Self-assembly structures in ZnFexMn(2-x)O4 ceramics and effect on thermal properties

  • Bin Wang

Student thesis: Master of Science by Research

Abstract

The principle and history of thermoelectric materials were reviewed. As a focus topic of study in this field, the advantages of materials with nanostructure were studied. The methods to synthesize nanostructure were also summarized. ZnFexMn(2-x)O4 ceramic samples were produced using the solid-state synthesis method. After 14-20 hours mixing and milling, ZnO, Fe2O3 and Mn2O3 powders were sintered at 1300℃ for 4 hours and cooled down at rates of 180℃/hour and 6℃/hour. These bulk samples were of high density, over 95% of the theoretical value. XRD techniques and Rietveld Refinement were undertaken to identify the crystal structure and lattice parameters. As the ratio of Fe in the composition increased, the crystal structure transformed from tetragonal to cubic. In samples of tetragonal structure the c parameter decreased with increasing Fe ratio. However, the parameters of samples of cubic structure approximately remained constant.SEM techniques were undertaken to study the phase distributions and the grain sizes of samples. The back scattered electron (BSE) images indicated that there were self-assembled ordered sub-grain structures in the Mn-rich samples. The heat capacities and thermal diffusivities of samples were measured, based on which thermal conductivities were determined. The trends of temperature dependent thermal conductivities revealed a relationship with the crystal structures. Moreover, the samples with sub-grain structures showed relatively lower thermal conductivities which could be a benefit for the quality of thermoelectric applications.
Date of Award31 Dec 2012
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRobert Freer (Supervisor)

Keywords

  • thermoelectric
  • self-assembly
  • sub-grain structure
  • thermal conductivity

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