Synthesis, Characterization and Electrical Properties of the Sodium Conductor NaxGa4+xTi1-xO8 (X~0.7) and its Analogs

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New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
The material NaxGa4+xTi1-xO8 (x~0.7) (NGTO) is believed to be a 1-dimensional conductor of sodium and, as such, has potential technological importance. Furthermore, the structure of NGTO is such that it possesses single dimensional tunnels (or channels) along which conduction is presumed to occur, which are large enough in size to accommodate a variety of alkali ions in addition to sodium. The focus of this work was two-fold: 1) prepare and characterize single crystal and polycrystalline NGTO samples and 2) replace the sodium in the NGTO with other ions (K+, Li+, Ag+) through a variety of methods and subsequently characterize these analogs. Initially, the synthesis of polycrystalline NGTO was explored and improved through the examination of batch components and processing methods. Attempts were then made to synthesize various alkali analogs. The thermal, electrical, physical, and chemical properties were studied using a multitude of characterization techniques. For polycrystalline NGTO, the total electrolyte conductivity varied among samples from approximately 10-7 – 10-5 (Ω-cm)-1 at 400°C to approximately 10-3 – 10-2 (Ω-cm)-1 at 1000°C. The activation energy was calculated to be between 0.86 – 1.08 eV. A bulk conductivity of ~10-2(Ω-cm)-1 at 550°C with an activation energy ~0.28eV was calculated for single crystal NGTO. For NGTO exposed to ion-exchange treatments, the measured conductivity decreased with increasing ion size for potassium and silver exchanged samples. However, samples exposed to lithium exchange treatments exhibited a lower conductivity than any of the other samples.
Advisory committee members: Scott Misture, Walter Schulze, Alastair Cormack. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Materials Science and Engineering at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University