In situ measurement of cation order and domain growth in an electroceramic

In situ methods are ideally suited for the study of the development of property-critical structural features during materials processing. As an example of their potential in the area of complex oxide electroceramics, here, we apply in situ synchrotron powder diffraction to investigate the ordering processes responsible for optimizing the microwave dielectric properties of the commercial electroceramic barium zinc tantalate. The collection of synchrotron diffraction data with high resolution and high intensity during processing has allowed the growth of cation site order within a domain and the size of the ordered domains to be separated during the multistage thermal treatment processing used by industry. Domain growth does not commence until the extent of order within a domain is maximized. Analysis of the superstructure intensities with the Avrami equation shows that nucleation is not important in this process. Domain growth then occurs by the curvature-driven Allen-Cahn mechanism. The complex nature of the ordering is confirmed by the coexistence of two phases whose temporal evolution divides into two stages according to the two stages of ordering and domain growth mentioned above. The implications of these observations for industrial processing procedures aimed at reducing the processing time are discussed.