Giant dielectric response with metastable phase crystallization from Ba1-xCaxTi2O5 glasses

Ba1-xCaxTi2O5 glasses (0 <= x <= 0.80) were fabricated by containerless processing. All glasses had two crystallization temperatures, T-x1 and T-x2. The dielectric constant (epsilon') increased at T-x1 and the large value was maintained during the existence of the first crystallized phase in the lightly Ca2+-doped region (0 <= x <= 0.15). An instantaneous jump of epsilon' at T-x1 was observed when 0 <= x <= 0.07, but there was no jump when 0.10 <= x <= 0.15. Synchrotron X-ray diffraction measurements showed that in the region 0 <= x <= 0.15, the first crystallized phases were nearly isomorphous with alpha-BaTi2O5; the lattice constant decreased with the Ca2+ content when 0 <= x <= 0.10. The first crystallized phase exhibited a second-order nonlinear optical effect when 0 <= x <= 0.07, confirming the polar crystal structure. From these results we found that the polar crystal structure is a crucial factor for the instantaneous jump of epsilon' at T-x1. We determined that the giant dielectric jump at T-x1 was caused by the polar nanocrystals formation and the large epsilon' could be explained by the Maxwell-Wagner effect. (c) 2012 Elsevier B.V. All rights reserved.