International Journal of Engineering Research ISSN:2319-6890)(online), 2347-5013(print) Volume No.3, Issue No.4, pp : 267-270 01 April 2014 IJER@2014 Page 267 Synthesis of Yttria-Doped Bi 2 o 3 Nanopowders Via Sol Gel Used in Electrolyte of Solid Oxide Fuel Cell M. Mallahi,V. Mazinani, A. Shokuhfar, M.R. Vaezi 1 Mechanical Engineering Department, K. N. Toosi University of Technology, Tehran, Iran M.Mallahi@ymail.com Abstract : Oxide ion conductors have been studied for many years because of their application in devices with high economical interest such as solid oxide fuel cells, oxygen sensors , dense ceramic membranes for oxygen separation. In this paper nanopowders were synthesized via sol gel method. The sintering temperature to complete phase transition are above 500˚c. As-prepared yttria doped Bi2O3 nanocrystals were characterized by X-ray diffraction (XRD) a nd transmission electron microscope (TEM). Transmission electron microscope (TEM) investigations revealed that the average particle size is less than 30 nm for these powders. It's worth noting that results show a good agreement of both methods. The morphology of the powders were observed on Field Emission scanning electron microscope (FESEM). Ionic conductivity measured by AC impedance spectroscopy. Ke ywor ds : Nanopowders , Sol-gel , Electron microscopy, Impedance spectroscopy, Substituted Bi2O3. Introduction: In recent three decades, sol-gel process is developed into a wide research subject. This process due to its reaction in liquid phase, room temperature and the type of the precursors which are applied for obtaining new materials is scientifically and technologically attracts attentions significantly. Over the last decades, Bi2O3-based materials with high oxygen ionic conductivity have been extensively studied for their potential use as solid electrolyte in fuel cell [1]. The delta face- centered cubic (fcc) phase of pure Bi2O3 has high oxide ion conduction at high temperatures, but it is only stable between 730 ºC and 825 ºC (melting point). During cooling from high temperature, large volume change is accompanied with phase transformation from the delta phase into monoclinic alpha phase having low electrical conductivity. Introduction of a proper amount of Yttria (2 5mol% Y2Ο3) or some rare earth oxides into the FCC phase stabilizes this structure down to lower temperatures[2-3]. Application of nanocrystalline ceramics can lead to the development of electrochemical devices that have considerably lower operating temperatures and can exhibit significantly improved ionic conductivity [4]. Hence, the present work has been focused on preparation of mixed nanopowders of 75 mol% Bi2O3+25 mol% Y2O3 by sol gel method and fabrication of dense single phase nanocrystalline Bi2O3-Y2O3 solid electrolyte and study of the electrical conductivity. 2. Experimental 2.1. Raw materials Bi (NO3)3.5H2O (98% in purity), HNO3 (67.5% in purity), Y(NO3)3.6H2O, Citric acid (AR grade), PEG4000 ,were purchased from Merck and used as received. 2.2. Devices XRD diffraction studies were carried out by Philips (PW3710) diffractometer with CuKα radiation source (λ=0.151478 nm).The TEM picture was recorded with Zeiss EM 10C instrument at the accelerating voltage of 100 kV. IR transmittance and absorption spectra were measured on the two samples prepared by KBr pellet technique in the wave number range of 400– 4000 cm -1 on (FTLA 2000-100) model. Field emission scanning electron microscopy measurements studies were performed using Hitachi S4160 model. Ionic conductivity was measured by an AC impedance analyzer technique with Model4274A multi-frequency Hewlett-Packard LCR meter in the frequency range of 100 Hz–100 kHz. The sintered pellet was placed between both faces of silver electrodes. The experiments were carried out in steps of 20 °C from 300°C up to 800 °C with 15 min stabilization time per step. 2.3. Synthesis Mixed nanopowders of 75 mol% Bi2O3+25 mol% Y2O3 have been prepared by sol gel method. The analytically pure Bi(NO3)3.5H2O and Y(NO3)3.6H2O, in molar ratio of 3: 1, were dissolved in dilute nitric acid to prepare a nitrate solution containing a total metal ion (B 3+ ,Y 3+ ) concentration of 0.1 mol/L. In order to prevent agglomeration, 3 wt. % PEG4000 (polyethylene glycol of average molecular weight equal to 4000) was added as a surfactant. The solution was continuously stirred using a magnetic needle for 2 h and then a sol formed. The sol was heated to 90 °C for 1h to form a yellowish gel. This gel was decomposed at 160°C in oven .The gel initially started to swell and filled the beaker producing a foamy precursor. This foam consists of homogeneous flakes of very small particle size.The mixed oxide nanopowders synthesized as above were pressed uniaxially into disk-shaped pellets having an outer diameter of 10 mm and a thickness of 1 mm at a relatively low pressure of