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27 April 2024

» arxiv » 1503.8102

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Crystal structure and phonon softening in Ca3Ir4Sn13
D. G. Mazzone ; S. Gerber ; J. L. Gavilano ; R. Sibille ; M. Medarde ; B. Delley ; M. Ramakrishnan ; M. Neugebauer ; L. P. Regnault ; D. Chernyshov ; A. Piovano ; T. M. Fernandez-Diaz ; L. Keller ; A. Cervellino ; E. Pomjakushina ; K. Conder ; M. Kenzelmann ;
Date:	27 Mar 2015
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* ~ 38 K the x-ray diffraction data can be satisfactorily refined using the space group Pm-3n. Below T* the crystal structure is modulated with a propagation vector of q = (1/2, 1/2, 0). We find evidence for a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry. 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 Sn12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single crystal diffraction data.
Source:	arXiv, 1503.8102
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