Texture development in Bi1.5Pb0.5Sr1.7Y0.5Co2O9−δ layered cobaltite by high-temperature compression deformation and its effect on thermoelectric properties

Texture development in Bi_1.5Pb_0.5Sr_1.7Y_0.5Co₂O_9−δ (BPSYO) layered cobaltite by plastic deformation is examined experimentally by high-temperature uniaxial compression, in order to develop a method to reduce the resistivity of thermoelectric cobaltite by controlling the spatial arrangement of the (0 0 1) conductive CoO₂ layers. It is found that the present oxide can be plastically deformed up to a true strain of −2.2 at 1113 K with strain rates in the order of 10⁻⁵ s⁻¹. It is concluded that high-temperature compression is effective both for densification and texture development. Evolution of (0 0 1) (compression plane) texture is experimentally confirmed as expected from the crystal structure, where a dislocation that has a small Burgers vector may move in the (0 0 1) plane. The formation of a sharp (0 0 1) texture results in a reduction in resistivity to about one-tenth of that of the specimen without texture. The estimated value of the dimensionless thermoelectric figure of merit is 0.11 at 973 K, which is close to the practical level of a thermoelectric material.     

A transmission electron microscopy study of the A-site disordered perovskite Na0.5Bi0.5TiO3

A transmission electron microscopy study of Na_0.5Bi_0.5TiO₃ (NBT) crystals shows two types of ferroelectric domains characterized by interface boundaries lying in the {1 1 0}_C and {1 0 0}_C planes. A one-dimensional {1 0 0}_C modulated texture is also observed locally. The electron diffraction study reveals the presence of (0 0 1)_T tetragonal platelets a few cells thick within the R3c matrix. They develop within the three basal {1 0 0}_C planes of the prototype phase and represent relics of the high-temperature tetragonal phase. The loss of symmetry compared to the average structure of NBT can thus clearly be attributed to the existence of these tetragonal platelets. The {1 0 0}_C modulated texture corresponds to a modulation of strain induced by the coexistence of two types of octahedra tilting systems: a⁻a⁻a⁻ for the rhombohedral matrix and a⁰a⁰c⁺ for the tetragonal platelets. These (0 0 1)_T platelets indirectly intervene in the relaxation process classically encountered at about 230 °C, in marked contrast to the behaviour of Pb(Mg_1/3Nb_2/3)O₃.     

MFM analysis of the magnetization process in L10–A1 FePt patterned film fabricated by ion irradiation

Ga⁺ ions at a dose of 0.1 at.% (1.5 × 10¹⁴ ions cm⁻²) were irradiated by focused ion beam (FIB) onto L1₀ FePt films with a [0 0 1] crystalline texture normal to the film plane, and two-dimensional patterns composed of squares with high-coercivity (L1₀ structure, 300 × 300 nm² and 100 × 100 nm²) separated by a soft magnetic region (A1 structure) 100 nm wide were fabricated. The magnetic domain structure of patterned film was observed by in-field magnetic force microscopy (MFM). In the remanent state, the domain with magnetization normal to the film surface was observed in the central part of the L1₀ square, while the narrow domain with reversed magnetization is at the circumference of the square. The magnetization process is discussed based on the MFM observations.     

Effect of additives on the properties of plasma electrolytic oxidation coatings formed on AM50 magnesium alloy in electrolytes containing K2ZrF6

A plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was obtained in a K₂ZrF₆–NH₄H₂PO₄–KF–C₆H₅O₇Na₃ electrolyte solution. The influence of the electrolytes on the properties of the PEO coating had been investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), roughness determination and electrochemical measurements. The experimental results show that 10 g L^? 1 K₂ZrF₆ and the presence of 8 g L^? 1 NH₄H₂PO₄ are beneficial for the passivation effect of the solution on AM50 Mg alloy as well as the compactness of the PEO coating. Many pores with large dimension on the surface of the coating are filled with coating compounds (mainly MgF₂), and the characteristics of these pores are influenced by the concentration of KF. The addition of KF and C₆H₅O₇Na₃ enhances the growth rate of the coating. The coating shows high corrosion resistance in the presence of 10 g L^? 1 K₂ZrF₆ combined with 8 g L^? 1 NH₄H₂PO₄, 3 g L^? 1 KF and 5 g L^? 1 C₆H₅O₇Na₃.     

