Studies on Characteristic of Infrared Spectra of Superconductor Bi-Sr-Ca-Cu-O System

Abstract

We made the superconductor of Bi₂Sr₂CaCu₂O_γ by the solid state reaction. According to the results of measurement by infrared spectrophotometer with the varying of wave number from 4000 to 400 cm^?1. We discovered three infrared absorption peaks at room temperature, i.e., peak A₁ at 500–550 cm^?1, peak A₂ at 800–840 cm^?1 and peak A₃ at 1370–1420 cm^?1. We find that peak A₁ is due to impure phase, peak A₂ is related with the crystal structure and peak A₃ is caused by the vibration of the atom layers of calcium.     

Critical current densities of high pressure oxygen sputtered thin films of YBa2Cu3O7−x by non-resonant rf absorption method

The critical current densities (J _c) have been measured at 77K in high pressure oxygen sputtered thin films of YBa₂Cu₃O_7−x superconductor using the non-resonant rf absorption technique. High values ofJ _c (∼ 10⁵ A/cm²) are observed in these relatively large area (∼ 1·2 cm²) films.     

Electrical resistivity and critical temperature of Bi-based High-TC superconductors to 1 GPa

Abstract

We have measured the electrical resistance R of a sintered, two-phase, high-T_C superconductor with the nominal composition BiSrCaCu₂O_x, as a function of T and p. We find d(lnR)/dp ? -0.06 GPa^?1 at 295 K, while dT_C/dp is 2.5 K/GPa for the phase with T_c ? 76 and 2 K/GPa for that with T_C ? 106 K.     

Letters to the editor

Abstract

Optical absorption spectra of TeO₂ crystals, irradiated at room temperature by up to 2·10¹⁸ cm^?2 10-MeV electrons and subsequently annealed to 575K, are studied. The dependence of Urbach absorption edge parameters in TeO₂ on the electron beam fluence is discussed. The irradiation-induced near-edge broad (2.5–3.5eV) absorption band is shown to be related to oxygen vacancies, annealing at 475–525K.     

Critical current in silver clad Y-Ba-Cu-O superconducting wires

Silver clad wires of highT _c superconductor Y₁Ba₂Cu₃O_7−x have been fabricated through the powder metallurgy technique. The reacted wires show a midpointT _c of 84K. A critical current density of 26·4 A cm⁻² (77K, 0T) is obtained in these wires. The wires, however, turn complete normal only at a current density of 280 A cm⁻². The reasons for low critical current density obtained in these wires are discussed.     

Scaling analysis of phase transition in Hg-based superconductor

With the vibrating-reed technique, the internal friction (IF) Q⁻¹ is measured for sing-phase (Hg_0.66Pb_0.34)Ba₂Ca₂Cu₃O_8+x superconductor as a function of temperature at low applied magnetic field up to 0.5 T and as a function of frequency at normal state temperatures. An IF peak associated with flux motion can be found below T_C. The IF peak becomes higher and shifts towards lower temperature with increasing magnetic field. In addition an IF peak is found near 200 K. By scaling analysis we have demonstrated that the internal friction around the peak temperature can be collapsed into a single curve, indicating that the IF peak below T_C is originated from a phase transition associated with a vortex glass transition and a structural phase transition occurs at around 200 K in the superconductor.     

Coexistence of superconductivity and magnetic order in YBa2Cu4O8

⁵⁷Fe Mössbauer spectroscopy, magnetic susceptibility and powder x-ray-diffraction measurements were used to study superconductivity and magnetic order in YBa₂(Cu_1?xFe_x)₄O_8+δ. T_c is decreasing with x, disappearing for x>x_c≈0.04. For xc iron substitutes Cu, predominantly in the Cu(1) site exhibiting a single quadrupole Mössbauer spectrum at 90 K. For x>x_c magnetic order is observed in the Cu(2) site, T_N=380 (5) K for x=0.1 and H_eff (Cu(2), 4.2 K)=510(2) kOe. However, the most surprising discovery is that for x=0.025, for which T_c=27(2) K, the Fe in the Cu(1) site orders magnetically at T_N=30(2) K and H_eff (Cu(1), 4.2 K)=461(2) kOe. The coexistence and competition between superconductivity and magnetic order in the Cu(1) and Cu(2) sites in YBa₂Cu₄O₈ are discussed in terms of the previously observed phase diagrams for Y_1?xPr_xBa₂(Cu_1?yFe_y)₃O_z.     

