The Study On Dielectric Tunability Of Antiferroelectric Ceramic/polymer Composites

Electronic information functional materials with high dielectric tunable properties have broad application prospects in tunable filters,phase shifters and sensors,etc.Therefore,the research on dielectric tunable materials has become a hot field.In practical applications,the desired materials properties are quite well known:higher tunability,relative low dielectric constant（ε_r）,low dielectric loss（tanδ）and good mechanical processing performance.Dielectric constants of ceramics with perovskite structure have strong dependence on electric field,but they have high dielectric constants and poor mechanical performance.The mechanical processing performance of polymer materials is excellent,and dielectric loss is low,but they do not have dielectric tunable properties.Therefore,it is reasonable to believe that an effective approach to advanced high-tunability materials with good mechanical performance is to harness the advantage of both ceramic and polymer.Traditional perovskite ferroelectric（FE）ceramics have higher tunability,but both theirε_r and tanδare higher.Besides,FE materials usually require a large electric field of MV/cm scale to changeε_r significantly.For antiferroelectric（AFE）ceramics,ε_r and tanδare relatively low,and the phase transition and the lattice constant can be abruptly changed under the influence of the electric field and temperature,which exhibits good tunability,making them potential candidates for the ceramic phases.In addition,the dielectric properties of polymer have important effects on the electric field distribution within the composite under the applied electric field,which in turn affects the dielectric tunable properties of the composites.Therefore,we chose PBLZST anti-ferroelectric ceramics as the ceramic phase,and Polyvinylidene fluoride（PVDF）and polystyrene（PS）were chosen as polymer phases.Conductive phases with different mass ratios and different morphologies were added into the composites to improve the electric field distribution rate of the ceramic phase,enhancing the tunability of the composites.At first,PBLZST/PVDF and PBLZST/PS were prepared by solution blending method and molded by hot-pressing.The effects of polymers with different polarities on their dielectric tunable properties were studied.When the external electric field was200/mm,the maximum dielectric tunability(n_max)of PBLZST/PVDF was 8.3%,tanδ=0.059,ε_r=65 and the factor of merit（FoM）was 1.41;PBLZST/PS had n_max=7.0%,tanδ=0.023,ε_r=51,FoM=3.04.The results showed that the dielectric tunable properties of composites with nonpolar PS were better.Secondly,based on the introduction of the conductive phase,the conductivity of the polymer phase can be improved,so can the dielectric tunability of the composite.Nickel（Ni）nanoparticles and carbon（C）nanoparticles were used as the conductive phases.The results showed that the addition of an appropriate amount of conductive phases improved the dielectric adjustable ratio of the composite material,but the content of the composite material played a role in shielding the electric field on ceramic particles.Although the metal filler has excellent electrical conductivity,its density is large and easy to settle,so PBLZST/PS/Ni showed worse dielectric tunable properties than PBLZST/PS/C.When the external electric field was 200V/mm,with 1.0wt%loading of Ni,PBLZST/PS/Ni had n_max=15.7%,tanδ=0.045,ε_r=72,FoM=3.46;with 1.0wt%loading of C,PBLZST/PS/C had n_max=17.7%,tanδ=0.036,ε_r=124,FoM=4.88.The results showed that carbon fillers had better effects on the dielectric tunable properties of the composites.Finally,in order to investigate the effect of the geometries of conductive phases on the electric field distribution in the composites,CNT and GNS were added in PBLZST/PS composites separately.When the external electric field was 200V/mm,with 0.4wt%loading of CNT,PBLZST/PS/CNT had n_max=16.7%,tanδ=0.019,ε_r=107,FoM=8.47;with0.6wt%loading of GNS,PBLZST/PS/GNS had n_max=20.0%,tanδ=0.027,ε_r=118,FoM=7.36.