Simple synthesis of bulk YBa₂Cu₄O₈ using copper iodide and bromide

We present a solid-state reaction method for simply synthesizing high-T_c superconductor YBa₂Cu₄O₈ (Y-124) without the use of high-pressure oxygen, catalyst or sophisticated heat treatment. This technique is characterized by using cuprous iodide or bromide in place of the conventionally used copper oxide. T_c (zero-resistance) of 77 K and 68 K are obtained for samples using copper iodide and bromide, respectively. For the sample synthesized by use of CuI, X-ray diffraction spectrum suggests a single Y-124 phase. The magnetic susceptibility measurement shows a superconducting transition temperature of 83 K, which is characteristic of the Y-124 superconductor.