A new family of Pb based 1222 cuprates (Pb,Mg)(Sr,R)2(R′,Ce)2Cu2Oy (R,R′:rare-earth element)

A series of new Pb based 1222 cuprates, (Pb,Mg)(Sr,R)₂(R′,Ce)₂Cu₂O_y, has been reported in this paper. The structure of the compounds has been determined by the powder X-ray diffraction method. It crystallizes in a tetragonal lattice with space group I4/mmm and lattice parameters a = 3.818 Å and C = 29.085 Å for R,R′=Nd,Dy. XRD results show that the structure is isostructural with (Pb,Cu)(Sr,R)₂(R′,Ce)₂Cu₂O_y with the (Pb,Mg)O layer replacing the (Pb,Cu)O layer. Resistivity measurements show that the compounds are semiconductors under the present experimental conditions.     

Electronic structure of (Nd, Ce)2(Ba, Nd)2Cu3Oy

The dependence of T_c on oxygen content was determined for (Nd_0.67Ce_0.33)₂(Ba_0.67Nd_0.33)₂Cu_3.01O_y. It was found that superconduction appears in a range of y=9.10−9.16 and that T_c is enhanced remarkably by the increase of oxygen content. In an oxygen content range where superconduction appeared, the Ce valence was nearly +4 and the Cu valence changed from 2.31 to 2.33. The conductivity was measured in a wide temperature range between T_c and 1200 K as a function of oxygen partial pressure. The high-temperature conductivity increased with increasing oxygen content. It was found that both carrier concentration and mobility are increased with oxygen content. The conduction at low temperatures was semiconductor-like, and increased with increasing oxygen content, where the energy gap E_A-E_V between acceptor level and top of filled band approached zero.     

Synthesis and properties of Hg0.7Pb0.3(BaSr)2Ca2Cu3Oz superconductors

We have synthesized Hg(Pb)-1223 with substitutions of Sr for Ba, i.e. Hg_0.7Pb_0.3Ba_2−xSr_xCa₂Cu₃O_z (x = 0.0–2.0) by the ampoule method. The spray-drying method and thermal decomposition under vacuum were applied for the preparation of homogeneous precursors. Samples with T_c = 110–128 K were obtained without oxygen annealing. We found that substitution of Ba by Sr remarkably relaxed the requirements on the precursors preparation and allowed their handling under ambient conditions.     

(Tl, Pb, Cu)Sr2(Tl, Pb, Cu)2Cu2O8−δ: a nonsuperconducting Tl-1222 cuprate with both heavy atom single and oxygen depleted double layer motifs

An account is given of the synthesis and structural investigation of a newly discovered tetragonal (Tl, Pb, Cu)Sr₂(Tl, Pb, Cu)₂Cu₂O_8−δ compound (Tl-1222^* phase) with both (Tl, Pb, Cu)O single and oxygen depleted (Tl, Pb, Cu)₂O_x double layer motifs, space group I4/mmm, lattice parameters a=3.8405(2), c=29.2536(5) Å, and D_x=7.46 g cm⁻³. Micaceous and highly reflecting black single crystals of 1 mm×1 mm×3–5 μm size were obtained from a Tl₂O₃- and CuO-rich partial melt. The as-grown compound is nonsuperconducting. The very thin crystals are extremely liable to bend out of shape. Deterioration could not be observed within the period of a year under ambient conditions. The complex crystal structure has been solved using single crystals. We take note of the similarity of the unit cell dimensions to superconducting (Tl, Cu)₂Ba₂(Ca, Tl)Cu₂O₈ (Tl-2212 phase) with TlO double rocksalt layers, and compare crystal-chemical details of similar compounds. Apart from the possibility of obtaining superconducting properties by suitable doping, the mechanical properties of the new material are very attractive from the point of view of its use as highly scattering composite layers of an X-ray monochromator.     

