F. Wu

Growth and polarization features of highly (100) oriented Pb(Zr0.53Ti0.47)O3 films on Si with ultrathin SiO2 buffer layer

Highly (100) oriented Pb(Zr0.53Ti0.47)O3 (PZT) films were prepared on Si substrates with ultrathin SiO2 buffer layer by pulsed laser deposition. Hysteresis measurements show that saturation polarization, remnant polarization and coercive field of the films reach 26 μC/cm2, 10 μC/cm2 and 70 kV/cm, respectively. The thickness of SiO2 buffer layer is found to play a significant role on phase purity and orientation of PZT as well as the prevention of interdiffusion. It is also found that the grain size and the interdiffusion between PZT and Si are the key factors for the ferroelectric properties of the films, which are discussed together with the synthesis condition in detail.

A new Cu Kα2-elimination algorithm

This paper presents a new algorithm to remove the Cu Kα2 profile in X-ray powder diffraction patterns. Previous algorithms for α2 elimination can be divided into two categories. The first category assumes the shape identity of the α1 and α2 components. The second category uses parameters by fitting experimental data. The first category is not accurate and the second one is instrument-dependent. The algorithm presented here uses the Cu Kα emission profile obtained from monolithic double-crystal measurements. Therefore, it is more accurate and less instrument-dependent than the previous methods. This algorithm has been tested and applied in software for diffraction data processing. The present method can be extended to remove Kα2 lines of other radiations.

Correction of zero shift in powder diffraction patterns using the reflection-pair method

Zero shifts of 2θ usually represent one of the most serious systematic errors in powder patterns obtained by diffractometers, and they cannot be readily diagnosed and corrected. Frequently, large zero shifts hinder indexing of the patterns. Programs exist to refine the lattice constants and calculate the zero shift, but they need the indexing results. We have derived an equation, based on the reflection-pair method, to calculate and correct the zero shift before indexing. The equation has been tested on many experimental data and the effectiveness of the method has been confirmed. The method is very useful in ab initio crystal structure determination using powder data.

Crystal growth and superconductivity of heavily La-doped Bi-2201 single crystals

Abstract A number of La-doped Bi-2201 single crystals were prepared by self-flux method. The qualities of the crystals have been checked by X-ray diffraction patterns (XRD) and electron diffraction patterns from transmission electron microscopy (TEM). The correlation between the actual composition of La determined by Energy-Dispersive X-ray (EDX) analysis and the c -axis parameter determined from XRD shows a linear behavior, being consistent with previous reports. A new superconducting phase with T c as high as 36 K has been discovered for the first time in heavily La-doped Bi 2 Sr 2− x La x CuO 6+ y single crystals ( x ≥0.8) in which one normally could not observe the superconductivity. Since our samples have been post-annealed in flowing oxygen and heavily La-doped samples are normally in the region with an antiferromagnetic background, it is natural to attribute the appearance of the high T c superconductivity to the electronic phase separation induced by the cooperative interactions between the antiferromagnetic background and the mobile holes (given by excess oxygen).

The high-pressure synthesis and superconductivity of Pr0.5Ca0.5Ba2Cu3Oz

The bulk superconductorss of Ca-doped Pr-123 phase, Pr0.5Ca0.5Ba2Cu3Oz were prepared at 1000 degrees C under high pressure of 5GPa. The superconducting properties of the sample depend on the synthesis conditions. The sample synthesized under high oxygen pressure was a nearly single orthorhombic 123 phase, and shows a superconducting transition at 52K with a Meissner signal of 12%. However, the sample prepared under a reduced environment is a high purity tetragonal 123 phase and has a much higher critical temperature (T-c = 97K) than that in orthorhombic phase. The results demonstrate that suppression of superconductivity by Pr in bulk Pr-123 phase can be compensated by appropriate hole doping with Ca.

