Measuring Ionic Conductivity in Mixed Electron-ionic Conductors Based on the Ion-blocking Method

doi:10.15541/jim20170125

Abstract

Abstract:

Ionic conductivity is common in liquid-like thermoelectric (TE) materials and it helps to understand the abnormal electrical and thermal transports. However, in experiment, accurately measuring the ionic conductivities in liquid-like TE materials is very difficult because of the very small contribution from ions to the total conductivity. In this study, based on the ion-blocking method proposed by Yokota, a home-made instrument has been built to accurately measure the ionic conductivity of liquid-like TE materials. The basic construction of this instrument and the measurement principles are introduced. The related factors that might influence the measurement accuracy are also analysed. Finally, the ionic conductivities for two typical liquid-like TE materials are presented to show the validity of our home-made instrument.

Key words: thermoelectric, ionic conductivity, ion-blocking method, ionic activation energy

CLC Number:

TQ174

LIU Yong-Ying, QIU Peng-Fei, CHEN Hong-Yi, CHEN Rui, SHI Xun, CHEN Li-Dong. Measuring Ionic Conductivity in Mixed Electron-ionic Conductors Based on the Ion-blocking Method[J]. Journal of Inorganic Materials, 2017, 32(12): 1337-1344.

Figures/Tables 9

Fig. 1 Sketch map (a) and optical image (b) for the home- made instrument built for the ionic conductivity measurement.

Fig. 2 (a) Sketch map of the ion motion process when a current is switched on and off. (b) A typical potential variation curve on a sample caused by the ion motion. (c) Process 1 is for current on and process 2 is for current off

Fig. 3 Variations of potential and temperature difference on a filled CoSb3 sample at 227℃ in (a) nearly thermal-insulating condition and (b) thermal-conducting condition under different current densities. Both the potential and temperature difference are measured between the two R-Type thermocouples pasted on the sample

Fig. 4 Variations of potential (a) and temperature difference (b) on a Cu1.94S sample at 477℃ in thermal-insulating condition and thermal-conducting condition

Fig. 5 (a) Potential variation curves for Cu1.99S under different test current densities at 477℃. (b) σi values calculated based on the potential variation curves shown in (a)The inset in (a) shows the optical image of the sample after the measurement under 0.512 A/cm2. Obvious Cu precipitation is observed on the sample’s surface

Fig. 6 Potential variation curves for Cu1.99S measured under different distances between the two R-type thermocouples at 227℃

Fig. 7 Resistance variations of uncoated and coated Cu7PSe6 samples at 277℃^The inset shows the optical images of these two samples

Table 1 Ionic conductivities for Cu1.99S and Cu7PSe6 calculated by using the Yokota’s method (σiY), the data of process 1 (σi1) and process 2 (σi2), and the average data of process 1 and process 2 (σiA)

Sample	T/℃	σ_iY/ (S∙m^-1)	σ_i₁/ (S∙m^-1)	σ_i₂/ (S∙m^-1)	σ_iA/ (S∙m^-1)
Cu_1.99S	177	58	57	58	58
	227	97	98	96	97
	277	137	137	138	137
	327	178	179	175	177
	427	298	291	310	300
	452	309	305	314	309
	477	327	326	328	327
	502	349	351	347	349
	527	369	356	376	366
Cu₇PSe₆	127	50	55	50	53
	177	79	81	79	80
	227	118	117	118	118
	277	163	172	163	167

Fig. 8 (a) Ionic conductivity (σi) and (b) ionic activation energy (Ea) for liquid-like TE materials^Ionic conductivities are calculated by Eq. (5)

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