Highly (1 0 0)-textured Pb(Zr0.52Ti0.48)O3 film derived from a modified sol–gel technique using inorganic zirconium precursor

Highly (1 0 0)-textured Pb(Zr_0.52Ti_0.48)O₃ films have been prepared on platinized silicon substrate by a modified sol–gel technique using inorganic zirconium precursor. The X-ray diffraction analysis on the crystallinity and texture evolution of sol–gel lead zirconate titanate (PZT) films revealed that the films were well crystallized to perovskite phase when annealed at 550 °C, and that highly (1 0 0) preferred orientation dominated in the PZT films after annealed at 650 °C. The (1 0 0)-oriented PZT film exhibited the remnant polarization of 26.3 μC/cm² and the coercive field of 100 kV/cm.     

Influence of microstructure on the chemical inhomogeneities in nanostructured longitudinal magnetic recording media

Energy-filtered transmission electron microscopy and spectrum imaging at nanometer spatial resolution were used to correlate microstructure, specifically crystallographic texture and grain-boundary character, with the chemical inhomogeneities in sputtered CoCrPtB thin-film media. These data show that the average Cr grain boundary segregation is reduced in the sputtered CoCrPtB material with a strong (1 1 0)_Co texture compared to a microstructure with a weak (1 0 0)_Co texture.     

Effects of degree of deformation on the microstructure,mechanical properties and texture of hybrid-reinforced titanium matrix composites

Titanium matrix composites reinforced by TiB whiskers and La₂O₃ particles are synthesized in a consumable vacuum arc remelting furnace by an in situ technique based on the reaction between Ti, LaB₆ and oxygen in the raw material. The titanium matrix composites are hot rolled with degrees of deformation of 60%, 80%, 90% and 95%. The effects of the hot rolling degree of deformation on the mechanical properties of the composites are investigated by experiment and modeling. In particular, the variation in the inclination of the TiB whiskers during rolling is quantified in the model. The results show that, with increasing degree of deformation, the mechanical properties of composites are improved. Modeling of the mechanical properties reveals that grain refinement and TiB whisker rotation during rolling contribute to the improvement in the yield strength of the titanium matrix composites. Electron backscatter diffraction and transmission electron microscopy observations are used to study the texture of the composites. It is found that the orientation relationships between Ti matrix and TiB whiskers are [1 1 ?2 0]_Ti || [0 1 0]_TiB, (0 0 0 1)_Ti || (0 0 1)_TiB and (1 ?1 0 0)_Ti || (1 0 0)_TiB. TiB whiskers rotate in the rolling direction (RD) with increasing degree of deformation, which results in a higher intensity [1 1 ?2 0]_Ti || RD fiber due to the special orientation relationship between TiB and the Ti matrix.     

Preparation and properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The NbMo-matrix composites reinforced with (0–60 vol%) ZrB₂ were fabricated by hot-pressing at 2400 °C for 10 min under a pressure of 50 MPa in dynamic vacuum in the induction heating furnace specially designed in our institute. The optimum ZrB₂ content in NbMo solid solution was determined to be 30 vol% for excellent comprehensive mechanical property. NbMo-30 vol% ZrB₂ has the highest density of 99.63%, the most uniform microstructure, high fracture toughness of 5.75 MPa m^1/2. The highest ZrB₂ concentration that reacts with NbMo solid solution is at the range of 30 to 45 vol%. The types of the formed niobium borides were decided by the original ratio of Nb to B. The distribution of Mo and Zr was mutually exclusive in low ZrB₂ content composites, however, there was Mo₂Zr in high ZrB₂ content composite. Except for NbMo-45 vol% ZrB₂, the compressive strength increased with ZrB₂ content (from 927.09 MPa to 1635.91 MPa). The Young's modulus values were directly proportional to ZrB₂ content. The fracture toughness (from 6.34 MPa m^1/2 to 3.99 MPa m^1/2) was inversely proportional to ZrB₂ content. The big residual ZrB₂ particles in high ZrB₂ content samples such as NbMo-45 vol% ZrB₂ and NbMo-60 vol% ZrB₂ was the main reason for nonhomogeneous microstructure, low density (94.09% and 94.83%, respectively) and low fracture toughness (4.58 MPa m^1/2 and 3.99 MPa m^1/2, respectively).     

