Extended defects in natural diamonds: Atomic Force Microscopy investigation

Surfaces of natural diamonds etched in high-pressure experiments in H2O, CO2 and H2O-NaCl fluids were investigated using Atomic Force Microscopy. Partial dissolution of the crystals produced several types of surface features including the well-known trigons and hillocks and revealed several new types of defects. Besides well-known trigons and dissolution hillocks several new types of defects are observed. The most remarkable ones are assigned to anelastic twins of several types. The observation of abundant microtwins, ordering of hillocks and presence of defects presumably related to knots of branched dislocations suggests importance of post-growth deformation events on formation of diamond microstructure. This work confirms previous reports of ordering of extended defects in some deformed diamonds. In addition, the current work shows that natural diamonds deform not only by dislocation mechanism and slip, but also but mechanical twinning. The dominant mechanism should depend on pressure-temperature-stress conditions during diamond transport from the formation domain to the Earth surface.Comment: Submitted to special issue (1st European Mineralogical congress, Frankfurt, Germany, September 2012) of European Journal of Mineralogy. 21 page, 9 figure

Electron-Beam Domain Patterning in Sr0.61Ba0.39Nb2O6 Crystals

The characteristics of electron-beam domain writing (EBDW) on the polar and nonpolar surfaces of the field-cooled (FC) and zero-field cooled (ZFC) Sr0.61Ba0.39Nb2O6 (SBN) crystals are presented in the range of accelerating voltage U from 10 to 25 kV. The exposure characteristics of the domain diameter d and length Ld (when writing on the polar and nonpolar surfaces, respectively) were measured. With increasing exposure time, d tends to a saturation value, whereas Ld grows linearly, the frontal velocity Vf being of 40 μm/s. At U = 25 kV the achieved d and Ld are of 7 and 40 µm, respectively. The observed peculiar features of EBDW—specifically the domain widening with exposure times and the effect of the polarization state of the crystal on the domain stability—are accounted for by the relaxor features inherent to this material. The effects of electron-beam (EB) irradiation on the local hysteresis loops is evidence of a domain fixation