Observation and studies of 98 K superconductivity in oxygen-deficient tetragonal Pr0.5Ca0.5Ba2Cu3O7-δ synthesized under high-pressure

We report the first observation of superconductivity in a bulk Pr1-xCaxBa2Cu3O7-delta (0.4 less than or equal to x less than or equal to 0.6) system synthesized under high pressure with different oxygen environments. The highest T-c of 98 K was observed for the oxygen-deficient tetragonal Pr0.5Ca0.5Ba2Cu3O7-delta sample. Our results unambiguously demonstrate that Pr has a mixed valency greater than 3+. We conclude that hole depletion is the primary cause of the suppression of superconductivity by Pr in PrBa2Cu3O7, eliminating the hypothesis based upon pair-breaking

Critical current density and flux pinning in Gd1−xYxBa2Cu3O7−y epitaxial thin films

Low-electric-field E=j(s) curves, normalized dynamical relaxation rate Q(T)=d ln(j(s))/d In(E), and experimental critical current density j(s)(E = E(c)) were measured from 10 to 85 K with the magnetic sweeping method. By taking a general assumption for the activation energy U(j(s), T) = U-c( T)f [j(s)(T)/j(c)(T)], with t = T/T-c, we obtained the U(j, T=O K) relation by scaling all the E-j(s) curves of different temperatures to one smooth curve with U-c(T) and j(c)(T) determined by the so-called generalized inversion scheme. It is shown that the important parameter c = In(upsilon(o)B), which was actually taken as a fitting parameter in, the scaling process in previous work, can be predetermined. It is also found that the resulting U(j, T=O K) relation based on the E=j(s) curves for T less than or equal to 79 K can be well interpreted with the collective-pinning model. However, the data for T>79 K start to deviate from this interpretation, which may be attributed to the reverse hopping of vortices.

The microstructure of and films

(PZT 53/47) is a polycrystalline film with coarse square-shaped grains. The surface morphology can be improved by reducing the cooling rate at the Curie temperature region; however this morphology still does not meet the requirement of device engineering. (PZT 20/80) film has been synthesized, to reduce the lattice mismatch between PZT and substrate. This film has a smooth surface without any evident crystalline features. A TEM of the cross-sectional (YBCO) integrated film shows there is no interaction between the PZT, YBCO and substrate. particles are detected in the PZT film.

Preparation of the single phase LaBa2Cu3Oy superconductor with Tc(0)=97 K and suppression of the substitution of La for Ba

The effect of processing conditions on phase formation, solid solution range and superconductivity for the La1+zBa2−zCu3Oy system was investigated systematically again to obtain and understand the optimum preparation condition of La-123 superconductors. The results indicate that (1) the solid solution ranges are z=0.20–0.70 and z=0 for La1+zBa2−zCu3Oy sintered and cooled in air and in N2, respectively. (2) In LaBa2Cu3Oy, La can substitute for Ba, but Ba cannot substitute for La. This substitution is suppressed when LaBa2Cu3Oy was sintered and cooled in N2. (3) A single phase LaBa2Cu3Oy superconductor with the highest Tc of 97 K was obtained for the first time when the sample is sintered at 900°C for 40 h in N2 and cooled down to 305°C in N2, then treated in dried flowing O2 for 40–60 h.

Superconductivity, microstructure and pressure effect on Tc of Hg-based compounds prepared under high pressure

High-temperature superconductors of the mercury-based system were synthesized under high temperature and high pressure. The measurements of resistance and DC magnetic susceptibility for the samples prepared at 20-35 kbar and 850-degrees-C for 1-3.5 h show that the as-synthesized sample (1) prepared at 20 kbar, 850-degrees-C for 1.5 h was a multiphase of Hg-1212 and Hg-1223 phases and showed superconducting transitions of both 132 and 120 K. The sample (2) prepared at 30 kbar, 850-degrees-C for 3.5 h has Hg-1212 as the major phase with only a small amount of impurity phase. The intergrowth of Hg-1212/Hg-1223 was found in the sample (1). The dependence of pressure on T(c) for the Hg-1212 and Hg-1223 phases, measured under hydrostatic pressure, shows that dT(c)/dp is 0.17 and 0.23 K/kbar, respectively, in the pressure range below 10 kbar.