Non-doped Samples Research Articles

Fluctuation conductivity in the 110-K phase of Ni-doped (Bi,Pb)-Sr-Ca-Cu-O superconductors.

The fluctuation conductivity above ${\mathit{T}}_{\mathit{c}}$ was measured in (Bi,Pb)-Sr-Ca-(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$,${\mathrm{Ni}}_{\mathit{x}}$)-O superconductors having the 110-K phase. The temperature dependence of the paraconductivity can be described by a power law following Aslamazov-Larkin theory. For nondoped (x=0) samples, the conductivity data show a two-dimensional fluctuation of the order parameter, whereas Ni-doped samples show lower-dimensional fluctuations and reduced widths of the resistive transition. The critical exponent of the power law and its amplitude are well correlated with ${\mathit{T}}_{\mathit{c}}$, which decreases monotonously with increasing x up to \ensuremath{\sim}0.02 and then saturates around 90 K over the range 0.02\ensuremath{\lesssim}x\ensuremath{\le}0.1. The observed crossover from two- to one- (or lower-) dimensional behavior with increasing Ni dopant level may be related to a fractal nature for the system. The ${\mathit{T}}_{\mathit{c}}$ reduction of the present system is discussed from the standpoint of pair-breaking effects induced by the Ni doping.

Preparation of Bi based high-Tc superconductors containing Pb and Sb by the sol-gel method

Preparation of Bi based high-Tc superconductors having Pb and Sb elements has been attempted using the sol-gel method. Production of the high-Tc phase was promoted by doping a little Sb (0.05 mol) together with Pb. The nominal composition of the system is Bi0.96Pb0.19Sb0.05Sr1.0Ca1.1Cu1.6Oy. It has been found that the reaction scheme of Sb doped samples is different from that of Sb nondoped samples.

Defect chemical study of Nd 2−xCe xCuO 4−δ

Oxygen nonstoichiometry δ and electrical conductivity σ were measured of Nd 2− x Ce x CuO 4− δ( x=0,0.05 and 0.10 at partial oxygen pressures ( P 02) between 10 -3 and 1 atm at temperatures from 873 to 1273 K. For the sample with x=0, δ was proportional to P − 1 6 02 between 973 and 1073 K. ϐ showed the same oxygen pressure dependence above 973 K, while ϐ was independent of oxygen pressure at low σ extent. The defect structure has been interpreted in terms of a model assuming doubly charged oxygen vacancies (Vö) predominate in Nd 2CuO 4− δ at large values of δ above 973 K and that the intrinsic ionization predominates at near stoichiometric composition ( δ=0). At 1173 and 1273 K where deviation from −1 6 power of P o2 was observed, the contration dependent activity coefficient of Vö has been taken into account by using regular solution approximation, and the interaction energy Ω v and standard Gibbs free energy change of the Vö formation has been calculated. In addition, standard Gibbs free energy change for the intrinsic ionization reaction and the mobility of electrons were estimated. The defect model has been applied to the Ce doped systems, and the calculated δ values show good agreement with experimental data. It is suggested that the carrier concentration in Ce doped systems is mainly governed by the concentration of Ce and that δ values tend to decrease compared with non-doped samples. The fact that it is also necessary to heat-treat the oxides doped with Ce to x=0.15−0.20 under low P o2 atmospheres, strongly suggests the important role of oxygen vacancies or reduction of the Cu oxidation state to promote superconductivity.

Attractive force and residual magnetism in AgO-doped and non-doped YBCO

The attractive force profiles as a function of separation between a magnet and AgO-doped and non-doped YBCO disks have been measured at 77 K. As expected the attractive force for the AgO-doped sample is significantly greater than that for the non-doped sample. The force profiles have the general shape predicted by previous investigations at 4.2 K by other authors, where the flux present upon cooling is assumed to be trapped as the magnet is withdrawn. Significant differences in detail are observed however, and these can be attributed to flux leakage at the higher temperature used in the present studies.

Variation in Tc for Bi2Ca1Sr2Cu2Oy doped with Fe and subjected to vacuum annealing

Substitution of Fe for Cu in Bi2Ca1Sr2Cu2Oy was found to be more effective in reducing Tc than in YBa2Cu3Oy. The authors discovered that the superconductivity which has been lost in Fe-doped Bi2Ca1Sr2Cu2Oy can be greatly recovered in vacuum at about 400 degrees C. This suggests that the exchange interaction between the magnetic moments and superconducting pairs is not predominantly in pair-breaking mechanisms, leading to the loss of superconductivity in high-Tc ceramics. As the non-doped and Fe-doped Bi2Ca1Sr2Cu2Oy samples were subjected to vacuum annealing, the lattice parameter c was found to increase and Mossbauer data revealed that both the local structure around Fe (or Cu) sites and the relative number of Fe (or Cu) sites associated with different values of quadrupole splittings Delta Q1 and Delta Q2 varied. This implies that the increase in Tc for the annealed samples is related to the local distortion of Cu-O layers. The optimum value of Tc ( rho =50%) for Bi2Ca1Sr2Cu2Oy as high as 94 K can be obtained by annealing the sample in a vacuum at 500 degrees C for 30 min.

