Pd addition in high Tc YBaCuO oxide

A small amount of Pd addition increases T_c for the YBa₂Cu₃O_7−y oxide. The maximum offset, midpoint and onset temperatures of the YBa₂(Cu_0.999Pd_0.001)₃O_7−y oxide are 92.1, 95.0 and 105 K, respectively. Excess addition of Pd decreases T_c. The T_c change is consistent with the results of the lattice constants.     

Study of the crystalline structure of the superconducting phase of the YBaCuO ceramic compound

We present the results of a study of the crystalline structure of the high-temperature superconducting (above 110K) phase in the single-phase ceramic compounds YBaCuO. We have concluded that the crystal symmetry of this HTS phase with chemical composition Y_1.2Ba_0.8CuO_4−δ is orthorhombic type with crystallographic lattice constants a=0.3815 nm, b=0.3457 nm, c=2.650 nm.     

The superconductivity,structure and microstructure of BaYScCu oxides

We added small amount of Sc (0.05–0.35at.%) to BaYCu oxide and found that the superconductivity deteriorated drastically when the Sc content reached 0.325at.%. X-ray and electron diffraction showed that the orthorhombic perovskite structure changed to multi-phase structure with unidentified phases. The microstructures observed by TEM are of needle like morphology. Their phases are not yet identified.     

The effect of Sc on the superconductivity of the BaYCu oxides

The oxide compounds of Ba_0.6Y_0.4−xSc_xCu (x=0.05−0.35) have been prepared. It was found that the superconducting transition temperatures of the samples vary with the contents of Sc and when Sc>0.325, the samples become nonsuperconducting.     

Zero resistance at 148.5K in fluorine implanted YBaCuO compound

Fluorine ions with an energy of 180keV at a dose of 1×10¹⁵ ions/cm² have been implanted into YBa₂Cu₃O_x. After annealed at 800°C, the resistance of the new Y-Ba-Cu-F-O compound drops to zero at 148.5K.     

Superconductivity of LaMCuO system (MBa,Sr and Ca

Superconductivity of the compounds of LaMCuO system with K₂NiF₄ type structure has been studied. For the sintered compounds with MBa, Sr and Ca, the highest onset transition temperatures, T_ci, estimated from resistivity measurement are about 36.9K, 43.0K and 23.5K, respectively and the highest temperatures where the resistivity vanishes, T_cf, are about 27.8K, 34.0K and 15.5K, respectively. Almost complete Meissner effect has been confirmed by low frequency ac susceptibility measurement. Crystals of the compounds with MBa and Sr have been prepared. As the result of the preliminary experiment for a crystal with Ba, it is found that T_cf of the crystal is higher than any one of the sintered specimens with MBa, while the T_ci of the crystal is nearly the same as the highest one of the sintered specimens.     

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T_c(ϱ=0) is 90.3K for ErBaCuO and 91K for YbBaCuO.     

Infrared detection by Tl?Ba?Ca?Cu?O superconducting films

The response of polycrystalline Tl–Ba–Ca–Cu–O superconducting thin films on short laser pulses has been investigated for radiation between 10 m and 500 m wavelength. Fast signals with time constants less than 1 ns were observed for wavelengths longer than about 100 m whereas for shorter wavelengths only a bolometric signal could be detected.     

Electron diffraction and electron microscopic study of BaYCuO superconducting materials

Electron microscopy and electron diffraction have been applied to show that the orthorhombic phase in the compound Ba₂YCu₃O_7−δ is responsible for the high superconducting transition temperature. A positive correlation is found between the volume fration of the orthorhombic phase and the superconducting transition temperature. By means of an “in-situ” heating experiment it is found that the orthorhombic phase is formed on cooling from a high temperature tetragonal phase with disordered vacancies. It is suggested that the low temperature tetragonal phase that occurs in the same specimens as the orthorhombic phase also contains an ordered arrangement of vacancies different from that present in the orthorhombic phase. The order-disorder transition associated with the structural vacancies is shown to be reversible, provided there has been no oxygen loss.     

