Variation of optimum yttrium doping concentrations of perovskite type proton conductors BaZr1-xYxO3-α (0≤x≤0.3) with temperature

A solid state reaction method was used to prepare the perovskite-structured compounds BaZr1-xYxO3-alpha (x=0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3). The X-ray diffraction (XRD) pattern indicated that the target perovskite phases were obtained. With increasing Y concentration the unit cell parameters of BaZ(1-x)Y(x)O(3-alpha) samples were expanded, and Y doping became more difficult. However, high synthesis temperature is helpful to promote Y doping. The SEM results showed that the samples exhibited poor sinterability with increasing Y-doping content. Thermal gravimetric (TG) curves analysis showed the more mass decreasing of BaZr1-xYxO3-alpha (0 <= x <= 0.3) samples at high temperature with more Y doping and more proton introducing. The electrochemical impedance spectra (EIS) of specimens showed that conductivities of BaZr1-xYxO3-alpha (0 <= x <= 0.3) increased with increasing temperature from 300 to 900 degrees C in wet air. At 900 degrees C, the conductivity of BaZr1-YxO3-alpha (0 <= x <= 0.3) first increased with increasing doped amount of Y, and reached the highest value of 1.07x10(-3) S/cm when x was 0.2, then decreased gradually with further increasing Y content. At 600 degrees C, BaZr0.75Y0.25O3-alpha displayed the highest conductivity, while the conductivity of BaZr0.7Y0.3O3-alpha was the highest at 300 degrees C. The results indicated that there should be an optimum Y doping concentration yielding the highest conductivity at a constant temperature, and the optimum Y doping concentration should increase in the humidity atmosphere as the temperature decreases. So increasing the Y-doping concentration is helpful to improve the conductivities of BaZ(1-x)Y(x)O(3-alpha) materials at low temperature.