Local probing of Hg neighboorhood in HgBa2CuO4+delta

Electric field gradients (EFG) on mercury sites of the Hg1201 high-T-C supe rconductors were measured with the perturbed angular correlation (PAC) tech nique. In Hg1201 samples where PAC detects higher oxygen content the EFGs h ave decreased to lower values indicating an elongation of the Hg-apical oxy gen dumbbell. On the same samples the asymmetry parameter of the EFG become s non-zero below 100 K, showing that the charge distribution near the Hg-ap ical oxygen chain becomes non-axially symmetric at low temperature.