C-axis oriented ultrathin films with good crystallinity were deposited by laser ablation on both SrTiO3 and NdGaO3 substrates. The full width at the half maximum of the rocking curves of the (005) peak δω of our ultrathin films with thickness d ≤ 150 Å is less than 0.11°, and the χmin of the 150 Å films on SrTiO3 determined by RBS is equal to 8.5%. SrTiO3 and NdGaO3 have different degrees of lattice mismatches of 2% and 0.2%, respectively, with YBa2Cu3O7−δ at the deposition temperature of 700 °C. To study the impact on the growth of YBa2Cu3O7−δ thin films by the lattice mismatch, the thickness dependence of the crystallinity of the films on SrTiO3 and NdGaO3 substrates was compared. δω of the films deposited on SrTiO3 increases slightly from 0.085° to 0.11° as d increases from 50 Å to 150 Å, but δω increases rapidly from d ≍ 150 Å and saturates at 0.35°. In contrast, films on NdGaO3 showed a rather flat thickness dependence of δω which is below 0.1°. We interpreted the rapid increase in δω of the films on SrTiO3 in terms of strain relaxation. Lattice matching is one of the key factors to obtain good crystallinity. The grains of the films on SrTiO3 and MgO are not flat and smooth but have “mosaic texture.” In contrast, the films on NdGaO3 have no mosaic texture. The possible origins of the mosaic texture are also discussed.

In the framework of an extensive research program for the production of textured and ductile high Tc BiSrCaCuO (BiSCO) wires and tapes, the influence of processing (by melt-quenching) parameters on the crystallization behavior, the quantitative and qualitative evolution of the crystallized phases, the chemical changes in the bulk, and the superconductive properties of various initial compositions of bulk BiSCO glass ceramics, prepared by melt-quenching, have been studied. The elemental composition of the samples changes drastically during heat treatments, affecting mainly Pb, but Sr and Ca also. The identified crystallographic phases, by XRD, were the low Tc superconducting “2201” (Bi2Sr2CuO6) phase, the high Tc superconducting “2212” and “2223” phases, and the Ca2PbO4, Ca2CuO3, CuO, CaO, Bi2Sr3-xCaxOy, and (Ca, Sr)3Cu5O8 “impurities” compounds. A crystallization sequence from the amorphous state is proposed, involving a reaction at 800 °C between “2223”, CaO, Ca2CuO3, and Bi2SrCaxOy to form “2212” + Ca2PbO4 + CuO and a 2(“2212”) → “2223” + “2201” disproportionation reaction that takes place with the intake of oxygen at a higher temperature. Decomposition of Ca2PbO4, which occurs also at high temperature, causes an increase of “2212”, which favors the increase of “2223” through the disproportionation reaction. The glass transition starts around Tg = 400 °C, and the crystallization reactions from the amorphous state proceed in two steps, at Txl = 465 °C and Tx2 = 504 °C. The Bi2Sr3-xCaxOy “2212” and “2223” phases are among the first to crystallize as early as after a 1 h treatment (in air) at 488 °C. A gain in weight is observed by thermogravimetry, caused by intake of the oxygen necessary for the formation of the high Tc superconducting phases. The oxygen intake starts as early as 600 °C. The Tc onset for the “2223” phase is at 122 K, and at 85.5 °C for the “2212” phase. Coefficients of thermal expansion have been measured and shown to differ according to crystallographic direction of expansion. The resistivity is increased on cooling, indicating semiconducting behavior of the 2223 BiSCO ceramic (semiconductor-to-metal transition temperature: 210–220 K).

The heat capacity and the enthalpy associated with the reported oxygen vacancy order-disorder transition in Ba2In2O5 were measured by high temperature step scanning calorimetry. The transition temperature is 1205 ± 2 K. The transition appears first order or nearly so. The enthalpy and entropy of transition are 1.3 kJ/mol and 1.1 J/mol K, respectively. The latter is only 4.8% of the configurational entropy, arising from mixing one vacancy and five oxygens per formula unit, 22.5 J/mol K. This suggests that the transition involves only a small fraction of the oxygen vacancies and implies extensive short-range order, SRO, in the high temperature phase.

