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A prototype of material design is presented by taking a superconductivity research on boron crystals as instance. Aside from prediction of Tc, the most important role of CMD for superconductivity research is very similar to that of other field. Given candidates for high-Tc material, a big problem remaining to experimentalists is how to synthesize such a material. Many people believe that diamond could have high Tc around 40 K, if a sufficient level (more than 10 at.%) of doping is achieved. This is the most serious problem with which everyone in this field is concerned. Theoretically speaking, crystal growth and related techniques are somewhat dirty subjects, and thereby are usually the last one which theorists study. The strategy of the author for solving this issue is use of combination of first-principles calculations and thermodynamic consideration. This is an extremely powerful tool for material researches. In this paper, the author's experience on superconductivity research is presented form the standpoint of material design. A special topic is chosen in the superconductivity of semiconductors, especially, those of high refractory materials such as C and B, because of the strong electron-lattice interactions. Boron is particularly interesting because of its exotic structure, that is, icosahedron-based structure. It is expected to exhibit a high Tc superconductor, if the matrix is made to be metallic. The most common phase of boron, β boron, was proven to undergo superconductivity transition at high pressure (160 GPa). However, crystal structure at such high pressures has yet been clarified. Even phase diagram of boron was not known. Our approach to this subject is a kind of integrated study based on DFT calculation and thermodynamic investigation. The first thing to do is determination of the phase diagram. Phase diagram is quite important for material research; something like a lighthouse shinning on the dark. Without this help, experimentalists would have much difficulty to synthesis new materials. We are the first to predict the phase diagram of boron. Since then, a profound progress has been achieved in this field. Based on our prediction of the phase diagram, we know that α phase is the most stable phase at high pressure. It is advantageous to examine superconductivity of α phase at high pressures, because of its stability. In addition, the structure of α phase is relatively simple. With these benefits, the author led experimentalists to study superconductivity of α phase. Our collaborators finally discovered the superconductivity of α phase at high pressure. Significant progress has been achieved regarding the metallization mechanism. Of further importance, we have theoretically solved a difficult issue of doping to α phase. An efficient method of doping is use of high pressure. Experimentalists are almost about catching of this doping. |
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