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Materials Science at Oregon State University

Graduate Student Seminars

Date: Thursday, Oct 15th
Presenter: Laura Oliveira and Nitish Kumar, OSU Materials Science

Abstract


Laura Oliveira Abstract
First principles thermal transport calculations in advanced materials

Many solid-state properties (e.g.: mechanical, optical, magnetic) are temperature dependent and an atomistic-level understanding of thermal transport is paramount to a wide array of applications, even ones not directly related to heat transfer. Classical and ab initio molecular dynamics (MD) simulations alike can provide valuable insight into phononic thermal transport and its mechanisms. In this talk, we present our findings concerning thermal transport in defect-laced graphite and the open- and closed-pore structures of the flexible metal-organic-framework (MOF) MIL-53, and discuss the methods used. We also introduce a new method to quantify and mitigate simulation noise in equilibrium MD (Green-Kubo) thermal conductivity calculations, and a novel thermal conductivity model for breathing MOFs.

Bio:
Laura obtained undergraduate degrees in Physics and Mathematics at the New Mexico Institute of Technology and is currently a PhD student at OSU under the guidance of Dr. Alex Greaney. She does computational research in Materials Science with a focus on thermal properties of materials. She is also currently studying isomerizing properties of photoisomers under constraint.

Nitish Kumar Abstract
Transport properties of BaTiO3-Bi(Zn1/2Ti1/2)O3 ceramics for high temperature capacitor applications

Recently, ceramics based on BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) have been shown to exhibit excellent properties (relative dielectric constant > 1000, high breakdown strength) that enable the material to be used for high energy density and high temperature capacitor applications. Multilayer ceramic capacitors based on this material have demonstrated energy densities approaching ~3 J/cm^3, which is superior to commercially available devices. One of the reasons for widespread use of ferroelectrics like lead zirconate titanate in plethora of applications is their well-understood defect chemistry. The same needs to be done for BT-BZT and other Bi-perovskites before they can be fully exploited for applications. A significant (~2 orders of magnitude) improvement in the electrical resistivity was recently reported in these BT-BZT ceramics with addition of BZT to the solid solution, which was also accompanied by a change in the polarity of the majority charge carrier from p-type for BT to n-type for the BT-BZT solid solution. This points towards an unintended donor doping in BT-BZT ceramics. Even though there is no obvious mechanism for donor doping in these ceramics, the cause may be linked to the formation of an intermediate phase BaBiO3 with Bi5+ on the B-site, the presence of oxygen vacancies being compensated by electrons, the loss of zinc and bismuth during processing, and other mechanisms. With the help of techniques like high-energy diffraction, XPS, TGA with in-situ mass spectroscopy, and other experiments, this presentation will include findings, which aim to help understand the underlying defect mechanisms in BT-BZT ceramics.

Bio:
Nitish Kumar is a PhD student in Materials Science working for Prof. David P. Cann at Oregon State University. His current research aims at studying underlying defect mechanisms in bismuth-containing perovskite systems to make them more suited for applications. He has nine peer-reviewed journal articles and has delivered four conference presentations so far. He has also 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 Oregon Lottery Graduate Scholarship, Graduate Student Travel Award and award at American Society for Metals Student Competition. At the moment he is looking for a good postdoc position!