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Crystal structure and phonon softening in Ca3Ir4Sn13

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Mazzone Daniel et al.,
Project Superconductivity in Unconventional Metals and its Interplay with Magnetism
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Original article (peer-reviewed)

Journal PHYSICAL REVIEW B
Volume (Issue) 92(2)
Page(s) 024101
Title of proceedings PHYSICAL REVIEW B
DOI 10.1103/physrevb.92.024101

Abstract

We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T > T* approximate to 38 K, the x-ray diffraction data can be satisfactorily refined using the space group Pm (3) over barn. Below T*, the crystal structure is modulated with a propagation vector of (q) over right arrow = (1/2,1/2,0). This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Delta(120 K) = 1.05 meV. Using density functional theory, the soft phonon mode is identified as a "breathing" mode of the Sn-12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single-crystal diffraction data.
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