Lithium boro-hydride LiBH4

Abstract

Polycrystalline LiBH has been studied by Raman spectroscopy in the temperature interval 295-412 K and the frequency range 4 21 2 2700-130 cm. The Raman active modes are consistent with the presence of a (BH) ion having a distorted tetrahedral configuration. 4 As the temperature is increased the sudden disappearance of mode splitting points to the onset of a structural phase transition that leads to 2 a higher local symmetry of the (BH) tetrahedron. The transition occurs at |384 K, is of first-order and has a hysteresis of about 8 K. A 4 strong and discontinuous broadening of bands remaining after the transition suggests the onset of large vibrational amplitudes of the 2 (BH) tetrahedra about their trigonal axis. 4

LiSc(BH4)4: A Novel Salt of Li+ and Discrete Sc(BH4)4− Complex Anions

“…Raman spectra of the alkali borohydrides have shown significant broadening of the B-H bending modes in the disordered phase. 39,40 Finally, we have performed DFT calculations on a model complex comprising two Sc(BH 4 ) 4 units separated by four Li atoms to simulate a truncated tetragonal unit cell. Initially, the Li atoms were placed on the (0 0 0.6) between the two Sc complexes.…”

Structural and spectroscopic studies on the alkali borohydrides MBH4 (M = Na, K, Rb, Cs)

“…The Raman set-up is the same as that described previously [3,18]. It consists of an Argon ion laser (488 nm excitation wavelength) and a Kaiser Optical Holospec monochromator equipped with a liquid nitrogen cooled CCD camera.…”

“…Their solid-state structures contain relatively mobile tetrahedral [BH 4 ] − units, the ordering of which tends to induce structural phase transitions. In LiBH 4 , for example, a phase transition occurs at 384 K that originates from the reorientation motion of the [BH 4 ] − ions as shown by synchrotron diffraction [2] and Raman spectroscopy [3]. While the disordered high temperature (HT) phase has hexagonal symmetry the ordered low temperature (LT) phase has orthorhombic symmetry [2][3][4].…”

“…In LiBH 4 , for example, a phase transition occurs at 384 K that originates from the reorientation motion of the [BH 4 ] − ions as shown by synchrotron diffraction [2] and Raman spectroscopy [3]. While the disordered high temperature (HT) phase has hexagonal symmetry the ordered low temperature (LT) phase has orthorhombic symmetry [2][3][4]. The structure of the sodium compound NaBD 4 has been investigated by neutron diffraction [5,6].…”

“…The transition temperatures as measured by heat capacity studies were found to be 76 K for KBH 4 , 44 K for RbBH 4 and 27 K for CsBH 4 [10]. A great number of spectroscopic studies have been performed on both hydrides and deuterides [3,[11][12][13][14][15][16][17]. However, according to Memon et al [15][16][17] the work published before 1982 suffers from incorrect and misleading interpretations because Fermi resonance type interactions had not been fully taken into account.…”