First Principle Calculation of Lattice, Electronic Structures and Hole Concentration of Ca-Doped YBCO

This work analyzes the lattice, electronic structures and hole concentration of calcium-doped YBCO compounds using density functional theory. The investigation was conducted on two models, Y 0.875 Ca 0.125 Ba 2 Cu 3 O 7 (YCa123) and Y 0.875 Ca 0.125 Ba 2 Cu 4 O 8 (YCa124), using density functional theory. The results reveal that calcium substitution induces changes in the lattice structure, including a decrease in the lattice constant and a distortion of the Cu-O 2 plane. Furthermore, the electronic structure was also altered, leading to changes in the density of states above the Fermi level. The hole concentrations were also calculated and were found to be 0.19 and 0.16 for YCa123 and YCa124, respectively. These results indicate that the hole concentration of YCa124 is lower than that of YCa123, consistent with the parabolic curve relationship between hole concentration and superconducting transition temperature. The results suggest that Cu (2) atoms fluctuate between the states of Cu + and Cu 2+ , which may be crucial for understanding electron-electron pairing mechanism. These results could aid in the development of more efficient and practical superconducting materials through targeted doping strategies.