How the Surface Resistance Rs of Patterned High-Tc Superconducting Thin Film Is Affected by the Film''s Edge

This paper defines an effective microwave surface resistance for the nonuniform distribution of microwave surface resistance R _s in the strip of a microstrip. It is proved that is equivalent to the expression of R _s used in experiments, and that the is dominated by the edge part, i.e., the area of width ²/2t from the strip edge, where is the magnetic penetration depth and t is the film thickness. Under the assumption that where is the component of rf magnetic field along the film thickness and n is an integer, the ratio of the contributions of the edge part and the rest of the strip to is calculated by using an approximate analytical expression of the surface current density distribution J _s in the strip and calculated by the London equation. The effect of film's edge on R _s was studied using a microstrip resonator. It is found that the perfectness of the edge could affect the magnitude of the power dependence of R _s significantly, which agreed with our analysis.     

Superconductivity of YBa2?xNdxCu3Oy Solid Solution

The solubility of Nd at the Ba sites and the superconductivity of YBa_2–x Nd _x Cu₃O _y were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures , however, exhibits two-step variation with the increase of x. For x0.25, are all above 92 K. The highest of 94 K was obtained for x=0.25. For x0.3 drops sharply to about 84 K. Finally falls to 30 K and is below 10 K for x=0.5. The two-step variation of T _c might be an indication of the existence of two trap levels for holes.     

Effect of the addition of Y2O3 on the structure, microstructure and piezoelectric properties of PZT(53/47)

In this work, an attempt is made to study system with x=0.0125, 0.025, 0.050, 0.075 and 0.1. It was shown that there is limited solid solubility (0.625 mol %) of or 1.25 mol % of in PZT(53/47). For higher levels of dopant, mainly two other extra second phases were detected. The first was a Zr-rich phase in which some and small amounts of was dissolved. The second one was a Pb solid solution composed of mainly PbO, and which was initially also seen in calcined samples. The formation of Zr-rich phase is thought possibly to originate due to the sublimation of Pb from source during the sintering process. For higher x values, a structural shift towards Ti-rich region of PZT's phase diagram is seen. All piezoelectric parameters of the doped samples such as , are seen to decline sharply compared to that of undoped samples. Increasing the level of dopant gave rise to the increase of conductivity and dielectric loss of sintered samples. The formation of non-ferroelectric extra phases, and the Zr/Ti change of the main formed phase is believed to be responsible for this behavior.     

Field Dependence of the Vortex Structure in d-Wave and s-Wave Superconductors

The vortex structure and its field dependence are studied in the clean limit on the basis of the quasi-classical Eilenberger theory to find their difference between - and s-wave pairings. We show the -wave nature and the vortex lattice effect on the local density of states around the vortex, and on the field dependence of the spatially averaged density of states. The -wave pairing introduces a fourfold symmetric structure around each vortex core in the pair potential and the internal field. With increasing field, their contribution becomes significant to the whole structure of the vortex lattice state.     

Vibronic Superconductivity in the Copper Oxides

Two equilibrium bond lengths coexist in the (001) CuO₂ planes of the copper-oxide superconductors; (Cu–O)_loc > (Cu–O)_itin correspond, respectively, to the antiferromagnetic parent and overdoped phases. In the range 0 < p 0.1 holes/Cu atom of these planes, each hole occupies an itinerant-electron cluster of 5 to 6 Cu atoms in a (CuO)_loc matrix at temperatures T > T*; below T*, a spinodal phase segregation between parent and vibronic phases occurs. Evidence is cited for a condensation in the vibronic phase on lowering the temperature to one hole per 3 Cu atoms in alternate Cu–O–Cu rows. Ordering of the holes at a leads to the formation of itinerant vibronic states, and BCS coupling of the heavy fermions below T _c gives a superconductive condensate of symmetry .     

Phonon Vibration and Conduction of La2 ? xSrxCuO4 ? δ and La1.85 ? xSr0.15 + xCu1 ? xCoxO4 ? δ

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 0.5) and La_{1.85 – x} Sr_{0.15 + x} Cu_{1 – x} Co _x O_{4 –} (0 x 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane stretching vibration mode (689 cm^–1). The softening of the phonon vibration mode gives an index of the weakening of hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

Thermodynamic Functions of Fermi Gas with Quadruple BCS-Type Binding Potential with dx2 - y2 d_{x^2 - y^2 } -Wave-Pairing Symmetry

A gas of spin 1/2 fermions with an interaction V+W = -||^-1 _k,k g _k,k(k)(k) b _k b _-k - 2 _k(k)n _k+ n _k-, where n _k± = a _k±, b _k = a _k+ a _k- and a _k, satisfy Fermi anticommutation relations, is investigated in the -pairing case. W+V₄ is nonzero only within a thin layer of one-fermion energies around the chemical potential , and (k) denotes the characteristic function of the corresponding range of momenta. Two cases are studied: 1⁰ = 0, 2⁰ = 0.10025 eV. In the first case the system exhibits a first order transition, in the second, the transition is second order. Temperature dependence of the system's thermodynamic functions is examined and compared with that of the s-pairing case.     

