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.     

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.     

Structure and properties of (1 − x)BiFeO3 · xPbFe2/3W1/3O3 (0 ≤ x ≤ 1) solid solutions

(1 ? x)BiFeO₃ · xPbFe_2/3W_1/3O₃ ((1 ? x)BFO · xPFWO) samples with 0 ≤ x ≤ 1 have been prepared by a standard ceramic processing technique and characterized by X-ray diffraction, dielectric measurements, and Mössbauer spectroscopy. The system has been shown to contain a continuous series of perovskite solid solutions. The solid solutions in the range 0 ≤ x < 0.32 have a rhombohedral structure and those with 0.32 ≤ x ≤ 1 have a cubic structure. Increasing the BFO content from 0 to 40% leads to rapid degradation of the dielectric permittivity peak that occurs at 180 K in PFWO and is due to the relaxor behavior of this component. At higher BFO concentrations, the electrical conductivity of the solid solutions increases by about two orders of magnitude. The temperature dependences of permittivity for the samples containing ～80% BFO have prominent maxima around 430 and 520 K, whose position is frequency-independent. The solid solutions exhibited no piezoelectric or pyroelectric effect, probably because they were insufficiently poled in a field of 10 kV/cm at 300 K. At higher electric field intensities, the samples experienced breakdown.     

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.     

Dielectric properties of the Sr1−x La x Sn1−x Co x O3 system

The possibility of the formation of a solid solution in the Sr_1–x La _x Sn_1–x Co _x O₃ system has been explored. Single-phase solid solution forms in the compositions for x0.10. All single-phase solid solution compositions have a cubic structure similar to SrSnO₃. The dielectric behaviour of these solid solution compositions has been studied as a function of temperature and frequency. The frequency dependence of dielectric constant and dielectric loss in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. Microstructural studies show the presence of well-faceted grains. The average grain size in these samples is small.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Analysis of the Low Temperature Magnetic Contributions to the Specific Heat of?(Nd x Y1?x )2/3Ca1/3MnO3 (x=0, 0.1)

The low temperature specific heat of the colossal magnetoresistance compounds (Nd _x Y_1?x )_2/3Ca_1/3MnO₃ (x=0, 0.1) for 0.4??T<2 K in magnetic fields up to H=9 T has been studied. Applied magnetic fields lead to the drop of the low temperature specific heat by more than 2 orders, which implies a large magnetic contribution. Experimental data were successfully fitted by the sum of the hyperfine C _hyp , the linear T-dependent C _sg and the spin waves C _sw contributions. The C _sg attributed to the glassy state of the magnetic systems of the studied insulating compounds exponentially decreases with the increase of H up to ??5 T. The C _sw providing the best fitting of the experimental data is attributed to the ferromagnetic spin waves with pseudo gap ??(H) in the spin?Cwave spectrum which increases linearly with the increase of the applied magnetic field. The ??(0)??0.8 K is approximately the same for both compounds studied.     

层状LixCo1/3Ni1/3Mn1/3O2（0．5≤x≤1）的结构转变及其热稳定性研究

采用固相合成法制备了具有良好层状结构的LiCo1/3Ni1/3Mn1/3O2.通过化学方法对其进行去锂处理,制备了LixCo1/3Ni1/3Mn1/3O2(0.5≤≤1)系列样品,并利用XRD、TEM以及HR-TEM等方法对其微观结构进行了系统表征.计算与实验结果表明.当0.778≤x＜1时LixCo1/3Ni1/3Mn1/3O2的结构依旧保持O3结构,而当0.5≤x＜0.778时其结构由初始的六方结构转变为单斜结构,同时电子衍射花样模拟及高分辨像模拟证明其对称性由R3m转变为P2/m.锂离子与去锂后形成的空位的有序排列是其对称性发生转变的主要原因.DSC/TG实验表明,LixCo1/3Ni1/3Mn1/3O2的热稳定性随去锂程度的不断加深而减弱;当加热至300～400℃时发生了由单斜结构向尖晶石结构转变的放热反应.     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.     

Conduction in nanostructured La1?x Sr x FeO3 (0 ≤ x ≤ 1)

We investigated electrical properties of nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO₃ with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO₃ from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe⁴⁺ ions in addition to Fe³⁺ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La_0.9Sr_0.1FeO₃.     

Properties of Nd1 – x Gd x CoO3 Solid Solutions

NdCoO₃, GdCoO₃, and Nd_{1 – x} Gd _x CoO₃ solid solutions with x= 0.1–0.9 are prepared by solid-state reactions, their lattice parameters are determined, and their electrical conductivity and thermal expansion are measured between 300 and 1110 K in air. All of the solid solutions are found to have an orthorhombically distorted perovskite structure and to exhibit anomalies in conductivity and thermal expansion, due to a semiconductor–metal transition.     

