Electrical properties and microstructure of nanocrystalline La2−xAxMo2O9−δ (A = Ca, Sr, Ba, K) films

Dense, crack-free and uniform nanocrystalline La2−xAxMo2O9−δ (A = Ca, Sr, Ba, and K; x = 0, 0.05) (LAMOX) films were successfully synthesized on polycrystalline Al2O3 substrates by a modified sol–gel method. Pure LAMOX phases with an average grain size of 200–300 nm were obtained when the annealing temperature was about 650 °C. The cell parameter of nanocrystalline LAMOX films is larger than that of the corresponding microcrystalline samples. The conductivity of the nanocrystalline pure La2Mo2O9 film reaches 0.07 S/cm at 600 °C, much higher than that of the corresponding bulk materials. The 2.5%Ca, Sr, Ba, and K-doping can suppress the phase transition occurred at 580 °C in pure La2Mo2O9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La2Mo2O9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones. The increase of unit cell free volume resulted from the intrinsically larger cell parameter of nanocrystalline grains may be mainly responsible for the enhancement of conductivity and decrease of activation energy.