  The dielectric tuning and loss of (Ba,Sr)TiO3:MgO bulk composites depend
strongly on the connectivity and interaction among the two phases. To
investigate this relationship, the polar structure and dynamics of these
composites is mapped as a function of space and time using a pair of
three-dimensional probes: second-harmonic confocal scanning optical microscopy
(SH-CSOM), which maps ferroelectric polarization in three dimensions, and
time-resolved scanning optical microscopy (TR-CSOM), which maps polarization
dynamics along two spatial dimensions and one time dimension. SH-CSOM
measurements reveal a high degree of homogeneity within the (Ba,Sr)TiO3
regions, while TR-CSOM measurements indicate that topologically connected
regions respond with a spatially uniform phase.