Superconductivity at 27 K in Nb-1222 cuprate: NbSr2(GdCe)2Cu2Oy

Samples of NbSr₂Gd_2−xCe_xCu₂O_y have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49<x<0.51 that has TaSr₂ (NdCe)₂Cu₂O_y structure [1], the cell parameters being a=3.8669±0.0046 Å and c=28.742±0.0048 Å. Superconductivity was found by resistance measurements in the sample of NbSr₂Gd_1.5Ce_0.5Cu₂O_y: the onset transition temperature is 27.4 K, and zero resistance appears at approximately 13 K.     

Phase transition and superconductivity of (Ba,Sr,La)2YCu3Oz (z>6.9)

A series of (Ba,Sr,La)₂YCu₃O_z (z>6.9) samples is studied to elucidate the relationship between structure, cation composition and oxygen content. The concentration of La plays an important role in the orthorhombic to tetragonal phase transition. The tetragonal structure is stabilized by increasing oxygen content and decreasing average ionic radius of cations on the Ba site. The phase transition is explained in terms of the random distribution of CuO₅ pyramids in the BaO–CuO_x slab. Superconductivity does not depend significantly on the phase transition.     

A new layered cuprate superconductor: GaSr2(Y, Ce)2Cu2O9−δ

A new layered cuprate compound with a nominal composition of GaSr₂Y_2−xCe_xCu₂O_9−δ has been prepared. It crystallizes in a tetragonal lattice with cell parameters: a = 3.812 Å, c = 28.16 Å. The structure of the compound belongs to the same family of 1222 phase and is derived from that of GaSr₂LnCu₂O₇ by replacing the single Ln³⁺ layer with a double fluorite (Y, Ce)₂O₂ layer. Like other parent cuprate compounds of superconductors, the as-prepared samples showed antiferromagnetic and semiconducting behavior. After treatment under high oxygen pressure, the samples exhibited bulk superconductivity with transition temperatures between 12–14 K.     

Fabrication, microstructure and critical current density of screen-printed Ag-(Bi, Pb)2Sr2Ca2Cu3Ox superconducting tapes

The influence of the sintering conditions on the microstructure and critical current density J_c has been studied on screen-printed Ag-(Bi, Pb)₂Sr₂Ca₂Cu₃O_x tapes with a ceramics mono-layer core. Three kinds of fabrication processes, which consist of a combination of cold working (rolling and/or pressing) and sintering, are applied. Four times repetition of pressing and sintering after the pre-sintering produces the highest c-axis alignment and achieves J_c= 1.5 × 10⁴ A/cm² (77 K, 0 T). The J_c versus θ data with an angle θ between B and the c-axis elucidate the relation between the anisotropy ratio γ=J_c(Bc)/J_c(B|c and the half-height angular width Δθ of a peak for Bc. This is related to both grain alignment and the J_c value. An increase in J_c, which comes from an improvement for grain alignment, enhances γ and narrows Δθ. The J_c versus θ data are fitted to the expression J_c(B, θ)=J _c(B, 90°)/[(γ−1)|cos θ|ⁿ+1] by regarding both γ and n as adjustable parameters. Fabrication of screen-printed tapes with multilayers (1≤N≤5) is presented, where the critical current increases from 8.0 A to 30.2 A at 77 K and 0 T as N increases.     

Effect of lead addition to Bi-based 2222 superconducting cuprates Bi2-xPbxSr2(Y, Ce)2Cu2O10+δ

Bi_2-xPb_xSr₂(Y, Ce)₂Cu₂O_10+δ, a new family of lead containing Bi-2222 compounds has been synthesized and effects of annealing in high pressure of oxygen studied. Lead-free Bi₂Sr₂(Y, Ce)₂Cu₂O_10+δ synthesized under flowing oxygen is known to be non-superconducting, but annealing under high oxygen pressure (100 bar) at 500°C, induced superconductivity with T_c=25 K. On substitution of lead (x>0.4), the superconductivity appears even in samples synthesized under flowing oxygen (1 bar). T_c increases with oxygen annealing pressure for all compositions, and it also increases with Pb content at a given oxygen pressure. These findings are discussed.     

