Preparation And Dielectric Performance Of BaTiO₃/SrTiO₃ Core-shell Structure

Hetero-structured BaTiO₃-SrTiO₃（BaTiO₃ is the core,and the concentrate of Sr is 10%,15%,20%and 25%）and SrTiO₃-BaTiO₃（SrTiO₃ is the core,and the concentrate of Sr is 40%）core-shell particles were synthesized using a two-step synthesis process.The lattice mismatch between BaTiO₃ and SrTiO₃ is about 2%-3%.Therefore,there are lattice strains at the BaTiO₃/SrTiO₃ interfaces.The lattice strain was identified in the core-shell particles and significantly influenced the dielectric properties of the SrTiO₃-BaTiO₃ ceramics at high frequency.Therefore,we researched the effects of lattice strain on the dielectric properties of SrTiO₃-BaTiO₃ ceramics systematically.In this paper,we demonstrate an ingenious method to design the stable negative capacitance by dielectric resonance.And we present a combined experimental and theoretical investigation of the dielectric resonance and electrical property in BaTiO₃-SrTiO₃ bulk ceramics which are consist of epitaxial core-shell heterostructures.The dielectric resonances are well fitted by Lorentz model and explored under various temperature near Curie temperature.Notice that the negative permittivity is functionally equivalent to the negative capacitance（C=εΜεr/（47πkd））.The negative capacitance of the BaTiO₃-SrTiO₃ bulk ceramics can be regulated by composites and temperature.The SrTiO₃-BaTiO₃ ceramics was prepared using a hot-pressing method and showed small grain size and high density.The two-phase interfaces of BaTiO₃ and SrTiO₃ were observed in the ceramics and the lattice strains were also maintained.The dielectric properties of the SrTiO₃-BaTiO₃ ceramics prepared by the lattice strained core-shell particles were investigated.Compared with Ba_0.6Sr_0.4TiO₃ ceramics,SrTiO₃-BaTiO₃ ceramics exhibited broader Curie peaks,enhanced polarization（1.9 μC/cm² and 4.47μC/cm² at 15 kV/cm respectively）,higher dielectric frequency stability which was confirmed by the increase of resonance frequency（from 470 MHz to 700 MHz）and weakened dielectric nonlinearity.The mechanism behind the improved dielectric and ferroelectric properties of SrTiO₃-BaTiO₃ ceramics was explained based on the formed 90° domain walls and the enhanced polarization caused by the lattice strains.