High pressure and high temperature in situ X-ray diffraction studies in the Paris-Edinburgh cell using a laboratory X-ray source^†

Abstract

We have developed a new laboratory experimental set-up to study in situ the pressure–temperature phase diagram of a given pure element or compound, its associated phase transitions, or the chemical reactions involved at high pressure and high temperature (HP-HT) between different solids and liquids. This new tool allows laboratory studies before conducting further detailed experiments using more brilliant synchrotron X-ray sources or before kinetic studies. This device uses the diffraction of X-rays produced by a quasi-monochromatic micro-beam source operating at the silver radiation (λ(Ag)_{Kα 1, 2}≈0.56 Å). The experimental set-up is based on a VX Paris-Edinburgh cell equipped with tungsten carbide or sintered diamond anvils and uses standard B-epoxy 5 or 7 mm gaskets. The diffracted signal coming from the compressed (and heated) sample is collected on an image plate. The pressure and temperature calibrations were performed by diffraction, using conventional calibrants (BN, NaCl and MgO) for determination of the pressure, and by crossing isochores of BN, NaCl, Cu or Au for the determination of the temperature. The first examples of studies performed with this new laboratory set-up are presented in the article: determination of the melting point of germanium and magnesium under HP-HT, synthesis of MgB₂ or C-diamond and partial study of the P, T phase diagram of MgH₂.

Keywords:

• X-ray diffraction
• laboratory set-up
• Paris-Edinburgh cell
• high pressure crystallography
• phase diagram
• phase transitions

Acknowledgements

The authors thank the masters students V. Valenti (2011), Le T.N. Huynh (2012) and A. Vauthelin (2013) who participated actively in the related experiments during their internship. This work was supported by Agence Nationale de la Recherche (ANR), project ‘CrystalPress’ No. ANR-07-JCJC-0030 (CSD4). Part of this work was supported by the Pole SMINGUE of Université Joseph Fourier Grenoble.