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Plastically deformed diamond anvils. (a) Anvils squeezing a layer of powdered cubic BN supported by Re gasket. (b) Optical image of the culet after pressurizing to . The tips of the anvils are flats of diameter and bevelled at . In another run (c,d) we used anvils with flats bevelled at , and a purely metallic gasket (Re). A black spot at the center of the culet is the sample: compressed nitrogen. In this experiment only one anvil (c) was plastically deformed and exhibited the characteristic luminescence (started at ). This plastic deformation under pressure of in situ has been seen in reflection light as an irregular picture of the flowing material. The opposite, paired anvil (d) seen in reflected light revealed a different picture typical for undamaged anvils at megabar pressures. The concentric rings result from interference of light due to a large variation of refractive index in the stressed tip of the diamond anvil. This anvil did not show any luminescence and also, it did not reveal any signs of plastic deformations after recovering.
Luminescence of a plastically deformed diamond. Typical photoluminescence spectra taken from the center of the culet with the marked laser excitation lines (ambient pressure). Intensive the sharpest lines in the spectra are the first-order Raman scattering of diamond. The most prominent bands of luminescence are marked with arrows. The first spectrum excited with the argon laser line has low luminescence at wavelengths below and the first- and second-order diamond Raman lines are clearly resolved.
The electron backscattering diffraction (EBSD) patterns of (a) undeformed diamond and (b) a typical pattern taken from the plastically deformed region [Fig. 1(b)]. The bright bands (Kikuchi bands) contain the angular relationship between planes, the symmetry of the crystal and orientation information. Using the Hough transform the pattern (b) was indexed to find the orientation of the crystal under the beam. The patterns taken from different points of the deformed working face [the (100) plane] were indexed as diamond with the misorientation of .
Pressure distributions between diamond anvils (the profile of an anvil is shown below in scale) for different gaskets. With cBN powder gasket and anvils of culet bevelled at , the pressure distribution (circles) changes from conical to truncated in shape resulting in an imprint similar to that shown in Fig. 1. A softer cBN-epoxy gasket squares) was loaded with anvils of culet bevelled at .
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