The (Sr, Ca)_n+1Cu_nO_2n (Cl, O)₂ superconducting homologous series have been briefly introduced. The emphasis is on the special charge reservoir block of the oxyhalide high T_c superconductror (HTSC), which consists of the halide layer instead of the routine oxide layer. Consequently the apical oxygen related to the p-type HTSC is missed in the compound whereas the apical chlorine bridges the conducting layer and the charge reservoir. In the context a novel hole doping mechanism named “apical oxygen doping” was introduced through partially substituting oxygen for chlorine. This chemical doping leads to an 80 K superconducting transition in the high pressure synthesized double layered (Sr, Ca)₃Cu₂O₄ (Cl, O)₂ oxyhalide. Not only the high T_c, the oxyhalide cuprate superconductor also demonstrates the comparable physical properties to those of the full oxide HTSC, indicating the promising prospects to develop new high T_c oxyhalide superconductors.

high T_c superconductors  /  apical oxygen doping  /  high pressure high temperature synthesis