Synthesis and Para-conductivity Analyses of TlBa2(Ca 3 − y Mg y )Cu4 O 1 2 − δ Superconductors

TlBa ₂(Ca _3?yMg _y)Cu ₄ O _12?δ (y=0,0.5,1.0, 1.5,2) superconductors are synthesized at normal pressure, and the influence of doped Mg atoms on the superconductivity parameters at the microscopic level is investigated by carrying out para-conductivity analyses of conductivity data. The samples have shown tetragonal structure, and the unit cell volume decreases with increased Mg doping. The onset temperature of superconductivity [ T _c(onset)] and zero resistivity critical temperature [ T _c(R=0)] decreases with Mg. Maximum magnitude of diamagnetism is observed in the samples with Mg of y=2. The apical oxygen mode of the type Tl-O _A-Cu(2) and CuO ₂ planar oxygen modes are softened as observed in fourier transform infrared spectrometer (FTIR) absorption measurements. The fluctuation-induced conductivity (FIC) analyses of conductivity data have shown the enhancement of inter-plane coupling and coherence length along the c-axis. These analyses have shown an increase in the coherence length along the c-axis and the inter-layer coupling J. The enhancement of inter-plane may possibly be arising due to a small decrease in the value of the order parameter of the carriers from ∣ψ∣ ²=1 in the CuO ₂ planes in Mg-doped samples. The values of B _c0(T), B _c1(T), J _c(0) are suppressed with the increased incorporation of Mg, which most likely arises due to the weak coupling of the grains induced by Mg doping.     

Skeletal architecture and microstructure of the calcifying coral Fungia simplex

This study presents the characterization of the skeletal structure of the coral Fungia simplex, a hermatypic resident of the shallow zones of tropical reefs. In contrast to most cnidarians, this species has a unique multi-septal skeletal architecture. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed the skeletal microstructure to be made up of bundles of thin needles of prismatic crystals. X-ray diffraction (XRD) indicated that the crystals are composed of aragonite with a preferred orientation exposing the {221} planes parallel to the septal surface and tilted by 20° with respect to the growth (c-) direction.     

Study of CuO Nano-particles/CuTl-1223 Superconductor Composite

Synthesis and characterization of (CuO) _x /Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ ; {(CuO) _x /CuTl-1223} composites with x=0 %, 10 %, 15 % and 20 % have been reported. The fluctuations induced conductivity (FIC) analysis of (CuO) _x /CuTl-1223 composite has been carried out using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models in the temperature regime well above the critical temperature (T>T _c ). The electrical resistivity versus temperature curves of as-prepared and oxygen post-annealed (CuO) _x /CuTl-1223 composite were fitted by using above mentioned models to extract the microscopic parameters such as zero temperature coherence length along c-axis{ξ _c (0)}, inter-layer coupling (J), dimensional critical exponent (λ) and inter-grain coupling constant (α) etc. It has been observed that the cross-over temperature (T _o ) fits very well the two-dimensional (2D) and three-dimensional (3D) AL equations and shifts towards the lower temperature regime with the enhanced weight percentage of CuO nano-particles. The shifting of AL 3D region to higher temperature after oxygen post-annealing indicates the restoration of oxygen and optimization of charge carriers in conducting CuO₂ planes. The gradual decrease in the value of inter-grain coupling constant (α) with the increase of CuO nano-particles content reflects an improvement in the inter-grain coupling resulting into an increase in the coherence length (ξ _c ) along the c-axis. Almost all superconductivity parameters have been improved after oxygen post-annealing. The suppression of superconductivity parameters in the composite with x=20 % limits the optimum doping level of CuO nano-particles in (CuO) _x /CuTl-1223 composite.     

