TlBa_2 Ca_2 Cu_3 O_9(Tl-1223) films have promising applications due to their high critical temperature and strong magnetic flux pinning. Nevertheless, the preparation of pure phase Tl-1223 film is still a challenge. W...TlBa_2 Ca_2 Cu_3 O_9(Tl-1223) films have promising applications due to their high critical temperature and strong magnetic flux pinning. Nevertheless, the preparation of pure phase Tl-1223 film is still a challenge. We successfully fabricate Tl-1223 thin films on LaAlO_3(001) substrates using dc magnetic sputtering and a post annealing two-step method in argon atmosphere. The crystallization temperature of Tl-1223 films in argon is reduced by 100℃ compared to that in oxygen. This greatly reduces the volatilization of Tl and improves the surface morphology of films. The lower annealing temperature can effectively improve the repeatability of the Tl-1223 film preparation. In addition, pure Tl-1223 phase can be obtained in a broad temperature zone,from 790℃ to 830℃. In our study, the films show homogenous and dense surface morphology using the presented method. The best critical temperature of Tl-1223 films is characterized to be 110 K, and the critical current J_c(77 K, 0 T) is up to 2.13 × 106 A/cm^2.展开更多
Tl2Ba2Ca2Cu3O10 was reported to be a superconductor with a highest transition temperature of 125 K among the homologous series of Tl2Ba2Can-1CunO2n＋4. The direct information on the Cu ion site at the atomic level is ...Tl2Ba2Ca2Cu3O10 was reported to be a superconductor with a highest transition temperature of 125 K among the homologous series of Tl2Ba2Can-1CunO2n＋4. The direct information on the Cu ion site at the atomic level is important for elucidating the superconductivity mechanism. The local bond properties of Tl2Ba2Ca2Cu3O10 were studied using the average band-gap model. The calculated results show that the covalency of Cu（1）-O bond is 0.561, and the average covalency of Cu（2）-O is 0.296. Mossbauer isomer shifts of 57Fe in Tl2Ba2Ca2Cu3O10 were calculated using the chemical surrounding factor, defined by covalency and electronic polarizability. It is verified that for lower doping, Fe substitute the Cu at the Cu （1） site in forms of Fe^3＋ and Fe^4＋; for higher doping, Fe^3＋ and Fe^4＋ ion occupies Cu（1） and Cu（2） site respectively. The studies show that the determination of the correspondence between spectrum components and actual copper sites occupied by MSssbauer nucleus was made easier with the aid of the calculation results of the chemical bond parameters.展开更多
After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<s...After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<sub>c</sub>（0） 120 K was discovered in Tl-Ba-Ca-Cu-O system. In this note, the crystal structure of the superconductor with T<sub>c</sub>（0） 120. 3 K and bulk critical current density of 1630 A/cm<sup>2</sup> at LN<sub>2</sub> temperature have been studied.展开更多
A series of superconducting phases has been synthesized by powder sintering in T1-Ba-Ca-Cu-O system and the crystal structures of these superconducting phases have been determined with the X-ray powder diffraction met...A series of superconducting phases has been synthesized by powder sintering in T1-Ba-Ca-Cu-O system and the crystal structures of these superconducting phases have been determined with the X-ray powder diffraction method. All of these superconducting phases belong to the tetragonal symmetry. They have the same lattice constant α but a different lattice constant c. The crystal structures of these superconducting phases are composed of two units, i. e. intercalation (single T1-Olayer or double T1-O layers) and oxygen deficient pseudo-perovskite unit Ba_2Ca_(n-1)Cu_nO_(2n+1) (n is an integer). These superconducting phases can be divided into two types. Type Ⅰcontains only one single T1-O layer as an intercalation with primary tetragonal lattice and space group P4/mmm. Type Ⅱ contains two T1-O layers in an intercalation with a body-centered tetragonal lattice and space group I4/mmm. The chemical formulas of Type Ⅰand Type Ⅱcan be generalized as TIBa_2 Ca_(n-1) Cu_nO_(2n+2.5) (n=1, 2, 3, 4) and T1_2Ba_2Ca_(n-1)Cu_nO_(2n+4) (n=1, 2, 3, 4) respectively. T_c increases as n increases. Under the condition that n is the same, Type Ⅱ has higher T_c than Type Ⅰ. The relations among crystal structures of the superconducting phases are discussed. A method which can deduce the crystal structure of superconducting phase from the d-value of the first diffraction line or from lattice parameter c is proposed. This method has been confirmed by experimental data.展开更多
Crystals of Tl-2223 and Tl-2212 have been successfully grown by self-flux method. The typical dimension in 1.0×1.0×0.1 mm3, and crystals as big as 2.0×2.0×0.3mm3 were also obtained. The transition ...Crystals of Tl-2223 and Tl-2212 have been successfully grown by self-flux method. The typical dimension in 1.0×1.0×0.1 mm3, and crystals as big as 2.0×2.0×0.3mm3 were also obtained. The transition temperature of crystals of Tl-2212 and Tl-2223 were 110 and 119K, respectively. Detailed studies on the effect of the cooling rate as well as Tl content were conducted. The results of X-ray diffraction experiments, SEM and EDX are also presented. AC susceptibility measurements were carried out on a Tl-2212 single crystal under various external magnetic fields applied normal to a-b plane. Measurements of reflectance spectra were also applied to a single crystal of Tl-2223 to investigate the optical anisotropy of Tl-2223.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 51002081the Fundamental Research Funds for the Central Universities of Chinathe Research Program of Application Foundation and Advanced Technology of Tianjin under Grant No 15JCQNJC01300
文摘TlBa_2 Ca_2 Cu_3 O_9(Tl-1223) films have promising applications due to their high critical temperature and strong magnetic flux pinning. Nevertheless, the preparation of pure phase Tl-1223 film is still a challenge. We successfully fabricate Tl-1223 thin films on LaAlO_3(001) substrates using dc magnetic sputtering and a post annealing two-step method in argon atmosphere. The crystallization temperature of Tl-1223 films in argon is reduced by 100℃ compared to that in oxygen. This greatly reduces the volatilization of Tl and improves the surface morphology of films. The lower annealing temperature can effectively improve the repeatability of the Tl-1223 film preparation. In addition, pure Tl-1223 phase can be obtained in a broad temperature zone,from 790℃ to 830℃. In our study, the films show homogenous and dense surface morphology using the presented method. The best critical temperature of Tl-1223 films is characterized to be 110 K, and the critical current J_c(77 K, 0 T) is up to 2.13 × 106 A/cm^2.