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na_1/2Ln_1/2)TiO₃> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (_f) (where Ln represents a lanthanide: La⁺³, Pr⁺³, Nd⁺³ and Sm⁺³). On the other hand, MgTiO₃ ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO₃-(1 – x)(Na_1/2 Ln_1/2) TiO₃. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO₃ and Na_1/2 Ln_1/2)TiO₃ phases. Its dielectric characteristics (Q ^*f, temperature coefficient and dielectric constant) are intermediate between (Na_1/2 Ln_1/2) TiO₃ and MgTiO₃ and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q ^*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.     

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.     

Ferroelectric properties of (1 − x)Bi(Zn1/2Ti1/2)O3–xPbZrO3 ceramics

The (1 − x)Bi(Zn_1/2Ti_1/2)O₃–xPbZrO₃ solid solution ceramics were prepared by using solid-state reaction method, and their ferroelectric properties were investigated. It was found that the perovskite structure is stable for compositions with x ≥ 0.900. Within this composition range, the crystal structure of the solid solution preserves the orthorhombic symmetry of PbZrO₃ (PZ). The Curie point of the ceramics was found to decrease with increasing Bi(Zn_1/2Ti_1/2)O₃ (BZT) content. The intermediate ferroelectric phase of PZ was stabilized by BZT addition and exists within a much wider temperature range in the solid solution.     

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.     

Evolution of the tetragonal to rhombohedral transition in (1 − x)(Bi1/2Na1/2)TiO3 − xBaTiO3 (x ≤ 7%)

Abstract

(1 ? x)(Bi_1/2Na_1/2)TiO₃ ? xBaTiO₃ has been the most studied Pb-free piezoelectric material in the last decade; however, puzzles still remain about its phase transitions, especially around the important morphotropic phase boundary (MPB). By introducing the strain glass transition concept from the ferroelastic field, it was found that the phase transition from tetragonal (T, P4bm) to rhombohedral (R, R3c) was affected by a strain glass transition at higher temperature for x ≥ 4%. In these compositions, the T–R transition was delayed or even totally suppressed and displayed huge thermal hysteresis upon cooling and heating. Also, isothermal phase transitions were predicted and realized successfully in the crossover region, where the interaction between the T–R transition and the strain glass transition was strong. Our results revealed the strain glass nature in compositions around the MPB in this important material, and also provide new clues for understanding the transition complexity in other (Bi_1/2Na_1/2)TiO₃-based Pb-free piezoelectric materials.     

Preparation and dielectric properties of Pb[(Zn1/3Ta2/3)0.8−x(Mg1/3Nb2/3)xTi0.2]O3 ceramics

A PbTiO₃ component of 20 mol% was substituted into a Pb[(Zn_1/3Ta_2/3),(Mg_1/3Nb_2/3)]O₃ system to promote the perovskite formation, especially at Pb(Zn_1/3Ta_2/3)O₃-rich compositions. Perovskite formation yields after the heat treatments were determined by X-ray diffraction. Weak-field dielectric properties of the ceramics were investigated as functions of temperature and frequency. A quite high value of the maximum dielectric constant (37,900 at 1 kHz) was realized, whereas the dielectric maximum temperatures of the entire compositions stayed nearly constant. Microstructure developments in the sintered ceramics were also examined.     

(1-y)Ca1-xLa2x/3 TiO3-yCa(Mg1/3 Nb2/3)O3系陶瓷的缺位结构与微波介电性能研究

采用固相合成法制备了(1-y)Ca1-xLa2x/3 TiO3-yCa(Mg1/3Nb2/3)O3系列固溶体陶瓷材料,研究了该体系微波介电性能与微观结构的关系.研究结果表明:当体系组成为0.5Cao6Lao267 TiO3-0.5Ca(Mg1/3Nb2/3)O3时,在1400℃下烧结保温4小时所得到材料的微波介电性能最佳:εr=55,Q×f值=45000GHz(7.6GHz下),τf=0.04×10-6/℃.同时还探讨了三价阳离子La3 固溶时产生的A点缺陷Vca2 对固溶体结构及微波介电性能的影响.     

Magnetization reversal and ferrimagnetism in Pr1−x Nd x MnO3

Detailed magnetic properties of Pr_{1? x} Nd _x MnO₃ (x = 0.3, 0.5 and 0.7) have been reported. All the samples crystallize in orthorhombic perovskite structure with Pnma space group. Magnetization measurements under field cooled (FC) protocal reveal magnetization reversal at low temperatures and low magnetic field. This indicates clear evidence of two magnetic sublattices aligned opposite to each other. There is a well-defined maximum around 48 K in the x = 0.7 sample (i.e. Pr_0.3Nd_0.7MnO₃) in the χ′ value which is identified as paramagnetic to ferrimagnetic transition. The peak value shifts to higher temperature with decrease of x and width of the maximum broadened. It is also observable that with decrease of Nd, both the value of χ′ and χ″ decrease. An attempt is made to explain the magnetization reversal within the framework of available models.