Deborah J. Jones

The isomorphous acid salts α-Zr(HPO4)2.H2O, α-Ti(HPO4)2.H2O and α-Zr(HASO4)2.H2O : Comparative thermochemistry and vibrational spectroscopy

Abstract A set of isomorphous acid salts of ideal general formula α-M IV (HXO 4 ) 2 · H 2 O [α-zirconium phosphate (α-ZrP), α-titanium phosphate (α-TiP) and α-zirconium arsenate(V) (α-ZrAs)] has been investigated. In the case of α-ZrP, different preparative techniques were used to yield samples of differing crystallinity. Sample characterisation was by X-ray powder diffraction, thermochemical techniques (TG and DSC), and optical spectroscopies (infrared and Raman). Thermochemical findings included (i) phase transitions in anhydrous TiP occur at higher temperature than for ZrP, (ii) condensation of the acid anions at lower temperature for the arsenate than for the phosphates, (iii) dependence of temperatures of thermal events in α-ZrP on the crystallinity of the material. Bands and lines occurring in the optical spectra of these materials have been discussed and assigned.

The crystal structure of RbHSeO4: A neutron diffraction study of the paraelectric phase

Abstract The structure of the paraelectric phase of RbHSeO 4 has been determined at 387 K by neutron diffraction. The structure consists of chains of hydrogen bonded SeO 4 groups extending along the crystallographic b axis. Two different hydrogen bonds have been characterized, with Oue5f8O distances of 2.524(4) and 2.583(3) A. In the shorter Oue5f8Hue5f8O hydrogen bond the hydrogen atom is disordered, suggesting that the ordering of hydrogen participates directly in the phase transition to the ferroelectric phase.

EXAFS and XANES study of (Si, Ge) mullite gels and glasses prepared by slow hydrolysis of alkoxides

Local structures in optically clear gels, glasses and mullite ceramics in the Al2O3SiO2GeO2 system have been studied using X-ray absorption spectroscopy at the aluminium, silicon and germanium edges. In mullite, 3Al2O32SiO2, and the corresponding germanates, both in gel and thermally treated phases, as well as in 8Al2O32SiO2 and Al2GeO5, aluminium is in a hexacoordinate environment, the extent of distortion of which is variable. For the last-mentioned aluminogermanate, GeO4 tetrahedra are rapidly formed, and the local environment within the first shell remains stable up to the ceramic state. Longer distance order is observed for the gel and crystal phases, but not for the intermediate glasses. SiO bonds are longer in mullite gels than the corresponding ceramics, probably due to the existence of bridging hydroxyl groups in the former.

Acid sulphates of trivalent metals: A new class of protonic conductors☆

Abstract A novel class of layer structured proton conductors HM (III) (SO 4 ) 4 · n H 2 O, n =1 or 4, in which hydrated proton species are intercalated in an anionic macrostructure, has been studied. Protonic conduction properties are discussed in relation to the nature of the intercalated species and the crystal structure.

Layered proton conducting trivalent metal acid sulphates: intercalation reactions, characterisation by incoherent inelastic neutron scattering and exafs spectroscopies

Abstract Members of the series of acid salts HM(III)(SO 4 ) 2 · n H 2 O, n =1 or 4, M(III)=Al, Fe, In, etc., are protonic conductors ( σ =10 -4 -10 -5 ω -1 cm -1 at 25° C ) of pronounced two-dimensional structure. Hydrated proton species intercalated between the anionic layers [M(SO 4 ) 2 2H 2 O] - n have been identified by incoherent inelastic neutron scattering (IINS) spectroscopy. HFe(SO 4 ) 2 ·4H 2 O is a promising ion exchange and intercalation agent. The products of its redox reactions with lithium, sodium, ammonium and zinc ions have been investigated by IINS and extended X-ray absorption fine structure spectroscopies.