Ruixing Liang

Superconductivity, magnetism and oxygen nonstoichiometry of Ba2Y(Cu1−xMx)3Oy (M = Zn and Ni)

Abstract The effects of both the atomic substitutions and the change of oxygen content on the superconductivity and magnetic properties of Ba 2 Y ( Cu 1− x M x ) 3 O y (M = Zn and Ni) solid solution systems have been investigated. The Ni ion in the solid solution was found to be trivalent and have a magnetic moment of ≈ 2.4μ B . At the same oxygen content, the substitution of Cu by Zn always gives a steeper depression of T c than the substitution by Ni. The dependence of T c on the oxygen content indicates that T c is not depressed by the change of the hole concentration through the substitutions of Cu by Zn and Ni. The Zn ion in the solid solution plays a similar role to the over-doped holes in the two aspects of (i) weakening significantly the antiferromagnetic correlation among Cu spins and (ii) inducing a deviation of the band structure from the simple Mott-Hubbard model.

The effect of La substitution on the superconductivity of Ba2YCu3Oy

Abstract The (Ba 1− x La x ) 2 YCu 3 O y solid solution has been characterized for its superconducting transition temperature T c , lattice parameters, oxygen content and carrier concentration. T c is found to have a relation to the oxygen introduction by La doping. The depression of T c in the region of x > x c ( x c =0.05) is attributed to the formation of [Cu(I)O 5 ] pyramids or [Cu(I)O 6 ] octahedra. A model is proposed to interpret the influence of [Cu(I)O 5 ] pyramids on the superconductivity. The fraction of uncooperative atoms in Cu(II)O 2 sheets is found to be a common parameter of T c for several kinds of cation substituted Ba 2 YCu 3 O y systems.

Evidence of Sr-Deficiency in Bi2Sr2-αCa1Cu2O8 and Preparation of Stoichiometric Semiconducting Bi2Sr2Ca1Cu2O8

When samples with the starting composition of Bi:Sr:Ca:Cu=2:2:1:2 were heat-treated under the oxygen partial pressure range from 1 to 0.0001 atm at 820°C, at least three different multiphase regions with the following component phases appeared: Bi2Sr2Cu1Oy+Sr-rich Bi-Sr-Ca-Cu-O+Sr-deficient Bi2Sr2-αCa1Cu2Ox, stoichiometric Bi2Sr2Ca1Cu2O8, and Bi2Sr2Ca1O6+Cu2O. The amount of Sr-deficiency in the Bi2Sr2-αCa1Cu2O8 homogenized sample with the stoichiometric composition of Bi2Sr2Ca1Cu2O8 exhibited semiconductivity.

The Effect of Substitution of La for Ba and Ce for Y on the Tc of Superconducting Ba2YCu3O7

It was found that La3+ enters the Ba-site of the high Tc superconductor Ba2YCu3O7-δ but Ce4+ does not enter the Y-site. Replacement of a small amount of Ba by La raises the transition temperature, Tc, but further increase of the La content results in a significant drop of the transition temperature. These results are interpreted in relation to the distribution of oxygen vacancy.

Synthesis and properties of a new d1 compound Sr4V3O9.8 with layered structure

Abstract A new layered compound Sr4V3O9.8 with the Sr4Ti3O10 structure was successfully synthesized and electrical resistivity and magnetic susceptibility measurements were carried out. The unit cell dimensions of Sr4V3O9.8 were found to be a = 0.38428(3) nm and c = 2.7902(2) nm. The slope of the resistivity vs temperature curve changed from slightly negative to positive at a temperature of ∼70 K as the temperature was increased. The magnetic susceptibility of the sample could be fitted by the Curie-Weiss law, χ = χ 0 + C (T - Θ) , with χ0 = 1.06 × 10−3 emu·mole−1, Θ = −66 K, and C = 5.88 × 10−2 emu·K·mole−1.

Superconductivity and magnetism in Co substituted YBCO compounds

Abstract Superconducting transition temperature Tc and magnetic susceptibility χ were measured on Co substituted YBCO system, YBa2[Cu1−xCox]3Oy. The observed characteristic dependence of Tc on the substitution concentration x w investigated taking the magnetic data into consideration. The operating mechanism of the Co ion at the Cu(I) site on the superconducting state in the [Cu(II)O] net-planes are inquired from the two viewpoints: (1) changes in electronic state and (2) magnetic moment induction at the Cu(II) site. The possibility of both being induced by displacement of the oxygen atom O(1) between Cu(I) and Cu(II) is considered.

Oxygen Content and Phase Diagram of the High-Tc Superconductor Ba2ErCu3Oy

The oxygen content of Ba2ErCu3Oy was determined by both thermogravimetric measurement and iodometric titration analysis. Four distinct regions were found in the diagram of log PO2 -1/T plots. These regions were proposed to correspond to: the first orthorhombic phase (OI), the second orthorhombic phase (OII), the tetragonal phase (T) and the coexistence of two phases. The partial molar enthalpy of oxygen, ΔO2 , was obtained as -194±6 kJ/mol for the OI phase, -166±4 kJ/mol for the OII phase and -142+4 kJ/mol for the T phase. A pseudobinary phase diagram was proposed based on the log PO2 -1/T plots, quenching investigation and high-temperature X-ray diffraction analysis.

Oxygen-deficient and ordered perovskite-type solid-solution system Ba1+xBi1−xOy(0 ≦ x ≦ 0.5, 3.00 ≧ y ≧ 2.75)

A new oxygen-deficient and ordered perovskite-type solid-solution system Ba1+xBi1−xOy(0 ≦ x ≦ 0.5, 3.00 ≧ y ≧ 2.75) was synthesized, with the estimated ionic configuration Ba(Ba2+xBi3+3.5−1.5x−yBi5+−3+0.5x+y)(Bi5+0.5)Oy. The lattice parameters and mean valence of bismuth in the samples annealed in one atmosphere of oxygen at 773 K were determined by the powder X-ray diffraction method and iodometric titration method, respectively. Samples with the compositions 0 ≦ x ≦ 0.05, 0.10 ≦ x ≦ 0.15, 0.20 ≦ x ≦ 0.425, 0.45 ≦ x ≦ 0.475, and 0.475 < x ≦ 0.50 were found to be monoclinic, rhombohedral, cubic, tetragonal, and cubic, respectively. Oxygen deficiency was observed in the entire range of the composition; the ordering of the oxygen vacancies was confirmed in the range X ≧ 0.45.

Synthesis of BaTlO2.5 with oxygen-deficient perovskite structure

Abstract A new oxygen-deficient perovskite BaTlO 2.5 was successfully prepared by a solid-state reaction technique. Orthorhombic unit cell dimensions refined from a powder diffraction pattern are a = 0.6257 ± 0.0001, b = 0.6038 ± 0.0001, and c = 1.7232 ± 0.0003 nm. The BaTlO 2.5 was found to be a semiconductor.

Influence of Annealing Condition on the Superconducting Behavior of High-Tc Oxide (Ba2Y)Cu3O7-x

The influence of annealing condition is presented for high Tc superconducting oxide (Ba2Y)Cu3O7-x via investigation of the structure and electrical resistivity. It is found that Tc depends strongly on the annealing temperature and annealing time. Tc is higher for the sample with the greater orthorhombic distortion, that is, the greater difference between the lattice constant a and b.