Fluctuation-Induced Conductivity Analysis of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Layered YBCO Single Crystal

In this work, a cylindrical YBa₂Cu₃O_7?x (Y123) sample having 20 mm diameter and 8 mm height was prepared by the cold-seeding method using an Nd123 seed, and the crystal growth process was performed in an alumina crucible with a Y₂O₃ layer. The structural orientation of the specimens was measured by an X-ray diffractometer (XRD). As a result of the X-ray diffraction data, only (00 l) peaks were observed, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Resistivity measurements of a 1.5-mm-thick rectangular sample were performed by a standard four-probe method at temperatures between 60 and 100 K at a rate of 4 K/min using a Physical Properties Measurement System (PPMS) under various constant magnetic fields from 1 to 5 T with the magnetic field parallel to the c-axis, which is the direction of pressing into the zero-field cooling regime (ZFC). Fluctuation-induced conductivity analysis was performed to investigate the availability of the sample for technology. The analysis showed that the critical exponents were in agreement with theoretical values; thus, it was seen that superconducting properties of the sample were good and the 3D fluctuation was dominant. Because of the large c?axis coherence length (ξ _c(0)) and small anisotropy, the superconducting properties became better. Furthermore, the fluctuations were reduced, and it was understood that the effective availability of the sample in technology will be possible.     

Effects of <Emphasis Type="Italic">β</Emphasis>-Sn grain <Emphasis Type="Italic">c</Emphasis>-axis on electromigration behavior in BGA Sn3.0Ag0.5Cu solder interconnects

The anisotropy of β-Sn grain can significantly affect the electromigration (EM) behavior in Sn3.0Ag0.5Cu (SAC305) solder interconnects. A real ball grid array (BGA) specimen with a cross sectioned edge row suffered electromigration for 600 h to investigate the effects of β-Sn c-axis on the behavior of electromigration in SAC305 solder interconnects. Scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used to obtain the microstructure and orientation of β-Sn grains in as-reflowed and low current density conditions. Besides, the orientation of c-axis had a great effect on the growth direction of IMCs in solder matrix. The solder interconnect with the Sn grain c-axis pointing the positive direction of ND would emerge serious electromigration phenomena. The density of Cu₆Sn₅ IMCs distributing at the surface of solder matrix increased obviously. However, when Sn grain c-axis was in the same direction with the opposite direction of ND, the original Cu₆Sn₅ IMCs in as-reflowed solder interconnect disappeared. Therefore, the results show that the solder interconnects will performance a different electromigration behavior due to the direction of c-axis in Sn grain: the growth direction of Cu₆Sn₅ IMCs in solder matrix will along the c-axis accompanied growing into solder matrix or gathering at the surface of the cross section.     

Transmission electron microscopy study of GdBa2Cu3O7−x containing nano-sized BaMO3 (M: Hf, Zr, Sn) rods fabricated by pulsed laser deposition

Three types of superconducting GdBa₂Cu₃O_7?x (GdBCO) layers containing rods of either BaHfO₃ (BHO), BaZrO₃ (BZO), or BaSnO₃ (BSO) were fabricated by pulsed laser deposition on Hastelloy substrates with a CeO₂ based textured buffer layer. The critical currents (J _c) values of the GdBCO layers containing those nano-rods are enhanced compared with those of pristine GdBCO layer in high magnetic fields. In order to investigate the relationships between their superconductive properties and their nanostructures, they were characterized in detail by transmission electron microscopy (TEM). TEM is the only method for direct observation of these nano-rods in the GdBCO grains. The GdBCO layers were mainly composed of c-axis oriented GdBCO grains containing numerous nano-sized rods. The crystal orientation relationships between the GdBCO and the nano-rods were as follows; (001)GdBCO//(001)nano-rods and (100)GdBCO//(100) nano-rods. The average diameters of the BHO and the BZO nano-rods were 4.5 and 5.6 nm, respectively. The BSO nano-rods were thicker than other rods. These nano-rods in the central region of the c-axis oriented GdBCO grains were aligned parallel to the c-axis of the GdBCO, while nano-rods in the outer region of the c-axis oriented grains were tilted away from the c-axis. With increase in the thickness of the GdBCO layers, the ratio of the BZO or the BSO nano-rods aligned parallel to the c-axis to those tilted away from the c-axis decreased, so that the J _c-B-θ profiles of the thicker GdBCO layers containing the BZO or the BSO nano-rods became flatter. The BHO nano-rods were homogeneously distributed throughout the GdBCO, and their average length of was less than that of the other nano-rods. The homogeneous distribution and short length of the BHO nano-rods enhanced the J _c values of the GdBCO layers containing them in high magnetic fields. The J _c-B-θ profiles of the GdBCO layers containing the BHO were independent of the layer thickness. From these results, we will discuss about the morphologies and distributions of suitable vortex pinning for applications of GdBCO coated conductor in high magnetic fields.     

