025 4652; fax: +82 42 350 3310. E-mail addresses: kkamalabharathi@gmail.com (K. K. Bharathi), dkkim@kaist.ac.kr (D.K. Kim). http://dx.doi.org/10.1016/j.materresbull.2014.11.017 0025-5408/ ã 2014 Elsevier Ltd. All rights reserved. Materials Research Bulletin 62 (2015) 5–10 Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.else vie r.com/locat e/mat resbu