Synthesis of transition metal oxides under extremely high oxygen pressure

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Recently great attention has been paid for high-pressure research. The advantage of high-pressure research is to make continuous change of sample volume without introducing randomness effect which is often caused by alloying and/or atom substitution. On the other hand high-pressure technique is well applied for material synthesis.In this project, we have built a high-pressure experiment system using a diamond anvil cell (DAC) which can generate very high pressure more than 10 GPa.. In this system, the material is sealed in the DAC with oxygen and can be heated by YAG laser. Diamond is transparent for infrared laser and it is designed that the laser beam can heat the material in the DAC in both direction. This laser heating method is usually used in the earth science in which interior materials have been synthesized. It is first time to use laser heating method in DAC for superconducting materials.The measurement system for synthesized sample has also built in this project. In order to … More measure the magnetic properties, AC susceptibility measurement system has been built. Special care is taken for detecting very small signal from the sample which placed in the very small high-pressure space. Our target pressure range is 10 GPa to 100 GPa. Using this system we studied superconducting transition, insulator-metal transition, and magnetic transition. Novel quantum transitions are expected to be discovered. The DAC are made from non-magnetic CuBe alloy and driven by pneumatic system to keep constant pressure at low temperature.In this work the laser heating under extremely high oxygen pressure has been carried out for La_2CuO_4 and YBa_2Cu_3O_7. The superconducting trnsition temperature(TC) of La_2CuO_4 is known to be sensitive to the excess oxygen accommodated in the material and T_c of YBa_2Cu_3O_7 is also sensitive to the oxygen defect. Thus these materials are good sample for testing our experiment system. Synthesis of nitride using DAC under high nitrogen pressure has also been tried for NbN.Since it is difficult to detect the superconductivity in DAC because of the amount of specimen is extremely small, SQUID magnetometer is also used with DAC. Special DAC was designed for SQUID.Discovery of new superconducting materials is expected in the high-pressure reserch. Less