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Lithium Hydride

Crystal: LiH

Structure: NaCl

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Lattice parameter:

2.042 Å

Density:

0.778 g/cm3

 

Stiffness constants: in 1011 dynes/cm2, at room temperature

 

c11: 6.71 (Ref.1) or 6.68

c12: 1.75 or 1.54

c44: 4.60 or 4.59

 

Compressibility (in 1011 dynes/cm2): 3.57*1012 ??

Poisson ratio:

 

Debye temperature: 815 or 920 K

Melting temperature: 961 K

 

Phonon spectrum discussed by:

J. L. Verble, J. L. Warren & J. L. Yarnell, Lattice dynamics of Lithium hydride, Phys.Rev. 168, 980 (1968)

W. Dyck & H. Jex, Lattice Dynamics of Alkali Hydrides & Deuterides with the NaCl type Structure, J. Phys. C14, 4193 (1981)

 

Transverse optic phonon T0 (k=0): 590 cm-1, or 11.15*1013 sec-1 (H)

Longitude optic phonon L0 (k=0): 21.10*1013 sec-1 (H)

and 16.58*1013 (D)

 

Gruneissen constant:

Ratio e*/e:

 

Photoelastic constants:

p11:

p12:

p44:

 

 

Band gap:

direct: ~6.5 eV. at room temperature (theory by D.H. Ewing & F. Seitz, On the electronic constitution of Crystals; LiF & LiH; Phys. Rev 50, 760 (1936) )

indirect: eV. at ° K

 

 

Plasmon energy:

Exciton energy:

 

Band structure discussed by:

A.B. Kunz, Self-consistent local orbitals for Lithium Halide Crystals, Phys. Rev. B2, 2221 (1970)

 

 

Static dielectric constant: 12.9

Optic dielectric constant: 3.61

 

Electron mobility:

Hole mobility:

Polaron coupling constant: a = ( for m*=1 )

Effective mass: conduction band:

valence band:

 

Electron affinity: ( in eV., from bottom of conduction band under vacuum)

 

Spin-orbit coupling: ( valence band)

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Other information:

 

 

 

 

G.L. Powell, G.E. Mc.Guire, D.S. Easton & R.E.Clausing, Auger Spectra of Lithium Hydride, Surf.,Sci. 46, 345 (1974)

 

 

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References:

 

1. D. Laplaze, M. Boissier and R. Vacher, Veocity of hypersounds in Lithium hydride by spontaneous Brillouin scattering, Solid State Comm. 19, 445 (1976)

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Supplement on LiH and LiD:

 

Raman scattering, defect luminescence, and phonon spectra of LiH, and LiD crystals.

Anthony Anderson and Fritz Luty, Phys.Rev. B28, 3415 (1983)

 

Two phonon Raman spectra of pure crystals were measured at 300K. and 10K. One phonon spectra were obtained from measurements of the resolved sideband structure of a strong zero-phonon emission line around 600 nm. This emission is produced by defects of very weak electron-phonon coupling, which are present in crystals either irradiated or containing a slight nonstoichiometric excess of Li. Both Raman and luminescence spectra show in their detailed resolved structure pronounced isotope shifts allowing a classification of the phonon modes involved. Comparison with data from neutron scattering and lattice-dynamics calculations gives very close agreement and identifies the modes as originating essentially from Xi and L points at the Brillouin-zone edges. Isotope effects on the zero-phonon lines of the defect luminescence are also observed and discussed.

 

 

Hartree-Fock study of Lithium hydride with the use of a polarizable basis set.

R. Dovesi, C. Ermondi, E. Ferrero, C. Pisani, & C Roetti. Phys. Rev. B29, 3591 (1984)

 

Crystalline LiH is studied at a linear combination of atomic orbitals-Hartree-Fock level of approximation with the use of a two-basis set: a minimal basis set comprising a single Slater-type orbital per atom (minimal closed-shell model), and an extended set comprising eleven independent s- and p-type atomic orbitals per unit cell (extended-basis-set model). The problem of an adequate treatment of long-range Coulomb interactions (which is of great importance with polarizable ionic systems) has been solved by including a Madelung potential in the Fock operator. Cohesive energy, bulk modulus band structure, x-ray structure factors, and electron-momentum distribution data are calculated and discussed. The agreement with experiment is in general very good with the extended-basis-set-model. The present study confirms the essential ionic nature of LiH.

 

 

 

Influence of long-range three-center potentials on the lattice dynamics of LiD.

H. Wendel, R.Zeyher. Phys.Rev. B21, 5544 (1980)

 

The long-range three-centre contribution to the dynamical matrix is calculated for LiD from first principles. In addition to nearest-neighbour Li-D overlap, the theory includes also second-nearest-neighbour D-D overlap of the localized wave functions. We find that the inclusion of the three-centre terms improves the agreement of the theoretical and experimental dispersion curves, especially in the TO branch. However, the corrections are rather small. In particular, it is shown that the long-range three-centre terms can account only partly for the large violation of the Cauchy relation found in LiD.