title: High-pressure X-ray diffraction, Raman, and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure.
abstract: Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.
authors: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors: Elissaios
authors: E
authors: Stavrou
authors: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon Saskatchewan, S7N 5E2, Canada.|Canadian Light Source, Saskatoon, Saskatchewan, S7N 2V3, Canada.
authors: Yansun
authors: Y
authors: Yao
authors: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors: Joseph M
authors: JM
authors: Zaug
authors: Lawrence Livermore National Laboratory, Physical and Life Sciences Directorate, P.O. Box 808 L-350, Livermore, California 94550, USA.
authors: Sorin
authors: S
authors: Bastea
authors: Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, United States.|Advanced Materials Research Laboratory, Department of Physics Engineering, Hacettepe University 06800, Beytepe, Ankara, Turkey.
authors: Bora
authors: B
authors: Kalkan
authors: DESY Photon Science, D-22607 Hamburg, Germany.
authors: Zuzana
authors: Z
authors: Konôpková
authors: Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, United States.
authors: Martin
authors: M
authors: Kunz