Study On Defects In Doped BaTiO₃/SrTiO₃ By Positron Annihilation Lifetime Spectroscopy

Ceramic functional materials are an important part of the electronics technology industry,and many excellent properties are not available in other materials.Now with the continuous development of scientific research,various new properties and applications of functional ceramic materials have been positively recognized and developed,and higher requirements are placed on the performance and quality of ceramic materials.Ceramic materials can often have special functions by doping other elements,meeting the needs of modern science.Through numerous studies,the realization of the performance of ceramic functional materials is determined by the internal defect structure.The positron annihilation lifetime spectrum（PALS）is an important means for studying materials lacking information.It has the advantages of non-destructive testing and high sensitivity,and is widely used in materials science,medicine,nuclear physics and other fields.In this paper,the defect information of doped functional ceramics is studied by using conventional characterization methods combined with PALS.（1）BaTiO₃powders were prepared by solid phase synthesis and hydrothermal gel method,and then BaTiO₃ceramics were obtained by pressureless sintering and spark plasma sintering（SPS）.According to XRD phase analysis,the powder is almost barium titanate,and the grain size calculated by Shelley’s formula is about 44 nm.The morphology and particle size of BaTiO₃sintered by pressureless sintering and SPS were observed by SEM.When sintered at 900-1300℃,the particle size increases,and the average particle size obtained at 1300℃is about 15μm,while the particle size of SPS is about 13μm,and almost no pore density is higher.PALS studies the defects of BaTiO₃ceramics at different sintering temperatures.It is found that with the increase of sintering temperature,some small voids disappear at high sintering temperatures,which reduces the average lifetime of positrons.（2）SrTi_1-xFe_xO_3-δpowders were prepared by solid-state synthesis method,and SrTi_1-xFe_xO_3-δceramics were obtained by high temperature sintering.The results of XRD phase analysis show that all the doped samples have perovskite structure.The lattice constant increases with the increase of Fe³⁺doping,which indicates that Fe³⁺has been successfully doped into SrTiO₃lattice.A large number of V_S"_rand V"_{T i}"were found in SrTi_1-xFe_xO_3-δceramics by PALS,defect chemistry and theoretical calculation,and the calculated value of Sr～0.15 was obtained.（3）BaTi_1-xAl_xO_3-δpowders were prepared by solid-state synthesis method,and BaTi_1-xAl_xO_3-δceramics were obtained by high temperature sintering at 1300℃.Combined with defect chemistry and PALS,Al³⁺doped as acceptor impurities occupiesTi site in the lattice of BaTiO₃in the form of Al’_Ti,and produces Al’_Ti,which reacts with association to formnAl’_Ti-V_O^..composite defects.