Synthesis and superconductivity of (Pb0.5Cd0.5)(Sr0.9R0.1)2(R′0.7Ce0.3)2Cu2Oy

New Pb based layered superconducting cuprates (Pb_0.5Cd_0.5)(Sr_0.9R_0.1)₂(R′_0.7Ce_0.3)₂Cu₂O_y with (R,R′) = (Eu,Gd), (Eu,Dy) and (Nd,Gd), have been successfully synthesized. The structure of (Pb,Cd)(Sr,Eu)₂(Gd,Ce)₂Cu₂O_y is determined using XRD data. The X-ray powder diffraction pattern can be indexed by the tetragonal structure with lattice parameters a = 3.8250 Å, C = 29.2235 Å and a space group of I4/mmm. The effects of synthesis conditions on (Pb,Cd)(Sr,Eu)₂(Gd,Ce)₂Cu₂O_y are studied and a T_c(onset) of 26 K is obtained by resistance measurements. It is isostructural to the superconductor (Pb,Cu)(Sr,Eu)₂(Eu,Ce)₂Cu₂O_y.     

Structural and magnetic properties of Ce(Cu,Ni)2 pseudobinary phases

The stability of the pseudobinary phases obtained by partial substitution of Ni with Cu, Ag or Au in the cubic Laves phase CeNi₂, or by partial substitution of Cu with Ni in the orthorhombic compound CeCu₂ has been investigated. No solid solubility of Cu, Ag and Au in the CeNi₂ cubic lattice could be detected. In contrast, pseudobinary orthorhombic phases, corresponding to the formula CeCus_2?xNi_x, exist over the range x = 0 to 1. For these phases, crystal structures and magnetic properties have been determined. In every case, the electronic configuration of cerium appears to be unaffected to the Ni content, and corresponds to the trivalent state. The Ni atoms are in a non-magnetic state. The magnetic susceptibility of CeCu₂ in the region from 530 to 900 K shows anomalous behaviour, which should be due to a metamagnetic transition.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Proper composition for superconductivity in Pb(Ba, Sr)2(Y, Ca)Cu3O7

Superconductivity and composition analysis of PbBaSr(Y, Ca)Cu₃O_y with fixed ratio of Sr/Ba = 1 were studied. Synthesis condition and superconductivity of Pb(Ba, Sr)₂(Y, Ca)Cu₃O_y with various ratio of Sr/Ba and Ca/Y were also studied. It was found that T_c increased with increasing Ca concentration, and that Sr-rich specimens allowed to contain more Ca. PbBa_0.8Sr_1.2Y_0.6Ca_0.4Cu₃O₇ showed superconductivity with zero-resistance temperature of 42 K, which was higher than PbBaSrY_0.7Ca_0.3Cu₃O₇ with maximum Ca content for Sr/Ba = 1. Decrease in averaged ionic radii of Ba and Sr in Sr-rich compositions would be favorable for the contraction of Cu-O bonds by hole-doping via Ca substitution for Y.     

Scanning tunneling and atomic force microscopy study of the misfit layer compounds (LaS)1.14(NbS2)n (n=1, 2) and [(Pb,Sb)S)]1.14NbS2

The misfit layer compounds (LaS)_1.14(NbS₂)_n (n=1, 2) and [(Pb,Sb)S]_1.14NbS₂ were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In these compounds the NaCl-type double MS (M=La, Pb, Sb) layers (Q layers) alternate with the NbS₂ layers (H layers) made up of NbS₆ trigonal prisms. It was possible to record AFM and STM images for only the H layers for (LaS)_1.14(NbS₂)_n, but for both the H- and Q-layers for [(Pb,Sb)S]_1.14NbS₂. Partial and total electron density plots of the H and Q layers were calculated to interpret the observed STM and AFM images. The bright spots in the STM and AFM images of the H layer correspond to S atoms, and those of the Q layer to Pb and Sb atoms. The STM images for the Q layers of [(Pb,Sb)S]_1.14NbS₂ suggest that a short-range ordering of the Pb and Sb atoms occurs in the (Pb,Sb)S sheets of the Q layer.     

