COMPLEMENTARITY OF OPTICAL AND INCOHERENT INELASTIC NEUTRON-SCATTERING SPECTROSCOPIES IN THE STUDY OF PROTON CONDUCTING MATERIALS

With the availability of incoherent inelastic neutron scattering (INS) data over spectral ranges comparable to those in optical vibrational (infrared and Raman) spectroscopies, the methods have become truly complementary, and the combination of information they provide particularly suited to the identification of the nature of protonic entities in proton conducting solids. The use of these techniques to recognise the extent of proton transfer to water in strong acid hydrates (e.g. perchloric acid monohydrate), and in layered solid acid hydrates (e.g. aluminium hydrogen sulphate mono-and tetra-hydrates, tin hydrogen phosphate and tungstophosphoric acid hexahydrate) is illustrated, so allowing the spectral fingerprint of oxonium and diaquahydrogen ions to be established. The application of vibrational spectroscopic methods to organic derivatives of layered proton conductors is also shown, with examples including ammonium-, tetramethylammonium- and aniline-exchanged metal hydrogen phosphates.