Chen Zhaojia

Zero resistance at 132K in the multiphase system of Bi1.9−xPbxSb0.1Sr2Ca2Cu3Oy with x=0.3, 0.4

Abstract Superconducting properties of the multiphase compounds of ( Bi 1.9− x Pb x Sb 0.1) Sr 2 Ca 2 Cu 3 O y have been investigated. Zero resistance at 132K has been observed with x =0.3 and 0.4. Two samples with 132K zero resistance were stable in low temperature circling (77K to 200K). Zero resistance were down to 112K( x =0.3) and 106K( x =0.4), but the a.c susceptibilities of the two samples still have large drop at 132K after several circles from 77K to room temperature.

The superconducting properties in Bi2−xSbxSr2Ca2Cu3Oy compounds (x=0.05, 0.1, 0.15, 0.2)

Abstract Superconducting properties of a new series Bi 2−x Sb x Sr 2 Ca 2 Cu 3 O y ( x =0.05, 0.1, 0.15, 0.2) have been reported in this paper. All of these samples have two superconducting transitions. The first superconducting transition is at about 120 K, zero resistance temperature is about 75 K. A new high- T c phase appears because of the substitution of Sb in the Bi-Sr-Ca-Cu-O system

Specific heat anomaly in Bi1.6Pb0.4Sr2Ca2Cu3Oy superconductor

Abstract The specific heat anomaly Δ C of Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O y was observed in the temperature range 80–100 K. It is estimated from Δ C that γ∼15 mJ/mol·K 2 and H c2( T =0)∼100 T in this sample. The specific heat anomaly confirmed the occurrence of bulk superconductivity of the high- T c phase in Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O y superconductor.

Study on the specific heat anomalies of La2−xSrxCuO4−δ polycrystalline samples

Abstract The specific heat anomalies of La 2− x Sr x CuO 4− δ polycrystalline samples ( x =0.25, 0.20, 0.16, 0.15, 0.14, 0.12, 0.10, 0.08) were measured. The specific-heat jump at the superconducting transition temperature changes systematically with Sr substitution. The maximum specific-heat jump corresponds to the sample with Sr content x = 0.16. The bulk superconducting phase diagram is similar to that deduced from resistivity measurement. The measurement shows that only the sample with x = 0.16 presents optimal electronic single phase properties and the superconducting transition temperature T c directly related to the electron density of states at the Fermi level N ( E F ).

Two transitions in single crystal GdBa2Cu3O7−y near Tc

Abstract The specific heat near Tc for superconducting single crystal GdBa 2 Cu 3 O 7−y has been measured with an instrument of differential calorimeter at low temperature. Two transitions were observed between 80.7K and 87.5K. They are separated from each other, and the temperature interval φ T between the two specific heat peaks is 3.5K. It is supposed that the specific heat jump at higher temperature is due to structural transition and the one at lower temperature is superconducting transition.

The influence of Pb on the stability of the Bi-type modulated structure

Abstract The mechanism of the Bi-type modulated structure was studied in Bi-based high-temperature superconductors with nominal compositions of Bi2Sr2CaCu2Oy, Bi1.85Pb0.15Sr2CaCu2Oy and Bi1.8Pb0.35Sr2Ca2Cu3O y. It was found that the three samples annealed in oxygen flow showed the presence of Bi-type modulation in electron diffraction patterns; after the samples were annealed in nitrogen atmosphere the Bi-type modulation still existed for the sample Bi2Sr2CaCu2Oy but disappeared completely for the Pb- doped samples Bi1.85Pb0.15Sr2CaCu2Oy and Bi1.8Pb0.35Sr2Ca2Cu3Oy. This suggests that doping Pb in the Bi-Sr-Ca-Cu-O system strongly changes the stability of the Bi-type modulation. It is confirmed that the driving force of Bi-type modulation is not the consequence of extra oxygen for the charge balance, but the adjustment of the BiO layer to the lattice mismatch.

The effect of constituent content on superconductivity and phase in BiPbSbSrCaCuO system

Abstract In this paper the effect of constituent content on superconductivity and phase in BiPbSbSrCaCuO system is reported. The zero resistance temperature Tce reaches as high as 132K when Sb = 0.1 and Tce is decreased dramatically with increasing either Sb-content or Cu-content in BiPbSbSrCaCuO system while the corresponding phase is changed fundamentally. A orthorhombic cell with a =23.16 A , b =9.48 A , c =6.20 A is proposed for a predominant phase in nominal composition Bi1.6Pb0.4SbxSr2Ca2Cu3Oy (x=0.3–1.0) of non-superconducting system.

Zero resistance at 117 K in Bi1.6Pb0.4Sr2Ca2Cu2+xOy compounds

In the Pb-doped Bi-Sr-Ca-Cu-O system, optimization of the composition and heat treatment conditions at which a greater amount of the high-Tcphase forms has been reported in our early paper [1], where the temperature of zero resistance was 107K. Recently, we have achieved zero resistance at 117 K and observed an a.c. susceptibility step at around 150 K by changing the Cu composition in the Bi1.6Pb0.4Sr2Ca2Cu2+xOy system (x=0, 0.4, 0.8, 1.2, and 1.6).

The synthesis and structure of a new Bi-based copper oxide with (Bi, M)O monolayers: (Bi, M)Sr2(R, Ce)3Cu2O11−δ

Abstract A new layered cuprate, (Bi, M)Sr 2 (R, Ce) 3 Cu 2 O 11−δ (M+Cd, Cu; R: rare earth elements) (Bi-based “1232”), has been synthesized. The structure of the compounds has been determined by the powder X-ray diffraction method. It is found that the cell parameters are approximately equal to a = 3.85 A and c = 17 A . Comparison of the calculated and observed diffraction intensities shows that the structures are similar to that of (TI, Cu)Sr 2 (R, Ce) 3 Cu 2 O 11 . The behavior of the resistivity dependence on temperature is directly related to that heat treatment.

Possible Transition in D-Valine and L-Valine Single Crystal Samples

The specific heats and temperature dependence of the x-ray powder diffractions for the D-valine and the L-valine single crystal samples have been studied. It is found that there is a specific heat jump at 272.0 K for the D-valine samples but no jump at the same temperature for the L-valine sample. The lambda like transition means that the co-operative effect is involved in this transition. There is no crystal structure transition in the temperature range of 123-293 K for the D-valine sample. The transition of the D-valine sample might be the possible D-L transition which is proposed by Abdus Salam.