The Role of Oxygenation on Superconducting Properties of RE3Ba5Cu8O18 (RE=Y, Sm and Nd) Compounds

This study reports the effects of oxygenation on new high-T _c cuprates having the structure of RE₃Ba₅Cu₈O₁₈ (RE=Y, Sm and Nd) and T _c (on) values of 96.5–97.5 K. The measurements have shown that excess oxygenation has no important contribution to the T _c (on) values, but it improves T _c (off) values significantly. From these three systems, RE = Nd is the most sensitive one to the oxygenation. Its T _c (off) value increases by 13 K (from 78 K to 91.1 K) with post-annealing.     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

An Investigation of Y<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18</Subscript> Doping with Ag Nanoparticles and Its Application as Superconductor

Y₃Ba₅Cu₈O₁₈ superconductors were prepared through a standard solid-state reaction and the structural properties of the samples were studied through XRD and the Rietveld refinement method. The effect of silver nanoparticles doping on the Y₃Ba₅Cu₈O₁₈ superconductors was studied as well. It is known that the size of nanoparticles is increased during aging. Therefore, two batches of samples with 1 and 2 wt% of Ag nanoparticles and the size range of 30, 200, 500, 700, 800, and 1000 nm were prepared. After preparing the samples and observing the Meissner effect, the crystallography, critical current density, critical temperature, magnetic susceptibility, SEM, and EDX experiments of the samples were carried out. The results of the critical current density measurements showed that the sample with 2 wt% Ag nanoparticles and the size of 700 nm has the maximum current density. In both batches of samples, increasing the nanoparticle size to 700 nm led to an increase in the critical current density. The crystallography studies showed that silver nanoparticles do not insert into the superconductor’s frame. Actually, they are placed in the samples as a distinct phase.     

Superconductivity,Magnetism, and Magnetoresistancein RuSr<Subscript>2</Subscript>R<Subscript>1.4</Subscript>Ce<Subscript>0.6</Subscript>Cu<Subscript>2</Subscript>O<Subscript>10–δ</Subscript> (R = Eu,Sm)

Samples with nominal compositions RuSr₂R_1.4Ce_0.6Cu₂O_10–δ (R = Eu, Sm) were synthesized and their superconducting (SC) and magnetic properties were compared. A coexistence of AFM and FM ordering below the FM transition temperature was established in the two samples. It was shown that their SC properties are affected by a spontaneous vortex phase (SVP). The first critical fields of the two samples were calculate — H_cl≈ 70 Oe for R=Eu and 60 Oe for R=Sm. It was shown that the improved superconducting properties of the Sm-containing sample do not affect its FM behavior. A sizable magnetoresistance was observed in the two samples at T<T _c.     

Microwave dielectric properties of Ba<Subscript>5</Subscript>Nb<Subscript>4</Subscript>O<Subscript>15</Subscript> ceramic by molten salt method

Ba₅Nb₄O₁₅ powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in a certain proportion. Subsequent calcination of the mixtures led to Ba₅Nb₄O₁₅ powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba₅Nb₄O₁₅ powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba₅Nb₄O₁₅ ceramics with good microwave dielectric properties of ε_r = 39.2, Q × f approximated as 27,200 GHz and τ _f  = 72 ppm/°C have been obtained.     

Sol-Gel Synthesis and Photoluminescence of RE<Subscript>x</Subscript>Lu<Subscript>2-<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> (RE = Y,Gd) Nanophosphors

RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) nanophosphors with x = 0.4, 1.0, and 1.6 were synthesized using rare-earth salicylate coordination polymers as precursors for the luminescent species RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) composed of polyethylene glycol both as a dispersing medium and fuel. Their particle sizes were around 100 nm as determined by scanning electron microscopy and x-ray diffraction.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 706–710.Original English Text Copyright © 2005 by Zhou, Yan.This article was submitted by the authors in English.     

