First principle calculation of electronic structures and hole concentration of YBCO family compounds

Yttrium barium copper oxide (YBCO) family compounds are similar in structure but have different superconducting temperatures. It is well known that superconducting properties arise from the crystal lattice and electronic structure of compounds. This work reveals and discusses the electronic structures of YBCO family compounds (YBa2Cu3O6, YBa2Cu3O6.5, YBa2Cu3O7, and YBa2Cu4O8) based on density functional theory (DFT). The electronic structure results show that Cu–O chains are the trigger components for conduction, and only Cu–O chains and Cu-O2 planes play important roles in electronic and superconducting properties. The results also reveal that additional hole doped will be non-trivially distributed between the Cu–O chains and the Cu-O2 planes, and hence a more comprehensive method is required to calculate the hole concentration in the Cu-O2 plane. This work also demonstrates the calculation of hole concentrations using DFT. By DFT calculation, the Y1236 has hole concentration of 0.5 and the hole doped of Y12365, Y1237 and Y124 are 0.09, 0.16 and 0.10, respectively. The results are consistent with the cuprate-superconductor phase diagram and the bond-valence sum (BVS) calculations.