Far-infrared probe of energy gap in LaO1−xFxFeGe compound

We report on the electrical resistivity and far-infrared reflectance measurements of LaO_1?xF_xFeGe samples. Furthermore, we introduce a new method to probe the energy gap and determine its value. The onset transition temperature was 22.8 K for x = 0.13, and a clear anomaly was observed at 90 K in the ρ(T) curve for x = 0.11 with T_c = 20.6 K. We clearly observed the phonon-suppressed feature in reflectance spectra where F-doping caused a strong suppression of a peak at 200 cm^?1. The energy gap above T_c, 2Δ = 2.10 meV, was determined from the measured spectra based on the changes in reflectivity by F-doping.     

Upper critical fields of superconducting Gd and Tm doped LaSn3: Effects of crystalline electric fields

The temperature dependence of the upper critical fields, H_c²(T), are presented for (La_1-xGd_x)Sn₃ and (La_1-xTm_x)Sn₃. For samples with nearly the same T_c, H_c²(T) of the Tm-doped LaSn₃ samples are always larger than those for the Gd-doped samples. The results are interpreted in terms of crystalline electric field splitting of magnetic levels of the Tm³⁺. Pure LaSn₃ is found to be a Type I superconductor.     

Double metal-insulator peaks and effect of Sm substitution on magnetic and transport properties of hole-doped La0.85Ag0.15MnO3

La_0.85−xSm_xAg_0.15MnO₃ (x=0−0.2) ceramics were prepared using the conventional solid-state synthesis method to investigate the effect of Sm³⁺ substitution on magnetic and electrical transport properties. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, T_c decreasing from 283 K (x=0) to 164 K (x=0.2) with increasing Sm³⁺. The observed slope in susceptibility, χ′ versus temperature curves below T_c indicates the possible presence of FM and AFM phases in the metallic region. In addition, a deviation from the Curie-Weiss law above T_c in 1/χ′ versus T curves indicates the existence of a Griffith's phase in the x=0.05−0.2 samples due to the Sm³⁺ ion substitution. The Griffith temperature, T_G was found to decrease from 295 K (x=0.05) to 229 K (x=0.2). Electrical resistivity measurements of the samples in zero field showed transition from metallic behavior to insulating behavior as the temperature was increased. For x=0, two metal-insulator, MI transition peaks were observed at T_p1=282 K and at T_p2=250 K. Both peaks shifted to lower temperatures with the increase in Sm³⁺. The relative resistivity of the first peak to the second peak decreases with increasing Sm³⁺ for x>0.05 while at x=0.2 the T_p1 peak was strongly suppressed. Magnetoresistance, MR was observed to weaken with Sm³⁺ substitution. The metallic region of the ρ(T) curve of the x=0−0.15 samples was fitted to the model of electron-electron and electron-magnon scattering while the insulating region was fitted to the variable range hopping, VRH model. The resistivity behavior indicated that the substitution of Sm³⁺ weakened the double exchange process and enhanced the Jahn-Teller effect. Our results indicated that the T_p1 peak is strongly related to the double-exchange mechanism while the T_p2 peak is suggested to originate from magnetic inhomogeneity.     

Investigation of impurity effects in La2?xSrxCu1?yMyO4 (M=Ga,Zn) by electronic specific heat

The electronic specific heat C_el was studied at T≤10K on Ga- and Zn-doped La_2−xSr_xCuO₄ (0.16≤x≤0.22). In pure La_2−xSr_xCuO₄ (0.16≤x≤0.22), the C_el at T<T_c contains only a T² component but no T-linear one, which is peculiar to a clean d-wave superconductor. Partial substitution of Ga or Zn for Cu changes the T²-term of C_el into a quite different one described by the sum of a T-linear and a nearly T³ term. The coefficient of the T-linear term, γ, markedly increases with Zn-or Ga-content. The λ/λ_N vs. T_c/T_co relation for Zn-doped samples with x≥0.2 is in good agreement with the theoretical curve for resonant impurity scattering in a d-wave superconductor, while those for Ga-doped samples and for Zn-doped samples with x<0.2 deviate slightly from the theoretical curve. Such a deviation will be discussed in relation to the change in the magnetic properties of the present system caused by impurity-doping.     

