using optical microscopy (OM), LEO scanning electron microscopy (SEM) and JEOL 2000FX transmission electron microscopy (TEM).
Samples for OM and SEM analyses were grounded, polished and etched in 2 wt.% Nital for 10 s. Samples for TEM analysis were mechanically
polished to 30 μm thick, punched to a disk of 3 mm diameter by a copper
disk cutter and then jet polished to thin foil specimens in perchloric acid
(10%) and acetic acid (90%) mixture under 20 V at 15 °C. The electrical
conductivity was measured using Microhmmeter (DO5000 series).