GaxIn1 ? xBiyAszSb1 ? y ? z/InSb and InBiyAszSb1 ? y ? z/InSb heterostructures grown in a temperature gradient

Heterophase equilibria in the Ga _x In_{1 − x} Bi _y As _z Sb_{1 − y − z} -InSb and InBi _y As _z Sb_{1 − y − z} -InSb systems have been analyzed within the simple solution approximation. Ga _x In_{1 − x} Bi _y As _z Sb_{1 − y − z} /InSb and InBi _y As _z Sb_{1 − y − z} /InSb heterostructures have been grown in a temperature gradient, and their composition and structural perfection have been assessed.     

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.     

Electrical properties and microstructure of CdxHg1 ? x ? yCrySe crystals

Crystals of the Cd _x Hg_{1 − x − y} Cr _y Se (x = 0.4, y = 0.1) quaternary solid solution have been grown by the Bridgman method, and their microstructure and electrical properties have been studied. The crystals are shown to contain various types of inclusions in the form of filaments and triangles.     

Characterizations of InzGa1?z As1?x?yN xSbyP-i-N structures grown on GaAs by molecular beam epitaxy

The GaAs-based double-heterojunction P-i-N structures using In_zGa_1–zAs_1–x–yN_xSb_y as the i-layer is investigated for the first time using solid source molecular beam epitaxy. High quality coherent bulk InGaAsN_3.45%Sb (0.5 m) with a lattice-mismatch of 2.6 × 10^–3 can be achieved due to the surfactant properties of antimony, while the bulk InGaAsN_2% at 0.5 m with 1.06× 10^–3 mismatch is fully relaxed. Rapid thermal annealing (RTA) resulted in 25 meV low temperature (LT) photoluminescence (PL) full-width half-maximums (FWHM) for the bulk InGaAsNSb layers. InGaAsNSb experiences 30% less blueshifting with subjected under the same annealing conditions as InGaAsN with similar N content. Room temperature (RT) absorption measurements are in the range of 0.9–1.4 eV. The absorption edge of 1.41 m is achieved for sample D4.     

Electrical conductivity of LaCoxFe1 ? xO3 ? δ and LaLi0.1CoxFe0.9 ? xO3 ? δ (0 ≤ x ≤ 0.4) oxides

We have studied the effect of Co and Li concentrations on the phase composition and electrical conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} and LaLi_0.1Co _x Fe_{0.9 − x} O_{3 − δ} perovskite-like oxides synthesized in air at 1470 K. Single-phase materials with an orthorhombic crystal structure were obtained in the range 0 ≤ x ≤ 0.3. The composition dependences of conductivity have a minimum at x _c = 0.1 and 0.2, respectively. In the range x > 0.1, the conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} increases with increasing Co concentration for T > 700 K and decreases for T < 600 K. The conductivity of La(Li_0.1Co _x Fe_{0.9 − x} )O_{3 − δ} in the range 0 ≤ x ≤ 0.1 and for x ≥ 0.2 increases with Co concentration throughout the temperature range studied.     

On the high-temperature superconductivity of SrxLa2?xCuO4?δ

The superconducting properties of Sr_xLa_2–xCuO_4– are analyzed by employing the model of interaction between charge carriers and the oxygen-displacive modes of the lattice. The role played by the hole concentration, as related to the Sr content x and oxygen deficiency, is thoroughly emphasized. The critical temperature, the ratio of twice the superconducting gap to the critical temperature, and the isotope shift are estimated as functions of the hole concentration and compared with the experimental data.     

Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25?xCo0.75?xCu2xO3?δ and LaMn0.75?xCo0.25?xCu2xO3?δ

This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ and LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO₃–LaCoO₃–“LaCuO₃”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ), the Mn-rich series (LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (α_max = 19.6 × 10⁻⁶ K⁻¹) and electrical conductivity (σ_max = 730 S/cm at 800 °C) than the Mn-rich series (α_max = 10.6 × 10⁻⁶ K⁻¹, σ_max = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15. I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India.     

Band gap modified Al-doped Zn1?xMgxO and Zn1?yCdyO transparent conducting thin films

Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films were prepared on glass substrates by sol–gel method. The codoping thin films showed preferential c-axis orientation, and the lattice constant c evaluated from the shift of the position of (002) peak displayed an increasing evolution from x = 8 at.% to y = 8 at.%, indicating a roughly statistical substitution of Mg²⁺ and Cd²⁺ for Zn²⁺ in their solid solution. The effects of narrowing and widening band gap (E _g) on conductivity of (Cd, Al) and (Mg, Al) codoped ZnO thin films were simultaneously investigated using transmission spectra and electrical measurements. The transmittances of these films are obviously decreased by vacuum annealing to 50–60%. However, the carrier concentration and Hall mobility both increase, and resistivity decreases with narrowing band gap in 1 at.% Al-doped Zn_1−x Mg _x O and Zn_1−y Cd _y O thin films from x = 8 at.% to y = 8 at.%. It is revealed that the conductivity of Al-doped ZnO thin films could be enhanced by this simple band gap modification.     