In order to investigate microstructural variation by 2-1-1 addition in partially melted Y–Ba–Cu–O, a specimen resulting from 2-1-1 added to 1-2-3 was heat-treated through the peritectic temperature. Microstructure was observed on the directionally solidified region near the interface of the two samples. The 2-1-1 addition results in a homogeneous microstructure where no remnant liquid phase is present. It reduced the 1-2-3 plate thickness, as well as suppressed the formation of microcracks due to the tetragonal-to-orthorhombic phase transition or the thermal contraction during cooling from the peritectic temperature. The formation of microcracks induced by the phase transition seems to be closely related to the process of oxygen diffusion into a sample. We discuss the formation of microcracks in terms of the oxygen diffusion along the plate boundaries and of the thickness of 1-2-3 plates. The decrease in the plate thickness and the fine dispersion of 2-1-1 particles contribute suppression of the formation of microcracks and their propagation.

This article addresses issues associated with in situ growth of superconducting YBa2Cu3O7−δ thin films by ion beam sputtering. High oxygen partial pressure during ion beam deposition can cause significant beam broadening and oxidation of filaments and grids. Also, many of the targets used for processing YBCO are unstable when sputtered in a high oxygen partial pressure. It is shown that ion beam sputtering can produce YBCO films of comparable quality to those produced by laser ablation or dc magnetron sputtering. Typical film properties are Tco = 91 K and Jc (77 K) = 106 A cm−2. It appears that the oxygen gas pressure during the postdeposition cooldown has a more important influence on film properties than the oxygen partial pressure during deposition.

Sixty−70 μm diameter preceramic fibers, extruded from THF solutions containing 1:2:3 stoichiometric mixtures of yttrium, barium, and copper carboxylates, were pyrolytically transformed into ceramic fibers using controlled heating schedules and reactive atmospheres. The objectives of the work reported here were to identify appropriate processing conditions such that during pyrolysis the preceramic fibers would (1) eliminate the organic ligands without pore or void formation, (2) reach full density with a controlled grain size, and (3) form orthorhombic phase, 123 fibers with reasonable mechanical properties. The mechanisms of organic ligand decomposition and loss were examined using mass spectral fragmentation and TGA. Microstructural and phase evolution were correlated with heating schedules and atmospheres, using XRD, DTA, SEM, and limited flux exclusion studies. The mechanisms of decomposition of the spinnable mixtures suggest intermolecular rather than intramolecular decomposition pathways. Different pyrolysis atmospheres were also examined to explore methods of controlling the degradation process. Slow pyrolysis in air followed by oxygen anneals appears to give superior fibers in terms of controlled grain size and phase. The pyrolyzed fibers exhibit the appropriate orthorhombic phase according to x-ray powder diffractometry. Preliminary flux exclusion measurements demonstrate that the fibers are superconducting although the measured δTc is not exceptional.

A simple and convenient method for the synthesis of YBa2Cu3O7−x powder is described. The technique involves autoignition of a citrate-nitrate gel resulting from a thermally induced oxidation-reduction reaction to yield an ash that upon calcination produces the desired compound. The resulting powder is pure, homogeneous, and possesses a reasonably fine particle size. The autoignition is restricted to a particular range of citrate-nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good potential for large-scale production.

Ni3Fe is a compound that exhibits long-range ordering below 500 °C and a disordered structure above this temperature. Thus, Ni3Fe allows study of the effect of ordering on mechanical properties. This paper discusses the tensile properties of Ni3Fe produced via powder metallurgical routes. Some samples subsequently were densified by containerless hot isostatic compaction. Ni3Fe was consolidated with elemental nickel and iron powders that were solid state sintered. Composites of Ni3Fe with 5 vol. % Y2O3 were prepared by presintering cold isostatically pressed rods, followed by containerless hot isostatic pressing. The influence of Y2O3 particles on flow stresses of ordered and disordered Ni3Fe was determined. Ordering of Ni3Fe increased both strength and hardness with a small effect on ductility. For the Ni3Fe–Y2O3 composite, the increase in the strength in both ordered and disordered matrix conditions was accomplished by a large reduction in elongation.

A model proposed by Tinkham1 to explain the resistance versus temperature broadening found in high Tc superconductors in applied magnetic fields is extended to “foot and knee”-structured data taken on polycrystalline YBa2Cu3O6+δ. The proposed extension involves a series combination of two types of superconductors. For this series combination to result, a critical ratio of the two types of superconductors must be met—a result common to both percolation and randomized cellular autonoma theory. This critical ratio is investigated via statistical computer models of a polycrystalline superconductor having two phases of crystallites—one with substantially lower Jc than the other.

