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

Abstract

Contrary to previous studies that identified the ground state crystal structure of the entire R 3 Co series (R is a rare earth) as orthorhombic P nma, we show that Y 3 Co undergoes a structural phase transition at T t ≃ 160 K. Single crystal neutron diffraction data reveal that at T t 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 P nma structure of Y 3 Co. 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 T t .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 Y 3 Co as a system with the charge density wave instability.

Electronic Structures, Magnetism, and Phonon Spectra in the Metallic Cubic Perovskite BaOsO3

“…There are a few additional unstable modes along the M -Γ and the Γ-R lines. The latter is similar to the instability of the transverse acoustic mode observed in the possible charge-density-wave (CDW) Y 3 Co. [29] However, consistent with the strong three-dimensionality in BaOsO 3 , no indication of CDW is observed in our calculations. We also performed these calculations with two compressed volumes, which are 4% and 8% smaller than the optimized value, to investigate effects of pressure on the instability.…”

Phonon density of states and anharmonicity ofUO2

“…We consider now the comparison of measured and simulated PDOS spectra as quantitative tests of our lattice dynamics simulations for UO 2 , which in turn provides a sensitive test of our ability to describe the strongly correlated electronic structure of UO 2 . First-principles lattice dynamics simulations of PDOS for non-strongly correlated materials typically achieve a high level of agreement with PDOS measurements for metals (Al), 37 semiconductors (Si), 12 thermoelectrics (AgPb m SbTe 2+m ), 38 intermetallics (Y 3 Co) 39 to oxides (ZnO). 40 Compared to these materials, the accuracy of the current PDOS simulations for UO 2 is rather limited.…”

“…Overall, none of the simulations reproduce the zone boundary peak energies and spectral weight features of the experimentally measured PDOS as well as those for the non-strongly correlated examples cited above. [37][38][39][40] The low energy uranium dominated TA and LA peak positions deviate by only 1 -2 meV, but the higher energy oxygen vibration dominated peaks are shifted upward (or downward) in energy by 3 -5 meV relative to the measured PDOS. Considering the PDOS measurements reported in the present work and the PDOS spectrum of Dolling in Fig.…”

“…First-principles lattice dynamics simulations of PDOS for non-strongly-correlated materials typically achieve a high level of agreement with PDOS measurements for metals (Al) [37], semiconductors (Si) [12], thermoelectrics (AgPb m SbTe 2+m ) [ 38], intermetallics (Y 3 Co) [39] to oxides (ZnO) [40]. Compared to these materials, the accuracy of the current PDOS simulations for UO 2 is rather limited.…”

Field-induced magnetic phase transitions and metastable states in Tb3Ni

“…Among the rare-earth intermetallic compounds, R 3 T (T = Co, Ni) compounds possess the highest content of rare-earth metal within the binary R − T systems and exhibit a rich variety of physical properties: unconventional superconductivity [7,8], charge density wave [9], giant magnetoresistance effect [10,11], multi-component magnetic structures exhibiting coexistence of commensurate and incommensurate propagation vectors [12,13], field-induced magnetic phase transitions [13][14][15][16] and giant magnetocaloric effect [17][18][19][20]. R 3 T compounds crystallize in a low-symmetry orthorhombic structure of the Fe 3 C type described with the space group P nma [21].…”