물성 향상을 위한 열처리를 이용한 바륨 스터네이트 박막의 결함 재분배에 관한 연구

Abstract

The technologically useful properties of oxide materials often depend upon the types and concentrations of the defects it contains. For example, defects mediate dopant diffusion in oxides used for microelectronic devices in ways that are vital for device fabrication. Defects also affect the performance of oxide-based sensors, catalysts, photo-active devices, and photovoltaic cells. Defect formation in the oxide affects various properties in a variety of ways. Extended line defects generally degrade electrical, physical properties such as carrier scattering, lowering crystallinity. On the other hand, point defects typically affect electronic properties such as carrier type, concentration or mobility. In order to control the behavior of these defects and maximize the performance of the applications, various means of defect engineering have been developed and implemented. In this regard, this thesis focuses on the defect control of BaSnO3 epitaxial films for enhancing various properties by post-annealing process. The first topic is about line defect control of BaSnO3 thin films. We developed High-T annealing process to enhancing room-temperature electron mobility in Ladoped BaSnO3 (LBSO) thin films with thermal strain induced. Simple annealing under an N2 environment consistently doubled the electron mobility of the LBSO films on the SrTiO3 (STO) substrates to as high as 78 cm2V-1s-1 at a carrier concentration of 4.0 x 1020 cm3.This enhancement is mainly attributed to annihilation of extended defects as a consequence of compressive strain induced by the difference in the thermal expansion coefficients of LBSO and STO. Our study suggests that thermal strain can be exploited to reduce extended defects and to facilitate electron transport in transparent oxide semiconductors. The second them is about the synthesis of nanoparticles on stannate support by controlling cation defect. In situ exsolution of metal nanoparticles is emerging as an alternative technique to deliver thermally stable and evenly dispersed metal nanoparticle, which exhibit excellent adhesion with perovskite oxide support. Despite a number of studies on the demonstration of conducting oxide support with metallic nanoparticles by exsolution, the electrical conductivity was limited by localized d electron transport in widely used perovskite oxide support. Here, we provide the first demonstration that Ni metal nanoparticles (NPs) with high areal density (~ 175 m-2) and fine size (~ 38.65 nm) are exsolved from A-site deficient perovskite stannate support (La0.2Ba0.7Sn0.9Ni0.1O3- (LBSNO)). The NPs are strongly anchored and impart coking resistance, and the Ni-exsolved stannates show exceptionally high electrical conductivity (~ 700 S·cm-1). The exceptional conductivity is attributed to conduction between delocalized Sn 5s orbitals, along with structural improvement towards ABO3 stoichiometry in the stannate support. We also reveal that an experimental condition with strong interaction must be optimized to obtain Ni exsolution without degrading the perovskite stannate framework. Our finding suggests a unique process to induce formation of metal NPs embedded in stannate with excellent electrical properties. The present studied will (i) provide a simple and effective method for reducing the density of extended defects in LBSO films to boost their RT e (ii) offers an opportunity to design new heterostructures that bear metal NPs and perovskite oxide to obtain excellent electrical transport, catalytic activity based energy storage and conversion applications.