R. E. Salomon

SIMPLIFIED PREPARATION OF REBA2CU3O7-X VIA THE ACETATE METHOD

High-quality bulk REB a 2 Cu 3 O 7− x (RE = Y,Eu,Gd,Nd,La) was synthesized by a solution method. Stoichiometric amounts of yttrium, barium, and copper acetates were dissolved in glacial acetic acid. The acid was boiled away leaving a glassy acetate precursor. This precursor has shown amorphous scattering in XRD, a phenomenon consistent with atomic level mixing of reactants. The glassy precursor was subsequently heat-treated with a 5 °C/min ramp to 900 °C and a 2 h soak at 900 °C in air. The final product was obtained after heat treatment under oxygen at 550 °C with slow cooling to room temperature. Final products were analyzed by XRD, SEM, and four probe de-resistivity measurements. The mechanism of both precursor and product formation was examined through substitution studies and XRD. It was found that a combination of a rare earth acetate, barium acetate, and acetic acid was necessary for the formation of an amorphous precursor.

d-Hole localization and the suppression of superconductivity in YBa2(Cu1-xZnx)3O7−y

The temperature and Zn concentration dependence of the electrical resistivity, specific heat, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectra of YBa2(Cu1−xZnx)3O7−y withy∼0.1 has been measured forx≤0.16. In addition, the temperature and field dependence of the magnetization has been measured for 2<T<300K and 0<H<9.0T, along with the temperature and quasihydrostatic pressure dependence of the electrical resistivity for selected samples for 0<P<13 GPa. The substitution of Zn for Cu in YBa2Cu3O7−y causes a rapid and nearly linear depression of the superconducting transition temperature,Tc, withTc going to 0 K forx≥ 0.10. YBa2(Cu1−xZnx)3O7−y retains the YBa2Cu3O7-y orthorhombic structure forx≤0.16 for both the superconducting and nonsuperconducting samples. Initially, the unit cell volume increases nearly linearly with Zn content; however, an abrupt change occurs in the vicinityx=0.8–0.10. Forx<0.10, the temperature dependence of the electrical resistivity,ρ(T), is metallic-like (dρ/dT>0) andρ increases gradually with increasing Zn content. However, forx≥ 0.10,ρ(T) becomes semiconductor-like, with a very rapid increase of the resistivity with increasingx. The electrical resistivity, magnetic susceptibility, EPR spectra, and specific heat all indicate that thed-holes associated with the Cu ions become localized in the nonsuperconducting phase,x>-0.10.

Dielectric Behavior of Ice with HCl Impurity

The complex dielectric behavior of ice doped with HCl has been measured in the concentration range 2 × 10−6 to 2 × 10−4M. The dissociation of HCl in ice was calculated as a function of temperature for ice doped at 2 × 10−6M. The results at 1 × 10−5M and below conform to the Debye model with a single relaxation time. The data suggest that, in a limited concentration range, HCl is substitutionally incorporated into the ice lattice.

Dielectric Behavior of NaOH‐Doped Ice

The dielectric behavior of ice doped with different NaOH concentrations was investigated in the 0° to − 25°C temperature range. In the lower concentration range of 1–4 × 10−6M NaOH, the conductivity behavior was similar to pure ice. At higher concentrations in the range of 7 × 10−6M NaOH, significantly higher conductivities were observed with the low‐frequency conductivity being about 5 × 10−8 (Ω·cm)−1 and exhibiting only a slight temperature dependence. At lower temperatures the static dielectric constant was found to decrease with increasing NaOH concentration. The dielectric relaxation times and corresponding activation energies were about the same as for pure ice. The over‐all behavior is distinctly different from that of HF, HCl, and NH3‐doped ice. The model postulated to explain the observed results involves the interstitial incorporation of Na bonded to an (OH) site in its normal lattice position. It is postulated that this mode of incorporation causes lattice distortion that increases either the c...