Ferroelectric properties of SrTiO3-PbTiO3 solid solutions

Dielectric properties of ceramic samples of Sr_1−x Pb_xTiO₃ solid solutions for x varying from 0 to 0.3 have been studied. The ferroelectric phase transition in this system has been established to persist down to x=0.005. Within the x values of 0.002 to 0.05, the ferroelectric transition temperature is shown to follow the relation T _c=A(x−x _c)^1/2, with A=440 K and x _c=0.002. Fiz. Tverd. Tela (St. Petersburg) 39, 714–717 (April 1997)     

Photoinduced IR absorption in WO 3 : determination of the polaron binding energy

Photoinduced IR absorption measurements are reported on WO₃. A photoinduced midinfrared small polaron peak centered at 4800 cm^-1 (0.59 eV) was observed. The data were analyzed in the framework of the photon-assisted small-polaron hopping theory and briefly compared to previously published infrared absorption measurements in WO₃ and photoinduced IR absorption measurements in high T _c cuprates. Received 20 April 2001 and Received in final form 13 July 2001     

Influence of Y2Cu2O5 nanoparticles doping on superconducting properties of YBa2Cu3O7-δ

ABSTRACT

The blue phase of YBa₂Cu₃O_{7- δ} (YBCO) family, Y₂Cu₂O₅ (Y202) nanoparticles were prepared and doped into (YBCO) superconductor and the effect of doping on critical current density and critical temperature was investigated. Y202 nanoparticles with particle sizes of 47, 107 and 206?nm were prepared by a sol–gel combustion method and added into the YBCO superconductor by 0.5–2?wt.%. XRD and scanning electron microscope measurements were used to characterize the samples. The measurement of critical current density at 77?K revealed that the doped superconductors had larger critical current density compared to the undoped superconductors. For a fixed dopant concentration, by increasing the size of nanoparticles, the J_c was increased. For the samples including 0.5?wt.% of nanoadditives, J_c was higher. The highest critical current density of 137?A/cm² was measured for the superconductors containing 0.5?wt.% of 206?nm Y202 nanoparticles. Also, by increasing the nanoparticles concentration, the T_c was reduced.     

Incommensurate magnetic structure and crystal field in ErNi2B2C Studied by 166Er Mössbauer spectroscopy and specific heat measurements

¹⁶⁶Er Mössbauer absorption spectra have been recorded in the superconductor ErNi₂B₂C (T _c = 10 K), in zero field and in the temperature range 1.4 K–40 K. The spectra in the magnetically ordered phase (T _N ? 5.5 K) are characteristic of an incommensurate magnetic structure with a maximum Er³⁺ moment of 8.2 μB. We show that the magnetic transition is first order, with a small temperature range where magnetically ordered and paramagnetic domains coexist. The analysis of the magnetic and quadrupolar hyperfine interactions below and above T _N suggests that the Er³⁺ ground doublet is close to |J = 15/2; J _z = ± 1/2 > and shows that there is a low lying (? 10 K) excited doublet. The measured Er³⁺ electronic relaxation rate 1/T₁ shows an anomaly at 10 K (T _c suggesting that the conduction electrons that are exchange coupled to the 4f spin take part in the formation of the superconducting state. We also present specific heat data for Er _x Y_{1 ? x} Ni₂B₂C and Er_0.2Lu_0.8Ni₂B₂C which also evidence a low lying doublet and from which we propose a modified (improved) Er³⁺ crystal field level scheme (0, 9, 62, 71, 73, 181, 212 and 216 K) where the energies of the higher levels are consistent with published neutron scattering data.     

