Similarity of structural changes in HgBa2CuO4+δ induced by extra oxygen and by high pressure

Abstract

The structural changes in HgBa2CuO4+δ (Hg-1201) induced by the extra oxygen atoms in the Hg plane and by high pressure were investigated using computer simulation techniques. Without partial replacement of Hg by Cu, the most favorable oxygen interstitial position is the O3 site (0.5, 0.5, 0), while with partial replacement of Hg by Cu, the extra oxygen atom can be located at the O4 site (0.5,0,0.087). These results agree excellently with experimental results. Under high pressure, the Cu-O2 bond is compressed much more and the Hg-O2 bond is compressed much less compared with the unit cell in the c direction. The Ba-O2 interlayer distance is found to have the largest compressibility, four times as much as that of the lattice parameter c. The Ba-O2 interlayer distance becomes zero at 87 GPa, implying occurrence of structural transition. Our simulation found the structural changes induced by O3 oxygen and by high pressure are similar: the Cu-O2 bond and Ba-O2 interlayer distance are shortened while the Hg-O2 bond is relatively elongated. This result agrees with the experimental result.