Preparation of High-Tc Oxide Films via Flaming Solvent Spray

Thick films of the high-temperature superconductors YBa2Cu3O7−x and Bi1.7Pb0.3Sr2Ca2Cu3O10 have been prepared by spraying an ignited ethanol, ethylene glycol, or liquid ammonia solution of stoichiometric amounts of the metal nitrates (or acetates) onto polycrystalline MgO. The flaming spray is mechanically forced to traverse a region directly in front of the substrates. This new method is simple and inexpensive, and eliminates the problem of substrate cooling encountered in normal spray pyrolysis methods. Since decomposition of the solvent and metal salts occurs before deposition, the resulting films are relatively free of craters and nonuniformities common with spray methods. The method can be adapted to coat large areas and irregular or nonplanar shapes (i.e., cylinders), which could have useful magnetic shielding properties. The films were characterized by XRD and show single-phase material with preferredc-axis orientation. For YBa2Cu3O7−x, resistance vs. temperature measurements show aTc onset at 90 K and aTc0 at 76 K. Silver nitrate has been added to some of the solutions in an attempt to improve contact among individual grains.

Pressure and field dependence of the magnetic transition in GdBa2Cu3O7-x

Abstract The influence of hydrostatic pressure and of magnetic field strenght is presented for the low temperature antiferromagnetic ordering temperature ( T N =2.3 K) of GdBa 2 Cu 3 O 7- x . Data are presented for both superconducting and normal samples, the superconducting sample having a sharp 95 K transition and the oxygen-depleted normal sample being a semiconductor. For both systems the Neel temperatures, extrapolated to zero measuring field, are identical: T N = (2.33±0.03) K. The effect of pressure is to raise the transition temperature slightly for both samples, d T N /d P =+0.03 K/kbar for the superconducting sample and +0.04 K/kbar for the normal sample. The temperature dependence of the heat capacity made in several fixed external magnetic fields and the isothermal magnetization for T T N provide a measure of the antiferromagnetic-paramagnetic phase boundary, which shows T N approaching T =0 K at about 2.5 T.

Relaxation of polar cylinders in strong electric fields

The problem of rotational diffusion of a polar cylinder about its long axis in an electric field has been solved. The solutions apply to the high as well as the low field limits. The results are presented as a function of a reduced time and the variable κ, which is a measure of the ratio of mean electrical energy to thermal energy. Asymptotic expansions are obtained for the distribution function and the fractional polarization. The eigenvalues and even solution of a Whittaker–Hill–Ince differential equation have been calculated as functions of κ. Asymptotic expansions of the eigenvalue and solution of this equation are given.

Magnetic properties of a high Tc superconductivity related system Y1−xPrxBa2Fe3O8

We studied Pr substitution for Y in a 123 high T c superconductor related system, Y1−x Pr x Ba2Fe3O8 using of x‐ray diffraction, magnetization, and 57Fe transmission Mossbauer spectroscopy. The Fe sublattices are magnetically ordered through the whole system. The Pr substitution, however, suppressed the Fe ordering temperature. The low temperature susceptibility across the system increases with increased Pr concentration x, and an additional antiferromagnetic ordering at 24 K is observed for x=1, indicating a possible Pr ordering. The averaged magnetic hyperfine field at Fe sites measured at 15 K is also reduced as x increases. The dramatic effect of Pr substitution for Y in this system, which is not observed in studies of Y substitution by other rare‐earth elements, is interpreted as the effect of the hybridization between the Pr 4‐f electrons and the electrons in the Fe(2)O2 layers, similar to the Pr hybridization in Y1−x Pr x Ba2Cu3O7−y system.

Light heavy-fermions in Zn and Ni doped 123 Cu-O superconductors

Abstract The temperature dependence of the specific heat C(T) has been measured for YBa2(Cu1−xMx)3O7 (YBCO) with M = Zn and Ni and 1.2 λ LT = C(T) T at T = 1.5 K reaching values of 100–150 mJ⧸mol K2 for modest Zn and Ni doping. This γLT dependency for Zn doped YBCO has been associated with a localization of d-holes within the CuO2 planes caused by a disorder induced disruption of hybridization within the planes.

Preparation of YBa 2 Cu 3 O 7− x using barium hydroxide flux

High quality bulk YBa 2 Cu 3 O 7− x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O 2 ). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.