Ferroelectric domain contribution to the tunability of Ba _0.8Sr_0.2TiO₃ ceramics

Polarization contributions to the tunable properties of Ba _0.8Sr_0.2TiO₃ ceramics were quantitatively studied by microwave measurements. The width of the ferroelectric domain walls (90° domain walls) decreased with decreasing average grain size. The variation in domain size with grain size for grains smaller than 10 μm was roughly proportional to the square root of the grain size, consistent with previous reports on BaTiO₃. The smaller size of the 90° domains (i.e., higher domain-wall density) resulted in greater tunability at an applied DC electric field of 6.7 kV/cm. The tunability of the specimen with a domain size of 161nm was 26.5%, which was 4.4 times that of the specimen with a domain size of 259nm (T = 6.0%). Under a relatively low DC field, the density of the domain-wall motion was the dominant factor determining the overall tunable properties, while the contributions of the ionic and electronic polarizations were relatively small in Ba_0.8Sr_0.2TiO₃.