Magnetic ordering on Yb3+ in YbBa2Cu3O7−x

The high critical temperature superconductor YbBa₂Cu₃O_7−x has been studied over the range 0.05 to 95K using ¹⁷⁰Yb Mössbauer absorption spectroscopy. Magnetic ordering occurs within the Yb³⁺ sublattice at 0.35K. The saturated magnetic moments are 1.7μ_B. At all temperatures the hyperfine parameters show the presence of distributions attributed to some disordering of the oxygen vacancies.     

London penetration depth and coherence peak in ammonia-intercalated fulleride superconductors

The compound (NH₃)_xNaRb₂C₆₀ (x ～ 1.6) has been studied by¹H nuclear magnetic resonance. The proton line shows no shift at any temperature, while lineshape analysis of the low-temperature (30 K) spectra reveals the presence of a Knight shift interaction of pure anisotropic nature, whose amplitude has been estimated. Relaxation measurements show a single-exponential recovery of the magnetization at all investigated temperatures and fields. A Korringa behavior is observed below 65 K and a clear Hebel-Slichter coherence peak is detected just below T_c. The London penetration depth can be estimated from the line broadening observed below T_c, which yields λ ≈ 825 nm.     

Quasi two-dimensional magnetic order of Tb3+ spins in Pb2Sr2Tb1−x Ca x Cu3O8 (x = 0 and 0.5)

Neutron diffraction experiments were performed to study the magnetic ordering of the Tb⁺³ sublattice in the high-T _c superconductor Pb₂Sr₂Tb_1?x Ca _x Cu₃O₈ (x = 0.5) and the undoped parent compound (x = 0). For the parent compound, a quasi two dimensional (2D) phase with a finite antiferromagnetic correlation along the c-direction and a three dimensional phase with ferromagnetic correlation along the c-direction were found. The coexistence of the two phases is likely to be related to structural imperfections such as stacking faults, strains, oxygen disorder or cation vacancies. The superconductor with a superconducting transition temperature of T _c = 71K exhibits a quasi 2D magnetic ordering of the Tb sublattice with a finite ferromagnetic correlation along the c-direction. The correlation lengths along the c-direction for the quasi 2D phases are 32 and 26Å for x = 0 and 0.5, respectively. The magnetic saturation moments are with 9.1 and 8.8 μ _B in excellent agreement with our mean-field crystal-field calculations. 2D short range correlation could be observed up to about 8T _N and is described by a Lorentzian distribution of magnetic intensity perpendicular to the 2D rod in reciprocal space.     

Electronic superconductor Pr2CuO4−x Fx: Magnetic correlations at high temperatures (150<T<600 K) according to 19F NMR data

The longitudinal and transverse relaxation rates of ¹⁹F nuclei in Pr₂CuO_4−x F_x (x=0.20) samples are measured at high temperatures (150 K<T<600 K). A feature is found in the temperature dependence of the relaxation rates at temperature T′≅300 K. The magnetic properties of the electronic superconductor Pr₂CuO_4−x F_x as a possible system with a stripe ordering of carriers and spins are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 328–332 (25 February 1997)     

Optical investigations of anisotropy of the conducting π-electron system in crystals of the organic superconductor (EDT-TTF)4[Hg3I8]1 − x

The polarized reflectance spectra of microcrystals of the new organic superconductor (EDT-TTF)₄[Hg₃I₈]_{1 ? x} (T _c = 8.1 K for x = 0.027; T _c = 7 K at 0.3 kbar for x = 0.019) have been investigated in the spectral region of 700–6000 cm^?1 (0.087–0.740 eV) at temperatures ranging from 10 to 300 K. A quantitative analysis of the spectra has been performed in the framework of the phenomenological Drude and Drude-Lorentz dispersion models, as well as in the framework of the theoretical “phase phonon” model that takes into account the interaction of free electrons with intramolecular vibrations. The effective mass of charge carriers m*, the width of the initial metallic π-electron band W, and the integral t of the electron transfer between the molecular π-orbitals of neighboring molecules have been determined. In the low-frequency range (700–1600 cm^?1), the vibrational structure associated with intramolecular vibrations of the EDT-TTF molecule has been revealed. It has been shown that the most intense feature (ω = 1330 cm^?1) of this structure is caused by the interaction of “quasi-free” electrons with intramolecular vibrations.