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

合成了新的铁氧铌酸盐Sr_2Cr_2Fe_2As_2O_2。具有Fe-As四面体间层状结构的铁氧磷属化合物，如Sr 2Cr 2Fe 2As 2 O2，有望获得更高的超导转变温度。然而，无论是元素替代掺杂事业或施加13 GPa的压力，并没有造成的超导性在Sr 2Cr 2Fe 2As 2 O2。Sr_2Cr_2Fe_2As_2 O_2体系超导电性的抑制可能是由于Cr原子的磁序所致。我们尝试用金属钨坩埚制备Sr_2Cr_2Fe_2As_2O_2单晶样品。然而，电炉中的气体纯度不足以防止金属坩埚熔化。结果，我们不能生长Sr 2Cr 2Fe 2As 2 O2的单晶样品。Sr_2Cr_2Fe_2As_2O_2和某些元素的取代化合物很弱，因此高压合成是合适的。建立了高压霍尔电导率测量系统。

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.