Synthesis of SmFeAsO Polycrystalline Bulks With Improved Purity by High-Energy Milling

Methods for synthesizing high purity, undoped SmFeAsO (Sm1111) polycrystalline bulks and doping hydrogen into these bulks were investigated. Regarding the Sm1111 polycrystalline synthesis, the formation of robust impurities during high-temperature sintering presents a notable challenge. Undoped Sm1111 polycrystalline bulks with improved purity were successfully synthesized by introducing high-energy milling using a planetary ball-mill apparatus, even at a relatively low temperature of 550°C. Based on the changes in lattice parameters, lattice defects are likely introduced by high-energy milling. Furthermore, hydrogenation of the undoped Sm1111 was attempted, and the effectiveness of the hydrogen-doping methods was evaluated by resistivity measurements. The resistivity of almost all polycrystalline bulks in this study exhibited semiconductor-like behavior. However, an anomaly in resistivity at around 45 K was observed in the sample after annealing with CaH2.