A series of codoped nanocrystalline ceria compositions, Ce 1 - x M x Bi 0.4 O 2.6 - x (M = Ca, Sr, and Ba; x = 0.01−0.15) were hydrothermally synthesized at 240 °C and characterized by powder X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. All as-made Ce 1 - x M x Bi 0.4 O 2.6 - x crystallize in cubic fluorite-type structures and exhibit solid solution properties. The average particle sizes of Ce 1 - x M x Bi 0.4 O 2.6 - x compositions obtained from hydrothermal systems were determined by the Scherrer equation and transmission electron microscopy to be approximately 32, 20, and 15 nm for Ca, Sr, and Ba systems, respectively. The oxygen ionic conductivities of the codoped Ce 1 - x M x Bi 0.4 O 2.6 - x were investigated by an ac (alternating current) impedance technique as a function of temperature and alkaline earth element contents. The highest ionic conductivity for Ce 0.95 Ca 0.05 Bi 0.4 O 2.55 at 600 °C was 1.7 × 10 - 2 S·cm - 1 with the activation energy E a = 46.3 KJ·mol - 1 . In addition, the ionic transference numbers for the Ca, Sr, and Ba codoped systems were almost unit, showing their highly pure ionic conductivities.
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Zhao et al. (1999) studied this question.
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