A molecular dynamics simulation study of the velocities,mobility and activation energy of an austenite–ferrite interface in pure Fe

Molecular dynamics simulations have been used to obtain the mobility, in pure Fe, of a face-centered cubic (fcc)–body-centered cubic (bcc) interphase boundary with an orientation given by (1 1 0)_bcc//(7 7 6)_fcc and [0 0 1]_bcc//[?1 1 0]_fcc. The interface is best described by a 4.04° rotation, about an axis lying in the boundary plane, from the Nishiyama–Wasserman orientation and the boundary consists of a parallel array of steps (disconnections). An embedded atom method interatomic potential was employed to model Fe, and the free energy difference as a function of temperature between the fcc and bcc phases, which provided the driving force for boundary motion, was determined by a thermodynamic integration procedure. Although the boundary was found to be very mobile, the transformation did not proceed by a martensite mechanism. The boundary mobility was obtained for several temperatures in the range 600–1400 K and Arrhenius behavior was found with an activation energy of 16.5 ± 2.7 kJ mol^?1 and a pre-exponential factor equal to 7.8( ± 0.9) × 10^?3 mmol J^?1 s^?1. The activation energy is much lower than that extracted from experiments on the massive transformation in Fe alloys and possible reasons for the discrepancy are discussed.     

Effect of boron doped fullerene C60 film coating on the electrochemical characteristics of silicon thin film anodes for lithium secondary batteries

In this work, boron doped fullerene (B:C₆₀) films were prepared by the radio frequency plasma assisted thermal evaporation technique for use as a coating material for the silicon thin film anode in lithium secondary batteries. Raman and XPS analyses revealed that the boron atoms were well inserted into the fullerene film lattices. The effect of the B:C₆₀ film on the electrochemical characteristics of the silicon thin film was studied by charge–discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The B:C₆₀ coated silicon film exhibited a high reversible capacity of more than 1200 mAh g^?1 when cycled 50 times between 0 and 2 V at a current density of 1200 μA cm^?2 (1.5 C). The film also showed good rate capacity at different current densities and a more improved coulombic efficiency of 87.7% in the first cycle in comparison with that of the C₆₀ coated film electrode.     

BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates

BiFeO₃ (BFO) thin films of varying degrees of (1 1 1) orientation were successfully grown on SrRuO₃-buffered Pt/TiO₂/SiO₂/Si(1 0 0) substrates by off-axis radio-frequency magnetron sputtering. They demonstrate much enhanced ferroelectric behavior, including a much enhanced remnant polarization (2P_r ～ 197.1 μC cm^?2 at 1 kHz) measured by positive-up negative-down (PUND), at an optimized deposition temperature of 590 °C. The effects of film deposition temperature on the degree of (1 1 1) orientation, film texture, ferroelectric behavior, leakage current and fatigue endurance of the BFO thin films were systematically investigated. While the degree of (1 1 1) orientation is optimized at 590 °C, the defect concentration in the film increases steadily with increasing deposition temperature, as demonstrated by the dependence of leakage behavior on the deposition temperature. The polarization behavior is shown to strongly depend on the degree of (1 1 1) orientation for the BFO thin film. Oxygen vacancies are shown to involve in the conduction and dielectric relaxation of the BFO thin films deposited at different temperatures, as demonstrated by their dielectric and conduction behavior as a function of both temperature (in the range 294–514 K) and frequency (in the range 10^?1–10⁶ Hz).     

