composition at a fixed temperature. AC Conductivity. The total conductivity dependence on temperature and frequency can be given below as: T 7 dc 7 ac 7.
Synthesis and electrical transport properties of Gd doped nanocrystalline ceria Sk. Anirban, A. Sinha, and A. Dutta Citation: AIP Conf. Proc. 1536, 157 (2013); doi: 10.1063/1.4810148 View online: http://dx.doi.org/10.1063/1.4810148 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1536&Issue=1 Published by the AIP Publishing LLC.
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Synthesis and Electrical Transport Properties of Gd Doped Nanocrystalline Ceria Sk. Anirban, A. Sinha and A. Dutta* Department of Physics, The University of Burdwan, Burdwan-713104, India Abstract. In this paper we report synthesis and electrical properties of Ce1-xGdxO2- (x=0.05-0.2) materials. The materials were prepared using the citrate auto ignition method. The XRD patterns indicate the single phase of the prepared materials. The electrical properties were studied using impedance spectroscopy in a temperature range 2500 C to 5500C. It has been observed that the total ionic conductivity increases with the increase in Gd concentration. The electrical data analysis was done using the conductivity formalism. Keywords: Gd doped nanoceria, electrical properties, impedance spectroscopy. PACS: 66.30.Dn. 77.22.Gm.
material was taken out from the beaker, grounded and calcinated for six hours at temperature 6000C. Yellowish powder was formed which were made into pellets. Graphite paste was applied to both faces of the pellet to make the electrode. The electrical measurements were performed in a tube furnace using two probe methods. An LCR meter (Hioki, Model 3532-50) interfaced with the personal computer was used to collect the electrical data in the frequency range 42Hz to 5 MHz and in temperature range 250 to 5500C.
INTRODUCTION Nanostructured ceria, doped with different trivalent rare earth elements have recently emerged as smart materials with wide range of applications such as solid oxide fuel cells, oxygen pump, oxygen sensor etc.1,2 Among the various trivalent dopants Gd+3 and Sm+3 shows highest ionic conductivity at intermediate temperatures.3 Recently numerous efforts have been put to understand the ionic transport properties as well as relaxation in Gd doped nanoceria prepared through different routes4. In this paper we report ionic transport properties of Ce1-xGdxO2- (x=0.05-0.2) materials prepared through citrate auto-ignition method.
Results And Discussions DC Conductivity
EXPERIMENT
The dc conductivity for the compositions was calculated from complex impedance plots. The reciprocal temperature dependence of the dc conductivity for all compositions are shown in Fig.1 which obeys Arrhenius relation, (1) Vdc= V0 exp (-EV / kT ) where EV is the activation energy which was calculated from the least square straight line fits. In Fig 2, we have plotted the variation in dc conductivity with the composition. It has been found that at a particular temperature the dc conductivity increases with the increase in Gd content and then suddenly decreases for the composition with Gd=0.2. From the complex impedance plots it has been found that both the grain and the grain boundary conductivity contribute to the total conductivity of the materials. Also it has been found that the dc conductivity increases with the increase in temperature. The sudden
The nanocrystalline Ce1-xGdxO2- (x=0.05-0.2) were prepared through the low temperature citrate auto ignition method. The starting materials were Cerium nitrate hexahydrate [Ce(NO3)3,6H2O] (99.9%), Gadolinium Oxide(Gd2O3) (99.9%) and anhydrous citric acid which were taken in proper stoichiometric proportion. First Gd2O3 was dissolved in DI water and nitric acid was added drop wise until the solution becomes clear. The solution was stirred for six hours at temperature 800C. The pH of the solution was measured at regular interval. After that proper amount of weighted Ce(NO3)3, 6H2O and citric acid were mixed with the solution and again stirred for about six hours at temperature 900C to 1000C. The solution became yellowish and gel/foam was formed. After a few minutes the auto-ignition process started and the whole process completed within a minute. The whole
Proceeding of International Conference on Recent Trends in Applied Physics and Material Science AIP Conf. Proc. 1536, 157-158 (2013); doi: 10.1063/1.4810148 © 2013 AIP Publishing LLC 978-0-7354-1160-9/$30.00
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decrease in conductivity for the composition with Gd =0.2 mol% is unclear and needs further investigations.
on the temperature at low frequency but this dependency is weaker at higher frequencies. It has also been observed that the dc conductivity is approximately equal to ac conductivity at low frequency. The conduction mechanism in the ac domain can be explained with the help of Correlated Barrier Hopping (CBH) model.
x = 0.05 x = 0.1 x = 0.15 x = 0.2
-4
-3.0
-6
l o g 10 [ V' (Z) (:-1cm-1) ]
l o g 1 0 [ V d c ( : -1 c m -1 ) ]
-2
-8
-10 1.0
1.2
1.4
1.6
1.8
2.0
1 0 0 0 / T ( K -1 )
log
-3.5
-4.0
-4.5
2
3
4
5
6
7
8
l o g 10 [ Z ( r a d s ) ] -1
T = 673 K
FIGURE 3. The ac conductivity spectra for a composition at different temperatures.
-4.5
CONCLUSIONS -5.0
Gd doped nanocrystalline ceria was synthesized using citrate auto-ignition method. The electrical properties of the samples were measured using impedance spectroscopy. It was found that the dc conductivity increases with the increase in Gd concentration which was attributed as the effect of both grain and grain boundary conductivity. The ac conductivity was found to follow the exponential frequency dependence.
10
[ V d c ( : c m -1 ) ]
FIGURE 1. The reciprocal temperature dependence of dc conductivity for different compositions. The straight lines indicate the least square straight line fits.
x = 0.1 T = 723 K T = 748 K T = 773 K T = 798 K T = 823 K
-5.5 0.05
0.10
0.15
0.20
x(mol % ) FIGURE 2. The variation of dc conductivity for different composition at a fixed temperature.
ACKNOWLEDGEMENTS One of the authors (AD) thankfully acknowledges the financial assistance from DST (Govt. of India) (Grant no: SR/FTP/PS-141) and also UGC for CAS scheme.
AC Conductivity The total conductivity dependence on temperature and frequency can be given below as: T dc ac The power law that governs this property is given by (3) ac ac s where Z is angular frequency, A and s are temperature dependent parameters. The frequency exponent s measures the interaction between the mobile ions. Figure 3 shows the variation of the frequency /(Z), of sample x = 0.1 as a function of frequency of alternating current. In all samples, the ac conductivity is nearly constant at low frequencies and, above a certain characteristic frequency; it increases according to the power law given in eqn 3. The ac conductivity strongly depends
REFERENCES 1. J. Luo, R.J. Ball and R. Stevens, J. Mat. Sci. 39(1),235240 (2004). 2. J.A. Lane, S.J. Benson, D. Waller and J.A. Kilner, Solid State Ionics 121, 201-208 (1999). 3. R. Gerhardt-Anderson and A.S. Nowick, Solid State Ionics 5, 547-550 (1981). 4. E. Ruiz-Trejo and J. Maier, Journal of The Electrochemical Society, 154(6), B583-B587 (2007); A. K. Baral and V. Sankaranarayanan, Appl Phys A 98, 367-373 (2010).
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