Manipulating and Quantifying the Compositional Heterogeneity in Sol−Gel Processed K(Ta1-xNbx)O3

Abstract

A series of K(TaxNb1-x)O3 (KTN) samples were prepared by two different sol−gel processes and by the reaction of mixed oxides. The local and long-range structures of the sol−gel-processed materials were examined as a function of heat treatment using a combination of powder diffraction and EXAFS studies. The compositional homogeneity of the perovskite solid solution products was also examined by EXAFS. The local structures around both the niobium and tantalum in the sol−gel-processed samples change on heating prior to crystallization. EXAFS provided evidence for the existence of Ta−O−Nb links in the dry KTN gels. The data for the perovskite KTN samples prepared using a conventional alkoxide sol−gel route are consistent with a random distribution of tantalum and niobium in the solid solution. However, the materials prepared by the direct reaction of mixed oxides were highly inhomogeneous, even after several regrinding and heating cycles. An alternative sol−gel method that employed prehydrolyzed precursors wa...