Pb1−x Bi x /Bi/Pb1−x Bi x Josephson junction

A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb_1–x Bi _x (0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K.     

The dielectic response of K x Al x Ti8−x O16 and K x Mg x/2 Ti8−x/2 O16

Materials of the hollandite structure with the general formulae K_x Al_x Ti_8–x O₁₆ and K_x Mg_x/2 Ti_8–x/2 O₁₆ have been synthesized in the composition range 1.6x2.0 and their dielectric properties have been measured in the temperature range 77 to 800 K and the frequency range 10^–3 to 10⁶ Hz. The observed response shows a whole range of features characteristic for both charge carrier and dipolar polarization processes and these are seen as being associated with the one-dimensional transport in channels in the hollandite structure. At low temperatures the dominant response is the universal dielectric relation in which the loss follows the law x() ^n–1, with the exponent n<1 and equal specifically to approximately 0.7. This is followed at 120 to 180 K by a distinct loss peak superimposed on the above law, and finally at higher temperatures by a region of strong dispersion which is associated with strongly interacting many-body processes between charged carriers restricted by defects to move in limited regions of the channels.     

Lattice-matched epitaxial Pb1 − x Mn x Se/PbSe1 − x S x heterojunctions

This paper examines the possibility of producing lattice-matched p-n heterojunctions based on epitaxial n-Pb_{1 ? x} Mn _x Se (x = 0.02) and p-PbSe_{1 ? x} S _x (x = 0.04) films. The heterojunctions have been grown by molecular beam epitaxy in a single processing cycle, without breaking the vacuum, using a compensating Se vapor source in the growth process. Optimal conditions have been found for the growth of structurally perfect (W _1/2 = 90″-100″) epitaxial films and fabrication of lattice-matched heterojunctions based on such films, photosensitive in the IR spectral region.     

Electrical properties of In/Yb/n-Hg1 − x Cd x Te contacts

The specific contact resistance, _c, and the modified sheet R _sk, of In/Hg_{1 – x} Cd _x Te contacts incorporating a Yb diffusion barrier were measured as a function of the layer thickness and composition (x = 0.32–0.65). Significant increases in _c, were evident only for x 0.56 and at Yb thicknesses between 2.5 and 6.0 nm, depending on the x-value. Analytical examination of the interfaces by Rutherford backscattering spectrometry (RBS) also showed a progressive reduction in the extent of inward diffusion of In with increasing thickness of the Yb interlayer.     

Microscopic Scenario for x = 1/8 Anomaly in La2 − x Sr x CuO4

We adopt a t ₁-t ₂-t ₃-J-G model for explanation of x = 1/8 anomaly in La_{2 ? x} Sr _x CuO₄ family compound. The calculated charge susceptibility shows a maximum near Q = (π, π) at intermediate temperatures and near (π, π/2) as temperature approaches zero, in agreement with neutron scattering experiments. Coulomb repulsion G between the first neighbors turns out to be the source of Charge Density Waves (CDW) in narrow band t ^eff ₁, t ^eff ₂, t ^eff ₃ < G. For physically realistic hopping values we obtain the CDW amplitude e _Q = x. The in-phase domain structure as a candidate for “stripe” picture is proposed.     

MOCVD of p-Cd x Hg1 – x Te/GaAs Heteroepitaxial Structures

Metalorganic chemical vapor deposition from Cd and Te alkyl compounds and Hg vapor is used to grow p-type Cd _x Hg_{1 – x} Te epitaxial layers on semi-insulating GaAs(111)Bsubstrates by the interdiffused multilayer process (alternating CdTe and HgTe layers) at a substrate temperature of 350°C, followed by postgrowth annealing. Layers are obtained with x = 0.2–0.4, 77-K carrier concentrations in the range (1–5) × 10¹⁶ cm^–3, and 77-K carrier mobilities from 200 to 400 cm²/(V s). The rocking curves of the epilayers have a full width at half maximum in the range 2–4 min of arc.     

