Structure determination of the new layered compound Cs2TiP2O8 and ionic conductivity of Cs2MP2O8 (M = Ti, V)

A new titanium pyrophosphate Cs2TiP2O8 with a layer structure and isotypic with Cs2VP2O8 has been synthesised using solid state reactions. The structure determination of this material, from X-ray powder diffraction, shows that it crystallises in the orthorhombic space group Pnma with the parameters a = 13.521(0) Angstrom, b = 7.253(2) Angstrom and c = 9.439(9) Angstrom. The basic structure of this new compound consist in [Ti2P4O16](infinity) layers parallel to the (100) plane sandwiching Cs atoms. These layers built up from TiO5 square pyramids and P2O7 groups forming [TiP2O8](infinity) and [TiPO7](infinity) chains running along [010] and [001] directions respectively. The ionic conductivity was measured and compared for the compounds Cs2MP2O8 (M = Ti,V) over the frequency range 1 Hz-10 MHz, and temperatures between 523 K and 873 K for Cs2TiP2O8, and between 423 and 703 K for Cs2VP2O8, using complex impedance diagrams. The conductivities were analysed by an Arrhenius equation of the form sigma = sigma(0) exp(-E-a/kT). The activation energy calculated were E-a(Ti) = 0.80 eV and E-a(V) = 0.88 eV.