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Light-induced phase transition in AlD_{3} at high pressure

DOI: 10.1103/PhysRevB.84.104111 DOI Help

Authors: Stanislav Besedin (Russian Academy of Sciences) , Andrew Jephcoat (Diamond Light Source) , Alla Irodova (Russian Research Center, Kurchatov Institute)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 84 (10)

State: Published (Approved)
Published: September 2011

Abstract: Trivalent aluminum hydride in the rhombohedral α phase (R3̅ c space group) was studied at high pressures in a diamond-anvil cell by means of Raman scattering, x-ray diffraction, observation of optical transmission, and the density functional simulations. At P≈53 GPa the heavier isotope AlD3 undergoes a first-order structural phase transition which was found to be stimulated by the laser irradiation used for the Raman-scattering measurements. In the new high-pressure phase Al atoms form a lattice with a monoclinic unit cell (P21/c space group) over which a superstructure is developed when pressure is varied. The superstructure is formed by regular displacements of the Al atoms with the period over three unit cells; the propagation vector is k2=(1/31/31/3). The undistorted P21/c lattice itself appears as superstructure over the rhombohedral R3̅ c one resulting from the displacive structure transformation with the propagation vector k1=(1/201/2). The band gap as given by the density functional calculations and evidenced from the sample transparency behavior at high pressures remains greater than the laser photon energy used (Eph=2.41 eV). That indicates that bond weakening/breaking due to electron excitation across the band gap is not the cause of the phase transition. A likely mechanism of the light action is that structure transformation is driven by phonons, which are excited due to strong electron-phonon coupling in the α phase.

Subject Areas: Physics

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Added On: 16/09/2011 11:52

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