Nanocrystalline La_2Mo_2O_9 and Its Characterization

摘要

In this work, both the thermal expansion and electrical conductivity of nanocrystalline La_2Mo_2O_9 were studied. The nanocrystalline powder of La_2MO_2O_9 was obtained by sol-gel method, and with the help of SHP (superhigh pressure) up to 4.5 x 10~4 atm at 700°C for a short time, and the nanocrystalline powder was densified without obvious particle size growth. The electrical conductivity of nanocrystalline La_2Mo_2O_9 was one order of magnitude lower than that of the micro-crystalline sample at the same temperature. Owing to the phase transition, the microcrystalline La_2Mo_2O_9 has an abrupt increase of thermal expansion with a peak value of 48 x 10~(-6) K~(-1) at 556°C. For the nanocrystalline material, the peak value increases to 112 x 10~(-6) K~(-1) at 520°C. On the other hand, above 600°C the significant growth of particle size of the nanocrystalline La_2Mo_2O_9 was observed, accompanying by a tremendous increase of thermal expansion with a peak value of 1565 x 10~(-6) K~(-1) at 620°C. The electrical conductivity of La_(1.6)Nd_(0.4)Mo_2O_9 at 800°C is 0.14 S·cm~(-1) which is about one third higher than that of La_2Mo_2O_9.