A study on martensitic transformation in Ti50−x/2Ni50−x/2Cu x alloys with X≤10 at%

The effect of Cu additions on the martensitic transformation sequence and temperature in Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–10 at% are investigated by ER, DSC, X-ray and IF measurements. Experimental results show that the transformation sequence of Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–4 at% proceeding as two-stage B2RB19 transformation on cooling and Ti_50–x/2Ni_50–x/2Cu _x alloys with x=5, 10 at% have no martensitic transformation. The addition of Cu in Ti_50–x/2Ni_50–x/2Cu _x alloys assists the formation of R-phase, a behaviour which is quite different from that in Ti₅₀Ni_50–x Cu _x alloys. Both the Ms and T _R temperatures decrease rapidly with increasing Cu addition in Ti_50–x/2Ni_50–x/2Cu _x alloys with x: 1–4 at%. It is proposed that the Cu+Ni effects on the Ms temperature in Ti_50–x/2Ni_50–x/2Cu _x alloys is similar as Cu +Ni effects in Ti₅₀Ni_50–x Cu _x alloys and as Ni effects in as-quenched Ni-rich TiNi alloys.     

Structural and Transport Properties of La2/3 – x Li3x □4/3 – 2x Ta2O6 Perovskite-Like Solid Solutions

The homogeneity range of La_2/3–x Li_{3x 4/3 – 2x} Ta₂O₆ perovskite-like solid solutions was determined. The transport properties of the La_2/3–x Li_{3x 4/3 – 2x} Ta₂O₆ oxides were shown to correlate with their lattice parameters and composition. Lithium-doped lanthanum metatantalate with an orthorhombically distorted perovskite-like structure is a good solid electrolyte with high lithium ion conductivity.     

Current-voltage characteristics of Si/Si1 − x Ge x heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si_{1 ? x} Ge _x (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si_{1 ? x} Ge _x wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration N _Ge in Si_{1 ? x} Ge _x crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with N _Ge ≤ 15 at %, the I–U curves of Si/Si_{1 ? x} Ge _x heterodiodes are satisfactory in the entire range of current densities (1 mA/cm²–200 A/cm²). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si_{1 ? x} Ge _x heterostructures.     

Magnetic Phase Transition and Electronic Anomalies in La1.96−x Y0.04Sr x CuO4 around x∼1/8

La-NMR, Hall coefficient and sound velocity have been measured in order to investigate the correlation between the magnetic ordering, the prominent change of transport properties, the suppression of T _c and the structural transformation around x1/8 in La _1.96–x Y _0.04 Sr _x CuO ₄. By the substitution of 0.04/2 Y for La-sites, the structural transformation to the low temperature tetragonal phase (LTT) is caused at 57±14 K for samples around x0.115. The. prominent decrease of the Hall coefficient followed by the sign reversal and the magnetic ordering are observed around x0.115 below temperatures T _s and T _N, respectively. T _s vs x shows a bell shaped curve with the maximum value of 65 K at x00115 where most prominent suppression of T _c appears. T _N shows similar x dependence to T _s with the maximum value of 40 K at x0.115. The change of the electronic state below T _s and the suppression of T _c become more prominent and the magnetic ordering is observed more wide range of x under the LTT phase.     

High-k gate stack Hf x Ti1−x ON/SiO2 for SiC MOS devices

In order to reduce the electric field in the gate dielectric and thus solve the reliability problem, high dielectric-constant (k) gate dielectrics Hf _x Ti_1?x O₂ and Hf _x Ti_1?x ON were applied in SiC metal-oxide-semiconductor (MOS) devices for the first time. An ultra-thin thermally grown SiO₂ was used as an interlayer between SiC and the high-k materials to block electron injection into the low-barrier high-k materials. Incorporating nitrogen (by sputtering in an Ar/N₂ ambient) into the hafnium–titanium oxide stacked with a SiO₂ interlayer (Hf _x Ti_1?x O₂/SiO₂) resulted in better gate dielectric for MOS capacitor, such as less oxide charges and better interface quality. Incorporation of nitrogen also increased the dielectric constant of the oxide, but caused higher dielectric leakage, which was suppressed by the SiO₂ interlayer.     

