Layered compounds with the general formula MOXO4·yH2O (M=V, Nb; X=P, As) were prepared. The content of water y was controlled by keeping the samples in an atmosphere with various relative humidities (RH). Depending on RH, the formation of several hydrates of niobyl phosphate and arsenate was observed and their basal spacings (d) were determined, namely, NbOPO4·H2O, d=6.4Å, at 11% RH and lower, NbOPO4·2H2O, d=7.0Å, at 22–33% RH, NbOPO4·3H2O, d=7.8Å, at 43–84% RH, and NbOPO4·5H2O, d=8.0Å, at 92% RH and above; NbOAsO4·H2O, d=6.2Å, at 0–16% RH and NbOAsO4·3H2O, d=7.9Å at 33% RH and above. As follows from ac and dc conductivity data, NbOXO4·yH2O compounds are practically pure protonic conductors, whereas VOXO4·yH2O compounds are mixed protonic–electronic conductors and the protonic component increases with y. Two intercalates of MOXO4·yH2O with inorganic acids were prepared. A new intercalate of H3AsO4 into VOAsO4·yH2O with the formula VOAsO4·0.5H3AsO4·yH2O (y=0.5–0.8) has the cell parameters a=6.37 and c=8.81–9.13Å at 0–22% RH. Above 22% RH, the intercalate decomposes and the parent VOAsO4·yH2O with H3AsO4 adsorbed on the surface is formed. Another intercalate with formula NbOPO4·H3PO4·yH2O (y=2–4 at 0–75% RH) has the cell parameters a=6.43 and c=9.56–9.70Å at RH from 0% to 5% and a=6.48 and c=11.2Å at RH from 33% to 75%. Both intercalates are more conductive than their MOXO4·yH2O hosts and their conductivity increases with increasing RH of the surrounding atmosphere. Like NbOPO4·yH2O, also NbOPO4·H3PO4·yH2O can be considered pure proton conductor and its conductivity at 20°C reaches 5×10−3Scm−1 for y=4.

Gels of amorphous and α-layered Zr(HPO4)1.0(O3PC6H4SO3H)1.0, hereafter Zr(SPP), in DMF were used to prepare composite proton conducting membranes based on polyvinylidene fluoride (PVDF) with Zr(SPP) loading from 5 to 25 wt.%. The membranes prepared with α-Zr(SPP) are less compact and homogeneous than those obtained with the amorphous filler. In the latter membranes, the size of the filler particles, determined by TEM microscopy, is in the range of 10–20 nm. Proton conductivity and water content of the membranes made of amorphous Zr(SPP) were determined as a function of temperature from 80 to 130 °C, at 90% RH, and as a function of RH, at 100 °C. In all cases the conductivity is nearly constant up to 120 °C and decreases irreversibly at higher temperatures. With increasing filler loading up to 25 wt.%, the conductivity increases by a factor of 30 and reaches 2·10−3 S/cm, at 120 °C and 90% RH; under these conditions, the H2O/SO3H molar ratio is 8.5. Moreover, in the RH range 60–90%, H2O/SO3H increases with RH from 5 to 8.5, while the conductivity rises by an order of magnitude independent of filler loading. The membrane linear swelling in water at 80 °C was also investigated and discussed on the basis of the filler hydration.

The aim of the present paper is to test the capability of nonstoichiometric CuO as a conductance sensor material. The surface conductivity changes in CuO were measured in the presence of various donor-acceptor couples. The influence of water and oxygen was investigated as well as NO2 and CO. NO2 had a very high sensitivity.Kinetic schemes of surface reactions are also reported and discussed. (C) 2003 Elsevier B.V. All rights reserved.