Electronic Properties and Superconductivity of Electron-Doped La1?x/2Pr1?x/2CexCuO4

La_1−x/2Pr_1−x/2Ce _x CuO _y (LPCCO) samples with doping level up to 20% have been synthesized and their electronic and superconductive properties are studied. X-ray diffraction revealed that the LPCCO system is a pure phase system with a T’214 structure. Magnetic and resistive measurements show that the system is superconducting at 0.08≤x<0.20 with T _cmax=25 K at x=0.12. An anti-ferromagnetism transition was also observed in under-doped PLCCO (x=0.05) with the window width of the anti-ferromagnetism phase being significantly narrower than that NCCO and PCCO systems. The behavior of the Ce doping is compared with Sr doping in this system, and the mechanism is discussed.     

Laser bonding and characterization of Kapton? FN/Ti and Teflon? FEP/Ti systems

Kapton^? FN and Teflon^? FEP (fluorinated ethylene propylene) polymers are resistant to most chemical solvents, heat sealable, and have low moisture uptake, which make them attractive as packaging materials for electronics and implantable devices. Kapton^? FN/Ti and Teflon^? FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Laser-bonded samples were tested with a micro-testing machine under lap shear load and the bond strength was determined. The bond strength for the Kapton^? FN/Ti and Teflon^? FEP/Ti systems was found to be 3.32 and 8.48 N/mm², respectively. The failure mode of the mechanically tested samples was studied by using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Chemical interactions during laser bonding of Kapton^? FN to titanium were studied by using X-ray photoelectron spectroscopy (XPS). The XPS results give evidence for the formation of Ti–F bonds in the interfacial region.     

Ferromagnetic Resonance in Ga1?xMnxAs

We report on ferromagnetic resonance measurements of Ga_1–x Mn _x As thin films with Mn contents 0.022 x 0.051. For x 0.036 and the external magnetic field normal to the thin film, we observe several resonances, which we identify as spin wave resonances. The non-quadratic mode spacing can be consistently explained by a linear gradient in the magnetic properties of the films. From the measurements, the exchange constant A can be deduced for different Mn contents x.     

Relation of Structure and Superconductivity in Self-compensated Y1?xCaxBa2Cu3?xAlxOz System

The co-doped compounds of Y_1−x Ca _x Ba₂Cu_3−x Al _x O _z , with x from 0.1 to 0.4, were synthesized through a solid-state reaction method. Structural and superconducting properties have been investigated by X-ray diffraction, Rietveld refinement, and DC magnetization measurement. The lattice constant a decreases while b increases with the addition of x. The difference between a and b diminishes gradually. Careful study of the crystalline structure shows that the critical temperature (T _c ) changes monotonically with some local structural parameters, such as the difference between Ba and Cu(2) atoms’ Z coordinates, the bond length of Cu(2)–O(4), and the bond angle of Cu(2)–O(2)–Cu(2), which are all closely related to the interaction between the perovskite block and the rock salt block in the unit cell. The results indicated that the influence of the crystalline structure on superconductivity is important and independent of the carrier concentration.     

Normal-state Conduction Mechanisms in GdBa2Cu3?xRuxO7?δ Superconducting Phase

Bulk superconducting samples of type GdBa₂Cu_3−x Ru _x O_7−δ , Gd-123, with x=0.0–0.3 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD), scanning electron microscope (SEM), electron dispersive X-ray (EDX) and electrical-resistivity measurements were performed in order to investigate the effect of Ru⁴⁺ ions substitution on Gd-123 phase. Enhancement of both phase formation and the superconducting transition temperature T _c for GdBa₂Cu_3−x Ru _x O_7−δ phase up to x=0.05 was observed from XRD and electrical-resistivity measurement, respectively. This enhancement was confirmed with the calculated relative volume fraction. For x>0.05, suppression of both phase formation and T _c was obtained and the superconductivity was completely destroyed around x=0.3. The normal-state electrical resistivity was analyzed by the two- and three-dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap CG. The results showed that the dominant mechanism was CG for x≤0.075, while was 3D-VRH for x≥0.15.     

Kinks in the a/2?111? screw dislocation in Ta

We study the structure and formation energy of kinks in the 1/2a〈111〉 screw dislocations in metallic Tantalum (Ta) using molecular dynamics with a first principles based many-body interatomic potential. In our study, four a/3〈112〉 kinks are constructed in a quadrupole arrangement in the simulation cell. To the simulation cell, we impose periodic boundary conditions in the directions perpendicular to the [111] direction and fix boundary condition in the [111] direction. We find that two, energetically equivalent, core configurations for the 1/2a〈111〈 dislocation lead to 8 distinguishable single kinks and 16 kinds of kink pairs. The different mismatches of the core configurations along [111] direction attributed to the differences in the formation energy for various types of kinks. Formation energies for all possible kinds of isolated single kinks and kink pairs have been determined. It was found that 0.730 eV was the lowest energy cost to form a kink pair in the a/2〈111〉: screw dislocation in Ta. This revised version was published online in June 2006 with corrections to the Cover Date.     