Influence of annealing times on morphological characteristics of ceramic thin films by RF-magnetron sputtering using Zn-enriched (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramic target

The BaO–SrO–ZnO–Nb₂O₅ ceramic thin films have been deposited by radio frequency (RF) magnetron sputtering, using a Zn-enriched (Ba_0.3Sr_0.7) (Zn_1/3Nb_2/3)O₃ target, followed by annealing in O₂ atmosphere at 1,200 °C for 15, 30, 45, and 60 min. The results show that the surface morphologies of samples are crack-free and compact with well-crystallized structures. Grain sizes of thin films annealed at different times increase with the increasing annealing times, and when the annealing time is of 45 and 60 min, the grains change from spherical shape to columnar shape. RMS values of the thin films decrease with the increase in the annealing times from 15 to 30 min, while the RMS values increase with the increase in the annealing times from 30 to 60 min.     

Effect of Nano-Oxides Addition on the Mechanical Properties of (Cu<Subscript>0.5</Subscript>Tl<Subscript>0.5</Subscript>)-1223 Phase

In this study, superconducting samples of type Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ ,(Cu_0.5Tl_0.5)-1223, added by SnO₂ and In₂O₃ in nano-scale were prepared by a solid-state reaction technique. The concentrations of both SnO₂ and In₂O₃ were varied from 0.0 to 1.0 wt.% of the total sample’s mass. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination, respectively. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature (T _c0). An increase in T _c is observed up to x=0.6 wt.% for (SnO₂) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ , followed by a systematic decrease with increasing nano-SnO₂ addition for x>0.6 wt.%. While, for (In₂O₃) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ the T _c is slightly changed with x. Room temperature Vickers microhardness measurements were carried out at different applied loads (0.49–2.94 N) for the study of the mechanical performance of the prepared samples and examination of the effect of different nano-oxides addition on the microhardness of (Cu_0.5Tl_0.5)-1223 phase. Furthermore, the true microhardness values (H _o), for both additions, were evaluated through different models and their results were compared with those estimated from the experimental results in the plateau region. Also, some important mechanical parameters, such as Young’s modulus (E), yield strength (Y), fracture toughness (K) and brittleness index (B), were calculated for both additions. The results clarified that these parameters are strongly dependent on both the applied loads and the nano-oxides addition.     

A novel method to control oxygen stoichiometry and thermoelectric properties in (RE)BaCo<Subscript>2</Subscript>O<Subscript>5+<Emphasis Type="Italic">δ</Emphasis></Subscript>

Rare earth cobaltites of the type (RE)BaCo₂O_5+δ (RE = Y, Gd, Eu and Nd) were synthesized by solid state technique. A novel, fast quenching technique was used to tune the oxygen content in these compounds. Room temperature Seebeck and electrical resistivity measurements were used to infer the oxygen content. A maximum in the S and ρ was observed for all the compositions when δ value was close to 0·5.     

Synthesis and Superconductivity in Ba-doped (Ru,Cu)(Sr,Nd)<Subscript>2</Subscript>(Nd,Ce)<Subscript>2</Subscript>Cu<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">z</Emphasis></Subscript> Compounds

We prepared various (Ru_0.5Cu_0.5)(Sr_1.67−x Ba _x Nd_0.33)(Nd_1.34Ce_0.66)Cu₂O _z samples with varying Ba contents by x=0, 0.1, 0.2, 0.33, 0.5 and 0.835. X-ray diffraction revealed that the phase purity of the samples increases as the Ba-doping content increases and single- phase compounds could be obtained for samples with 0.1≤x≤0.33. Contrary to the Ba-free sample, superconductivity could be induced by partially substituting Ba for Sr and superconductivity with onset T _c of about 15 K is observed for the sample with x=0.2. The superconducting behavior of the Ba-doped samples is discussed in conjunction with thermoelectric power measurements.     