(Bi,Pb)2Sr2Ca2Cu3Oy单相样品的超导电性与载流子浓度

对(Bi,Pb)₂Sr₂Ca₂Cu₃O_y单相样品进行不同条件下的热处理,通过X射线衍射、电阻-温度关系、交流磁化率,以及Hall系数等测量,发现样品均具有较好的单相性,随着热处理条件的变化,其超导转变中点温度(T_c)有规律地分布在100—110K之间,T_c随载流子浓度(n_H)的增加而升高。实验结果表明,热处理条件对样品的相结构、超导 关键词：     

metamagnetic behavior of linear chain pyridine compounds: Co(Pyridine)2Cl2, Fe(Pyridine)2Cl2, Fe(Pyridine)2(NCS)2 and Ni(Pyridine)2Cl2

Magnetic phase transitions in the pyridine (pyr) compounds Co(pyr)₂Cl₂, Fe(pyr)₂Cl₂, Fe(pyr)₂(NCS)₂ and Ni(pyr)₂Cl₂ have been observed at applied magnetic fields of ～0.7, 0.7, 1.1 and 2.7 kG respectively. These low field phase transitions are observed in the Fe and Ni compounds at T = 4.2 K, and in the Co compound at T < 3K, and are consistent with metamagnetic behavior. Magnetic saturation is not achieved in any of these compounds for fields of 60 kG, reflecting high anisotropy.     

Preparation and luminescent properties of phosphor MGd2(MoO4)4: Eu (M=Ca, Sr and Ba)

Intense red emitting phosphors MGd₂(MoO₄)₄: Eu³⁺ (M=Ca, Sr and Ba) have been synthesized by the simple sol-gel technique. The formation processes and the phase impurity of phosphors are characterized by thermogravimetry-differential thermal analysis (TG-DTA) and power X-ray diffraction (XRD). The narrower size distribution and the regular shape of the phosphor particles are also measured by Field emission scanning electronic microscopy (FE-SEM). Photo-luminescent properties of the phosphors are performed at room temperature. Their excitation spectra present strong absorption at 395 nm near-UV light and 465 nm blue light, which match well with commercial LED chips. The phosphors exhibit satisfactory and excellent red light dominated by 616 nm and their photoluminescence intensity is about 3-4 times stronger than that of phosphor YAG under the 465 nm excitation. In addition, the optimal concentrations of Eu³⁺ for phosphors MGd₂(MoO₄)₄ (M=Ca, Sr and Ba) have also been determined.     

The formation mechanism of Bi2Sr2Ca2Cu3Ox superconducting phase

The mechanism and dynamic model of the formation of 2223 phase are presented and verified in the paper. It reveals that with the solubilization of part of the 2212 phase, 2223 phase is formed by the reaction being carried out according to a nucleation and growth mechanism in the presence of liquid phase, which conforms to the JMA dynamics equation. The addition of a little 2223 phase as nucleator, regrinding and resintering can promote the formation of 2223 phase. But the quick formation rate of 2223 phase may lead to irregularity of the 2223 phase structure, which degrades its electric and magnetic properties, while annealing treatment can improve its superconductivity.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

T*相超导体(Bi,Sr)2(Y,Ce)2Cu2Oy的性质研究

研究了T^*相超导体（Bi，Sr）₂（Y，Ce）₂Cu₂O_y的成相规律，发现缓冷对T^*相单相样品的制备是有利的．淬火样品的主相物质为Ce₂Y₂O₇，完全不含T^*相结构．在室温到熔化温度的范围，热分析未观察到结构相变．在240—460℃，相对每个Cu原子超导体失氧约0.1个氧．氧气中烧结并缓冷到室温的样品在30K出现零电阻现象 关键词：