| Due to variation of dielectric constant under applied electric field, dielectric tuning material has important application in the key components of phased array radar. Although it has been widely researched, there still exist the problem of decreasing dielectric loss and improving dielectric tunability at same time. In addition, with energy and environment problem are increasingly prominent, novel ferroelectric materials for energy storage become the new research hotspot. As a kind of ferroelectric material, BaTiO3 is perovskite structure (ABO3)with high dielectric constant and low dielectric loss. In order to further reduce the dielectric loss, maintain higher tunability, improve breakdown strength and increase energy storage density, BaTiO3-based materials were selected as the research subject. By composite with metal oxide (MO) as the second phase, their tunable dielectric and energy storage characteristics were studied, the influence of the second phase (properties, content, and distribution) and preparation process were explored. The main work were as follows:(1) Sr2+ substituted BaTiO3/Y2O3 composite ceramics were prepared by conventional sintering. With increasing of Y2O3 content, dielectric permittivity, dielectric loss and tunability decrease significantly,at the same time, FOM increase first and then decreased,Ba0.6Sr0.4TiO3/Y2O3 composite with 5 at% Y2O3 obtains optimal FOM, 73.60. The existence of the second phase of Y2O3 reduce grain size and then the grain boundary clamping effect to electric domain increase, which diminish the contribution of polar clusters in the matrix and result the decrease of dielectric tunability. After addition Y2O3, the breakdown strength of Ba0.6Sr0.4TiO3/Y2O3 ceramics (?70 kV/cm) increase, energy storage density are slightly down,but energy efficiency increase significantly. Under the electric field of 71 kV/cm, energy storage density and energy efficiency of Ba0.6Sr0.4TiO3/Y2O3 composite with 10 at% Y2O3 are 0.26 J/cm3 and 91.85% , respectively.(2) Sn4+ substituted BaTiO3/MgO composite ceramics were prepared by conventional sintering and spark plasma sintering (SPS). Compared with conventional sintering, SPS sintering inhibits diffusion of Mg2+ in the matrix. Dielectric constant and dielectric loss of BaTi0.85Sn0.15O3/MgO composite ceramics by conventional and SPS sintering also decrease significantly with the content of MgO increasing, and the dielectric tunability still maintain a relatively high value (>40%). 90 %mass BaTi0.85Sn0.i5O3+10 %mass MgO composite by conventional sintering obtains optimal FOM, 114.23. BaTi0.85Sn0.i5O3/MgO composite ceramics by SPS sintering present layer-plate substructure. Meanwhile, the dielectric breakdown strength and energy storage density of BaTi0.85Sn0.15O3/MgO by SPS sintering are improved significantly. The high dielectric breakdown strength of 190 kV/cm, energy storage density of 0.5107 J/cm3 and energy storage efficiency of 92.11% are obtained in 90 %mass BaTi0.85Sn0.15O3+10 %mass MgO composite by SPS sintering.(3) BaTiO3/La2O3 powders were prepared by the low-temperature soft chemical method and traditional solid-state method, and BaTiO3/La2O3 composite ceramics were prepared by conventional sintering. The grain size of BaTiO3 ceramic prepared by chemical method(3.05 ?m) is far smaller than solid-state method (31.11 ?m). This suggests that the low-temperature soft chemical method is the effective way to obtain small grain BaTiO3 ceramics. With the content of La2O3 increasing, the dielectric constant of the BaTiO3/La2O3 composite ceramics by chemical and solid-state method also decrease significantly, tunability and FOM increase first and then decrease. Among them, BaTiO3/La2O3 composite with 10 at%La2O3 by chemical method has the biggest tunability and the optimal FOM, 31.718% and 123.66, respectively. |
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