Indian Journal of Engineering & Materials Sciences Vol. 16, December 2009, pp. 390-394 Effect of Ni doping on structural and dielectric properties of BaTiO 3 Yogeswar Kumar a , Md Ahamad Mohiddon a , Alok Srivastava b & K L Yadav a * a Smart Materials Research Laboratory, Department of Physics, Indian Institute of Technology, Roorkee 247 667, India b Department of Physics, DAV (PG) College, Dehradun 248 005, India Received 3 March 2009; accepted 17 September 2009 Polycrystalline samples of Ba 1-x Ni x TiO 3 (BNT), where x = 0, 0.03, 0.05, 0.07 and 0.10 have been synthesized by solid-state reaction technique. No phase change in the crystal structure has been observed with Ni doping in barium titanate up to x = 0.10, however a decrease in crystallite size, lattice strain, c/a ratio and grain size has been found with Ni doping. The different results presented may be related to, and are explained by, the grain size and its distribution in the ceramic bulk. Ni doping in BaTiO 3 exhibit many interesting features, such as shift in transition temperature, increasing diffuse phase transition and decreasing dielectric constant. The evolution from a normal ferroelectric phase transition to a diffuse phase transition has been observed with increasing Ni concentrations. The dielectric study of samples poled in magnetic field (data shown for BNT, x = 0.03 here) suggests that T c and maximum dielectric constant increase with increasing magnetic poling strength along with decreasing nature of diffusivity thus showing multiferroic nature. Keywords: Ceramics, X-ray diffraction, Dielectric properties, Grain size, Diffuse phase transition BaTiO 3 (BT) is one of the most common ferroelectric material with a wide range of applications including micro-electro mechanical systems (MEMS), multilayer ceramic capacitors (MLCs), PTC thermistors, piezoelectric transducers, microwave devices, different type of storage information devices, infrared sensors 1-4 etc. BaTiO 3 has a general ABO 3 type structure where A and B are cations of different sizes, with the 6 fold coordinate B cation in the middle, the 12 fold coordinate A cation in the corner and the anion, commonly oxygen, in the centre of the face. The packing of the ions can be thought of as the A and O ions together forming close-packed array. The phase of BaTiO 3 at room temperature is tetragonal and it transforms to cubic phase above 130ºC. It also exists in orthorhombic phase at 0ºC and in rhombohedral phase below -90ºC. Above 1460°C, BaTiO 3 exits in hexagonal phase 5 . Although the primitive cube is the idealized structure, differences in radius between the A and B cations can alter the structure to a number of different so-called distortions, of which tilting is the most common one. With perovskite tilt the BO 6 octahedron twists along one or more axes to accommodate the difference. The ferroelectric properties of ABO 3 type perovskite ceramics (here barium titanate) can be efficiently controlled by doping with different doping elements 6-9 . The possible applications of Ni doped barium titanate (hereafter BNT) materials in the bulk form are still explored over a wide range of compositions and controlled ion substitutions. Few reports are available on this issue where the micro-structural changes in Ni doped barium titanate 10 , dielectric characteristics of Ni-ion doped BaTiO 3 nanoparticles 10 (Ni is doped at Ti-site), exaggerated grain growth in Ni doped BaTiO 3 (Ni concentration ~0.7 mol%) to study 11 hexagonal phase in BaTiO 3 dielectric characteristics of BT co-doped 12 with Ni and Nb, electrical transport properties of Mn and Ni doped BT at high temperature 13 , valence change and phase stability of Ni doped BT annealed in O 2 and H 2 are discussed 14 . The ionic radii of Ni 2+ (r 6 2+ = 0.69Å) is less than both the ions Ba 2+ (r 6 2+ = 1.35Å) and Ti 4+ (r 6 4+ = 0.61 Å) and hence it can occupy both A and B sites. As per our literature survey no systematic dielectric study of Ni-doped BaTiO 3 has been reported. In this paper, the synthesis, characterisation and dielectric properties of Ni-doped BT have been studied and the effect of magnetic field on the dielectric properties of BNT has been analysed. Experimental Procedure The compositions Ba 1-x Ni x TiO 3 , where x = 0, 0.03, 0.05, 0.07 and 0.10 were prepared by conventional ______________ *For correspondence (E-mail: klalyfph@iitr.ernet.in)