Revealing the role of dopants in mitigating degradation phenomena in sodium-ion layered cathodes

Prevention of the degradation of sodium-based layered cathode materials is the key to developing high-performance and high-stability sodium-ion batteries. In this study, the working mechanism of Mg and Ti dopants in mitigating degradation was investigated through the use of first-principles calculations. More specifically, the effects of each dopant in suppressing the phase transition, lattice expansion and shrinkage, and possible oxygen generation during repeated charging and discharging processes were validated. The results showed that the pristine structure exhibits irreversible O3-P3 phase transition after 75% desodiation, while doping with Mg or Ti effectively delays this transition. In addition, the change in lattice parameters as well as in the volume during desodiation was investigated. It was found that both dopants reduce the magnitude of structural change, which potentially improves the structural stability. Furthermore, introducing the dopants increases the thickness of the Na diffusion channel, possibly leading to an enhanced rate capability. Finally, the oxygen atomic charge variation during charging indicated that doping can enhance the oxygen stability by reducing the initial charge of oxygen as well as its increase during desodiation

이원자 분자로 구성된 응집상에서 분자동력학과 리아프노프 불안정성 연구

학위논문(박사) - 한국과학기술원 : 화학과, 2001.8, [ [iii], 97 p. ]We developed a molecular dynamics simulation method to evaluate the full spectrum of Lyapunov exponents for simple fluids and rigid diatomic fluids. And we calculated the Kolmogorov-Sinai entropy (KS entropy) and self-diffusion coefficients. We show the general trends and characteristic features of the spectra of the Lyapunov exponents, and discuss the different contributions between translational and rotational degrees of freedom depending on the density. It is found that, the KS entropy, when expressed in terms of the average collision frequency, is uniquely related to the self-diffusion coefficient by a simple scaling law for simple fluids. This behavior is also observed in diatomic molecular systems. For the three-dimensional diatomic molecular system, we can relate both translational diffusion coefficients and rotational diffusion coefficients to the respective portions of KS entropy.한국과학기술원 : 화학과

First-Principles Study of Multiferroic Mn-doped InP

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Resistive switching characteristics of epitaxial NiO thin films affected by lattice strains and external forces

We investigated the resistive switching characteristics of NiO films grown epitaxially on two single-crystal Rh and Ni substrates. Two epitaxial NiO films were relatively small compressive strained on the Rh substrate, and confirmed by the x-ray diffraction experiments that the strain was relatively large compressive on the Ni substrate. Comparing the forming, SET, and RESET voltages of NiO resistive switching random access memory capacitors, NiO films grown on the Ni substrates showed relatively higher voltages than Rh substrates. We propose that this compressive strain has an effect on raising the forming, SET, and RESET voltages. Furthermore, we observed that the forming voltage decreases while reducing the compressive strain by applying pressure to the NiO thin film grown on the Ni substrate with an atomic force microscope tip. In addition, we showed that relaxation of compressive strain by external force by first-principles calculations can reduce the oxygen deficiency energy and lower the forming voltage and working voltages, which supports the experimental results well

Nanostructure Fabrication based on Scanning Probe Microscope

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Epitaxial growth and switching characteristics of epitaxial BiFeO3 thin films on Pt/mgO(001)

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Rhombohedral 구조를 가지는 BiFeO3 에피 박막의 자성특성 강화현상과 오비탈 혼성

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Multiscale Approach for the Electronic and Magnetic Properties of Complex Oxide Ferroic Materials

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비선형 브라운 진동자의 진동 이완

학위논문(석사) - 한국과학기술원 : 화학과, 1996.2, [ 58 p. ]We study stochastic dynamics driven by white and colored noise by means of the Fokker-Planck process. Two methods for solving the Fokker-Planck equation is introduced. The one is the projection operator method and the other is the matrix continued fraction method. In the white noise limit the study of a nonlinear Brownian oscillator using the projection operator method shows that the vibrational relaxation rate is enhanced not only by the friction and temperature, but also by the nonlinear part of the potential, which suggests that there is a coupling between the nonlinearity and randomly fluctuating force. By the matrix continued fraction method we obtain the similar results. In the case of colored noise, changing the correlation time we examine the trend of the relaxation time of the harmonic oscillator in terms of the projection operator method. And then we compare the results with those of the matrix continued fraction method.한국과학기술원 : 화학과

Non-volatile Memory Device using Ferroelectric Polymer Nanodot and Carbon Nanotube

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