Solubility of NiO in Pechini-derived ZrO₂ examined with SQUID magnetometry

The solubility of NiO in ZrO₂ was studied by X-ray diffraction, TEM, and SQUID magnetometry. Lattice parameter measurements from a similar, established oxide system, NiO−10YSZ, were first used to show that SQUID magnetometry can effectively measure solubility. ZrO₂ specimens with 0, 0.5, 1, 2, 3, and 5 percent by mol NiO were prepared via the Pechini method. The specimens were calcined in air at 500, 600, and 1000 °C. The paramagnetic response of the specimens measured with SQUID magnetometry revealed that up to 5 percent by mol NiO is soluble in ZrO₂ for specimens calcined at 500 and 600 °C. The relatively large solubility compared with NiO−10YSZ occurs due to the very fine grain size (5–10 nm). The fine grain size is also responsible for stabilizing the tetragonal phase of ZrO₂. At the 1000 °C calcination temperature, the ZrO₂ is entirely monoclinic, exhibits larger grains (>45 nm), and only dissolves about 0.5 percent by mol or less NiO. The correlations between grain size, ZrO₂ polytype, and NiO addition are discussed.