文摘Tl2Ba2Ca2Cu3O10 was reported to be a superconductor with a highest transition temperature of 125 K among the homologous series of Tl2Ba2Can-1CunO2n＋4. The direct information on the Cu ion site at the atomic level is important for elucidating the superconductivity mechanism. The local bond properties of Tl2Ba2Ca2Cu3O10 were studied using the average band-gap model. The calculated results show that the covalency of Cu（1）-O bond is 0.561, and the average covalency of Cu（2）-O is 0.296. Mossbauer isomer shifts of 57Fe in Tl2Ba2Ca2Cu3O10 were calculated using the chemical surrounding factor, defined by covalency and electronic polarizability. It is verified that for lower doping, Fe substitute the Cu at the Cu （1） site in forms of Fe^3＋ and Fe^4＋; for higher doping, Fe^3＋ and Fe^4＋ ion occupies Cu（1） and Cu（2） site respectively. The studies show that the determination of the correspondence between spectrum components and actual copper sites occupied by MSssbauer nucleus was made easier with the aid of the calculation results of the chemical bond parameters.
文摘After the discovery of high T<sub>c</sub> superconductivity in RE-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems, at the beginning of the year 1988, the superconductor with zero resistance transition temperature T<sub>c</sub>（0） 120 K was discovered in Tl-Ba-Ca-Cu-O system. In this note, the crystal structure of the superconductor with T<sub>c</sub>（0） 120. 3 K and bulk critical current density of 1630 A/cm<sup>2</sup> at LN<sub>2</sub> temperature have been studied.
文摘A series of superconducting phases has been synthesized by powder sintering in T1-Ba-Ca-Cu-O system and the crystal structures of these superconducting phases have been determined with the X-ray powder diffraction method. All of these superconducting phases belong to the tetragonal symmetry. They have the same lattice constant α but a different lattice constant c. The crystal structures of these superconducting phases are composed of two units, i. e. intercalation (single T1-Olayer or double T1-O layers) and oxygen deficient pseudo-perovskite unit Ba_2Ca_(n-1)Cu_nO_(2n+1) (n is an integer). These superconducting phases can be divided into two types. Type Ⅰcontains only one single T1-O layer as an intercalation with primary tetragonal lattice and space group P4/mmm. Type Ⅱ contains two T1-O layers in an intercalation with a body-centered tetragonal lattice and space group I4/mmm. The chemical formulas of Type Ⅰand Type Ⅱcan be generalized as TIBa_2 Ca_(n-1) Cu_nO_(2n+2.5) (n=1, 2, 3, 4) and T1_2Ba_2Ca_(n-1)Cu_nO_(2n+4) (n=1, 2, 3, 4) respectively. T_c increases as n increases. Under the condition that n is the same, Type Ⅱ has higher T_c than Type Ⅰ. The relations among crystal structures of the superconducting phases are discussed. A method which can deduce the crystal structure of superconducting phase from the d-value of the first diffraction line or from lattice parameter c is proposed. This method has been confirmed by experimental data.
文摘Crystals of Tl-2223 and Tl-2212 have been successfully grown by self-flux method. The typical dimension in 1.0×1.0×0.1 mm3, and crystals as big as 2.0×2.0×0.3mm3 were also obtained. The transition temperature of crystals of Tl-2212 and Tl-2223 were 110 and 119K, respectively. Detailed studies on the effect of the cooling rate as well as Tl content were conducted. The results of X-ray diffraction experiments, SEM and EDX are also presented. AC susceptibility measurements were carried out on a Tl-2212 single crystal under various external magnetic fields applied normal to a-b plane. Measurements of reflectance spectra were also applied to a single crystal of Tl-2223 to investigate the optical anisotropy of Tl-2223.
