Solid-State Synthesis and Some Properties of Magnesium-Doped Copper Aluminum Oxides
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1218-Z01-05
SOLID-STATE SYNTHESIS AND SOME PROPERTIES OF MAGNESIUM-DOPED COPPER ALUMINUM OXIDES Chang Liu1, Fei Ren2, Hsin Wang2, Eldon Case1 and Donald Morelli1 1
Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, U.S.A.; 2Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A. ABSTRACT Copper aluminum oxide (CuAlO2) with delafossite structure is a promising candidate for high temperature thermoelectric applications because of its modest band gap, high stability and low cost. We investigate magnesium doping on the aluminum site as a means of producing higher electrical conductivity and optimized Seebeck coefficient. Powder samples were synthesized using solid-state reaction and bulk samples were prepared using both cold-pressing and hot-pressing techniques. Composition analysis, microstructural examination and transport property measurements were performed, and the results suggest that while hot-pressing can achieve high density samples, secondary phases tend to form and lower the performance of the materials. INTRODUCTION/MOTIVATION Thermoelectric materials are under intense scrutiny for applications in waste heat recovery and solid-state refrigeration. To attain high efficiency in thermoelectric power generation, a large figure of merit, Z=σS2/κ, is required, where σ, S and κ are electrical conductivity, Seebeck coefficient and thermal conductivity, respectively. Since the thermoelectric efficiency is a fraction of the Carnot efficiency, operation at elevated temperature is desirable to achieve high efficiency. Most contemporary thermoelectric materials are binary and ternary semiconductor alloys based on chalcogenides and pnictides. Several major drawbacks of these materials include decomposition or oxidization at elevated temperature1, scarcity and toxicity of certain elements, and expensive preparation techniques. Oxide-based thermoelectric materials, on the other hand, have attracted much attention as promising candidates due to their high-temperature stability, low preparation cost and environment-friendly properties. Copper aluminum oxide (CuAlO2) with layered delafossite structure is an example1-2. It is hoped that delafossite structure compounds, like other oxides, may reach ZT near unity at high temperature and afford a cost-effective approach to thermoelectric power generation. In addition, CuAlO2 has band-gap energy on the order of 1.9 eV3, which is quite small compared with most oxides. It also possesses rhombohedral-polytype (R3m) delafossite structure, which is constructed by the alternating appearance of twodimensional close-packed Cu+ cation layers, O-Cu+-O linear bonds and slightly bent edge-shared Al3+O6 octahedra. Such complex structure can result in strong phonon scattering and low thermal conductivity. To enhance the electrical conductivity, optimize the Seebeck coefficient, and further reduce thermal conductivity, CuAlO2 has been doped with calcium (Ca) to generate excess charge ca
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