Vibrational Spectra of Ca(BH₄)₂

Abstract

IR and Raman data were obtained from R-, -, and mixed ( ,γ)-Ca(BH 4 ) 2 samples and from the deuterated ,γ phase mixture. The results obtained with R phase indicate that the DFT calculated values for the B-H stretching modes and the lattice vibrations are fairly close to the experimental values. The spectral behavior at temperatures around the transition to the phase shows a continuous transition and suggests the presence of disorder caused by reorientational motions of the [BH 4 ] -ion in the phase. The data indicate that there are more deformation bands observed for the mixed ( ,γ) samples than for the R phase which indicates structural variations between the and the γ phases.

Powder diffraction methods for studies of borohydride-based energy storage materials

“…The estimated enthalpy of the transition at $190 K ( Johnston and Hallett, 1953) is consistent with the transformation from the fully orientationally disordered high-temperature cubic phase to the orderedl owtemperature tetragonal phase. Therefore, the cubic phase should have the Fm " 3 3 m spaceg roup symmetry (Stockmayer and Stephenson, 1953), as later confirmed using synchrotron diffractiono nasingle crystala t2 00 K( Filinchuka nd Hagemann, 2008). On cooling below $190 K (Fischer and Züttel, 2004) or uponacompression to $6GPa at room temperature (Kumar and Cornelius, 2005) ap hase with closely relatedo rdered tetragonals tructure appears.…”

“…Av arietyo fr eactionsc an occur and in somec ases several competingr eactionsa re observed simultaneously.M etathesis, or double substitution reaction, is aw ellk nown mechanism for chemical reactions during ball milling,y ielding am etal borohydride and am etal chloride as ab yproduct. However,o ften bimetallic borohydrides aref ormedv ia morec omplex chemical reactions (Hagemann et al, 2008, possibly by ac ombination of metathesis and addition reactions, see Eqs.…”

Optical cell for combinatorial in situ Raman spectroscopic measurements of hydrogen storage materials at high pressures and temperatures

“…The most intense feature in the β-Ca(BH 4 ) 2 spectrum at room temperature has been reported in the ≈2290 to ≈2300 cm −1 range. 8 Assuming the attribution of this mode to the β-Ca(BH 4 ) 2 phase in all of these spectra is correct and that no new phases are being formed, the reason for the increase in Raman shift with increasing temperature is unknown. Temperature-induced anharmonic effects tend to result in a decrease in Raman shift.…”

“…Such intimate contact can cause contamination of the, often nanograined, powder, which could be especially troublesome at higher temperatures. 8 In contrast, for Raman spectroscopy there is no need to place the highly reactive powders in intimate contact with potential contaminates.…”

“…[8][9][10] Some high pressure in situ works have been reported but have involved the use of sapphire or diamond anvil cells to look at high-pressure phase transitions in single fully hydrogenated powders. [11][12][13] However, the small sampling area for anvil cells precludes the simultaneous measurement of more than one powder.…”