Mixed conductivity evaluation and sensing characteristics of limiting current oxygen sensors

doi:10.1016/j.surfin.2020.100762

Surfaces and Interfaces

Volume 21, December 2020, 100762

https://doi.org/10.1016/j.surfin.2020.100762 Get rights and content

Abstract

Strontium titanate based materials are promising candidates for fabrication of oxygen sensors. As a dense diffusion barrier layer of limiting current oxygen sensor, strontium titanate based materials should be able to control the diffusion rate of oxygen ions or accelerate the formation of limiting current. Based on this key question, indium oxide was introduced to strontium titanate based materials and then Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2 In₂O₃ (x = 0.04, 0.06, 0.08) composites were prepared. To understand the efficacy of doping indium oxide on the physical and sensing properties of the strontium titanate, the ionic and electronic conductivity were intently investigated. The obtained results demonstrated that the ionic and total conductivity simultaneously increased upon increasing the concentration of indium oxide dopant. Increasing the content of In₂O₃ accelerates the occurrence of limiting current of the sensor at lower voltages and then elevate the working life of the sensor.

Introduction

Based to the type of the diffusion barrier layer, the limiting current oxygen sensors (LCOS) are divided into pore type diffusion barrier layer (small pore diffusion barrier and porous diffusion barrier) and mixed conductor type dense diffusion barrier layer (DDBL). For LCOS with pore type diffusion barrier, the deformation of the pores in the diffusion barrier and the blockage of solid particles in the gas lead to the performance degradation of the sensor in the long-term [1], [2], [3], [4], [5], [6], [7]. Therefore, the LCOS with dense diffusion barrier dominates the above shortcomings due to its non-porous structure and having the advantages of stable performance and simple processing method [8], [9], [10], [11], [12], [13], [14], [15], [16], [17].

Furthermore, for traditional pore type diffusion barrier of LCOS, the oxygen sensitivity theory is that the oxygen molecules diffuse across the pores of diffusion barrier. However, for dense diffusion barrier type LCOS, the oxygen sensitivity theory is that the solid state ions (oxygen ions) diffuse into the dense diffusion barrier material [18], [19], [20], [21], [22], [23], [24], [25]. Materials which are used as a dense diffusion barrier layer for the fabrication of LCOSs should demonstrate good electronic and ionic conductivity [26], [27], [28], [29], [30], [31]. Cubic perovskite-type oxides (ABO₃) are promising candidates as dense diffusion barrier material to prepare LCOSs [32]. Among them, the cubic perovskite strontium titanate (SrTiO₃) are ideal candidates due to the ability for a high amount of metal doping and flexibility for oxygen ions movement [33]. Theoretically, donor-doped SrTiO₃, such as the doping of La or Y on Sr site and Nb on Ti site, can promote the electronic conductivity by producing electron according to the charge compensation [32], [33], [34], [35], [36], [37], [38], [39]. Similarly, acceptor-doped SrTiO₃, such as the doping of Fe, Mg, Sc, Cr or Co on Ti site promote the ionic conductivity by generating oxygen vacancy [40], [41], [42], [43], [44], [45], [46], [47], [48]. However, many considerable efforts have been only devoted to develop the electrical conductivity, but, the respective contribution of electrons and ions to the conductivity is not clear yet. Additionally, the diffusion mechanism of oxygen ions in dense diffusion barrier is not also clear. However, there are limited reports on oxygen sensors films based on strontium titanate doped with La, Fe co-doped [49], Mg-doped [50],[51] and Fe-doped [52], [53], [54], [55], [56], [57].

Applied to LCOS, doped SrTiO₃ should be electrically conductive and sensitive to detect oxygen. The reported studies on doped SrTiO₃ for sensor fabrication are incomplete and employing the strontium titanate as a dense diffusion barrier for LCOS may not be reported. In this study, we have used a new dense diffusion barrier for the fabrication of LCOS. The oxygen electronic and ionic conductivity of the novel materials has been separately measured in order to figure out the respective contribution of electrons and ions and then the diffusion mechanism of oxygen ions in the barrier material was clearly explored. The sensitivity of limiting current oxygen sensors using Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2In₂O₃ composite as dense diffusion barrier are investigated.

Section snippets

Experimental details

Y, Fe doubly doped SrTiO₃/In₂O₃ composite (Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2 In₂O₃ (x = 0.04, 0.06, 0.08)) was synthesized via solid state technique using SrCO₃ (AR, Sinopharm), TiO₂ (AR, Sinopharm), Fe₂O₃ (AR, Sinopharm), Y₂O₃ (AR, Sinopharm), and In₂O₃ (AR, Sinopharm) as starting materials [22],[25],[58]. After the chemical reagents were ground and annealed at 1100 °C for 10 h, the annealed powder was used to make the pellets with the diameter and thickness of 8 and 2 mm using mechanical

XRD and SEM analysis

Fig. 3 delineates the XRD spectra of Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2In₂O₃ (x = 0.04, 0.06, 0.08) sintered at 1400 °C for 10 h. It is clear that the indexed peaks are correspond to the cubic perovskite structural phase. The indexed peaks of Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2In₂O₃ samples are in accord with those of cubic SrTiO₃ in PDF 79–174. The peaks centered at 30.48°, 35.62°, and 50.95° correspond to the In₂O₃ in the PDF 88–2160 and the peaks located at 30.84°, 51.19°, and 60.77° are in

Conclusion

Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2 In₂O₃ (x = 0.04, 0.06, 0.08) was effectively synthesized using solid state reaction technique. The phase structure of this composite includes coexistence of two phases, cubic perovskite structure and cubic In₂O₃. The ionic and the total electrical conductivity of the prepared composite increase after rising the content of the In₂O₃. The limiting current oxygen sensor based on Y_0.08Sr_0.92Ti_0.6Fe_0.4-_xO_3-δ/x/2 In₂O₃ as dense diffusion barrier showed outstanding

CRediT authorship contribution statement

Ke Shan: Conceptualization, Methodology, Writing - review & editing. Zhong-Zhou Yi: Investigation, Resources, Software, Data curation. Xi-Tao Yin: Conceptualization, Software, Validation, Formal analysis, Validation, Data curation. Davoud Dastan: Conceptualization, Writing - review & editing, Data curation, Formal analysis, Supervision. Faizah Altaf: Resources, Software, Investigation, Supervision. Hamid Garmestani: . Faisal M. Alamgir: Validation, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was kindly supported by the National Natural Science Foundation of China (Nos. 51962004 and 51562009).

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Mixed conductivity evaluation and sensing characteristics of limiting current oxygen sensors

Abstract

Introduction

Section snippets

Experimental details

XRD and SEM analysis

Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

Sens. Actuators B

Sens. Actuators B

Environ. Nanotechnol. Monit. Manage.

J. Alloys Compd.

Int. J. Appl. Ceram. Technol.

Renew. Energy

Appl. Surf. Sci.

Solid State Ion.

Sens. Actuators B Chem.

Surf. Interfaces

Sens. Actuators B Chem.

Tribol. Int.

Sens. Actuator B

Compos. Part A

Composit. Part A

Adv. Powder Technol.

J. Eur. Ceram. Soc.

Int. J. Hydrog. Energy

Mater. Lett.

Solid State Ion.

Mater. Lett.

J. Eur. Ceram. Soc.

Ceram. Inter.

J. Solid State Chem.

Solid State Ion.

Solid State Ion.

Solid State Ion.

Sens. Actuators, B

Physica E

Sens. Actuators B