Tc-Mapping and Investigation of Water-Initiated Modification of YBa2Cu3O7-x Thin Films by Low Temperature Scanning Electron Microscopy

The Tc -mapping method using low temperature scanning electron microscopy (LTSEM) has been developed to study the spatial distribution of the critical temperature in high temperature superconducting (HTSC) films with a spatial resolution approaching 2 μm. To achieve so high a spatial resolution, a numerical deconvolution method was applied that eliminated distorting effects associated with the thermal diffusion and with the contribution from the absorbed beam current. The Tc -mapping method was used to investigate modification by water of YBa2Cu3O7-x films grown on (100) MgO and (110) LaAIO3 substrates. The rate of modification of a [110]-oriented YBa2Cu3O7-x/LaAIO3 film is found to be 40 times that of a c-axis oriented YBa2Cu3O7-x/MgO epitaxial film. It is argued that water-initiated modification of the films results from penetration of hydrogen into the films, rather than from out-diffusion of oxygen

J. Petrol.

A petrological study was carried out on Mg-skarn-bearing dunite cumulates that are part of the Neo-Proterozoic Ioko-Dovyren intrusion (North Baikal region, Russia). Skarn xenoliths contain brucite pseudomorphs after periclase, forsterite and Cr-poor spinel. Fine-grained forsterite-spinel skarns occur with the brucite skarns or as isolated schlieren. Field relationships reveal that the Mg-skarns formed from silica-poor dolomitic xenoliths by interaction with the mafic magma of the Ioko-Dovyren intrusion. Rapid heating of dolomitic xenoliths by the mafic magma caused the decomposition of dolomite into calcite + periclase, releasing much CO2. Further heating quantitatively melted the calcite. A periclase-rich restite was left behind after extraction of the low-density, low-viscosity calcite melt. The extracted calcite melt mixed with the surrounding mafic melt. This resulted in crystallization of olivine with CaO contents up to 1.67 wt %. A local decrease in the silica concentration stabilized CaAl2SiO6-rich clinopyroxene. Brucite/periclase-free forsterite-spinel skarns probably originated by crystallization from the mafic melt close to the xenoliths at elevated fO(2). The high fO(2) was caused by CO2-rich fluids released during the decomposition of the xenoliths. The above case study provides the first evidence for partial melting of dolomite xenoliths during incorporation by a mafic magma

Partial melting and assimilation of dolomitic xenoliths by mafic magma: the Ioko-Dovyren intrusion (North Baikal region, Russia)

A petrological study was carried out on Mg-skarn-bearing dunite cumulates that are part of the Neo-Proterozoic Ioko-Dovyren intrusion (North Baikal region, Russia). Skarn xenoliths contain brucite pseudomorphs after periclase, forsterite and Cr-poor spinel. Fine-grained forsterite-spinel skarns occur with the brucite skarns or as isolated schlieren. Field relationships reveal that the Mg-skarns formed from silica-poor dolomitic xenoliths by interaction with the mafic magma of the Ioko-Dovyren intrusion. Rapid heating of dolomitic xenoliths by the mafic magma caused the decomposition of dolomite into calcite + periclase, releasing much CO2. Further heating quantitatively melted the calcite. A periclase-rich restite was left behind after extraction of the low-density, low-viscosity calcite melt. The extracted calcite melt mixed with the surrounding mafic melt. This resulted in crystallization of olivine with CaO contents up to 1.67 wt %. A local decrease in the silica concentration stabilized CaAl2SiO6-rich clinopyroxene. Brucite/periclase-free forsterite-spinel skarns probably originated by crystallization from the mafic melt close to the xenoliths at elevated fO(2). The high fO(2) was caused by CO2-rich fluids released during the decomposition of the xenoliths. The above case study provides the first evidence for partial melting of dolomite xenoliths during incorporation by a mafic magma