Silicon (Si) clathrate compounds are composed of host Si atoms organized in three-dimensional frameworks and guest atoms enclosed in the Si cage-like frameworks. In the present study, single crystals of Si clathrates containing Na atoms, type-I (Na₈Si₄₆) and type-II (Na₂₄Si₁₃₆), were synthesized by using a Na-Sn flux. The single crystals having facets grew up to a few millimeters in size by evaporating Na from a Na-Si-Sn solution at 723–873 K. This synthesis procedure enabled selective synthesis of type-I and -II clathrates by controlling the heating temperature. One of the obtained single crystals was used as a seed for the following crystal growth of the type-II clathrate. The octahedral single crystal surrounded by {111} facets with a size of 3 mm was obtained on the seed crystal. Novel ternary clathrate, Na₈(Ga/Si)₄₆, and quaternary clathrates, (Sr/Na)₈(Ga/Si)₄₆, were synthesized by using Na-Ga-Sn composite fluxes.

  Pressure is one of the thermodynamic parameters together with the temperature to control the stability of materials. Ultra-high pressure in GPa ~ Mbar regions allows us to obtain novel materials and crystals. This review shows two crystal growth systems under ultra-high pressure and high temperature are shown in the first part, i.e. multi-anvil large press and laser-heating diamond anvil cell systems. In the second parts, our recent research results of crystal growth by solution growth techniques using these two systems are described including novel incompressible crystals, high aspect-ratio nanowires and rectangular hollow crystals of metal nitrides and oxides.

  Flux method is one of effective crystal growth technique to provide high-quality crystals, which can be applied to various functional materials. Usually, flux method takes long time to develop crystal materials, because of its complicated growth mechanism and various experimental parameters. This disadvantage prevents wide uses of this method for material applications. To solve these issues, we are incorporating informatics into the flux method. Possible prediction of crystal growth by machine learning would drastically change the workflow of material development. This report introduces our recent challenge to develop flux growth study using informatics. In detail, we show 3 topics. Firstly, we developed data-driven flux crystal growth system, based on Bayesian optimization. Here, we show machine-leaning design of experiment customized for flux method. Secondly, data format for flux method was statistically studied. Here, importance of raw material information and their description are proposed. Thirdly, we developed experimental automation system using robot. Here, application of the system to crystal purification process was carried out.

  The most of the oxide single crystals used as industrial products such as LiTaO₃ (LT), LiNbO₃ (LN), sapphire, Y₃Al₅O₁₂ (YAG), Gd₃(Al,Ga)₅O₁₂ (GAGG), etc. are produced by the Czochralski (CZ) method. In the CZ method, crucibles are regarded as indispensable for holding the melt. Especially in the case of oxides, crucibles are often used as a heat source, as well. However, the use of crucibles has long been a problem due to the following reasons: (1) crucibles limit the melting points of materials that can be handled and the atmosphere in which they can be grown, (2) crucibles are a source of impurities and other defects, and (3) crucibles are expensive (precious metals are used for growing materials with high melting points). In this paper, the Skull melt method, a melt growth method that does not use a crucible, is introduced. Oxide Crystal growth from Cold Crucible (OCCC) method, a fusion of the CZ method and Skull melt methods, was also introduced. In this report, the results of melt growth of GAGG and gallium oxide grown by the OCCC method are demonstrated. The fact that bulk single crystals of gallium oxide with a diagonal length of nearly 50 mm were obtained gives hope for the possibility of this method as a mass production technology.

  We developed a novel fabrication method for alloy crystal fibers with poor-workability by unidirectional solidification using an alloy-micro-pulling-down (A-μ-PD) method and ceramic crucibles with sufficient mechanical and thermal shock resistance. Ir, Pt, Ru and their alloy fibers were fabricated from the melt directly by the A-μ-PD method. Long alloy fibers could be obtained using a pinch-roller and winding machine. Ir and Ru fibers were composed of number of elongated grains oriented along a growth direction which is attributable to the unidirectional solidification. In addition, microstructure and mechanical properties of Co-Cr-Mo (CCM) alloy fibers fabricated by the A-μ-PD method could be controlled by the growth rate. Ratio of the fcc-γ-phase in the CCM alloy fibers systematically increased with increasing growth rate. The hcp-ε-phase CCM crystal fibers exhibited considerably improved strain because of the slipping line in the hcp structure.