Resistivity measurement of an a-axis-oriented YBa2Cu3O7-δ (YBCO) thin film was carried out in a stream of O2/Ar mixtures at 450–650 °C. Rapidly reversible change in the resistivity of the YBCO film was observed as a function of the oxygen partial pressure in the ambient atmosphere due to the oxygen in-/out-diffusion in the YBCO film. Resistivity measurement of YBCO thin films at higher temperatures of 450–650 °C was found to be quite effective to predict the influence of fabricating processes on the superconducting properties of YBCO films.

TEM studies have been conducted on melt-textured YBa2Cu3Ox samples that were uniaxially and isostatically deformed at high temperatures and compared with those of undeformed samples. Dislocation pile-ups along [100] and [010] are found to be the common feature between undeformed samples with the best Jc and the uniaxially deformed samples, and are suggested to be responsible for enhanced pinning when the magnetic field (H) is applied parallel to the a-b plane. Dislocation loops, tangles, and arrays are also observed, and are considered to contribute to pinning in field orientations other than H ‖ a-b. In addition to these dislocations, 〈301〉 type partial dislocations are found to be present in isostatically deformed samples. The strain field around these dislocations is considered to be an additional source of pinning in the intermediate field orientations.

Ag-sheathed tapes of Bi–Sr–Ca–Cu–O (BSCCO) and BSCCO–Ag superconducting cores were made by a powder-in-tube technique and subjected to repeated cycles of pressing and heat treatments. These thermomechanical treatments resulted in enhanced texturing and grain growth that improved the critical current density (Jc). Additions of Ag to the BSCCO core further increased texturing and brought an additional improvement in Jc. Strain tolerance of the tapes was evaluated by measuring Jc before and after application of a predetermined level of tensile strain in a uniaxial mode. The fraction of Jc retained after the strain application was higher in the BSCCO–Ag composite tapes than in the monolithic BSCCO. For a 1.2% applied strain, 90% of the initial Jc was retained in the BSCCO–Ag composite tape, compared to only 40% in the monolithic BSCCO tapes. The higher strain tolerance of the BSCCO–Ag tapes may be related to improved mechanical properties (strength, flexibility, and fracture toughness) and grain connectivity due to Ag addition.

The fatigue behavior of ferroelectric PZT capacitors with Ru and RuOx electrodes was studied. These capacitors show no sign of fatigue out to 1 X 1011 cycles, in sharp contrast to the degradation typically observed with Pt electrodes. Compared to Pt electrodes, the initial polarization was lower, but after fatiguing the polarization was comparable to or larger than that for Pt electrodes. Differences in polarization in response to switching and nonswitching pulses greater than 10 μC/cm2 were observed at 1 X 1011 cycles.

The microstructure and the composition profile of lead lanthanum zirconate titanate thin film fabricated using the sol-gel method were analyzed using the scanning electron microscope and scanning Auger microscope. The PLZT thin film consists of micron-scale spheroidal perovskite grains and nano-scale pyrochlore grains. The perovskite grain has a higher lead and lower oxygen and zirconium contents than the pyrochlore grain. The Auger spectra of the two phases were similar except for energy shift and extra fine structure of oxygen peaks. The Auger depth profile and SEM observation of the cross-sectional fracture surface showed higher perovskite content near the interface between PLZT and ITO films than the surface of the PLZT film.

To correlate structural and compositional parameters in the bismuth 2212 system, single crystals with the composition (Bi1−yPby)2Sr2(Ca1−xRx)Cu2O8+δ (R = Y, Er, Ho, Tm, and Yb; y = 0, 0.1; 0 ≤ x ≤ 0.5) have been studied at room temperature by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The main results are as follows: (i) The actual content, x, of R (R = Y, Er) in samples is in significant excess over its content x′ in the melt for x′ < 0.5. The opposite effect (but several times smaller) takes place for Ca. At x′ = 0.5, the x value practically coincides with x′. (ii) For all R under examination and x′ = 0.1, the value of x is within the limits of 0.43 ≤ x ≤ 0.51; i.e., x exceeds x′ several times. (iii) The total content of Ca, R (R = Y, Er), and Sr is close to 3 through the whole range 0 ≤ x′ ≤ 0.5. At x′ < 0.5 Ca is partly substituted for Sr, while R occupies only Ca crystallographic positions. Thus the actual formula of the samples is (Bi1-yPby)2+∊Sr2-z(Ca1+z-xRx)Cu2O8+δ. (iv) The evidence was received that the nonlinear dependence c(x) at x < 0.5 is connected with the partial substitution of Sr with Ca. The dependence of c, namely on the R = Y content in the denoted range of x, is close to linear with the slope ∂c/∂x = −0.67(2) Å/at.

