Defense Date

9-25-2013

Graduation Date

2013

Availability

Immediate Access

Submission Type

dissertation

Degree Name

PhD

Department

Chemistry and Biochemistry

Committee Chair

Jennifer A Aitken

Committee Member

Shahed Khan

Committee Member

Peter Wildfong

Committee Member

Skip H.M. Kingston

Committee Member

Julia Chan

Keywords

band gap, diamond-like semiconductor, neutron powder diffraction, photovoltaic, thermoelectric, X-ray powder diffraction

Abstract

CuIn1-xFexS2(x = 0 - 0.30), Cu1-xLixInS2(x = 0 - 0.40), and Cu1 xLixIn0.90Fe0.10S2 (x = 0 - 0.40) were synthesized via high-temperature, solid-state synthesis. Rietveld refinements of the neutron and synchrotron powder diffraction data of CuIn1-xFexS2 (x = 0 - 0.15) indicate that all Fe substituted materials are phase pure with the exception of the CuIn0.85Fe0.15S2 sample, which contains a minute secondary phase. These refinements also verify that iron resides on the indium site in the CuIn1 xFexS2 materials. Inductively coupled plasma (ICP) confirms that the actual stoichiometry is close to the nominal composition of the materials. Analysis of X-ray photoelectron spectroscopy (XPS) spectra determined the oxidation state of the copper, indium, and sulfur ions (Cu1+, In3+, and S2-), and Fe57 Mössbauer spectroscopy verified that the iron is in the 3+ oxidation state.

CuIn0.875Fe0.125S2 displayed the lowest total thermal conductivity of the Fe substituted CuInS2 series, 1.37Wm-1K-1 at 570K, as well as the highest thermopower, 172VK-1 at 560K. The electrical conductivity increases over six times upon going from CuInS2 to CuIn0.875Fe0.125S2. These improved properties result in an increase in the ZT of CuInS2 by over an order of magnitude for the x = 0.125 sample. Magnetic measurements reveal the x = 0 - 0.10 samples to be paramagnetic, while the sample in which x = 0.125 displays ferromagnetic ordering below 95K. A band gap of the CuIn1 xFexS2 solid solution was estimated to be in the range of 0.70 - 1.07eV, while Li substitution increased the band gaps of the Cu1-xLixInS2 series by a maximum of 0.31eV and the Cu1 xLixIn0.90Fe0.10S2 series by a maximum of 0.33eV.

Format

PDF

Language

English

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