Impurity doping effect on electrostrictive properties of (Pb,Ba) (Zr,Ti)O3

Abstract The effect of impurity doping on the electrostrictive properties (the magnitude of the induced strain and hysteresis) has been investigated for (Pb,Ba) (Zr,Ti)O3 ceramics. When doping with a donor impurity, the strain becomes larger and the degree of hysteresis becomes smaller than that observed for non-doped samples, while acceptor doping leads to a smaller strain and a larger degree of hysteresis. The strain and hysteresis are also influenced by the concentration of the metal oxide dopant.

Electrical properties of bismuth-doped non-stoichiometric strontium titanate ceramics

Pure and Bi-doped samples of SrTiO 3 with Sr/Ti ratios ranging from 0.980 to 1.010 were sintered in air at 1500 °C. Grain growth was promoted in the non-stoichiometric bismuth-doped compositions. Unlike the non-doped samples which were ohmic insulators, bismuth-containing specimens showed non-ohmic behaviour, with non-linear coefficients depending on stoichiometry. The dependence of resistivity on temperature and capacitance-voltage analysis were used to correlate the electrical characteristics with accepted models.

Electromigration in bipolar NPN transistors

Electromigration tests on bipolar devices with Al-1%Si and Al-1%Si-2%Cu were performed. These tests showed the following results: (1) Voids occurred in the aluminum collector stripe and pile-up of aluminum occurred at the emitter contact. Failure modes were open-circuit for the collector and resistive shunt for the emitter-base junction. The resistive shunt failure was enhanced by higher currents. (2) Whether open circuit or resistive shunt occurs earlier, depends on the relative cross sections of the aluminum used for the collector and for the emitter connections. (3) Doping with 2% Cu improved the lifetime about ten times compared to nondoped samples.

Deep Levels in Non-Doped and Donor-Doped GaP

Four deep electron-trap levels were detected by DLTS from the non-doped and Te- or S-doped LEC-grown GaP. Some discussions are given regarding their origin. The density Nt of these levels increased linearly with the net donor density ND for non-doped samples. Nt was reduced by doping Te with ND∼1017 cm-3, and then increased as ND1.7 for ND>1017 cm-3.

Effects of Indium on the Properties of N-Type CdS Thin Films Deposited by Spray Pyrolysis

ABSTRACTEffects of the doping level of indium impurity on electrical and optical properties of the CdS thin films, prepared with solution-sprayed method have been studied. The density of free carriers can be raised to an order of magnitude higher than that of non-doped case by increasing doping level of indium up to 0.01mole-% while indium doping does not significantly change the mobility from its value in non-doped samples. The optical energy gap is decreased with increasing indium content while the thermal activation energy remains unchanged. The experimental results are discussed in terms of the self compensation and radiative recombination phenomena.

Sprayed CdSCu 2S solar cells: Structural and chemical properties of airless sprayed CdS and CdZnS layers

Copper-doped CdS and CdZnS layers were prepared by airless spray pyrolysis on conductive glass. The observed Zn/Cd ratio was found to be higher in the solid phase than in the sprayed solution. Solid solutions were obtained which obeyed Vegard's law. Doping the sprayed solutions with a copper salt resulted in crystalline parameters that were smaller than those for the non-doped samples. Reactions of the layers with a Cu(I) solution were studied. The rates were found to depend linearly on the degree of lattice mismatch in the a direction and to vanish when the mismatch approached zero. At the same time, the reduction in the rate of formation allowed the attainement of a better stoichiometric ratio for a cuprous sulphide layer of a given thickness.

Photovoltaic effect in SBN and PLN ceramic ferroelectrics

Measurements of short-circuit photocurrent and open-circuit photovoltages on ferroelectric ceramic materials of Strontium Barium Niobate and Lead Niobate with 8% of Lantanum doped with Fe and Cu cations are presented. The time behaviour of the current as well as the sign of its steady value for non-doped samples are strongly influenced by grain boundary and polarization state. Photovoltaic response is greater in doped samples.A dependence of the photovoltaic effect with respect to the oxidation state of the material is observed. An account of experimental results is given on the basis of the different behaviour of grain and grain boundary with irradiation.