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• Vibrational properties of SrVO₂H with large spin-phonon coupling

  2022. Rasmus Lavén (et al.). Physical Review Materials 6 (2)

  Artikel

  The antiferromagnetic transition metal oxyhydride SrVO₂H is distinguished by its stoichiometric composition and an ordered arrangement of H atoms. The tetragonal structure is related to the cubic perovskite and consists of alternating layers of VO₂ and SrH. d² V(III) attains a sixfold coordination by four O and two H atoms. The latter are arranged in a trans fashion, which produces H–V–H chains along the tetragonal axis. Here, we investigate the vibrational properties of SrVO₂H by inelastic neutron scattering and infrared spectroscopy combined with phonon calculations based on density functional theory. The H-based vibrational modes divide into a degenerate bending motion perpendicular to the H–V–H chain direction and a highly dispersed stretching motion along the H–V–H chain direction. The bending motion, with a vibrational frequency of approximately 800 cm⁻¹, is split into two components separated by about 50 cm⁻¹, owing to the doubled unit cell from the antiferromagnetic structure. Interestingly, spin-phonon coupling stiffens the H-based modes by 50−100cm⁻¹ although super-exchange coupling via H is very small. Frequency shifts of the same order of magnitude also occur for V–O modes. It is inferred that SrVO₂H displays the hitherto largest recognized coupling between magnetism and phonons in a material.

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• Diffusional Dynamics of Hydride Ions in the Layered Oxyhydride SrVO2H

  2021. Rasmus Lavén (et al.). Chemistry of Materials 33 (8), 2967-2975

  Artikel

  Perovskite-type oxyhydrides are hydride-ion-conducting materials of promise for several types of technological applications; however, the conductivity is often too low for practical use and, on a fundamental level, the mechanism of hydride-ion diffusion remains unclear. Here, we, with the use of neutron scattering techniques, investigate the diffusional dynamics of hydride ions in the layered perovskite-type oxyhydride SrVO2H. By monitoring the intensity of the elastically scattered neutrons upon heating the sample from 100 to 430 K, we establish an onset temperature for diffusional hydride-ion dynamics at about 250 K. Above this temperature, the hydride ions are shown to exhibit two-dimensional diffusion restricted to the hydride-ion sublattice of SrVO2H and that occurs as a series of jumps of a hydride ion to a neighboring hydride-ion vacancy, with an enhanced rate for backward jumps due to correlation effects. Analysis of the temperature dependence of the neutron scattering data shows that the localized jumps of hydride ions are featured by a mean residence time of the order of 10 ps with an activation energy of 0.1 eV. The long-range diffusion of hydride ions occurs on the timescale of 1 ns and with an activation energy of 0.2 eV. The hydride-ion diffusion coefficient is found to be of the order of 1 x 10(-6) cm(2) s(-1) in the temperature range of 300-430 K, which is similar to other oxyhydrides but higher than for proton-conducting perovskite analogues. Tuning of the hydride-ion vacancy concentration in SrVO2H thus represents a promising gateway to improve the ionic conductivity of this already highly hydride-ion-conducting material.

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