Room-temperature-densified H_(3)BO_(3) microwave dielectric ceramics with ultra-low permittivity and ultra-high Qf value

With the rapid development of mobile communication technology towards 5G and 6G,the microwave dielectric materials with ultra-low permittivity and ultra-high Qf value are urgently demanded.Here,the excellent microwave dielectric properties are reported in H3BO3 ceramics with the molecular crystal structure,whose permittivity(2.84)and density(1.46 g/cm^(3))are record-low among the low-loss ceramics.The ultra-high Qf value of 146,000 GHz(or the ultra-low dielectric loss of 1.03×10^(-4) at 15 GHz)is also distinguished.Besides,the H_(3)BO_(3) ceramics can be densified at room temperature by a simple cold sintering process in a short time of 10 min,and this brings many advantages for the integration with microwave circuits.The large molecule volume originating from the molecular crystal structure and the low dielectric polarizabilities of H^(+) and B^(3+) are responsible for the ultra-low permittivity of H_(3)BO_(3) ceramics,and more microwave dielectric materials with ultra-low permittivity and ultra-high Qf value are expected to be explored in the molecular crystals.

Greatly enhanced permittivity in BaTiO_(3)-epoxy dielectric composites with improved connectivity of ceramic phase

BaTiO_(3)-epoxy dielectric composites were prepared by curing the liquid epoxy monomer that infiltrated into the partially-sintered BaTiO_(3)porous ceramics.The BaTiO_(3)volume fraction of the composites maintained around 58.6%with increasing the sintering temperature from 600℃to 1000°C,while the significant microstructure evolution,improved connectivity of BaTiO_(3)phase and dramatical increase in permittivity from 102 to 697 were observed.The permittivity and BaTiO_(3)volume fraction further increased to 2328 and 83.5%for the sintering temperature of 1250℃.The present composites had the permittivity 102 orders of magnitude higher than the 0-3 type ones,and the extraordinary results were mainly attributed to the improved connectivity of BaTiO_(3)phase that benefited from partial sintering.The connectivity also had a significant effect on the temperature dependence of permittivity,and good combination of temperature-stable high permittivity,low dielectric loss and relatively low ceramic fraction could be obtained by regulating the connectivity of BaTiO_(3)ceramic phase.