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-ge l routes, and the direct reaction of oxides and carbonates was explored. X- ray absorption spectroscopy measurements on xerogels prepared using alkoxid es indicated the presence of zirconium and titanium with coordination numbe rs >6 and <6, respectively. The use of acetic acid as a modifier changes th e local structure around zirconium in the xerogel. A calcium-rich phase was observed at low heat treatment temperatures regardless of the sample prepa ration route. Many of the initially prepared xerogels contained perovskite and the higher titanium content samples more readily crystallized to perovs kite 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 fluorit e-like material transformed to perovskite at higher temperatures. The avera ge composition of the perovskite present in the fluorite-perovskite mixture did not change as more of the fluorite was converted to perovskite by heat ing, suggesting that the two phases have the same zirconium-to-titanium rat io. The EXAFS analyses indicated that the average Zr-O and Ti-O bond length s are only weakly dependent upon solid-solution composition, even though th e average M-O bond length depends strongly on composition. The EXAFS data a lso suggest the cation distribution in the solid solution is to some extent dependent upon the sample preparation method.