All experiments were performed in BX90-type DACs equipped with Boehler-Almax type diamond anvils with culets of 250 or 120 μm 11. To conduct the experiments, pieces of metals (Y, Dy, Re, or Ag) or FeO were loaded into a DAC between two layers of dried sodium or potassium chlorides. Reactivity of alkali halides and heavy metals at high pressures Our ab initio calculations are in good agreement with the experimental results. The structures were solved and refined using in situ high-pressure synchrotron single-crystal X-ray diffraction in a DAC. Here we report the crystal structures of the chloride phases, Y 2Cl and D圜l, and chloride carbides Y 2ClC and Dy 2ClC, as well as the structure of iron chloride, FeCl 2. An iron chloride, FeCl 2, with the HP-PdF 2-type structure, was found to be a product of a chemical reaction between FeO and KCl in a LHDAC at about 160 GPa and 2100 K. In the present work we have shown that it is not the case under pressure, as our experiments, originally designed to study the HP behavior of metals (Y, Dy, Re, and Ag) in an “inert” pressure medium (NaCl) in a laser-heated diamond anvil cell (LHDAC), resulted in the synthesis of previously unknown chlorides, Y 2Cl and D圜l, and chloride carbides, Y 2ClC and Dy 2ClC, at about 40 GPa and 2000 K. Still, NaCl and KCl are considered to be chemically stable under HP, as in the absence of ionization-promoting species 9, 10, reactions are found in the presence of extra chlorine or sodium/potassium in a diamond anvil cell (DAC) 7, 8.īeing formed by highly electropositive and electronegative elements, NaCl and KCl, having a stable electron configuration, are not expected to react with transition or rare-earth metals. Recent experimental and theoretical studies 6, 7, 8 suggest, however, that the behavior of the Na-Cl and K-Cl systems at HP is complex, and several compounds with an unusual stoichiometry (like NaCl 3, Na 3Cl, Na 2Cl, and KCl 3) have been reported. Therefore, they have often been used as pressure calibrants 2, pressure transmitting media 3, and electrical and thermal insulators in HP experiments 3, 4, 5. Indeed, NaCl and KCl were thought to be chemically inert over wide pressure (up to 200 GPa) and temperature (up to 3000 K) ranges 1.
Alkali halides, particularly sodium and potassium chlorides, are chemically very stable and are usually not considered as precursors for the synthesis of new compounds in high-pressure (HP) studies.
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