Simple One-Step Synthesis and Superconducting Properties of SmFeAsO1-xFx

The recent discovery of superconductivity in REFeAsO (RE, rare-earth metal) has generated enormous interest because these materials are the first non-copper oxide superconductors with critical temperatures T-c exceeding 50 K as well as upper critical fields well above 100 T. However, for these new superconductors, very complicated synthesis routes, such as the complex two-step synthesis or high-pressure sintering, are required. Furthermore, there is the toxicity and volatility of arsenic to consider, sometimes a sealed quartz tube of arsenic exploded during annealing. We present a new method for producing high-temperature SmFeAsO1-xFx superconductors by using a one-step sintering process. Superconducting transition with the onset temperature of 54.6 K and high critical fields H-c2(0) >= 200 T were confirmed in SmFeAsO0.7F0.3. At 5K and at self field, critical current densities J(c) estimated from the magnetization hysteresis using the whole sample size and the average particle size have reached 8.5 x 10(3) and 1.2 x 10(6) A/cm(2), respectively. Moreover, J(c) exhibited a very weak dependence on magnetic field. This simple and safe one-step synthesis technique should be effective in other rare earth derivatives of iron-based superconductors.