Structural and Dielectric Properties of CuO, PbO and Bi2O3 Doped SrTiO3 Ceramics

Copper oxide, lead oxide and bismuth oxide each 10% doped separately with 90% SrTiO3 (ST) ceramic powders were processed by solid-state route technique. We reported the effect of Cu+2, Pb+2 and Bi+3 ions on the dielectric response of ST and copper addition established the substantial increase in dielectric constant (εr) than undoped ST from 303K-673K and low loss (tanδ) for good dielectric applications. In case of lead doped ST the strong relaxation dynamics of loss factor was observed at higher temperatures and dielectric constant plots established the curie transition temperature Tc = 653K revealing the structural transformation from cubic to tetragonal phase. But bismuth doped ST contrary to the expectations exhibited the decreasing trend of permittivity form 303K-525K and afterwards showed increasing nature with relaxations. The microstructure was examined by field emission scanning electron microscope (FESEM). Some additional phases SrCu3Ti4O12, PbTi3O7, SrBi3Ti5O18 and TiO2 rutiles were detected by X-ray diffraction technique. Introduction. Copper (II) oxide is a p-type semiconductor of band gap 1.2 eV used to produce dry cell batteries [1]. It can have applications as ceramic resistors, magnetic storage media, gas sensors, semiconductors and solar energy transformation. When transition metals are added up to the ST magnetic as well as ferroelectric properties can be induced. For instance in recent investigations Mn+2 ions could induce the electric and magnetic dipoles into the system. Likewise as in ref [2, 3] if Cu+2 ions occupy the Sr+2 site, dielectric and magnetic anomalies could be induced as the ionic radius of Sr+2 (0.144nm) is larger than Cu+2 (0.121nm). But on the other hand anti ferromagnetic spin ordering is being evolved, if Cu+2 ions occupy the Ti+4 sites. Even for the higher frequencies copper doped ST showed high dielectric constant. PbO is a toxic material and when doped to strontium titanate (ST) is found experimentally to be a glass ceramic material [4]. Glass ceramics have been commercially used at wide range and limited work has been done over the borosilicate glass ceramic system, in spite of its wide range of applications. The ferroelectric PST thin films have been termed as the candidate materials for the applications in various tunable microwave devices and in high density dynamic random access memories. On the other hand ferroelectric thin films have got much attention in manufacturing various functional devices for optical applications. No detailed report is available in the literature about the dielectric properties of PST ceramics. Both of the materials promote liquid phase sintering at low concentrations about 1-2 % only. Recently in case of bismuth oxide doped ST a novel microstructure was observed which is useful in understanding the grain boundary barrier layer capacitors (GBBLC) and efficient ferro-electric relaxations have been observed for the industrial applications when Bi2O3 doped with Ba0.8Sr0.2TiO3 ceramics [5].Yu Zhi et al [6] reported the low temperature and high temperature dielectric properties. In the recent literature Naidu et al. [2-4, 7, 8], Kumar et al. [9] and Maddaiah et al. [2, 10] investigated the effect of various elements (La, Mg, Mn, Cu, Zn & Bi) on electrical properties such as dielectric constant, loss, thermoelectric power, acconductivity and dc-conductivity of SrTiO3 electro ceramic material. In this study the author is © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/ Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954 MMSE Journal. Open Access www.mmse.xyz 330 intended to make a novel comparative study of the structural, micro structural and dielectric properties of CuO, PbO and Bi2O3 doped ST Ceramics to decrease the sintering temperature of strontium titanate which have not been discussed in earlier literature. Experimental Procedure The ceramic samples of CuO, PbO and Bi2O3 10% each doped individually with 90% SrTiO3 were prepared by solid state diffusion method. At the outset ST powders have been synthesized using the raw materials of SrCO3 (99.9% purity) and TiO2 (99.9% purity). The mixed powders were calcined at temperature 14000C for 13hrs and the shrinkage of compound was apparently identified. Latter ST was mixed separately with CuO, PbO and Bi2O3 and ball milled for nearly 12 hrs. After wards these samples were calcined at 10500C, 9500C and 11000C respectively each for 13hrs and the pellets of thickness 0.14cm and radius of 0.62cm have been prepared. The powders and the pellets sintered at 11000C, 10000C and 12000C respectively for 4hrs were characterized using XRD (BRUKER X-Ray Powder Diffract Meter, CuKα) at room temperature and HIOKI 3532-50 LCR HiTESTER (Japan) for structural, surface morphological analysis and dielectric properties respectively. LCR controller over the temperature range from RT to 6000C operated at the frequencies from 42 Hz-5MHz having the heating rate of 0.50C/min used for dielectric properties. Results and Discussions In fig.1, we reported the comparison XRD spectra of pure and doped ST. Diffraction maxima were observed in the diffraction spectra which are corresponding to the cubic perovskite lattice of ST. The effect of copper ions on the lattice parameter of undoped ST was clearly observed in ref [2] at low concentrations i.e. at low concentration of copper addition to pure ST decreases the lattice parameter (a). Similar reports were achieved in the present investigation. The lattice parameter of pure ST was reported in ref [2] and in case of CuO (10%) doped ST (90%) ‘a’ value was slightly decreased to 0.3893nm. Since the ionic radius of Cu+2 (0.121nm) is smaller than that of Sr+2 (0.144nm) [2]. Along with single perovskite phases some non-perovskite second phases have been detected that correspond to TiO2 rutiles and SrCu3Ti4O12 phases specified in fig.1. Furthermore the average crystalline size (DP=114.9nm) using Scherer formula and average dislocation density (ρ=8.03x1013(m-2) were established according to the following equations [11-14].