Synthesis and high-temperature electrical conductivity of Ln2Ti2O7 and LnYTi2O7 (Ln = Dy, Ho)

Ho2Ti2O7 and LnYTi(2)O(7) (Ln = Dy, Ho) pyrochlores have been synthesized using hydroxide coprecipitation, mechanical activation, and firing at 1600 degrees C. The bulk and grain-boundary components of their conductivity have been determined for the first time by impedance spectroscopy. The 740 degrees C bulk conductivity of Ho2Ti2O7 is 4 x 10(-4) S/cm, and that of HoYTi2O7 is 1 x 10(-3) S/cm, with activation energies E-a = 1.01 and 1.17 eV, respectively, suggesting that these materials are new oxygen-ion conductors. The bulk conductivity of DyYTi2O7 (3 x 10(-4) S/cm at 740 degrees C, E-a = 1.09 eV) is almost one order of magnitude lower than that of HoYTi2O7 (1 x 10(-3) S/cm at 740 degrees C, E-a = 1.17 eV).