Thin Films Grown by Pulsed Laser Deposition

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Ionic Conductivity in Yttria-Stabilized Zirconia Thin Films grown by Pulsed Laser Deposition

Jetske Karina Stortelder Master of Science Thesis Faculty of Science and Technology Inorganic Materials Science Mesa+ Institute for Nanotechnology Enschede, August 2005

Ionic Conductivity in Yttria-Stabilized Zirconia Thin Films grown by Pulsed Laser Deposition

Master of Science Thesis by Jetske Karina Stortelder Enschede, August 26th 2005

Graduation Committee Prof. Dr. Ing. D.H.A. Blank Dr. Ing. A.J.H.M. Rijnders Ir. F. Vroegindeweij Dr. H.J.M. Bouwmeester Dr. B.J. Ravoo Dr. Ir. B. Timmer (Texas Instruments)

Ionic Conductivity in Yttria-Stabilized Zirconia Thin Films grown by Pulsed Laser Deposition

Summary
In this report the ionic conductivity of yttria-stabilized zirconia (YSZ) is researched. YSZ transports oxygen through its lattice and can, for example, be used for the detection of oxygen and, indirectly, for harmful NOx gasses that contribute to environmental problems. The objective of this research was to determine the influence of the crystal structure on the ionic conductivity of YSZ thin films produced by pulsed laser deposition. The materials used for the electrodes and wiring of the samples, the measurement set-up and the sample configuration played an important role in obtaining successful impedance measurements in temperatures up to 900ºC. Part of this research was therefore contributed to finding the optimal conditions for ionic conductivity measurements on YSZ thin films. Four electrode materials were chosen and tested, knowing SrRuO3, Pt, Au and Pt-paste, but only SrRuO3 and Pt were useful until 700ºC. After that temperature the films started to segregate, which reduced the electrode contact area and increased the resistance. So none of the electrode materials was suitable to measure up to 900ºC in an oxygen environment. However, the results obtained from low temperature measurements can be extrapolated to higher temperatures to get an indication of the values at high temperatures. For the wiring gold was used. YSZ thin films were deposited on SrTiO3 as well as on NdGaO3, resulting in different crystallinities. On NdGaO3, the YSZ was deposited epitaxial in the [00l] directions and on the SrTiO3 in the [011] and [00l] directions. The activation energy of YSZ was around 0.87 eV, which was lower than the literature values. The activation energies decreased to unrealistic values for ionic conduction at temperatures above 700ºC. Here electronic contributions might have played a part. Also the ionic conductivities were at least one order of magnitude lower than expected, this was attributed to electrode segregation. The YSZ film on STO had the highest conductivity throughout the whole temperature range, which can be caused by the difference in crystallinity. Though before drawing hard conclusions the measurements should be repeated. So at this moment, no clear answer can be given on the question how the crystal structure of YSZ influences the ionic conductivity.

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Ionic Conductivity in Yttria-Stabilized Zirconia Thin Films grown by Pulsed Laser Deposition

Table of contents
Introduction ..............................................................................................................................4

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1.1 1.2

Theory ......................................................................................................................5 Oxygen transport...................................................................................................... 5 Yttria-stabilized zirconia.......................................................................................... 5

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Experimental methods............................................................................................7 2.1 Pulsed Laser Deposition........................................................................................... 7 2.1.1 The...
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