Effect of deformation and annealing on the formation and reversion of ε-martensite in an Fe–Mn–C alloy

Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1 1 2 9}〈3 3 6 2〉. The orientation relationship {1 1 1}^γ//{0 0 0 1}^ε and 〈110〉^γ//〈1 1 –2 0〉^ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite.     

Orientation dependence of the electrochemical corrosion properties of electrodeposited Cu foils

In this study, the electrochemical corrosion properties of electrodeposited Cu foils in a CuCl₂-containing acidic etching solution were investigated. The main passive product was CuCl and a trace amount of Cu₂O can also be detected. The (2 2 0)-oriented Cu foils exhibited higher corrosion potential and lower corrosion current density than those with (1 1 1) or (2 0 0) texture, suggesting a superior corrosion resistance against the etching solution. It is proposed that the preferred orientation and thus the differences in atomic stacking density on specific planes dominated the corrosion properties of the electrodeposited Cu foils instead of grain size or surface roughness.     

TEM analysis of the microstructure in TiF3-catalyzed and pure MgH2 during the hydrogen storage cycling

We utilized transmission electron microscopy (TEM) analysis, with a cryogenically cooled sample stage, to detail the microstructure of partially transformed pure and titanium fluoride-catalyzed magnesium hydride powder during hydrogenation cycling. The TiF₃-catalyzed MgH₂ powder demonstrated excellent hydrogen storage kinetics at various temperatures, whereas the uncatalyzed MgH₂ showed significant degradation in both kinetics and capacity. TEM analysis on the partially hydrogen absorbed and partially desorbed pure Mg(MgH₂) revealed a large fraction of particles that were either not transformed at all or were completely transformed. On the other hand, in the MgH₂+TiF₃ system it was much easier to identify regions with both the hydride and the metal phase coexisting in the same particle. This enabled us to establish the metal hydride orientation relationship (OR) during hydrogen absorption. The OR was determined to be (1 1 0)MgH₂ || (?1 1 0 ?1)Mg and [?1 1 1]MgH₂ || [0 1 ?1 1]Mg. During absorption the number density of the hydride nuclei does not show a dramatic increase due the presence of TiF₃. Conversely, during desorption the TiF₃ catalyst substantially increases the number of the newly formed Mg crystallites, which display a strong texture correlation with respect to the parent MgH₂ phase. Titanium fluoride also promotes extensive twinning in the hydride phase.     

Fabrication and thermoelectric properties of highly textured NaCo2O4 ceramic

Highly textured NaCo₂O₄ polycrystalline sample was fabricated by means of the cold high-pressure compacting followed by the solid-state reaction. X-ray diffraction and scanning electron microscope were employed to show that the plate-like grains within the sample are aligned along the pressing direction. The resistivity ρ and thermoelectric power S along the preferred {0 0 1} plane were measured in the whole temperature range from 15 to 973 K in air and the correlation between thermoelectric properties and texture was investigated. It was found that both ρ and S exhibit metallic behavior in the whole temperature range and the above sample exhibits lower ρ and higher S due to high texture and density. The power factor exhibits a steep rise above 400 K and reaches 761 μW m⁻¹ K⁻² at 973 K, suggesting a promising candidate for thermoelectric application at higher temperature. The change of slope in both resistivity and thermoelectric power curves at about 450 K might arise from the spin-state transition of Co ions in the CoO₂ blocks.     

