Ferroelectric Bi3.25La0.75Ti3O12 thin films on a conductive Sr4Ru2O9 electrode obtained by pulsed laser deposition

Strontium ruthenate and Bi_3.25La_0.75Ti₃O₁₂ (BLT) layers were grown on Si(100) substrate using pulsed laser deposition technique. Starting from a Sr₂RuO₄ target, we obtained single phase films composed of Sr₄Ru₂O₉; on these strontium ruthenate electrodes, textured and non-textured BLT were grown at 700 °C. Structural characterizations of these double layers were done by X-ray diffraction, scanning electron microscopy, normal and high-resolution transmission electron microscopy. The Van der Pauw's resistivity measurements indicate that Sr₄Ru₂O₉ can be used as a back electrode. The temperature dependence of the resistivity at low temperatures is , which corresponds to a variable-range hopping mechanism.     

Novel methodology to investigate superconducting dielectric resonators

An analytical method is presented for investigating the resonant behavior of a c-axis oriented YBa₂Cu₂O_7–(0) thin film on a resonator composed of LaAlO₃ (001). The concept of the negative dielectric medium for a superconductor is introduced within the framework of the two-fluid model, which permits us to treat a superconductor as any other penetrable materials so that only its electromagnetics are concerned. A conformai transformation is further suggested to map the original open boundary-value problem to a closed one. This not only makes the original problem readily solvable by using the variational technique, but is also a powerful tool for analyzing some kinds of problems such as the propagation characteristics of the superconducting microstripe and coplanar waveguide structures.     

Sample preparation of YBa2Cu3O7−δ for high-resolution electron microscopy

An overview is given of three techniques for preparing thin specimens of YBa₂Cu₃O_7-δ for high-resolution electron microscopy: grinding, cleaving, and ion milling. Advantages and disadvantages are described, with particular attention to the artefacts that may be introduced by the different techniques. It is concluded that the most serious problem encountered during high-resolution electron microscopy studies is a surface-initiated decomposition leading to the ultimate degradation of the structure. This problem was found to be most pronounced in ion-milled specimens.     

Transmission electron microscopy of nanocomposite CrB-N thin films

This paper reports on the preparation and characterization of CrBN nanocomposite coatings for low friction, low wear and high thermostability applications. Sputtered CrBN thin films were prepared in order to obtain a composite structure consisting of hard CrB₂ and CrN crystallites as well as hexagonal BN lubricant phase by unbalanced magnetron sputtering (UBM) of a CrB₂ target in an Ar/N₂ gas discharge. Coatings, with a total thickness of 4.5-5.5 μm, were deposited at 450 °C on silicon single-crystal substrates. A nanocomposite structure was obtained by increasing the nitrogen content of the sputtering gas. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy. The films were generally found to consist of crystallites of a 1-4 nm size embedded in amorphous matrix. This crystalline phase was identified by electron diffraction as hexagonal CrB₂ for low nitrogen content and cubic CrN for high nitrogen content. In the medium composition range, the structure was amorphous, still keeping the two-phase morphology. The use of high-resolution imaging mode helped to reveal the composition of the amorphous phase which seems predominantly to consist of boron nitride.     

On structure and stability of (Hg, Mo)-1212 superconductors based on SAED and EDS analysis

A superconductor with nominal composition Hg_0.8Mo_0.2Sr₂Y_0.5Ca_0.5Cu₆₊ withT _c up to 96 K has been isolated and carefully examined by electron diffraction and X-ray energy dispersive spectrum analyses. Its structure can be attributed to space groupP4/mmm and lattice constantsa=3.82 å andc=11.91 å. Inhomogeneous distribution of the cations was observed, which is considered to be the key to the broadening ofT _c in theR-T curve. The effect of humid atmosphere on the stability of the sample has also been investigated.     

Extraordinary behaviour of the Y1?xPrxBa2Cu3O7?δ system

Investigations of Y_1–x M _x Ba₂Cu₃O_7– (M=Ce, Th)c-axis oriented thin film specimens show that the rate of depression ofT _c withx is larger for M=Th, than for M=Ce and Pr, and suggest that Ce, like Th, is tetravalent in this compound. Hall effect measurements on Y_1–x Pr _x Ba₂Cu₃O_7– single crystals reveal aT ² dependence of the cotangent of the Hall angle in the normal state and a negative Hall anomaly belowT _c in the superconducting state, in agreement with recent reports. Our research shows that the depth, , of the negative Hall signal scales withT/T _c and that the maximum value of decreases linearly withx and vanishes atx0.24. Magnetoresistance measurements on Y_1–x Pr _x Ba₂Cu₃O_7– single crystals indicate that the irreversibility lineH(T ^*) obeys a universal scaling relation characterized by anm=3/2 power law nearT _c, with a crossover to a more rapid temperature dependence of belowT/T _c 0.6, similar to that observed for polycrystalline specimens.     

HRTEM and EELS Studies on Structural Defects in the Superconductor Sr2CuO2+δCl2−y Newly Synthesized Under High Pressure

Structural defects in the newly high-pressure synthesized superconductor Sr₂CuO_2+δCl_2−y have been studied by means of high-resolution transmission electron microscopy and parallel electron energy-loss spectroscopy. Two types of grain boundaries were found in the material. One is the amorphous boundaries usually lying in the ab-planes. The other is the structurally intact grain boundaries, and most of them are large-angle boundaries. One of the large angles frequently observed is the 90°〈110〉 asymmetrical tilt boundary. In some domains, periodicity lengths were changed due to the lattice distortion usually associated with atom deficiency. These domains can be regarded as “second-phase particles” embedded in the perfect grains. O-K electron energy-loss spectroscopy results suggest that those defect domains are in the hole-poor states. Quantitative composition analysis from energy dispersive of X-ray suggests the hole-poorness is caused by oxygen deficiency. Dislocations, such as the a[110] and c[001] edge dislocations, were also observed in the material. In most cases, those dislocations are very complex and exhibit stacking faults. PACS: 68.37.Lp, 67.80.Mg, 74.72.Jt     

Improvement of the Superconducting Transport Properties of YBa2Cu3O7?δ by BaZrO3 Doping

We have doped the YBa₂Cu₃O_7– superconducting ceramics with BaZrO₃ up to 75wt.% and studied the changes of some physical properties. The most important finding is the enhancement of the critical current density, which has a maximum at around 5 wt.% doping level. Compared with the undoped samples, the critical current density is four times higher if the doping compound is introduced prior to the calcination treatment, or two times higher if BaZrO₃ is introduced prior to the sintering treatment. The dependence of the critical current density on the doping level is consistent with the dependence of the Seebeck coefficient. We also observed a very small decrease of the critical temperature. The real density of the samples decreases with increasing doping level as expected from the ratio between the theoretical densities of YBa₂Cu₃O_7– and BaZrO₃, the effect being important for doping levels higher than 25 wt.%.