The thin films (Y/Ba/Cu = 1.0/2.7/4.7) which have a strong intensity corresponding to the c-axis peaks of the 124 phase (YBa2Cu4O8) in x-ray diffraction (XRD) patterns were prepared. The film structure and surface morphology of these films were observed by scanning electron microscopy (SEM), energy dispersive x-ray (EDX), transmission electron microscopy (TEM), and atomic force microscopy (AFM). It was found that the film on MgO(100) clearly has grain boundaries with many a-axis oriented grains of the 123 phase (YBa2Cu3O7−x). However, the film on SrTiO3(100) had a smooth surface, and a-axis oriented grains of the 123 phase couldn't be observed. This difference could not be explained by only the difference in the lattice mismatch.

Boron nitride (BN) thin films were deposited on monocrystalline Si(100) wafers using electron beam evaporation of boron with simultaneous bombardment by nitrogen and argon ions. The effect of film thickness on the resultant BN phase was investigated using Fourier transform infrared (FTIR) spectroscopy and high resolution transmission electron microscopy (HRTEM). These techniques revealed the consecutive deposition of an initial 20 Å thick layer of amorphous BN, 20–50 Å of hexagonal BN having a layered structure, and a final layer of the polycrystalline cubic phase. The growth sequence of the layers is believed to result primarily from increasing biaxial compressive stresses. Favorable surface and interface energy and crystallographic relationships may also assist in the nucleation of the cubic and the hexagonal phases, respectively. The presence of the amorphous and hexagonal regions explains why there have been no reports of the growth of 100% cubic boron nitride on Si.

Soluble metal oxo alkoxide precursors are useful for the production of homogeneous, micron-sized YBa2Cu3O7−x powders and the fabrication of superconducting YBa2Cu3O7−x films on large area and nonplanar substrates. This paper describes the synthesis and chemistry of a series of soluble metal oxo alkoxide precursors for the YBa2Cu3O7−x superconducting material and the effect of the thermal processing conditions on the formation of the superconducting phase. We have found that the direct conversion of the metal oxo alkoxide precursors to an amorphous or crystalline YBa2Cu3O6.5 phase without the intermediate formation of the individual metal oxides or carbonates allows the formation of the superconducting phase at temperatures as low as 720 °C. The prevention of the intermediate formation of the metal oxide and carbonate phases is achieved by the controlled thermolysis of the metal oxo alkoxide precursors in an inert atmosphere. The precursors have potential use in the low-temperature deposition of films on large area or nonplanar surfaces and for the production of homogeneous powders.

A definition for structure of atomic scale systems is introduced which extends the typical crystallographic description to include elements of the total charge density. We argue that the mechanical properties of intermetallic alloys are related to this extended structure. These relationships have their origin in the nature of the charge redistribution accompanying strain. The direction of this charge redistribution is determined solely by the extended structure, while its magnitude can be correlated with a quantification of this extended structure. We demonstrate these facts by determining the extended structure and nature of the charge redistribution resulting from uniaxial strain for two alloys with the L10 structure: CuAu and TiAl. While these alloys share the same crystallographic structure, their extended structures are different, with CuAu possessing the same extended structure as the allotropic fcc metals while TiAl does not. These different extended structures give rise to different charge redistributions, which are argued to be related to the intrinsically ductile behavior of CuAu and the tendency for TiAl to fail transgranularly.

Rare earth additions of 3 wt. % were added to the Zn−27% Al−2% Cu−0.02% Mg alloy, known as ZA-27. The as-cast microstructure of this alloy consisted of two phases of supersaturated face-centered cubic β′s and α′s together with a hexagonal close-packed rare-earth-containing zinc-rich phase termed E phase. The phase transformations in this alloy after aging at 100 °C and 200 °C were determined. The E phase was determined to have the lattice parameters a0 = 9.0348 Å and c0 = 13.2194 Å, giving c0/a0 = 1.4632. The chemical formula of the E phase was determined to be RE1Zn10.9Cu0.8. The addition of 3% rare earths into ZA-27 delayed the phase transformations of this alloy. This was caused by an increase in the aluminum content of the supersaturated β′s phase.