Structure and magnetoresistive properties of current-perpendicular-to-plane pseudo-spin valves using polycrystalline Co2Fe-based Heusler alloy films

We report current-perpendicular-to-plane giant magnetoresistance (CPP–GMR) of pseudo-spin valves (PSVs) with polycrystalline Co₂Fe(Al_0.5Si_0.5) (CFAS) and Co₂Fe(Ga_0.5Ge_0.5) (CFGG) Heusler alloy films. Strongly [0 1 1] textured polycrystalline Heusler alloy films grew on the Ta/Ru/Ag underlayer. Relatively large CPP–GMR values of ΔRA up to 4 mΩ μm² and ΔR/R up to 10% were obtained with 5 nm thick Heusler alloy films and Ag spacer layer by annealing CFAS PSV at 450 °C and CFGG PSV at 350 °C. Transmission electron microscopy revealed a flat and sharp interface between the [0 1 1] textured CFAS layers and the [1 1 1] textured Ag spacer layer. Annealing above an optimal temperature for each PSV led to reductions in MR values as a result of the thickening of the spacer layer induced by the Ag diffusion from the outer Ag layers.     

Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings

Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS₂/Sb₂O₃/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS₂ (～0.007). However, unlike pure MoS₂ coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ～1.2–1.4 × 10^?7 mm³ Nm^?1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS₂ with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS₂, resulting in predominantly self-mated “basal on basal” interfacial sliding and, thus, low friction and wear.     

Effect of heat treatment on pseudoelasticity in Fe–25.0 at.% Al single crystals

The pseudoelastic behaviour of Fe–25.0 at.% Al single crystals annealed in the D0₃, (α + D0₃), (α + B2) or B2 phase region was examined focusing on the dislocation and ordered domain structures. When large pseudoelasticity appeared in the crystals, 1/4[111] superpartial dislocations moved individually dragging the nearest-neighbour antiphase boundaries (NNAPB). During unloading, the superpartials were pulled back by the surface tension of the NNAPB resulting in pseudoelasticity. Large pseudoelasticity took place only in the D0₃-ordered crystals, while the crystals annealed in the (α + D0₃), (α + B2) or B2 phase region exhibited small strain recovery. The surface tension of the NNAPB in the D0₃ phase was higher than that in the B2 one resulting in the larger recoverable strain in the D0₃-ordered crystals. Since a specific type of ordered domain boundaries in the D0₃ phase played an important role in the pseudoelasticity, a coarsening of the ordered domains caused a decrease in strain recovery.     

Trigonal Ir9Al28, a new structure type and approximant to decagonal quasicrystals

During an investigation of the binary system Al–Ir, a new phase with composition Ir₉Al₂₈ was identified. After annealing at 780 °C, its structure was determined by single-crystal X-ray diffraction. Trigonal Ir₉Al₂₈ is the first representative of a new structure type with Pearson symbol hP236-14, a = b = 12.2864(4) Å, c = 27.341(1) Å, γ = 120°, space group P31c, no. 159. The crystal structure can be described likewise as stacking of eight puckered and flat layers with a sequence …P⁰PFpp⁰pⁱFⁱPⁱ… along [0 0 1], as a six-layer stacking sequence along [1 0 0], or as packing of pseudo-Mackay icosahedra. The Ir substructure with pseudosymmetry P6₃/mmc resembles the V₄Al₂₃ structure type. Pentagonal columnar clusters running along [0 0 1] show close resemblance to decagonal quasicrystals with six-layer period along the 10-fold axis.     

Phase equilibria between the B2, L12, and fcc phases in the Ir–Ni–Al system

The isotherms of the Ir–Ni–Al in the composition range up to 50 at% Al are presented at 1573 K. The phase constitution and microstructure of the Ir–Ni–Al alloys were examined using X-ray diffractometry (XRD), scanning electron microscopy (SEM) with an electron probe microanalyzer (EPMA), and transmission electron microscopy (TEM) after heat treatment at 1573 K for 168 h. The B2-NiAl and B2-IrAl phases connected with each other at 1573 K. The highest solubility limit of Ir into Ni₃Al was about 3.5 at% in the tested alloys. Then, a wide fcc + B2 and a narrow fcc + L1₂ and B2 + L1₂ two-phase region appeared in the isothermal section. In part of the B2 phase, a martensitic transformation from the B2 to the L1₀ phase was observed.