Dependence of Dopant Cations on Microstructure and Proton Conductivity of Barium Zirconate

Abstract

The effects of various cations ( Mg2+ , In3+ , Yb3+ , Tm3+ , Er3+ , Ho3+ , Gd3+ , Nd3+ , La3+ , Bi3+ , and Ga3+ ) were examined as dopants into the B site of perovskite barium zirconate. The solubility of In, Yb, Tm, Er, and Ho, whose ionic radii are close to that of zirconium ion, into the B site is more than 0.075 (normalXMO1.5=0.075) at 1600°C . In contrast, when there is a large difference of ionic radii between trivalent cations ( Nd3+ , La3+ , Bi3+ , and Ga3+ ) and zirconium ion, the solubility of trivalent cations into barium zirconate is less than normalXMO1.5=0.075 . The microstructure of sintered pellets and their conductivity in wet atmosphere were investigated. We could divide dopants into two classes based on the extent of proton conductivity and microstructure: “Y-type” and “Sc-type” dopants. Yb, Ho, Er, and Tm belong to Y-type dopants, which have a microstructural mixture of coarse and fine grains and higher proton conductivity. In belongs to Sc-type dopants, which have well-grown grains and lower proton conductivity.

Effect of isovalent cation substitution on conductivity and microstructure of sintered yttrium-doped barium zirconate

“…We investigated the dopant dependency of proton conductivity of barium zirconate where Sc, In, Yb, Tm, Er, Y, Ho and Gd were examined [21]. In the investigation, we found that the minimum points of activation energy and pre-exponential terms for bulk conductivity as a function of ionic radius of dopant cation exist at around 0.087 nm as seen in Fig.…”

“…steam electrolyzers, and many researchers are working on doped barium zirconate [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…Effect of various dopants on proton conductivity in doped barium zirconates[21]. (a) Activation energies for bulk conductivity as a function of ionic radius of dopants.…”

To Journal of Phase Equilibria and Diffusion Phase Relationship of the BaO-ZrO2-YO1.5 System at 1500 and 1600 °C

“…The sacrifice powders were synthesized by a conventional solid state reaction. [10,[18][19][20] The heat-treatment sample temperatures were checked using a thermal history sensor (Referthomo type H, AS ONE). The temperature deviation in the experiments was within 1600 ± 10 and 1500 ± 5°C.…”

“…Yttrium-doped barium zirconate is known to have the lowest protonic resistance of grain interior among trivalent cation-doped barium zirconate and this property attracts many researchers. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In the previous works, we investigated a sintering mechanism of 15% yttrium-doped barium zirconate (BaZr 0.85 Y 0.15 O 3-d ) at 1600°C based on the idea of twophase separation of yttrium poor barium zirconate and yttrium rich barium zirconate phase in the sample by conventional solid state reaction. [19,20] A phase separation at 1600°C was reported by Kojima et al [23] However, the points we discussed are that there is no phase separation in equilibrium at 1600°C, but traces of the phase separation at synthesizing temperature, 1300°C, might remain even at 1600°C.…”