DETERMINATION OF HYDROGEN-ATOMS ON LAMELLAR TITANIUM PHOSPHATES FROM NEUTRON POWDER DIFFRACTION DATA S.Garcia-Granda^a, M.A.Salvadó^a, P.Pertierra^a, J.Rodríguez^b, J.R.García^b and M.T.Fernández-Díaz^c. ^(a)Departamento de Química-Física y Analítica, ^(b)Area de Química Inorgánica Universidad de Oviedo (Spain), ^(c)Institut Laue-Langevin, Grenoble (France).

The layered phosphates of IV group elements have been widely investigated¹for their interest in practical applications in many fields: ion exchange, intercalation, proton conduction, catalysis, etc. In order to understand the behaviour of these compounds the determination of hydrogen-atom positions became a fundamental issue. In spite of the large incoherent contribution, full information about the position of hydrogen atoms can be obtained using neutron powder diffraction, futhermore the presence of hydrogen bonds implies changes in the fine structure when hydrogen is substituted by deuterium.

The complete crystal structure including hydrogen-atom positions of [[alpha]]- Ti(HPO₄)₂H₂O ([[alpha]]-TiP) and [[alpha]]-Hf(HPO₄)₂H₂O ([[alpha]]-HfP) were determined by Rietveld refinement and Fourier synthesis, using constant-wavelength neutron diffraction data². This work is one of few recent examples of determination of hydrogen atoms using neutron powder diffraction with an intense source. Orientation of water molecules in the cavities of [[alpha]]-TiP is similar that previously found for [[alpha]]-ZrP.

For [[alpha]]-HfP (see figure) although hydrogen bonding scheme is identical, orientation of water molecules in similar cavities was found to be different.

1. R.Llavona, J.R.García, M.Suárez and J. Rodríguez, Thermochimica Acta (1985) 86, 281.

2. M.A.Salvadó, P.Pertierra, S.García-Granda, J.R.García, J.Rodríguez and M.T.Fernández-Díaz, Inorganic Chemistry (Submitted).