Neutron diffraction ionic lattices

X-ray and neutron diffraction studies show that in these hydrides the H ion has a crystallographic radius between those of F and Cl". Thus the electrostatic lattice energies of the hydride and the fluoride and chloride of a given metal will be similar. These facts and a consideration of the Bom-Haber cycles lead us to conclude that only the most electropositive metals can form ionic hydrides, since in these cases relatively little energy is required to form the metal ion. 

Jacobson AJ, Tofield BC, Fender BEF (1972) Structures of BaCeOs, BaPrOs and BaTbOs by neutron-diffraction - lattice-parameter relations and ionic radii in 0-perovskites. Acta Cryslallogr Sect B Struct Crystallogr Crystal Chem B 28(Mar 15) 956-961... 

It should be stressed that the diffraction methods do not provide complete characterization of lattice distortions and ionic shifts in relaxors due to the compositional disorder of these materials and nanometric scale of polar order. Thus, local methods such as magnetic resonance and, in particular, NMR can be extremely useful in this case. In NMR experiments, the nuclei are sensitive to their local environment at a distance less than 1-2 nm. In addition, NMR operates at a much longer time scale (105-108 s) in comparison with the neutron or X-ray... 

As we have described, a great deal of experimental data on the q 0 vibrational energy levels in the metal azides have been obtained in the last few years. A consistent picture of the internal and external modes in different azide lattices has emerged from these studies. The question of the degree of lattice ionicity in different azide lattices has been raised as a consequence of the available data, but needs detailed theoretical analysis. Particularly noteworthy has been the recent measurement by coherent neutron inelastic scattering of vibrational modes in different directions of the Brillouin zone in a metal azide crystal—KNa- More sophisticated analyses of diffraction data have now yielded precise inter- and intraionic bond lengths, thermal amplitudes of azide ion motions and, most recently, the valence electron density about N3 in KN3, all of which provide important additional input for the characterization of interatomic forces in azides. 

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