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Materials Science at Oregon State University

Defects and transport mechanisms in BaTiO3-Bi(Zn1/2Ti1/2)O3 ceramics for high temperature capacitor applications

Date: Thursday, Oct 13th
Presenter: Dr. Nitish Kumar, Materials Science, University of New South Wales


Defects make materials beautiful and give PhD degrees to students like me. Polycrystalline BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) ceramics have been shown to exhibit superior dielectric properties for high temperature and high energy density applications as compared to the existing materials. At first their unique properties and suitability to miniaturization have been demonstrated. The energy density values (~2.8 J/cm^3) were higher than commercially available devices and the permittivity values were insensitive to temperature over a wide temperature range. Next, using resistivity and activation energy values for conduction, it was concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic-like for BT-BZT suggesting a change in the fundamental defect equilibrium conditions. While pure BT exhibits extrinsic p-type conduction, it is also reported that BT-BZT ceramics exhibit intrinsic-like n-type conduction, demonstrated using multiple experimental techniques. These results suggested towards a possible unintentional donor doping upon addition of BZT to the solid solution. Several candidates for donor doping were investigated using various advanced techniques. Using the results obtained and knowledge of thermodynamics, it was concluded that the defects in BT-BZT ceramics have an effect of shifting the conductivity minimum in conductivity-oxygen partial pressure plots to higher oxygen partial pressure values as compared to unmodified BT, resulting in significantly higher resistivity values and n-type conduction in air atmosphere. The results obtained for these materials provide an important tool to tailor transport properties and defects in similar systems, and bring them one step closer to commercial applications.

Nitish Kumar defended his PhD one month back under the supervision of Prof. David P. Cann at Oregon State. He has published 15 peer-reviewed journal articles and delivered 6 conference presentations so far. He interned at Hewlett-Packard Company and Technische Universit├Ąt Darmstadt, Germany as a part of his research. Prior to coming to OSU, he did his Bachelors in Materials and Metallurgical Engineering at Indian Institute of Technology, Kanpur (India) and a job at Superalloys Plant, Hyderabad (India) for one year. At OSU, he has received College of Engineering Outstanding Graduate Research Assistant Award, Oregon Lottery Graduate Scholarship, Graduate Student Travel Award and an award at American Society for Metals Student Competition. He plans to move to University of New South Wales, Sydney for his next adventure.