Materials Design of Complex Dielectric Crystals

Dielectric materials are insulators that can screen an external electric field. These materials are used in capacitors, high power applications, computer chips, and sensors, making them an essential part of today's electronic technology. The screening in these materials can originate from dipoles of various length scales, but the electronic and ionic contributions have attracted special attention as they are intrinsic to a material. Surprisingly, a microscopic description of polarisation was only formulated two decades ago, and its calculation became computationally feasible only recently. In light of this progress, it is timely to use these to develop new dielectric materials. In contrast to the conventional characterisation approach, where theoretical works follow experiments, this ``materials design'' approach aims to suggest new dielectric materials or new usage of conventional dielectric materials a priori to experimental findings. In this thesis, I show that a combination of conventional electronic structure methods and data science tools can be used synergistically to design dielectric materials. This thesis consists of three main results. Firstly, new properties of conventional materials are probed using electronic structure theory, in particular the dipole induced by F-doping in non-polar Ruddlesden-Popper phase Sr3Ti2O7 is discussed. Next, electronic structure calculation are combined with data science methods, to analyse the permittivity of 1364 materials. Finally, a fully data-oriented method for analysing distortions in dielectric materials is shown. Together these studies show the strength of combining conventional electronic structure and data science techniques and that their balance can be adjusted according to the problem of interest. These studies not only open a new path towards next-generation dielectric materials, but the methodologies are also significant as many of them are either newly developed or newly imported from different scientific fields. Therefore, works in this thesis are likely to promote further material discoveries.Open Acces

Thermal Conductivity Measurement of the Molten Oxide System in High Temperature

In spite of practical importance in the pyro-metallurgy process, thermal conductivity of molten oxide system has not been sufficiently studied due to its notorious convection and radiation effects. By an aid of appropriate modification of measurement technique and evaluations for systematic errors, thermal conductivity measurement at high temperature becomes feasible. In this chapter, thermal conductivity measurement technique for high-temperature molten oxide system was discussed along with related experimental errors. In addition, thermal conduction mechanism by phonon was briefly introduced. The laser flash method and hot-wire method, which are representative measurement methods for high-temperature system, were compared. During the measurement by using hot-wire method, the convection and radiation effects on measurement results were evaluated. In the hot-wire method, both convection and radiation effects were found to be negligible within short measurement time. Finally, the effect of network structure of molten oxide system on thermal conductivity was discussed. The positive relationship between thermal conductivity and polymerization in the silicate and/or borate system was presented. In addition, the effect of cation expressed by function of ionization potential on thermal conductivity was also briefly introduced. This chapter is partially based on a dissertation submitted by Youngjae Kim in partial fulfillment of the requirements for the degree of Doctor of Philosophy at The University of Tokyo, September 2015

In-situ observation and multi-physics simulation of reactive melt Infiltration of silicon melt into SiC-C Preform

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Models of Polaron Transport in Inorganic and Hybrid Organic-Inorganic Titanium Oxides

Polarons are a type of localized excess charge in materials and often form in transition metal oxides. The large effective mass and confined nature of polarons make them of fundamental interest for photochemical and electrochemical reactions. The most studied polaronic system is rutile TiO2 where electron addition results in small polaron formation through the reduction of Ti(IV) d0 to Ti(III) d1 centers. Using this model system, we perform a systematic analysis of the potential energy surface based on semiclassical Marcus theory parametrized from the first-principles potential energy landscape. We show that F-doped TiO2 only binds polaron weakly with effective dielectric screening after the second nearest neighbor. To tailor the polaron transport, we compare TiO2 to two metal-organic frameworks (MOFs): MIL-125 and ACM-1. The choice of MOF ligands and connectivity of the TiO6 octahedra largely vary the shape of the diabatic potential energy surface and the polaron mobility. Our models are applicable to other polaronic materials

ヒト胎盤栄養膜細胞分化モデルを用いた新規ヒト内在性レトロウイルスの探索

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 田中 栄, 東京大学准教授 近藤 健二, 東京大学講師 篠田 裕介, 東京大学講師 犬塚 亮, 東京大学講師 平田 哲也University of Tokyo(東京大学

Unveiling the role of differential growth in 3D morphogenesis: An inference method to analyze area expansion rate distribution in biological systems

The three-dimensional (3D) morphologies of many organs in organisms, such as the curved shapes of leaves and flowers, the branching structure of lungs, and the exoskeletal shape of insects, are formed through surface growth. Although differential growth, a mode of surface growth, has been qualitatively identified as 3D morphogenesis, a quantitative understanding of the mechanical contribution of differential growth is lacking. To address this, we developed a quantitative inference method to analyze the distribution of the area expansion rate, which governs the growth of surfaces into 3D morphology. To validate the accuracy of our method, we tested it on a basic 3D morphology that allowed for the theoretical derivation of the area expansion rate distribution, and then assessed the difference between the predicted outcome and the theoretical solution. We also applied this method to complex 3D shapes and evaluated its accuracy through numerical experiments. The findings of the study revealed a linear decrease in error on a log-log scale with an increase in the number of meshes in both evaluations. This affirmed the reliability of the predictions for meshes that are sufficiently refined. Moreover, we employed our methodology to analyze the developmental process of the Japanese rhinoceros beetle Trypoxylus dichotomus, which is characterized by differential growth regulating 3D morphogenesis. The results indicated a notably high rate of area expansion on the left and right edges of the horn primordium, which is consistent with the experimental evidence of a higher rate of cell division in these regions. Hence, these findings confirm the efficacy of the proposed method in analyzing biological systems

Generalized edema and heart failure caused from hypothyroidism and ferrous agent for hypochromic anemia

The patient was an 85-year-old female who has been treated for hypertension and atrial fibrillation (Af). She has visited outpatient clinic and has received regularly general blood tests for every six months. Hemoglobin (Hb) level was stable as 11.2-12.3 g/dL and MCV 88fL from 2017, but it decreased suddenly to 5.2 g/dL and 64 fL in Sept 2020. She did not feel any symptoms or signs. Further evaluations revealed that occult blood in stool and upper and endoscopic exams were negative. About 40 days after starting sodium ferrous citrate, she developed edema anasarca, bilateral pleural effusion and heart failure. Laboratory test showed hypothyroidism, and then the administration of thyroid hormone and diuretics brought her early improvement. As to this impressive case report, general clinical progress and some discussion of the relationship among anemia, edema anasarca, heart failure and hypothyroidism would be described