The High Pressure Synthesis And Physical Property Researches Of Cu-1234 High-temperature Superconducting Material

Superconducting materials have broad application prospects in transportation,energy,information and other fields.At present,cuperate superconductors are the only high-temperature superconducting materials that can be applied over 77K.However,most of cuperate superconductors contain rare earth elements,volatile elements or toxic elements.Therefore their application space is further limited.Cu-series superconductor Cu Ba₂Ca_n-1Cu_nO_2n+2+?(Cu12(n-1)n for short)only contains Cu,O and alkaline earth metals.The composition is simple,economical and safe,and environment friendly.Cu-1234 has the highest T_cin the Cu-series,the T_cof which can reach more than 118K.At the same time,it has a high critical current density J_cabove77K.The temperature dependence of J_ccan be comparable to that of YBa₂Cu₃O_6+?(YBCO),showing an important application prospect.This paper takes Cu-1234superconducting material as the research object,and carries out the following work:(1)The experimental conditions for the high temperature high pressure synthesis of Cu-1234 superconducting materials were optimized.A series of Cu-1234 samples were prepared,and their structures and physical properties were studied.The highest superconductivity T_cof Cu-1234 sample is about 118K,the superconductivity content can be up to 49%,and the superconductivity properties of Cu-1234 sample remain almost unchanged in three years.The positions and occupancy rates of each element of Cu-1234 were obtained by neutron diffraction experiments.The valence of copper in the complete outer and inner Cu O₂layer were calculated as+2.13 and+2.04respectively by BVS bond-valence theory.Post-treatment experiments below 500?in Atmospheric oxygen can simultaneously increase T_cand superconducting content,however high oxygen pressure heat treatment has almost no effect on T_c.Combined with X-ray absorption spectrum experiment,it is preliminarily judged that Cu-1234 is in the overdoped state.Due to the inhomogeneity of the temperature inside the high pressure chamber,the superconductivity properties and superconductivity content of the samples obtained are not uniformly distributed.Therefore,the preparation process need further optimization.(2)Preparation and physical properties research of Ti-doped Cu-1234 samples.By doping Ti atoms into the charge pool layer and introducing the pinning center,the magnetic flux pinning density is increased so as to increase the J_cvalue of the material.The experimental results show that with the increase of Ti nominal doping content,the lattice constant and cell volume of Cu-1234 gradually increase,and T_cgradually decreases by about 2K.The superconductivity content is basically unchanged before the nominal doping of Ti?0.2.When the nominal doping concentration of Ti is 0.1,the critical current J_cincreases by about 10%.When the nominal doping concentration of Ti is further increased to 0.3,J_cbegins to decrease due to the increase of impurity phase.