Study of the fluorite-pyrochlore-fluorite phase transitions in Ln_2Ti_20_7(Ln=Lu,Yb,Tm)

摘要

The ordering processes in Ln_2Ti_2O_7(Ln=Lu,Yb,Tm)are studied by X-ray diffraction,thermal analysis,infrared absorption(IR)spectroscopy,and electrical conductivity measurements.The coprecipita-tion method followed by freeze-drying was used for Ln_2Ti_2O_7 synthesis.The region of low-temperature fluorite phase existence is 600 deg C1,600 deg C.The conductivity values are 5.10~(-3)S/cm for Tm_2Ti_2O_7,6-10~(-3)S/cm for Yb_2Ti_2O_7,and 10~(-2)S/cm for Lu_2Ti_2O_7 at 740 deg C.This order-disorder transition leads to a 2 orders of magnitude conductivity growth and a 10-30 times permittivity increase in Ln_2Ti_2O_7 samples obtained at 1,700 deg C.