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, Tx1 and Tx2. The dielectric constant (ε′) increased at Tx1 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 ε′ at Tx1 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 α-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 ε′ at Tx1. We determined that the giant dielectric jump at Tx1 was caused by the polar nanocrystals formation and the large ε′ could be explained by the Maxwell–Wagner effect.