Synthesis and structural characterization of LaOFeP superconductors

High quality LaOFeP superconducting materials have been successfully synthesized by a two-step solid reaction method. We first prepared a La–Fe–P ternary alloy following a pre-alloying treatment; the resultant La–Fe–P ternary alloy was found to be the key precursor for producing the final LaOFeP superconductors in our experiments. The LaOFeP samples in general have a superconducting transition temperature of about T c ≈4.1 K as demonstrated by the measurements of resistivity and magnetic susceptibility. The volume ratio of the superconducting phase in the high quality sample is estimated to be as high as 95% at the temperature of 2 K. Structural analysis by means of x-ray diffraction, electron diffraction and high resolution transmission electron microscopy shows that the LaOFeP crystal has a layered tetragonal structure with a P 4/ nmm space group. Structural defects such as stacking faults in the LaOFeP sample have also been briefly discussed.