Results of a temperature-dependent crystallographic study of the solid
state protonic conductor alpha-Zr(HPO4)(2) . H2O are presented. Latti
ce parameters of this monohydrate and of its dehydrated phases, alpha-
Zr(HPO4)(2) and beta-Zr(HPO4)(2), have been determined in the temperat
ure range from 20 K to 650 K using X-ray and synchrotron powder diffra
ction. Neutron data of the protonated and of the deuterated monohydrat
es were refined by the Rietveld method, paying particular attention to
the H- and D-sites, respectively, The dehydration process has been st
udied by comparing temperature-dependent coherent and incoherent neutr
on scattering intensities with X-ray powder diffraction and DTA/TG mea
surements. Proton conduction mechanisms are discussed in the light of
these results.