Solution processing of calcium zirconate titanates, Ca(ZrxTi1-xO3:: An X-ray absorption spectroscopy and powder diffraction study

The preparation of perovskite calcium zirconate titanates (Ca[ZrxTi1-x]O-3) via an acetic-acid-modified sol-gel process, two different alkoxide sol-gel routes, and the direct reaction of oxides and carbonates was explored. X-ray absorption spectroscopy measurements on xerogels prepared using alkoxides indicated the presence of zirconium and titanium with coordination numbers >6 and <6, respectively. The use of acetic acid as a modifier changes the local structure around zirconium in the xerogel. A calcium-rich phase was observed at low heat treatment temperatures regardless of the sample preparation route. Many of the initially prepared xerogels contained perovskite and the higher titanium content samples more readily crystallized to perovskite upon heating. None of the processing routes led to the clean formation of perovskite at low temperatures. At intermediate temperatures a fluorite-related phase was always formed in addition to perovskite, and the fluorite-like material transformed to perovskite at higher temperatures. The average composition of the perovskite present in the fluorite-perovskite mixture did not change as more of the fluorite was converted to perovskite by heating, suggesting that the two phases have the same zirconium-to-titanium ratio. The EXAFS analyses indicated that the average Zr-O and Ti-O bond lengths are only weakly dependent upon solid-solution composition, even though the average M-O bond length depends strongly on composition. The EXAFS data also suggest the cation distribution in the solid solution is to some extent dependent upon the sample preparation method.