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A Metal Percolation Path in Metal/Semiconductor Composites and its Effect on Electric Conductivity in Different Ambiances

Qin, Fen (2020) A Metal Percolation Path in Metal/Semiconductor Composites and its Effect on Electric Conductivity in Different Ambiances. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Semiconducting oxides, owing to their unique electrical and chemical properties have been widely investigated and used as electrodes for renewable and sustainable energy system. Nevertheless, several limitations of semiconducting oxides electrodes still exist. One inherent problem is that the electric conductivity is relatively low and dependent on ambiance. This can be resolved by designing a composite with a complementary metal component.
This study is focused on the design, fabrication and characterization of metal - oxide composite with the desired configuration of a metal component and the stable electrical conductivity of the composite electrode. Outcome of this study is found to meet stringent requirements of energy devices including the interconnector of solid oxide fuel cells (SOFCs) and the transparent conductor (TC) of solar cells.
First, the crystallization of (La1-xSrx)MnO3 (LSM) was controlled using microwave radiation and its effect on the grain growth and electrical properties of LSM ceramics was studied. Second, Ni particles were added to LSM matrix to form a percolation path that maintains high electric conductivity in reducing ambiance. The addition of Ni particles also changed the sintering behavior of LSM ceramics using a self-induced liquid phase. The size of initial Ni particles was a critical factor influencing the formation of the percolation path and the appearance of the self-induced liquid phase. A stack of LSM and Ni-LSM composite layers was tested as the interconnector of fuel cells by exposing two ends to different oxidizing or reducing ambiance. Compared with LSM interconnector, this new interconnector showed high electric conductivity at the simulated operating condition of SOFCs.
Moreover, an effect of the aspect ratio of a metal component on the electric conductivity was explored. In LSM:Ni composites, the change in the aspect ratio modified the electric conductivity of the composite. A percolation threshold was reduced by employing highly anisotropic Ni particles. It was also observed that an increase in the aspect ratio could suppress the particle packing and subsequent densification in the composite processing. This concept of a percolation path is also applied to ZnO film to increase its electric conductivity and reduce its dependence on the ambiance. Ag nanowires with the aspect ratio ranging from 67 to 450 improved the electric conductivity. A simulation model explaining the effect of the Ag nanowires was developed by taking into account a junction resistance. In addition, a nanoscale engineering of Ag nanowire/nanoparticle mixture improved the figure of merit and decreased the diffuse scattering. A series of experimental and computational results show that nanowire embedded ZnO is a promising indium-free and affordable alternative to currently dominant ITO.
Overall, this dissertation showed detailed mechanisms underlying the excellent electric conductivity and good optical transparency of the metal – oxide composites and shed light onto the design rule of the electrode for different renewable energy devices.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Qin, Fenmayaya015@outlook.comfeq2
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairLee, Jung-kunjul37@pitt.edujul37
Committee MemberNettleship, IanNETTLES@pitt.eduNETTLES
Committee MemberBedewy, Mostafambedewy@pitt.edumbedewy
Committee MemberXiong, Weiweixiong@pitt.eduweixiong
Date: 28 September 2020
Date Type: Publication
Defense Date: 19 March 2020
Approval Date: 28 September 2020
Submission Date: 14 July 2020
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 191
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: semiconductor, solid oxide fuel cell, perovskite, metallic nanoparticles, nanowire
Date Deposited: 28 Sep 2020 20:21
Last Modified: 28 Sep 2022 05:15


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