ON THE USE OF LASER-HEATING IN A DIAMOND-ANVIL CELL

D. Andrault ¹, G. Fiquet ², M. Hanfland ³ and T. LeBihan ³

¹ Laboratoire des Géomatériaux, IPG-Paris, 4 place Jussieu, 75252 Paris France.
E-Mail: andrault@ipgp.jussieu.fr
² Laboratoire des Sciences de la Terre, ENS-Lyon, France.
³ European Synchrotron Radiation Facility, Grenoble, France

To perform reliable compression curve and structural analysis at extreme pressures, deviatoric stresses build on compression must be relaxed as much as possible. This is achieved when samples are annealed above 1500 K, after scanning of an infrared laser radiation (YAG or CO₂) across the pressure chamber. It results in a most significant increase of diffraction peaks sharpness, and accuracy in the unit cell parameters determination. In this type of experiments, ruby is avoided, and pressure is usually measured within the X-rayed zone using the primary pressure standard that is the platinum equation of state (EOS).

Angle dispersive X-ray diffraction spectra were acquired on beamlines ID30 and ID9 of ESRF (Grenoble, France), that provide a sufficient X-ray flux on a 15*15 µm spot to record high-quality 2d spectra on imaging plate in less than 10 min. We took advantage of the reliability of Bragg-line intensities to perform full-structure analyses (Rietveld) up to a maximum pressure of 120 GPa.

We here present results on the compression mechanism in oxides, including SiO₂-stishovite, MgSiO₃-perovskite, and MgCO₃-magnesite. In both cases, we report pressure evolution of important interatomic distances. For stishovite, we confirm the occurring of a CaCl₂-distortion above 54 (1) GPa, distortion that increases with pressure in a very similar manner than for second order Landau-type transformation.