Polymorphs and dielectric properties of BaTi 1x Ni x O 3 P.T. Phong a,⇑ , B.T. Huy b , Y.-I. Lee b , I.-J. Lee a a Department of Advanced Materials Chemistry, Dongguk University-Gyeongju, 707 Suckjang-dong, Gyeongju-Si, Gyeonbuk 780-714, Republic of Korea b Department of Chemistry, Changwon National University, Changwoon 641-773, Republic of Korea article info Article history: Received 14 June 2013 Received in revised form 12 August 2013 Accepted 27 August 2013 Available online 6 September 2013 Keywords: Ni-doped BaTiO 3 Dielectric property Colossal dielectric constant (CDC) Universal dielectric response (UDR) abstract We have studied the influences of the Ni doping on structural characterization and dielectric properties of BaTi 1x Ni x O 3 (x = 0.0–0.1) prepared by conventional solid-state reaction. The composition is character- ized by X-ray diffraction technique (XRD). Interestingly, there is the tetragonal-to hexagonal transforma- tion in the crystal structure of BaTi 1x Ni x O 3 at x = 0.06. Moreover, both hexagonal and tetragonal polymorphs coexist in the range 0.06 6 x 6 0.1. Complex dielectric constant (e), ac conductivity (r 0 ac Þ; the normalized imaginary part of impedance Z 00 =Z 00 max and electric modulus M 00 =M 00 max have been studied as a function of frequency and composition at room temperature and in the frequency range up to 13 KHz. The real part (e 0 ) of dielectric constant shows a step like relaxation behavior and has been explained qualitatively with the frame work of Kramers–Kronig transformation model. The universal dielectric response and the Jump relaxation model were considered and fitted for ac conductivity. The mismatch between the frequency dependence plots of Z 00 =Z 00 max and M 00 =M 00 max peaks is observed. The short range hopping model seems to be most appropriate model for the conduction mechanisms in BaTi 1x Ni x O 3 . Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Recently, the ABO 3 -type perovskite structure materials has been intensive topic in scientific studies because of their charge and orbital ordering, electrical and optical properties, magnetic phase transitions, colossal magnetoresistance (CMR) effect, and high dielectric constant. These materials have potential technolog- ical application as capacitors, sensors and photocatalysis [1,2]. Out of these materials, BaTiO 3 (BTO) with perovskite structure has been widely investigated due to its outstanding ferroelectric and dielec- tric properties. However, the production and application of the pure BaTiO 3 are limited because of low dielectric constant, poor dielectric temperature stability and high sintering temperature [3]. Some recent studies show that the structural and ferroelectric properties of BaTiO 3 can be efficiently controlled by doping with different doping elements [3–6]. The 3d transition metal can easily doped and substitute for titanium in BaTiO 3 due to their strong resemblance to the titanium ion in size and valence [4]. Further- more, a variety of reports describing the optical, dielectric and magnetic properties of BTO-based ceramics doped with different ions, such as Fe, Mn, Co have been published [3–7]. The substituted and non-substituted Ni-doped BTO ceramics have been investigated for their unique magnetic properties. In particular, the effect of Ni on grain growth behavior and phase stability of hexagonal BaTiO 3 system has been of interest in some recent reports [8,9]. As reported by Kahn et al. [10] the nickel may be oxidized during binder pyrolysis in air. Then NiO tends to diffuse into BaTiO 3 to change its dielectric properties; so the influence of Ni solutes on the dielectric properties can be more noticeable. On the other hand, many reports show the solubility of NiO in the BTO lattice is as 0.6–1.0 wt% [8,11,12] and the valence state of Ni ions in BTO lattice is proved as Ni + , Ni 2+ , Ni 3+ and Ni 4+ with Ni 4+ ions being the most predominant [8,13]. The Ni ions may occupy the Ba 2+ sites [12,14] or Ti 4+ sites [11]. However, to the best of our knowledge, very few reports have appeared in the literature related to the effect of the Ni ions added on the micro- structure and dielectric properties of BaTiO 3 ceramics so far. The purpose of the present paper is studying the structural and the ac conduction mechanism of the BaTi 1x Ni x O 3 (BTNO) with x in a range 0–0.1 over wide frequency ranges. XRD data shows the structural phase separation taking place at x = 0.06. The nat- ure of conduction mechanism in BTNO is explained by analyzing of the dielectric properties and ac conductivity at room temperature. 2. Experimental BaTi 1x Ni x O 3 ceramics (x = 0–0.1) were prepared using the solid-state reaction technique from high-purity BaCO 3 (99.9%), TiO 2 (99.99%) and NiO (99.99%) powders by mixing, grinding by using an agate mortar and pestle and calcinations in air at 1100 °C for 20 h. After the calcination, the obtained mixtures were pressed into pel- lets, and subsequent sintering in air at 1300 °C for 20 h. 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.08.190 ⇑ Corresponding author. Tel.: +82 54 770 2220. E-mail address: ptphong.nh@khanhhoa.edu.vn (P.T. Phong). Journal of Alloys and Compounds 583 (2014) 237–243 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom