Raman spectroscopy studies on M2RuH6 where M=Ca, Sr and Eu

Abstract

Characterization of ternary and quaternary metal hydrides by Raman spectroscopy appears to be rather scarce due primarily to the decomposition of the metal hydrides by the energy of the laser excitation source. We report the results of some recent room temperature Raman measurements collected with a 2-10 mW 488 nm laser source for M RuH where M5Ca, Sr and Eu. The assignments from this 2 6 study are combined with existing vibrational data for other metal hydrides.

First-principles study of the pressure dependence of the structural and vibrational properties of the ternary metal hydrideCa2RuH6

“…On the other hand, the calculated pressure variation of 5 shows a good agreement with the experimental behavior ͓͑d 5 / dP͔ expt = 9.49 cm −1 / GPa, ͓d 5 / dP͔ GGA = 11.44 cm −1 / GPa, and ͓d 5 / dP͔ LDA = 10.75 cm −1 / GPa͒. As pointed out by Barsan et al, 6 the stretching mode 9 is more sensitive to anharmonicity than the lower frequency bending mode 5 .…”

“…At both the LDA and GGA levels, the optimized Ru-H bond lengths are close to the value of 1.675 Å estimated for Ca 2 RuH 6 using the Badger's rule. 5 The vibrational frequencies above 800 cm −1 correspond to vibrations of the RuH 6 octahedron and, besides the IR and Raman inactive T 2u mode, they have been observed by IR and Raman spectroscopies ͑see 2 ͑T 2g ͒ is confirmed by the results of the DFT calculations, an excellent agreement between experiment and theory being observed for the GGA results. At the GGA level, the T 1u optical translational mode is predicted at 1 ͑T 1u ͒ = 185 cm −1 , and at 203 cm −1 at the LDA level.…”

“…5 The calculations were carried out within the local density approximation 10 ͑LDA͒ and generalized gradient approximation ͑GGA͒, 11,12 using the ABINIT code, [13][14][15] which is based on pseudopotentials and plane waves. It relies on an efficient fast Fourier transform algorithm 16 for the conversion of wave functions between real and reciprocal spaces, on the adaptation to a fixed potential of the band-by-band conjugate gradient method 17 and on a potential-based conjugate-gradient algorithm for the determination of the self-consistent potential.…”

“…4 From the experimental point of view, vibrational spectroscopies provide a convenient means to investigate the M 2 MЈH 6 hydrides and especially the strength of the MЈ -H bond. We have studied in the past Raman spectra of some members of this family of compounds, 5 completing previous infrared studies. 2 If one considers the issue of hydrogen storage in the solid state, one has to take into account the external variables temperature and pressure.…”

Pressure dependence of the Raman spectra of salts of hexahydridoruthenate(II), M2RuH6 (M=Ca, Sr, Eu) and their deuteride analogues

“…The material properties of hydrides are of general interest since complex transition metal hydrides have unique structures and chemistry [2]. The structures of ternary metal hydrides of the type M 2 RuH 6 , where M = Ca, Sr, Eu have been investigated by X-ray and neutron powder diffraction [3,4] and their vibrational spectra reported, mostly for infrared [5][6][7] with only one study of the Raman spectra measured at ambient conditions [8]. These studies, both on pure compounds and on mixed metal crystals, have shown that the vibrational wavenumbers correlate with the unit cell length.…”