Role of Cyclic Ether and Solvent in a Non-Alkoxide Sol−Gel Synthesis of Yttria-Stabilized Zirconia Nanoparticles

The effects of cyclic ether (epoxide versus oxetane), solvent, and drying method were examined for a non-alkoxide sol−gel synthesis of yttria-stabilized zirconia (YSZ). YSZ sol−gel materials, from 3 to 25 mol % Y 2 O 3, were successfully prepared with either propylene oxide (PO) or trimethylene oxide (TMO) in both aqueous and mixed ethanol−water solutions of Zr 4+ and Y 3+ chlorides. Supercritical drying (aerogels) produced fine, nanoparticulate networks, whereas drying under ambient conditions (xerogels) resulted in heterogeneous micrometer-sized hard agglomerates. The resulting materials were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption/desorption analysis, and elemental analysis by inductively coupled plasma−atomic emission spectroscopy. The cyclic ether and solvent were found to be critical factors in the resulting as-prepared aerogel surface area and morphology. For a given solvent, aerogels prepared with PO had higher surface areas than did those prepared with TMO. For example, the surface areas of aerogels prepared in water were 453 and 295 m 2 /g for PO and TMO, respectively. Following calcination to 550 °C, however, the crystallized YSZ powders were similar, consisting of homogeneous nanoparticles (∼10 nm) with spherical morphologies and high surface areas (>100 m 2 /g). Elemental analysis, XRD, and electron microscopy indicated that Y 2 O 3 and ZrO 2 formed a homogeneous nanostructure over a wide range of Zr/Y ratios, corresponding to 3−25 mol % Y 2 O 3 .