Synthesis and conductivity of new tantalum-containing lanthanum molybdate with Nd5Mo3O16+δ-type structure

Abstract

Aliovalent substitution molybdenum of tantalum into the La5Mo3–xTaxO16.5–x/2 composition (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) enabled the synthesis of a previously undescribed Ta-contained phase with the Nd5Mo3O16+δ type structure. Calcination of the initial oxides at 1250 °C yielded the single-phase composition La5Mo2.4Ta0.6O16+δ. The resulting phase was studied by Rietveld refinement, IR spectroscopy, scanning electron microscopy, and complex impedance measurements. The bulk conductivity of La5Mo2.4Ta0.6O16+δ sintered at 1250 °C is an order of magnitude higher than the conductivity of the low-temperature LAMOX modification and slightly lower than that of 8% YSZ, and reaches 10− 2 S/cm at 900 °C. Dense ceramic La5Mo2.4Ta0.6O16+δ sintered at 1400 °C is characterized by higher bulk conductivity (11.6 mS/cm at 600 °C and 850 mS/cm at 900 °C) than the high-temperature cubic modification of LAMOX and yttrium-stabilized zirconia. Hebb–Wagner polarization experiments show that La5Mo2.4Ta0.6O16+δ exhibits mixed oxide-ion/electronic transport in air, with electronic transport numbers tₑl = 0.08–0.15.