139La-NMR study of spin-flop and spin structure in La2−x Sr x CuO4(x∼1/8)

The external field dependence of the hyperfine field at La-site has been studied on La _2–x Sr _x CuO ₄ (x=0.115) and La _2–x Ba _x CuO ₄ (x=0.125), where the magnetic ordering in Cu-3d spins exists at low temperature. In La _1.885 Sr _0.115 CuO ₄, a significant decrease in the resonance line width was observed above a field of H _c 7.5T, which is the direct evidence of the spin-flop in the canted-spin system with Dzyaloshinski-Moriya interaction. The spin-flop field H _c of 7.5T is slightly lower than that in La ₂ CuO ₄ (H _c 10T), reflecting the decrease of the tilting angle of the CuO ₆ octahedra by the substitution of Sr ²⁺ ion for La-site.     

μSR Study in La2−x Sr x Cu1−y Zn y O4 with x≃l/8

In order to investigate the magnetic state around hole density 1/8 in LaSr-214, SR experiments were carried out for the samples of Zn-free La _2–x Sr _x CuO ₄ and Zn-doped La _2–x Sr _x Cu _1–y Zn _y O ₄. For Zn-free samples, -spin rotation was observed in x=0.115 below about T _r =10K, implying magnetic order, but not observed in x=0.125. On the other hand, Zn-doping brought about -spin rotation in x=0.125 sample below T _r =7K, implying growth of magnetic order but decreased T _r in x=0.115, meaning destruction of magnetic order. This indicates that Zn-doping pins dynamical spin modulation, resulting in static magnetic order in x=0.125 sample.     

Thermodynamic properties of Ca1 − x Er x F2 + x and Ca1 − x Yb x F2 + x heterovalent solid solutions

The heat capacity of single crystals of the Ca_{1 ? x} Er _x F_{2 + x} (x = 0.05, 0.10) and Ca_0.95Yb_0.05F_2.05 fluorite solid solutions was determined by adiabatic calorimetry in the temperature range 55–300 K. The results were used to obtain temperature dependences of the Debye characteristic temperature, entropy, and enthalpy for the solid solutions.     

Ba(Mgx/12Ta2x/12Zr(12-3x)/12)O3系统相关系的研究

目前的文献均表明钽镁酸钡Ba(Mg1/3Ta2/3)O3不易获得单一物相.我们在Ba(Mg1/3Ta2/3)O3结构不变的基础上,研究了Ba(Mgx/12Ta2x/12Zr(12-3x)/12)O3系统的相组成关系.用Zr4+置换Ba(Mg1/3Ta2/3)O3中的Mg2+和Ta5+离子对,在0＜x＜4范围内生成P-3ml固溶体,在x＜3.33时开始出现BaZrO3相,在3.33≤x＜4生成P-3ml固溶体单一物相.     

Interface structure and electrical properties of PtSi/Si1−x Ge x diodes based on silicon

PtSi/strained Si_1–x Ge _x (x=0, 0.2, and 0.25) Schottky-barrier diodes (SBD) with extended cutoff wavelengths have been demonstrated by combining pulsed laser deposition (PLD) and molecular beam epitaxy (MBE). Pt was deposited by PLD on the Si_1–x Ge _x alloys with a thin Si sacrificial cap layer fabricated by MBE. By the reaction of deposited Pt film on Si, a sacrificial cap layer silicide SBD has been fabricated. Auger electron depth profiling was performed on the films before and after in vacuo annealing to study the redistribution of composition in the reactions. High-resolution transmission electron microscopy was used to investigate the interface structure. We have found that Pt reacts mainly with Si to form silicides at 350 °C, leaving some Ge to segregate at the surface. With annealing at 600 °C for 3 min the interface of PtSi/Si_1–x Ge _x is smooth. Since lowered-barrier-height silicide SBD are desirable for obtaining longer cutoff wavelength Si-based infrared detectors, the Schottky barrier heights of the PtSi/strained Si_1–x Ge _x SBDs with smooth interfaces were substantially lower than those of PtSi/Si SBDs, i.e., decreased with increasing Ge fraction, allowing for tuning of the SBDs cutoff wavelength. At 293 K, the ideality factor has been found to be 2.00 and 1.32 for PtSi/Si_0.80Ge_0.20 and PtSi/Si_0.75Ge_0.25 diodes, respectively. We have shown that high quantum efficiency and near-ideal dark current can be obtained in the film of PtSi/strained Si_1–x Ge _x with an excellent interface fabricated by MBE and PLD, after annealing at 600 °C for 3 min.     

