SYNTHESIS AND IONIC CONDUCTIVITY OF NANOCRISTALLINE Y-DOPED Bi2O3 THIN FILMS 

J. Kusinski1, S. Kac1, S. Surblé2, G. Baldinozzi2, G. Petot-Ervas2
1University of Mining and Metallurgy, Laboratory Surface Engineering, 30054 Krakow, Poland, 2Research group CNRS/SPMS- Ecole Centrale Paris, 92295 Châtenay Malabry / SRMA-CEA Saclay, 91191 Gif sur Yvette, France

The -Bi2O3 phase is of considerable potential technological importance because this phase adopts an anion–deficient fluorite structure, with a concentration of oxygen vacancies close to 25 mol %. Consequently, this phase has an exceptionally high ionic conductivity, on the order of 1 ohm-1cm-1. Unfortunately, this structure is stable over a narrow range of temperature (729<T<825°C). To stabilize the -form at lower temperatures the most widely used method consists of doping Bi2O3 with large amounts of trivalent or heterovalent cations. In this work, dense nanocrystallized Y-doped Bi2O3 films were prepared by means of pulsed laser deposition method (PLD). The depositions were carried out in an oxygen atmosphere using a Nd-YAG laser with wavelength of 355 nm and laser fluency ranging from 8 J/cm2 to 12 J/cm2. Scanning and transmission electron microscopy, as well as X-Ray diffraction were used to characterize the films. Depending of the deposition time, the film thickness varied from 140 to 240 nm and the grain sizes from 5 to 30nm.
The electrical conductivity was investigated by impedance spectroscopy. Measurements were conducted in the temperature range of 24-430 °C and for oxygen partial pressures included between 1 atm and 10-5 atm. The obtained values are one order of magnitude higher compared to those proposed for pure microcrystalline -Bi2O3 polycrystals, due likely to grain size effects. They do not varied with the oxygen partial pressure and a plot of lnT vs T-1 yields activation energy of Ea»0.29 eV. Furthermore, it is important to point out that the nanostructured Y-doped Bi2O3 thin films exhibit an ionic conductivity about five order of magnitude higher compared to Gd-doped ceria polycrystals.