Study on the doping effect of Li-doped ZnO film

Zinc oxide (ZnO) is an excellent piezoelectric material with simple composition. ZnO film is applied to the piezoelectric devices because it has high resistivity and highly oriented direction at c-axis. Structural and electrical properties in ZnO films are influenced by deposition conditions. Lithium-doped ZnO (LZO) films were deposited by RF magnetron sputtering method using Li-doped ZnO ceramic target with various ratios (0 to 10 wt.% LiCl dopant). LZO films revealed high resistivity of above 10⁷ Ω cm with smooth surface when they were deposited with 4% LiCl-doped ZnO target under room temperature. However, their c-axis orientation was worse than the c-axis orientation of pure ZnO films. We have also studied on structural, optical and electrical properties of the ZnO films by XRD, AFM, SEM, XPS, and 4-point probe analyses. We concluded that LZO films were deposited with 4 wt.% LiCl-doped ZnO target and were apposite for piezoelectrical application.     

Synthesis of rod-shaped LaNi5 alloy via solid reduction method

A novel chemical synthesis technique that a large quantity of rod-shaped LaNi₅ alloy has been successfully synthesized using a solid reduction method was reported. The as-prepared alloy, proven via the XRD spectrum, was single-phased and hexagonal. The SEM and TEM photographs showed that the alloy was rod-shaped with a diameter in the range of 300–500 nm, and length of about 6–10 μm. The SAED pattern of LaNi₅ alloy clearly indicated the orientation alignment along the c-axis.     

Crystalline thin films of β-phase poly(9,9-dioctylfluorene)

The detailed structure of crystalline β-phase poly(9,9-dioctylfluorene) (PFO) films was studied by polarized optical measurements, transmission electron microscopy, and grazing-incidence X-ray diffraction. Crystalline β-phase PFO thin films were fabricated by a friction transfer technique and subsequent vapor treatment. Compared to the α-phase, the lattice parameters of the β-phase crystals shrank along the a-axis (film thickness direction) and elongated along the b-axis (side-chain direction), but the period along the c-axis (main-chain direction) remained nearly equal. These changes in molecular packing were consistent with a planar conformational change from the α-phase to the β-phase of PFO.     

Tunable Magnetic Interaction of Co-Doped SiC Monolayer Under Electric Field: Ab Initio Study

The magnetic properties of Co-doped silicon carbide monolayer under an external electric field are investigated using a first-principles method. In the absence of the electric field, magnetism is observed for both Si (Co_Si) and C (Co_C) sites. Then, the interaction between two Co atoms has been studied in the Co_Si system. Both antiferromagnetic (AFM) and ferromagnetic (FM) states have been found. The results show that the FM behavior is originated by the p–d hybridization between Co and its neighboring C atoms. When an electric field was introduced along the c-axis, the interaction between two Co dopants switched from FM to AFM, which could be dominated by the competition between p–d exchange and superexchange. Moreover, the magnetic anisotropy (MA) prefers to parallel to the a-axis and seems not to be turned into the c-axis under the electric field.     

High-Field Magnetism of the S=5/2 Kagome-Lattice Antiferromagnet KFe3(OH)6(SO4)2 for the Magnetic Field in the Kagome-Plane

We have performed electron spin resonance (ESR) and magnetization measurements on single crystals of K-Fe-jarosite along the a-axis (in the kagome-plane). We have calculated the resonance branches and the magnetization curve using a spin Hamiltonian including the interlayer exchange and the Dzyaloshinsky-Moriya (DM) interactions. By putting the same parameter values for the analyses along the c-axis (normal to the kagome plane), the calculated results show satisfactory agreement with the experimental ones. As a result, we have successfully explained all the experimental results with one set of the intra- and the inter-plane exchange and the DM interaction parameters.     

