Rapid preparation of YBa₂Cu₃O_7-x with T_c ∼ 90 K using a domestic microwave oven

High-T_c superconducting samples of YBa₂Cu₃O_{7-cursive Greek chi} with T_c ∼ 90 K have been prepared in a short time of 25 min, using a domestic microwave oven operated at 2.45 GHz and 200 W, without any post-heat treatment. Post-heat treatment is not necessary due to improvement of the sample environment during the microwave process. That is, a pellet of mixed powders of raw materials is surrounded by mixed powders of raw matetials and subsequenty wrapped in glass wool, in order to suppress rapid dissipation of heat from the surface of the pellet. This leads to successful preparation of homogeneous and oxygenated samples of YBa₂Cu₃O_{7-cursive Greek chi}.