High-Pressure Studies on Superconductivity in LaFeAsO1−x F x and SmFeAsO1−x F x

The pressure dependence on the superconducting transition temperature (T _c ) was investigated for the iron-based superconductors LaFeAsO_1−x F _x and SmFeAsO_1−x F _x . The T _c ’s increase largely for LaFeAsO_1−x F _x with a small increase of pressure, while a sharp decrease of T _c was observed for SmFeAsO_1−x F _x . The electrical resistivity measurements reveal pressure-induced superconductivity for undoped LaFeAsO and SmFeAsO. These pressure effects seem to be related to an anisotropic decrease of the lattice constants under high pressure from the x-ray diffraction measurements up to 10 GPa for the LaFeAsO_1−x F _x system.     

Synthesis, microstructure and thermal expansion studies on Ca0·5+x/2Sr0·5+x/2Zr4P6−2x Si2x O24 system prepared by co-precipitation method

We report on the synthesis, microstructure and thermal expansion studies on Ca_0·5?+?x/2Sr_0·5?+?x/2Zr₄P_6???2x Si_2x O₂₄ (x = 0·00 to 1·00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0·37. For x ≥ 0·5, in addition to NZP phase, ZrSiO₄ and Ca₂P₂O₇ form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 °C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0·75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0·00 to 0·37 and then decreases for x > 0·37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.     

Structural and electrochemical characterization of layered 0.3Li2MnO3·0.7LiMn0.35−x/3Ni0.5−x/3Co0.15−x/3CrxO2 cathode synthesized by spray drying

Cr doped 0.3Li₂MnO₃·0.7LiMn_0.35−x/3Ni_0.5−x/3Co_0.15−x/3Cr_xO₂ (x = 0, 0.02, 0.04, 0.06) as a cathode material for Li-ion battery has been successfully synthesized by spray drying and subsequent calcination. The effects of Cr dopant on the structural and electrochemical properties of this material have been investigated by XRD, SEM, EDS, charge–discharge measurements, Ac impedance spectroscopy as well as cyclic voltammetry. These results demonstrated that the element Cr distributed uniformly in these materials. With the Cr content increasing, lattice parameters a and c decrease and less Li ion locates in transition metal site. Among the synthesized Cr-doped materials, when x = 0.04, this material shows the best electrochemical properties. Between 2.5 and 4.8 V (vs. Li/Li⁺), the initial discharge capacities of the materials increased from 143 to 168 mA h g⁻¹ at a constant current density of 250 mA g⁻¹. After 50 cycles, the capacity retention of the materials raised from 83% to 93%.     

Relaxor behavior of (1 − x)BaTiO3–x(Bi3/4Na1/4)(Mg1/4Ti3/4)O3 (0.2 ≤ x ≤ 0.9) ferroelectric ceramic

The (1 − x)BaTiO₃–x(Bi_3/4Na_1/4)(Mg_1/4Ti_3/4)O₃ (0.2 ≤ x ≤ 0.9) ceramics were prepared by conventional solid-state reaction route. Their dielectric properties were found to follow a modified Curie–Weiss law and an empirical Lorenz-type relation in respective temperature regions. Their dielectric relaxation times fit well with the Vogel–Fulcher relation for x = 0.2, 0.3, and 0.4. For x = 0.5, 0.6, 0.7, and 0.8, however, the fitting curves of Vogel–Fulcher relation showed certain deviation from the experimental data. Based on the theoretical treatment of Landau–Ginsburg–Devonshire theory, an approximate treatment of the E-field dependence of the permittivity was adopted and found to describe well the field dependence of the permittivity for x = 0.3 at temperatures equal to and below T _m (temperature of maximum dielectric permittivity). A combined Langevin-type expression used in the present work appears to give a good account for the field dependence of the permittivity, assuming polar regions are of a statistical cluster size. For polar clusters of linear dimension L ~ 4–8 nm for instance, the fitted values of polarization are in the range of P ~ 6.2–9.8 μC/cm².