Phase Evolution And Properties Of BaMO₃-based High-Entropy Perovskite Ceramics

With the rapid development of the technological revolution,the demand for new materials is becoming more and more urgent,materials science faces the enormous challenge of continuously developing new materials with superior performance.In 2015,the appearance of high entropy ceramics provided a new idea and route for the development of high performance non-metallic materials with high entropy,and opened up a new field of material research.At present,the research focuses on the rock salt structure(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O and its derivatives discovered by Rost,while the research on perovskite structure ABO3 type highentropy ceramics with rich physical content is very little.Perovskite structure has a wide range of tolerance factor t constraints,showing excellent physical and chemical properties,and has great applications in solar cells,photocatalysis,dielectrics,ferroelectrics.Therefore,it is urgent to carry out the research of BaMO3 high entropy ceramics.In view of the above problems,based on the concept of high-entropy ceramics,the highentropy ceramics of BaMO3 perovskite structure were used as the target,and the five-,six-,and seven-component high-entropy ceramics were successfully prepared by solid-state reaction method.Phase transition,microstructure and dielectric properties were investigated in this work.Five-component Ba(Ti,Sn,Zr,Hf,Nb)O3 high-entropy oxides can be divided into three stages in the pre-sintering process,from multi-phase state to two-phase state with similar lattice size,and finally to single-phase state.Due to the existence of high valence Nb5+,the valence state of ceramics in the body is unbalanced,so that the calcined powder cannot be sintered at a higher temperature to form a single-phase ceramic,and the element distribution is unhomogeneous.In order to balance the valence state of the elements,the six-component Ba(Ti,Sn,Zr,Hf,Nb,Ga)O3 single-phase perovskite high entropy ceramics were successfully prepared by doping Ga3+ with similar ion radius and low valence state on the basis of five-component ceramics.The single-phase structure can be formed in the process of pre-sintering and sintering.At the same time,the effect of sintering temperature on the structure and properties of ceramics is studied.The dielectric shows frequency dispersion.The dielectric constant and dielectric loss decrease with the increase of frequency,but the dielectric constant is low.It is worth noting that in the high entropy perovskite system,the decrease of the mixed entropy will lead to the increase of the phase formation temperature,and the main driving force of the phase formation of the high entropy perovskite ceramics is high-entropy.In order to further improve the dielectric constant of the ceramics,seven-component Ba(Ti,Sn,Zr,Hf,Nb,Ga,Li)O3 single-phase high entropy perovskite ceramics were prepared by doping Li+on the basis of six-component ceramics.The dielectric properties of the ceramics were greatly improved.The dielectric constant reached 2920(@100 Hz),which was nearly 50 times higher than that of six element Ba(Ti,Sn,Zr,Hf,Nb,Ga)O3 ceramics,57.3(@100 Hz).The main mechanism of conductance loss and leakage current is Ohmic conduction.The valence states of elements in high entropy perovskite ceramics were studied by XPS in this work.