A new superconducting oxide GdBaCuO with Tc (ρ=0) above 92K

A new superconducting oxide Gd_xBa_1−xCuO_3−y with T_c (ρ=0) above 92K has been successfully synthesized by the ceramic technology. The samples with composition of x=0.5, 0.625 and 0.9 are all observed with high T_c superconductivity. The highest T_c for samples measured is observed in Gd_0.5Ba_0.5CuO_3−y which has a resistive midpoint of 95K with a width of 1.5K, and a zero-resistance temperature of 92.5K. The results of a.c. magnetic susceptibility measurement are also reported.     

Tl—Ba—Ca—Cu氧化物超导体的低场磁性

我们测量了 T1-Ba-Ca-Cu-O 高温超导样品在低磁场下的磁化率和电阻与温度的关系;观察到样品具有两个超导主相,T_c 分别为117K 与104K;估算出该样品在77K 下的下临界场H_(c1)大约为480G.样品的迈斯纳效应和磁屏蔽的测量结果表明,该样品的磁屏蔽效应很小.在外加低磁场下测量了样品的临界电流,研究了,I_c-H 关系,发现在30G 以下磁场范围内的实验结果与超导颗粒之间是无规并联的约瑟夫森弱连接的理论结果符合较好.     

Features of the spin fluctuations and superconductivity of Tl2Ba2CaCu2O8−δ according to 63Cu and 17O NMR data

Data on the NMR line shifts, the spin-lattice relaxation rate of ⁶³Cu and ¹⁷O nuclei, and the spin-spin relaxation rate of ⁶³Cu are obtained for Tl₂Ba₂CaCu₂O_8−δ (T _c =112 K) in the normal and superconducting states. The hyperfine constants at the copper and oxygen atoms in a CuO₂ plane are estimated from an analysis of the temperature dependence of the Knight shift. The temperature-dependent behavior of the long-and short-wavelength parts of the dynamic spin susceptibility is discussed by modeling an antiferromagnetic Fermi liquid. The possible relation between the characteristics of the spin-fluctuation spectrum and the superconducting transition temperature is analyzed for the oxide investigated. Zh. éksp. Teor. Fiz. 115, 991–1001 (March 1999)     

Compositionally dependent superconducting transition temperature of YBaCu oxides

The superconducting transition temperatures of a family of YBaCu oxides have been explored by dc resistivity measurements. Substitutions of magnetic and non-magnetic ions on Y, Ba and Cu sites are reported. For some compositions, achieving high superconducting transition temperatures is strongly dependent on growth conditions for the material.     

High-Temperature superconductivity in the Y–Ba–Cu–O system

High-temperature superconductivity in the Y-Ba-Cu-O system has been discussed with special reference to the identification and characterization of the pure monophasic compound responsible for the superconductivity. The crucial role of oxygen has been examined in the light of the structure and thermogravimetric analysis.     

High Tc superconductors with different Cu2+/Cu3+ ratios in the Y–Ba–Cu–O system

Studies on different phases in the Y-Ba-Cu-O system have revealed that T_C around 90 K is obtainable with different Cu /Cu ratios provided the correct oxygen proportion is maintained.     

Tl2Ba2Ca2Cu3O10的化学键性质和同质异能位移研究

在Tl2Ba2Can-1CunO2n 4(n=1,2,3,4)系列超导性氧化物中,Tl2Ba2Ca2Cu3O10具有最高Tc值(125 K)．利用电介质的平均能带模型计算了Tl2Ba2Ca2Cu3O10的局域化学键参数,得到Cu(1)-O键的共价性为0．561,Cu(2)-O键的平均共价性为0．296．应用化学环境因子计算了57Fe在Tl2Ba2Ca2Cu3O10中的穆斯堡尔同质异能位移,证实了57Fe在低掺杂时以Fe3 和Fe4 离子形式占据Cu(1)位置,而在高掺杂时以Fe3 和Fe4 离子形式分别占据Cu(1)和Cu(2)位置．结果表明,化学键理论计算有助于复杂晶体的穆斯堡尔谱的正确分析．