Effect of Nd substitution on structure and magnetic properties of Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet powders

The properties of light rare earth Nd substitution for heavy rare earth Dy in Dy₃Fe₅O₁₂ (DyIG) garnet ferrite have been studied. The Nd _x Dy_3–x Fe₅O₁₂ (x = 0, 0.25, 0.5, 0.75 and 1) (Nd:DyIG) garnet powders were prepared by sol–gel autocombustion followed by heat treatment. The structure and the magnetic properties of the annealed powders were measured with X-ray diffraction (XRD), the Fourier Transform Infrared (FT-IR) and the Physical Properties Measurement System (PPMS) techniques. The experimental results indicate that a single Nd:DyIG garnet phase structure can be obtained after the samples annealed above 800 °C. With the Nd substitution content increasing, the average lattice constants of the sample, the a−d super-exchange interaction strengthens and the magnetization of unit cell increase. The maximum saturation magnetization is 13.86 emu/g for x = 1, and coercive force is about 136 Oe, for x = 0.75. The reason of increasing in magnetization with Nd substitution is also discussed.     

Effect of Ba Substitution for Sr in the Pb-based 1212 Cuprate Containing Sulfur of (Pb<Subscript>0.75</Subscript>S<Subscript>0.25</Subscript>)Sr<Subscript>2</Subscript>(Y,Ca)Cu<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">z</Emphasis></Subscript>

We already reported on the synthesis of new Pb-based 1212 layered cuprates containing sulfur in the (Pb_0.75S_0.25)Sr₂(Y,Ca)Cu₂O _z system. There none of the samples showed superconductivity until after annealing under high O₂ pressure. More recently, we have discovered that the samples could be substituted by Ba for Sr up to x=0.6 in the composition of (Pb_0.75S_0.25)(Sr_2−x Ba _x )(Y_0.4Ca_0.6) Cu₂O _z . Then if the Ba-substitution is performed for Sr, some of the almost-single phase samples are found to show resistivity drops and magnetic anomalies without annealing under high O₂ pressure. Among the samples, a sample with the nominal composition of (Pb_0.75S_0.25)(Sr_1.5Ba_0.5)(Y_0.4Ca_0.6) Cu₂O _z is found to show the highest onset temperatures of a resistivity drop at about 35 K and a magnetic anomaly at about 31.5 K. These are higher than the highest values for the superconducting Ba-free sample of (Pb_0.75S_0.25)Sr₂ (Y_0.4Ca_0.6)Cu₂O _z which was annealed under high O₂ pressure.     

The Effects of Sb Substitution on Structural Properties in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> Superconductors

In this study, the effects of partial Sb³⁺ ion substitutions for the Y sites and the Cu sites on the superconducting properties of YBa₂Cu₃O _y (Y123) ceramic superconductors were investigated. The samples were prepared by the conventional solid-state reaction method and the properties of the samples were investigated by means of X-ray diffraction, AC magnetic susceptibility measurements, scanning electron microscope, and energy dispersive X-ray analysis. The critical temperatures were determined to be in the range of 80–92 K for both Systems I and II. It was found that Sb-addition leads to the formation of the non-superconducting YBa₂SbO₆ phase, which has a negative effect on the critical temperature, since the highest critical temperature was measured for pure Y123. However, the increasing substitution level has a negligible effect on the X-ray diffraction analysis peak intensities of the superconducting phases. In addition, SEM images showed that Sb substitution decreases the grain size and modifies the microstructure development, which makes the samples denser.     

Magnetic and Superconducting Properties of Doped and Undoped Double Perovskite Sr<Subscript>2</Subscript>YRuO<Subscript>6</Subscript>

