Relationship between chemical bond parameters and superconducting temperature in HgBa2Can-1CunO2n+2+delta (n=1, 2, 3, 4)

Bond covalency and valence of elements in HgBa2Can-1CunO2n+2+delta (n = 1, 2, 3, 4) were calculated and their relationship with T-c was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest T-c sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher T-c. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples.