Rubies high pressure powder

Figure 1. Schematic of an experimental setnp for high-pressure X-ray diffraction (XRD) experiments on nanocrystals nnder pressure of tens of GPa (1 GigaPascal s 10,000 atmospheres). Nanociystal powder is dissolved in a pressme medinm and placed between two opposing diamonds, which are clear to X-rays and visible absorption. The pressme is applied by bringing the diamond closer together, and measmed nsing pieces of ruby chips placed inside the pressme cell. The XRD diffraction peaks are Debye-Scherrer broadened by the finite size of the particles, yielding information on the shape and size of the nanocrystals before and after the transition, snch as shown in Figure 3.

Fig. 14. Transmission spectra of polymeric nitrogen as a fimction of temperature. Spectra are shifted vertically for clarity. The characteristic peak of the T) phase is marked by a vertical arrow. Inset (a) shows the pressure dependence of the absorption spectra of nitrogen at very high pressures and room temperature. Gray lines represent the Tauc fits to the speetra in an appropriate spectral range. The determination of the energy gap from these measurements is obscured by additional losses caused by the presence of a fine ruby powder in the chamber. The high-energy absorption edge is most probably due to stress-induced absorption of diamond anvils (Ref. 62). (b) Urbach plots at 200 GPa and different temperatures (shifted vertically). Gray lines are guides to the eye.

As noted above, a combination of high pressure diamond anvil techniques, all utilizing the ruby fluorescence method of pressure measurement, were used to carry out these experiments. These include (1) Fourier transform infrared (FTIR) spectroscopy for the kinetic measurements [9-11], (2) energy dispersive x-ray powder diffraction for crystallographic identification of the observed polymorphic forms and also compression measurements [12], (3) optical polarizing microscopy... 

Raman studies can be carried out at high pressure, using a diamond-anvil cell [40]. To calibrate the pressure, a small piece of powdered ruby can be enclosed in a metal gasket. Using the 514.5-nm line of an Ar laser, the sharp ruby Ri fluorescence line can be excited. This line exhibits a pressure-dependent shift (—0.753 cm /kbar) [41], The diamond-anvil cell is used in the 180° backscattering geometry. 

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