We report here SQUID (magnetization) measurements, along with supporting specific heat, Raman, SEM (scanning electron microscope), EDX (energy dispersive X-ray) and XRD (X-ray diffraction) measurements, on Cu-doped and undoped double perovskite Sr₂²⁺Y³⁺Ru⁵⁺O₆^2-\mathrm{Sr}_{2}^{2+}\mathrm{Y}^{3+}\mathrm{Ru}^{5+}\mathrm{O}_{6}^{2-} (abbreviated as SrY2116) system grown as single crystal using high-temperature solution growth technique. These measurements show the undoped system to be a nonmetallic (insulating) spin glass (SG) and the ∼5–30% Cu-doped (i.e. Cu-concentration/(Cu + Ru-concentration) ∼5–30%) system to be a spin glass superconductor (SGSC) with T _c (critical temperature) ∼28–31 K and superconducting volume fraction, f _sc∼2.2–9%. To mention, similar measurements done on undoped and Cu-doped BaY2116 and BaPr2116 systems show for them the same (SG, SGSC) behaviors. However they show a decrease in T _c and f _sc when diamagnetic Y³⁺ ions are replaced by Pr³⁺ spins, presumably due to enhanced internal pair breaking, and also decreased Cu–O–Cu overlap, owing to Pr³⁺ presence; these phenomena are known to exist in the Pr123 compound, PrBa₂Cu₃O_7−δ (δ∼0), due to ∼10% of Pr³⁺ ions having tendency to occupy Ba²⁺ sites. Measurements done on undoped and Cu-doped SrHo2116 show similar SG and SGSC properties. Further, the undoped and Cu-doped SrY2116 crystals grown by hydrothermal growth technique (i.e., grown using lower temperature and high pressure) show same behaviors. From these investigations it can be said that the undoped Ru-double perovskites (A₂BB′O₆, B′=Ru) are SG systems and that Cu-doped Ru-double perovskites (A₂BB′O _δ , δ∼6, B′=Ru_1−x Cu _x , 0<x≲0.3) are SG superconductors (SGSCs). Results are discussed.     

YBCO-Buffered NdBCO Film with Higher Thermal Stability in Seeding REBCO Growth and Recycling Failed Bulk YBCO Superconductors

In this work, we report a strengthened superheating effect caused by a buffering YBa₂Cu₃O _y (YBCO or Y123) layer in the Nd_1+x Ba_2?x Cu₃O_7?y (NdBCO or Nd123) thin film with MgO substrate (i.e., NdBCO/YBCO/MgO thin film). In the cold-seeding melt-textured (MT) growth, the NdBCO/YBCO/MgO film presented an even higher superheating level, about 20 °C higher than that of nonbuffered NdBCO film (i.e., NdBCO/MgO film). Pole figure (X-ray Φ-scan) measurement reveals that the NdBCO/YBCO/MgO film has better in-plane alignment than the NdBCO/MgO film, which may be the main origin of the enhanced thermal stability. Using this NdBCO/YBCO/MgO film as the seed and under a maximum processing temperature (T _max) up to 1120 °C, we succeeded in growing various RE_1+x Ba_2?x Cu₃O_7?y (REBCO, RE=Gd, Sm, Nd, RE refers to rare elements) bulk superconductors and recycling the failed REBCO (RE=Y) bulks in a simple and feasible process.     

Effect of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on microstructure,electrical properties,and aging behavior of ZnO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–MnO<Subscript>2</Subscript>–CoO varistor ceramics

The microstructure, electrical properties, and aging behavior of ZnO–V₂O₅–MnO₂–CoO–Dy₂O₃ varistor ceramics were investigated for different contents of Dy₂O₃. The microstructure consisted of ZnO grain as a main phase and secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, and DyVO₄. The average grain size increased from 7.6 to 10.1 μm and the sintered density slightly increased from 5.53 to 5.57 g/cm³ with the increase of Dy₂O₃ content. The varistor ceramics added with 0.05 mol% Dy₂O₃ exhibited the most nonlinear properties, with nonlinear coefficient of 30, and the highest stability against DC-accelerated aging stress. The Dy₂O₃ acted as an acceptor due to the decrease of donor density in the range of 2.73 × 10¹⁸/cm³ to 1.28 × 10¹⁸/cm³.     

Morphology and structure of rare earth borate (REBO<Subscript>3</Subscript>) synthesized by glycothermal reaction

The glycothermal reaction of the rare earth (RE) acetates with trimethoxyborane (RE/B = 1) at 315 °C for 2 h yielded REBO₃ for Tm, Yb and Y. For Gd–Er, REBO₃ was contaminated with amorphous products. Mixtures of RE(OAc)O, REBO₃ and amorphous products were obtained for Sm and Eu, while only RE(OAc)₂(OH) was obtained for La. The space group of the REBO₃ crystal obtained from Sm–Er and Y was P6₃/m, and mixture of REBO₃ crystals with P6₃/m and R c were obtained for Tm and Yb. Prolonged reaction time (6 h) yielded REBO₃ without contamination of the amorphous product or RE(OAc)O for Eu–Yb and Y. For the reaction of yttrium acetate and trimethoxyborane with Y/B ratio of 1/3–3/1 for 2 h, YBO₃ was only the binary oxide detected. The YBO₃ particles were spheroidal with a diameter of 1 μm. The selected area electron diffraction of a whole particle indicated that the each particle is a “single crystal” of YBO₃ grown from one nucleus.     

