Cost-effective solid-state reactive sintering method for high conductivity proton conducting yttrium-doped barium zirconium ceramics

Using cost-effective precursors of BaCO(3), ZrO(2), and Y(2)O(3), proton conducting ceramic pellets of BaZr(0.8)Y(0.2-) O(3-delta) (BZY20) were successfully fabricated with the help of a range of sintering aids including LiF, NiO, Al(2)O(3), and SnO(2). This simple and cost-effective solid-state reactive sintering (SSRS) method involved only a single high-temperature sintering step. The effect of various experimental conditions on the crystal structure, relative density, morphology, and total conductivity of the as-prepared BZY20 ceramic pellets were investigated in detail. Tunable experimental parameters included the type of sintering aid, the amount of aid, and the sintering temperature. NiO was determined to be the most effective sintering aid investigated. Under optimized conditions using 1-2 wt.% NiO as a sintering aid, dense BZY20 ceramic pellets (>95% relative density) with grain sizes as large as 5 mu m were successfully prepared at a relatively low sintering temperature of 1400 C. In comparison, most alternative sintering techniques for BZY require temperatures in excess of 1700 degrees C. Total conductivities as high as 2.2 x 10(-2) and 3.3 x 10(-2) S cm(-1) were obtained from the resulting pellets at 600 degrees C under dry- and wet-argon atmospheres respectively. These are among the highest values reported for BZY20, highlighting the potential of the NiO-modified reactive sintering approach to provide a simple, cost-effective, reduced-temperature route to achieve dense, large-grained parts for protonic-ceramic applications. (c) 2010 Elsevier B.V. All rights reserved.