Crystal structure and phonon softening in Ca$_3$Ir$_4$Sn${13}$ - Archive ouverte HAL Access content directly
Journal Articles Physical Review B: Condensed Matter and Materials Physics (1998-2015) Year : 2015

## Crystal structure and phonon softening in Ca$_3$Ir$_4$Sn${13}$

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D. G. Mazzone
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S. Gerber
• Function : Author
J. L. Gavilano
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R. Sibille
• Function : Author
M. Medarde
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B. Delley
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M. Ramakrishnan
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M. Neugebauer
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Louis Pierre Regnault
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D. Chernyshov
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A. Piovano
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T. M. Fernandez-Diaz
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L. Keller
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A. Cervellino
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E. Pomjakushina
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K. Conder
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M. Kenzelmann
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#### Abstract

We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca$_3$Ir$_4$Sn${13}$ 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 Pm3n. 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.

#### Domains

Physics [physics]

### Dates and versions

cea-01734608 , version 1 (14-03-2018)

### Identifiers

• HAL Id : cea-01734608 , version 1
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• DOI :

### Cite

D. G. Mazzone, S. Gerber, J. L. Gavilano, R. Sibille, M. Medarde, et al.. Crystal structure and phonon softening in Ca$_3$Ir$_4$Sn${13}$. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2015, 92, pp.024101. ⟨10.1103/PhysRevB.92.024101⟩. ⟨cea-01734608⟩

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