Crystal chemistry and domain structure of rare-earth doped BiFeO<Subscript>3</Subscript> ceramics

Bi_(1−x)RE _x FeO₃ (BREF100x, RE = La, Nd, Sm, Gd) has been investigated with a view to establish a broad overview of their crystal chemistry and domain structure. For x ≤ 0.1, the perovskite phase in all compositions could be indexed according to the rhombohedral, R3c cell of BiFeO₃. For Nd and Sm doped compositions with 0.1 < x ≤ 0.2 and x = 0.15, respectively, a new antipolar phase was stabilised similar in structure to PbZrO₃. The orthoferrite, Pnma structure was present for x > 0.1, x > 0.15, and x > 0.2 in Gd, Sm, and Nd doped BiFeO₃, respectively. For x > 0.2, La doped compositions became pseudocubic at room temperatures but high angle XRD peaks were broad and asymmetric. These compositions have been indexed as the orthoferrite structure. It was concluded therefore that the orthoferrite phase appeared at lower values of x as the RE ferrite, end member tolerance factor decreased. However, the compositional window over which the PbZrO₃-like phase was stable increased with increasing end member tolerance factor but was not found as single phase in La doped compositions at room temperature. On heating, the PbZrO₃-like phase in BNF20 transformed to the orthoferrite, Pnma structure. T _C for all compositions decreased with decreasing A-site, average ionic polarizabilty and tolerance factor. For compositions with R3c symmetry, superstructure and orientational, and translational (antiphase) domains were observed in a manner typical of an antiphase-tilted, ferroelectric perovskite. For the new PbZrO₃-like phase orientational domains were observed.     

Synthesis of New Pb-Based 1222 Cuprates Containing Phosphorus, (Pb0.75P0.25)Sr2(RE2–x–y Ce x Sr y )Cu2O z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb_0.75P_0.25)Sr₂- (RE_2–x–y Ce _x Sr _y )Cu₂O _z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single phase samples are obtained for 0.5≤x≤1.0 and y=0.1 in the cases of RE = Nd, Dy, Ho, Er, Tm, Yb and Y, while for 0.3≤x≤1.0 and y=0.1 in the cases of RE = Sm, Eu and Gd. The samples crystallize in a tetragonal lattice, the lattice parameters a and c are decreasing with the decrease of the ionic radius of the RE element. Even after annealing under 143 atm O₂ atmosphere at 400 °C, almost all the samples with the common values x=0.5 and y=0.1 are semiconductors with a transport process followed by three-dimensional variable range hopping. However, the samples of RE = Sm, Eu and Gd, which are of almost single 1222 phase, even for x=0.3 and y=0.1, show superconductivity with the onsets at about 25 K, 20 K and 22 K, respectively. Through this study, we find very important procedure for discovery of new superconducting 1222 compound.     

Giant dielectric and electrical properties of sodium yttrium copper titanate: Na<Subscript>1/2</Subscript>Y<Subscript>1/2</Subscript>Cu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

The electrical properties and dielectric response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic prepared by conventional solid-state reaction method and sintered at 1,090 °C for 5 h were investigated as functions of frequency and temperature. Main phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ with CaCu₃Ti₄O₁₂-like crystallographic structure and CuO secondary phase were observed in the X-ray diffraction pattern. Abnormal grain growth was observed just as observed in CaCu₃Ti₄O₁₂ ceramics. The Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic exhibits a high ε′ of ~2.04 × 10⁴ at 20 °C and 1 kHz and low tan δ (with the minimum 0.080 at 5 kHz). Impedance spectroscopy analysis reveals that Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. Giant ε′ response in Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramic is therefore attributed to an internal barrier layer capacitor effect.