Single crystal growth of iron oxypnictides and physical properties under high pressure

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New iron oxypnictide Sr2Cr2Fe2As2O2 successfully prepared. Higher superconducting transition temperature is expected in iron oxypnictides with the layered structures between Fe-As tetrahedrons, like Sr2Cr2Fe2As2O2. However, neither elemental substitution for doping careers nor applying pressure of 13 GPa, does cause the superconductivity in Sr2Cr2Fe2As2O2. Suppression of the superconductivity in Sr2Cr2Fe2As2O2 system is probably due to magnetic order of Cr atom. We tried to prepare single crystal samples of Sr2Cr2Fe2As2O2 with metal crucibles with tungsten metal. However, purity of gas in the electrical furnace was not enough to prevent the metal crucibles from melting. As a result, we could not grow the single crystal sample of Sr2Cr2Fe2As2O2. Sr2Cr2Fe2As2O2 and some kinds of elemental substituted compounds are very weak, so that synthesizing under high pressure is suitable for this material. Measurement system for Hall conductivity under high pressure was established.