Preparation And Physical Properties Of REO_1-xBiSSe(Re=La,Ce)

The Bi S₂-based superconductors Bi₄O₄S₃ and La O_1-xF_xBi S₂,discovered in 2012,have attracted extensive attention as new layered superconductors.For Bi S₂-based superconductors,scientists believe that the chemical pressure,high pressure effect in the plane and carrier doping may be the cause of inducing or enhancing the superconductivity.In this paper,the preparation process of La_1-xOBi SSe and Ce_1-xOBi SSe polycrystalline samples of new layered Bi SSe-based materials was studied.And the structure,magnetism and electrical transport properties of these samples were characterized.First of all,the preparation of La OBi SSe polycrystalline samples was studied by solid-state reaction method,which was prepared by the process of sintering temperatures of700?and holding times of 30 h.On this basis,a series of oxygen vacancy doped La_1-xOBi SSe(x=0,0.05,0.1,0.15,0.2)polycrystalline samples were prepared by the above process.The structure,element content,electrical properties and magnetic properties under atmospheric and high pressure of La_1-xOBi SSe have been investigated.The lattice constant c shrinks notably and the solubility limit of oxygen vacancy near x=0.1 in La_1-xOBi SSe system.With the increase of oxygen vacancy content,the metal-semiconductor transition is obviously inhibited.Although the superconducting transformation does not occur,the resistivity of the system is effectively reduced.Secondly,in reference to the preparation process of La_1-xOBi SSe polycrystalline samples,the optimal preparation process of parent phase Ce OBi SSe was explored,and it was found that the generation of Bi₂Se₃ impurities could be reduced by reducing the second sintering temperature.Therefore,a series of polycrystalline samples with high purity of Ce OBi S_2-xSe_x(x=0-1)and Ce O_1-xBi SSe(x=0-0.2)were prepared by the process of two sintering temperatures of 700?and 600?respectively and two holding times of 30 h.Then,from the perspective of local structure,the effect of replacing S with Se on the crystal structure of Ce OBi S_2-xSe_x(x=0-1)system was investigated.The results showed that the local in-plane disorder caused by replacing S with Se was inhibited by increased in-plane chemical pressure,and the inhibition effect reached the best in the Ce OBi SSe system.Therefore,the Ce OBi SSe system can be used as an ideal system to discuss the effect of carrier supply by oxygen vacancy on physical properties.The structure and electrical properties of the Ce O_1-xBi SSe(x=0-0.2)system were analyzed at last.The results show that unlike the La O_1-xBi SSe system,the lattice expansion of the Ce O_1-xBi SSe system is caused by the oxygen vacancy,which is attributed to the increase of the in-plane Bi-Ch1 distance and the inter-plane Bi-Ch1 distance.Moreover,the oxygen vacancy inhibits the CDW phenomenon in the parent phase of Ce OBi SSe sample,resulting in metal-semiconductor transition,and effectively reduces the resistivity of the system,thus improving the electrical conductivity of the sample.