Growth of highly oriented LiTaO3 thin film on Si with amorphous SiO2 buffer layer by pulsed laser deposition

High-quality single-phase, c-axis textured LiTaO₃ thin films have been deposited on Si(100) substrate with amorphous SiO₂ buffer layer for optic waveguide application by pulsed laser deposition under optimized conditions of 30 Pa oxygen pressure and 650 °C. The amorphous SiO₂ buffer layer with a thickness of 100 nm was coated on the Si(100) by thermal oxidation at 1000 °C. Li-enriched LiTaO₃ ceramic target was used during the deposition. In order to study the influence of oxygen pressure on the orientation, crystallinity and morphology, different oxygen pressures (10 Pa, 20 Pa, 30 Pa and 40 Pa) were used. X-ray diffraction (XRD) results showed that LiTaO₃ thin films exhibited highly c-axis orientation under 30 Pa. It was observed by scanning electron microscopy (SEM) that the as-grown film in the optimal conditions was characterized by a dense and homogeneous surface without cracks, and the average grain size was in the order of 25 nm.     

Investigation of the Upper Critical Magnetic Field and Activation Energy in MgB2 Thin Film

MgB₂ film with a thickness of about 600?nm was deposited on the MgO (100) single crystal substrate using a ??two-step?? synthesis technique. First, deposition of boron thin film was carried out by rf magnetron sputtering on MgO substrates and followed by a post deposition annealing at 850?°C in magnesium vapor. The upper critical field H _c2 has been estimated from temperature dependences of resistivity curves in both directions of the magnetic fields perpendicular and parallel to the c-axis. Resistivity measurements of the film were performed using a standard four-probe method under different magnetic fields up to 70?kOe in zero fields cooling regime. The upper critical magnetic field H _c2(0) at T=0?K for 90?% of R _n was calculated by the extrapolation H _c2(T) to the temperature T=0?K. The results showed that H _c2??ab(0) and H _c2??c(0) was found to be around 22?T and 18?T, respectively. Using extracted data, the zero-temperature coherence lengths and field anisotropy ratio were calculated. In order to determine the activation energy of thermally activated flux flow of the film, Arrhenius law was taken into account.     

c-Axis Transport in a Normal-State Bilayer Cuprate and Relation to Pseudogap

We study the effect of interband transitions on the normal-state optical conductivity, dc resistivity, and thermal conductivity along the c-axis, for a plane-chain bilayer cuprate coupled by a perpendicular hopping matrix element (t⊥). When t⊥ is small, the c-axis dc resistivity shows a characteristic upturn as the temperature is lowered, and the c-axis optical conductivity develops a pseudogap at low frequencies. As t⊥ is increased, intraband transitions start to dominate and a more conventional response is obtained. Similar pseudogap behavior is predicted in the thermal conductivity for which strong depression at low temperature is found. Analytical results for a simple plane-plane bilayer are also given, including the frequency sum rule of the optical conductivity.     

Superconducting behavior of high-T c YBa2Cu3O7 thin films with BaO impurity produced by pulsed laser deposition

We have investigated the superconducting behavior of high-T _c YBa₂Cu₃O₇ (YBCO) thin films containing BaO impure phase produced by pulsed laser deposition. The thin films were characterized by the standard four-probe method, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD showed that all these thin films contained BaO impurity, with thec-axis normal to the surface of the substrates. The presence of impurity existed from substrate temperatureT _s of 727 to 796°C. When these thin films with BaO impurity were measured under the magnetic fields, it was found that the critical current densityJ _c increased slightly with increase in magnetic fieldB within the range ofB≤500 G, in the case ofB perpendicular to thec-axis of the film.     

Effect of columnar defects on theJ c anisotropy of YBa2Cu3O7−δ thin films and YBa2Cu3O7−δ /PrBa2Cu3O7−δ multilayers

Epitaxial YBa₂Cu₃O_7?δ thin films (YBCO) and YBa₂Cu₃O_7?δ /PrBa₂Cu₃O_7?δ multilayers (Y/Pr) were irradiated with high-energy heavy ions (770 Mev²⁰⁸Pb) under various directionsφ relative to thec-axis. The irradiation resulted in columnar defects tilted byφ from thec-axis. The angular dependence of their pinning activity was studied by measuring the anisotropy of the critical current density. TheJ _c (B, T,?) behavior of the irradiated YBCO thin films showed an additional peak, which exceeds the intrinsic pinning peak, exactly at the irradiation direction. The Y/Pr multilayers, however, showed an isotropicT _c -enhancement by a factor of 5, without any additional structure in theJ _c(B, T,?) curve.     

