Electrical resistivity and phase transformation of hematite under shock compression

摘要: Electrical resistivity measurements of hematite (a-Fe203) were performed under shock compression in the range 240-760 kbar. The specimens used coarsely polycrystalline natural material from Bra- zil. electrical decreases gradually with increasing pressure to 440 kbar and discontinuously less than Icm several tens ohm centimeters at pressures 440-520 phase transformation pressure, implied Hugoniot equation-of-state is made clear. transition behavior into low-resistivity state depends on crystallographic axis propa- gation. that titanium oxide present only as a trace. Emis- sion spectrochemical analysis shows small amounts B, Ca, Si major impurities. Two types plate-shaped speci- mens, about 0.6 - 1.0 mm thickness 40 •70 2 area, cut material; planes one sample (noted type 1) are perpendicular ( 0112) crys- tallographic axis, which coincident principal axes octahedron formed by oxygen ions, other (type 2) parallel that. It not clear direction plane normal (0112) specimen corresponds. These orientations chosen ob- tain many samples possible. Specimens carefully polished both faces order provide good elec- trical contact driver target backing electrode. Although atmospheric room temperature was measured, it difficult obtain ohmic even vacuum evaporation deposition gold or coating silver paste surfaces. has 10 kg cm 1- 10-V range, including resistance. was, however, found experiments resistance changed, being lowered orders becoming upon application uniaxial stress components over kilobars (Kondo et al., 1979a). initial experiment estimated be 250 + 50 g extrapolation high-pressure values above results. conducted using double- stage light-gas gun, HS-2, Tokyo Institute Tech- nology. projectile, 20 diameter, consisted high-density polyethylene base 1.5-mm-thick copper