Computer-aided design of small patch antenna using (Al, Mg)TaO2 ceramics

The microwave dielectric properties of (AMT) ceramics and the design of small coplanar waveguide fed antenna (CPWFA) have been investigated. ( and ( have orthorhombic and tetragonal structure, respectively. As ( concentration increased, AMT ceramics transformed into the tetragonal structure. Specimens having tetragonal single phase could be obtained above x=0.6. As ( concentration increased, the grain size, dielectric constant and quality factor (Q) significantly increased and the temperature coefficient of resonant frequency changed from negative to positive. The of was realized at x=0.65 and the Q · f _O value and for this composition were 112 470 GHz and 26.1, respectively. Newly developed dielectric materials were used for 1.5 GHz band CPWFA design and fabrication. The size of the CPWFA can be reduced by using high dielectric constant AMT ceramics, insetting slits into the patch, and fabricating CPW feed line in the ground plane. The slits play a role in not only lowering a center frequency but also fine tuning for the proposed antenna together with the open stub of CPW feed line. The CPWFA with slits has a lower center frequency than the conventional CPWFA, which suggests that the antenna size can be reduced by as much as 16.3%. The structure simulations of the CPWFAs have been performed to obtain impedance matching and to investigate the effects of slits. Experimental results of the fabricated device were in good agreement with the simulation.     

Oblique Vortex Lattice Implies Unconventional Pairing Symmetry in High Temperature Superconductors

The symmetry of order parameters of YBa₂Cu₃O_{7 –} high temperature superconductor was studied with the Ginzburg–Landau theory. The vortex lattice of a YBa₂Cu₃O₇ superconductor is oblique at a temperature well below the transition temperature T _c, where the mixed s– state is expected to have the lowest energy, whereas very close to T _c, the -wave is slightly lower in energy, and a triangular vortex lattice recovers. The coexistence and the coupling between the s- and d-waves would account for the unusual behaviors such as the upward curvature of the upper critical field curve H _C2(T).     

Effect of PFT substitution on dielectric properties of PFW-PFN perovskite ceramics

Perovskite phase formation and dielectric characteristics of ceramic system with addition of were investigated in order to examine the influence of . The ceramic system powders were synthesized via a B-site precursor route. Peculiar behaviors of frequency dispersion in dielectric constant spectra in the paraelectric region were observed due to increasing conductivity. Lattice parameters, dielectric maximum temperatures, and maximum dielectric constants increased with increasing content.     

Pairing, Stripes, Lattice Distortions, and Superconductivity in Cuprate Oxides

We propose a model for a spatially modulated collective state of superconducting cuprates in which the electronic properties vary locally in space. In this model, the regions of higher hole density (called stripes) are described as Luttinger liquids and the regions of lower density (antiferromagnetic ladders) as an interacting bosonic gas of hole pairs. We show that the transition to the superconducting state is topologic and driven by decay processes among these elementary excitations in the presence of vibrations.     

High temperature exposure of low-oxygen SiC fibers (Hi-Nicalon) in CO-CO2 gas mixtures

The oxidation behavior and thermal stability of Si-C fibers (Hi-Nicalon) in CO-CO₂ gas mixtures were investigated at 1773 K, through mass change determination, XRD analysis, resistivity measurement, SEM observation and tensile test. Mass gain and cristobalite formation were observed at 2 × 10³ Pa, showing the occurrence of passive-oxidation of the fibers. The active-oxidation, which was characterized by the mass loss, involved the formation of carbon film at 5 × 10² Pa. 65–90% of the strength in the as-received state was retained after the active-oxidation at 10² Pa and after the passive-oxidation at 5 × 10⁴ Pa. Surface imperfections produced very large decrease in tensile strength in the CO₂ partial pressure range of 5×10² to 10⁴ Pa.     

Microstructural development of Ti-24Al-14Nb-3V-0.5Mo alloy during hot tensile deformation

Microstructure of the Ti-24Al-14Nb-3V-0.5Mo (at.%) alloy deformed from room temperature to 700°C was studied by the H-800 transmission electron microscope (TEM) equipped with a side entry goniometer stage capable of ±45° tilt on the X or Y axis operating under two-beam condition. Especially dislocation types and slip systems of the ₂-phase (D0₁₉) were analyzed in accordance with invisibility criterion. The results indicated that with increasing the deformation temperature from room temperature to 700°C, the slip of -type dislocations on prismatic planes in the ₂-phase was enhanced whereas that on basal plane (0001) with hexagonal networks morphology was suppressed during tensile deformation. Being immobile, the dislocation networks were thought to be mainly responsible for the low ductility at low temperature. When the test temperature was increased to 700°C, the -type dislocation glide on pyramidal planes was also observed, but the hexagonal dislocation networks formed by the slip of -type dislocations on basal planes were hardly seen. During the high temperature deformation microstructural refinement was also observed due to dynamic recovery and recrystallization. This, together with the precipitation of secondary ₂ phase and O phase during deformation all contributed to ductility of the present alloy at high temperature.     