Neutron structural investigations of Y1?xCaxBa2Cu3?yCoyO7±δ

The results of a systematic powder neutron study on Y_1–x CaxBa₂Cu_3–y Co _y O_7± for A (x=y=0), B (x=0;y=0.2), C (x= 0;y=0.4), D (x=y=0.2), and E (x=y=0.4) are investigated with a view to understanding the relation between the structural parameters and superconductivity. Rietveld refinements of the structures show that: (a) Co substitutes at the chain Cu(1) sites only, except for sample E, where the presence of a minor amount of Co at the planar Cu(2) site cannot be ruled out; (b) Co substitution reduced thec-parameter, which is reduced even further upon substitution of Ca at the Y-sites; (c) the occupancy factors of the chain O(1) site indicate an average coordination of 4.8 and 5.1 for Co for samples B and C, but only 4 for D and E; (d) Cu/Co(1) atoms for B and C display large thermal parameters, suggesting a displacement from their ideal centrosymmetric location; (e) the apical Cu(1)-O(4) bond lengthens upon substitution of Co in samples B and C but undergoes shortening upon substitution of Ca in the case of samples D and E. The apical Cu(2)-O(4) bond, on the other hand, shows just the opposite trend; (f) samples D and E show a reduction in the separation of CuO₂ layers and their oxygen content; and (e) the bond valence of the Cu(2) ion shows the lowest value of 2.127 for the nonsuperconducting sample C.     

Molecular beam epitaxy of Pb1 ? xEuxTe and Pb1 ? xSnxTe layers and related periodic structures

Layers and periodic Bragg structures based on Pb_{1 − x} Eu _x Te (0 < x < 1) and Pb_{1 − x} Sn _x Te (0 < x < 0.1) ternary solid solutions have been grown on (111) BaF₂ and (111) Si substrates by molecular beam epitaxy. X-ray diffraction measurements show that the layers in three-period EuTe/Pb_0.94Eu_0.06Te structures maintain the [111] crystallographic orientation normal to the substrate plane. In the interface plane, the [110] directions of the layers and substrate are parallel to each other. The full width at half maximum of the rocking curve of each layer of both the binary and ternary compounds is about 20′. The large optical contrast (40%) in such structures allowed us to reach 99.9% mid-IR reflectivity.     

Crystal structure and magnetic properties of high-coercivity Sr1 ? xPrxFe12 ? xZnxO19 solid solutions

Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe₂O₃, ZnFe₂O₄, and PrFeO₃. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe₂O₃ at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρ_x of the magnetoplumbite phase vary linearly according to the relations a(?) = 5.8869 − 0.0162x, c(?) = 23.027 + 0.449 x, V(?³)= 691.10 + 9.65x, and ρ_x(g/cm³) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr³⁺ for Sr²⁺ and Zn²⁺ for Fe³⁺ in the SrFe₁₂O₁₉ ferrite (formation of Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (n _s) of the x = 0.1 ferrite exceeds that of SrFe₁₂O₁₉ by 1.7% at 6 K and by 15.2% at 308 K. The 308-K n _s and coercive force (_σ H _c) of the x = 0.2 ferrite exceed those of SrFe₁₂O₁₉ by 7.6 and 8.5%, respectively.     

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.     

Microstructure and Young’s modulus of high-pressure LixNa1 ? xTayNb1 ? yO3 ceramics

The microstructure and elastic properties of ceramic samples of high-pressure Li _x Na_{1 − x} Ta _y Nb_{1 − y} O₃ perovskite solid solutions have been studied for the first time in relation to their composition and the synthesis temperature. The results demonstrate that, with increasing sintering temperature, the Young’s modulus of the Li_0.17Na_0.83Ta _y Nb_{1 − y} O₃ solid solutions decreases, which can be understood in terms of the recrystallization behavior of the disordered solid solutions under high-pressure synthesis conditions.     

Influence of Co Doping on the Zn Distribution in?Nd1.05Ba1.95Cu3?xZnxOz

The structural effects of Zn doping and Zn, Co co-doping in Nd_1.05Ba_1.95Cu₃O _z have been investigated by using neutron diffraction. The Zn atoms are found to occupy exclusively the planar sites in Nd_1.05Ba_1.95Cu_3−x Zn _x O _z samples with x≤0.4. An orthorhombic-to-tetragonal transition behavior was observed in the Nd_1.05Ba_1.95Cu_3−x Zn _x O _z (x=0–0.6) system, while a tetragonal-to-orthorhombic transition was observed in the Nd_1.05Ba_1.95Cu_2.8−x Zn _x Co_0.2O _z (x=0–0.6) system as the Zn doping content x increases. A comparative analysis of the structural behavior of Nd_1.05Ba_1.95Cu_3−x Zn _x O _z and Nd_1.05Ba_1.95Cu_2.8−x Zn _x Co_0.2O _z (x=0, 0.2, 0.4, 0.6) samples showed that the Co doping can induce an increase in Zn occupancy at the Cu(1) sites as the Zn doping concentration increases above x=0.4, implying that the distribution of Zn ions between the chain and planar sites can be tuned by the Co substitution for the chain Cu sites.