Impedance spectroscopy and direct current measurements of YSZ films
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Impedance spectroscopy and direct current measurements of YSZ films T. Petrovsky, H.U. Anderson, and V. Petrovsky Electronic Materials Research Center, University Missouri-Rolla, MO 65409, USA ABSTRACT In this study the electrical properties of thin films of Ysubstituted zirconia were investigated. The films were prepared using a polymer precursor technique and investigated in the temperature region 250 to 900oC. It was shown, that impedance spectroscopy (IS) and direct current (DC) conductivity measurements results are in good agreement for the films measured in plane for temperatures greater than 400oC. Due to the high resistance resulting from a planar geometry, the DC measurements were found preferable at temperatures 400oC) and DC measurements for thin YSZ film over the 250 – 900oC temperature region. The main advantage of DC measurements is the higher accuracy and the possibility of measurements over wider temperature range. Fig.4. summarizes the results of the measurements for thin films with different Y content. This figure shows temperature dependence of the conductivity for samples annealed at 900oC. It can be seen from the figure that the conductivity and activation energy are close to the bulk YSZ for the samples with 16 and 8mol%Y. The conductivity decreases at lower Y content which is also similar to that observed for bulk zirconia.
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0.1 D irect current Im pedance Fitting, E = 1.05eV
Conductivity, S [1/Ohm.cm]
0.01 1E -3 1E -4 1E -5 1E -6 1E -7 1E -8 0.8
E =1.05eV 1.0
1.2 1.4 1.6 Tem perature, 1000/TK
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Fig.3. Comparison of IS and DC measurements for YSZ thin film annealed at 900oC. 10
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Conductivity, S [1/Ohm.cm]
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Y /Z rO 2 a n n e a le d a t 9 0 0 C B u lk Y S Z , E = 1e V 8%Y E = 0 .9 4e V 16%Y E = 1 .0 5 eV
4%Y E = 0 .9 7e V
0%Y
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T em p e ra tu re , 1 0 0 0 /T ,K
Fig.4. Temperature dependence of the conductivity for zirconia thin films with different Y content annealed at 900oC.
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CONCLUSIONS • • • •
Different sample holder designs for high temperature conductivity measurements were analyzed. It was shown that the sample holder with separated electrode tubes provides low leakage and can be used for measurements of thin zirconia films. The leakage connected with the substrate was investigated, and it was shown that sapphire substrates are acceptable for investigation of zirconia thin films. The sample holder capacitance is fundamental limitation for in plane IS measurements for thin films. For this geometry, DC measurements can be used since the contact resistance is low compared to the total resistance. The electrical behavior of zirconia thin films with different yttrium content is similar to the bulk material with the same composition, if these films were annealed at temperatures exceeding 600oC.
ACKNOWLEGEMENTS This material results from collaborative efforts of the researchers in UMR. This work was partially supported by the US Department of Energy,
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