Mechanical properties of Gd123 bulk superconductors at room temperature

In order to investigate the mechanical properties of Gd123 single-grain bulk superconductors fabricated using a modified quench and melt growth method, tensile tests in the direction parallel and perpendicular to the c-axis have been carried out at 293 K by using the small specimens cut from bulk superconductors. As for the mechanical properties perpendicular to the c-axis, there was no significant difference between those in the crystal growth direction and those perpendicular to it. While the average value of the Young’s modulus of the bulk sample with 33.0 mol%-Gd211 secondary phase particles, 118 GPa, was higher than that of the bulk sample with 28.7 mol%-Gd211, 111 GPa, the average value of the tensile strength of the former, 36 MPa, was lower than that of the latter, 40 MPa. The tensile strength and the Young’s modulus in the c-axis, 10 MPa and 37 GPa, were quite low compared with those mentioned above. Poisson’s ratio based on the transverse strain in the c-axis, 0.15, was significantly smaller than that perpendicular to it, 0.30. In the specimens with higher length, however, the difference was decreased to some extent. With regard to the anisotropy of the Poisson’s ratio, the effect of a pre-existing micro-crack opening in the c-axis direction was discussed coupled with the constraints at the interfaces between the specimen and the sample holder.     

Effect of Praseodymium Concentration on the Excess Conductivity Near the Critical Temperature of Y1−z Pr z Ba2Cu3O7−δ Single Crystals

The evolution of the excess conductivity in Y_1?z Pr _z Ba₂Cu₃O_7?δ single crystals has been studied by systematically increasing the praseodymium concentration (0.05≤z≤0.5). The concentration dependence of the coherence length along c axis ξ _c (0) on the praseodymium content has been determined. The praseodymium concentration reduction from 0.0 to 0.5 results in a substantial broadening of the temperature interval where the excess conductivity takes place. The ξ _c (0) value increases more than fourfold and the 2D–3D crossover point is shifted in temperature.     

c-axis phonons and the enhancement of pairing correlations in high-temperature superconductors

We consider the two-dimensional Hubbard model including electron-phonon interaction. Strong local correlations (U→∞ limit) are taken into account within the mean-field approximation for auxiliary boson fields. Phonon-assisted transitions between intraand interlayer states are introduced as the source of coupling between two-dimensional CuO₂ layers. This type of processes effectively leads to the nonlinear (quadratic) interaction of intralayer electrons withc-axis phonons. We construct the Eliashberg equations for the resulting Hamiltonian and evaluate the superconducting transition temperatureT _c. Our model calculation demonstrates that a pronounced enhancement ofT _c in thed-wave channel is possible. The largest enhancement ofT _c tends to take place for small hole concentrations. This means that the coupling toc-axis phonons could compete with two-dimensional correlations responsible for the onset of antiferromagnetic order. It is remarkable that the two-dimensional features in the normal state are hardly affected by this specific interlayer interaction. Therefore,c-axis two-phonon-mediated interlayer coupling can cooperate with interlayer pair tunneling and substantially contribute to an increased pairing.     

Intrinsic effect of anionic surfactant on the morphology of hydroxyapatite nanoparticles and its structural and biological properties

This paper describes the potential effect of anionic surfactant on the morphology of hydroxyapatite (HA) nanostructures during hydrothermal synthesis. Sodium dodecyl sulfate (SDS) was used as an anionic surfactant. Various concentrations of SDS were used to study morphological changes in HA due to the presence of the surfactant. The final morphology, after treatment by a hydrothermal method, revealed that the anionic surfactant induced growth in one direction (a-axis) and inhibited growth in the other (c-axis) based on the charge distribution on the crystal faces of HA. Further structural analysis (by X-ray diffraction) confirmed this growth along the a-axis. In-vitro cellular analysis revealed that the plate-like nanoparticles possess better bioactivity than their bulk counterparts. Therefore, HA nanoplates could be used for applications that include controlled drug delivery and bone mineralization.