Characterization of Nickel Ions in Nickel-Doped Yttria-Stabilized Zirconia

The distribution of Ni2+ ions in NiO-doped 10YSZ powder is examined with Superconducting Quantum Interference Device magnetometry, a technique that is able to distinguish between randomly distributed Ni2+ ions in solid solution and ordered Ni2+ ions within NiO with high precision. Very high purity powders containing 0.01, 0.1, 0.5, and 1.0mol% NiO in 10YSZ (all levels below the solid solubility limit of NiO in 10YSZ) were made from acetate precursors and a modified EDTA (ethylenediaminetetraacetic acid)-citrate synthesis method. The powders were calcined in air at either 873 or 1273K. The 873K calcination leads to single phase YSZ particles about 10nm in diameter, and almost all of the NiO dopant exists in complete solid solution. The 1273K calcination leads to a larger YSZ particle size (55-95nm), and also to the formation and/or growth of NiO particles, the amount of which depends on the length of time of calcination. Upon sintering the powders in air (1773K, 1h), the NiO dissolves back into 10YSZ. The results demonstrate that particle growth during calcination leads to the exsolution of Ni2+ ions to form NiO. This has important implications for the synthesis of NiO-doped 10YSZ from chemical precursors.