Binding of Spin Polarons in Doped Antiferromagnets

By means of variational wave functions which construction is based on the spin polaron picture we calculate the energies of two hole states in the t–J model classified according to the momentum and the different irreducible representations of the point group. We concentrate on ratios J/t interesting from the experimental viewpoint and compare our results to exact diagonalization. and p-like pair symmetries are energetically most favorable. The caterpillar-type motion of two holes connected by a string of spin defects is responsible for hole binding, whereas the well-known broken bond mechanism does not produce binding for t/J>0/4.     

Bi2Sr2CaCu2O8+δ c-Axis Twist Josephson Junctions: A New Phase-Sensitive Test of Order Parameter Symmetry

Li et al. found that the critical current density across atomically clean c-axis twist junctions of Bi ₂ Sr ₂ CaCu ₂ O ₈₊ is the same as that of the constituent single crystal, , independent of the twist angle ₀ , even at and below T _c . We investigated theoretically if a -wave order parameter might twist by mixing in d _xy -wave components, but found that such mixing cannot possibly explain the data near to T _c . Combined with group theoretical arguments, we then conclude that the order parameter contains at least a substantial s-wave component, but does not contain any purported -wave component, except possibly below a second, unobserved phase transition. By studying tunneling models, we further conclude that the intrinsic c-axis Josephson tunneling in Bi ₂ Sr ₂ CaCu ₂ O ₈₊ is likely to be mostly incoherent.     

Room-temperature oxidation of La2?xSrxCuO4

A series of oxidized La_2–x Sr _x CuO_4+y compounds has been prepared by treating the starting materials with a solution of Br₂ in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content and (ii) a slight decrease in a along the whole range ofx. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x0.15, whoseT _c's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed.     

Growth of aluminium nitride whiskers by sublimation-recrystallization method

Aluminium nitride (AlN) with various morphologies was fabricated through a sublimation-recrystallization method. The influences of type of reactor and temperature gradient were explored, as well as the orientations and growth mechanism of the obtained AlN whiskers. In the early stage of preparation, a vapour-liquid-solid (VLS) mechanism dominated, producing AlN pillars, whiskers and noncrystalline fibres. In the later stage, as the catalyst liquid was removed by volatilization, the pillars and noncrystalline fibres stopped growing, but the growth of AlN whiskers continued through a vapour-solid (VS) mechanism. By Laue method and rotating-crystal method of x-ray diffraction, together with electron diffraction, most of the AlN whiskers were discovered to grow on planes , or , where l=0, 1, 2, 3, along crystal axes , or , where w=0, 1, 2, 3. Oblique grown whiskers also appeared, with a growth direction at an angle of about 54° to the growth plane, .     

Field Dependence of the Superfluid 3He A 1 and A 2 Transitions

We present new results on the magnetic field dependence of the superfluid transition temperatures of the A ₁ and A ₂ phases of ³He. The transition temperature has been measured up to 15 T, the up to 12 T, at the melting pressure. The temperature was measured by an in situ field independent glass thermometer. The results are in agreement with extrapolations from earlier experiments, and with calculations of the splitting versus magnetic field. We were also able to obtain an estimate of the quadratic terms of the splitting, and of each of the transition temperatures. The measured quadratic terms are smaller than calculated, the negative coefficient for the quadratic term being quite unexpected.     

μ+SR Study on Bi2Sr2Ca1−x Y x (Cu1−y Zn y )2O8+δ around the Hole Concentration of \frac{1} {8} per Cu

In order to study the effect in different high-T _c oxides from the La-system, muon spin relaxation measurements were applied to the Zn-substituted Bi-2212 system, Bi ₂ Sr ₂ Ca _1–x Y _x (Cu _1–y Zn _y ) ₂ O ₈₊ , around the hole concentration p= per Cu. It has been revealed that the magnetic correlation between Cu spins is anomalously enhanced in the Zn-substituted samples at per Cu, proving the existence of the effect" in the Bi-2212 system as well.     

Structural features of Σ = 19, [110] GaAs tilt grain boundaries

= 19, [110] tilt grain boundaries have been observed to facet parallel to particular planes; the facets lie along _A/ _B, ( )_A/ )_B and ( )_A/( )_B. The structural unit of the = 19 ( )_A/( )_B [110] boundaries consists of 5- and 7-member rings, which are similar to the core structure of a/2[110] edge dislocations. The polarities in each grain on either side of the boundaries has been confirmed by CBED methods; a lower number of anti-site type cross-boundary bonds occur along the boundaries compared to when the polarity of one grain is reversed. The presence of 7-member rings and anti-site cross-boundary bonds results in a more open atomic structure at the boundary, shortening the distance between the first and the second {331} atomic planes from the boundary plane by 40%.