Preparation And Properties Of Doped Cerium-Zirconates Proton Conductors

Perovskite solid solutions of doped cerium-zirconates with protonic conductivity were synthesized by high temperature solid-state reaction. BaCe_0.5-xZr_0.5-xYb_2xO_3-x (BCZY), SrCe_0.5-xZr_0.5-xYb_2xO_3-x (SCZY) and SrCe_0.5-xZr_0.5-xDy_2xO_3-x (SCZD) (2x=0.1, 0.15, 0.2, 0.25) were investigated. The calcinations temperature was determined to be 1200℃by DSC-TG (or DTA-TG). The structure was examined by XRD. The results indicated that the solubility was <0.25 and it was easy for BCZY and SCZY to crystallize in stable perovskite phases but it was difficult for SCZD. The bulk density was measured according to the Archimedes principle and the relative density achieved more than 95%. The high temperature conductivities were measured via a DC 4-probe method. The results showed that the conductivity of the same system increased with the elevation of temperature and increased with increasing dopant content when it was≤0.2, but decreased with increasing dopant content when it was > 0.2. The order of conductivity was BCZY-3 S/cm, 4.4×10^-2 S/cm and 1.6×10^-2 S/cm in wet hydrogen at 950℃. The conductivity in hydrogen (not only in wet hydrogen but also in dry hydrogen) was more than the one in air. Moreover, the difference of the conductivity between in wet hydrogen and in dry hydrogen was not obvious. The conductivity in wet hydrogen was only very slightly higher than the one in dry hydrogen, revealing that the effect of the import of water on conductivity was very low. The investigation of Sr(CeyZr_1-y)_0.8Yb_0.2O_2.9 (y=0.2,0.4,0.6,0.8) of SCZY indicated that the conductivity increased with increasing ratio of Ce/Zr. When the dopant content was 0.15, the conductivity increased with increasing ratio of Ce/Zr of SCZD, but the ratio of Ce/Zr played the main role on the conductivity at low temperature, and the values of conductivity were approaching at high temperature when the dopant content was 0.2.The order of stability for all the samples is BCZY>SCZY>SCZD which was obtained by endurance against moisture. And the stability decreased with increasing the ratio of Ce/Zr. The best proton conductor was SCZY among the three systems.