Temperature-driven phase transformation in Y3Co: Neutron scattering and first-principles studies

A. Podlesnyak, G. Ehlers, H. Cao, M. Matsuda, M. Frontzek, O. Zaharko, V. A. Kazantsev, A. F. Gubkin, N. V. Baranov

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Abstract

Contrary to previous studies that identified the ground state crystal structure of the entire R3Co series (R is a rare earth) as orthorhombic Pnma, we show that Y3Co undergoes a structural phase transition at Ttâ‰160 K. Single crystal neutron diffraction data reveal that at Tt the trigonal prisms formed by a cobalt atom and its six nearest-neighbor yttrium atoms experience distortions accompanied by notable changes of the Y-Co distances. The formation of the low-temperature phase is accompanied by a pronounced lattice distortion and anomalies seen in heat capacity and resistivity measurements. Density functional theory calculations reveal a dynamical instability of the Pnma structure of Y3Co. In particular, a transversal acoustic phonon mode along the (00ξ) direction has imaginary frequencies at ξ<1/4. Employing inelastic neutron scattering measurements we find a strong damping of the (00ξ) phonon mode below a critical temperature Tt. The observed structural transformation causes the reduction of dimensionality of electronic bands and decreases the electronic density of states at the Fermi level that identifies Y3Co as a system with the charge density wave instability.

Original languageEnglish
Article number024117
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume88
Issue number2
DOIs
StatePublished - Jul 26 2013

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