Investigation of the resistive transition of CaLaBaCu3O7 in magnetic fields up to 10 tesla and pressures up to 46 GPa

Abstract

The onset critical temperature T _co, of CaLaBaCu₃O₇, is measured as a function of pressure by means of a cryogenic diamond anvil cell. We find ?T _co/?p = 0.14 ± 0.02K/GPa. The pressure dependence of the upper critical field B _c2 as a function of pressure is determined for T/T_c , = 0.96. From this we found the corresponding volume dependence of the number of charge carriers to be much smaller than the value derived from Hall effect measurements in YBa₂Cu₃O₇.

Les dérivées par rapport à la pression de la température critique supérieure T_co , (avec ?T _co,??p = 0.14 ± 0.02K/GPa) et du champs critique B _c2 à T/T_c , = 0.96 ont été déterminé á l'aide d'une presse à diamants. Pour le composé CaLaBaCu₃O₇, la variation de la densité de charges en fonction du volume est beaucoup plus faible que celle détermiée par effet Hall dans YBa₂Cu₃O₇.     

Far infrared reflectance of a mixed phase Y-Ba-Cu-O superconductor

We have studied the far infrared reflectance of the mixed phase superconductor Y_1.2Ba_0.8CuO_4–y. The reflectance spectrum shows sharp phonon resonances and an electronic contribution that we attribute to reflection at a mesh-like structure of the conducting phase embedded in nonconducting material; in comparison, the reflectance of single phase superconducting material is mainly determined by the dynamical electronic conductivity.     

Ca3－x AgxCo4O9(x=0—0.05)氧化物的电输运性能

Ca位掺杂可以优化Ca₃Co₄O₉复合氧化物的电输运性能. 采用柠檬酸溶胶凝胶结合放电等离子烧结制备了Ca位微量掺杂Ag的Ca_3-xAg_xCo₄O₉(x=0—005)氧化物块体试样,通过X射线衍射、扫描电子显微镜、电参数测试仪分析了所得试样. 试验结果表明: 产物呈单一物相,Ca位微量掺杂Ag降低了Ca_{关键词： 3}Co₄O₉')" href="#">Ca₃Co₄O₉ 掺杂 电输运     

Electrical and structural properties of a stacked metal layer contact to n-InP

In this study, we found that the double metal contact structure in Pt/Al/n-InP diodes provides better rectification characteristics than conventional single-metal/n-InP Schottky diodes. The effective barrier height was measured to be 0.67 eV for a 400 °C-annealed Pt/Al/n-InP diode sample. The increase in the barrier height is attributed to the formation of Al₂O₃ at the metal/n-InP contact interface during thermal annealing. The formation of the phase Al₂O₃ phase was monitored by X-ray diffraction (XRD) analysis. The corresponding element profiles of Al and O were also confirmed at the metal/n-InP contact interface using secondary ion mass spectrum (SIMS) analysis. The lowering of the Schottky barrier height due to the inhomogeneity at the metal/n-InP junction is also discussed on the basis of the TE theory. The distribution of local effective Schottky barrier heights was explained by a model incorporating the existence of double Gaussian barrier heights, which represent the high barrier and low barrier of the full distribution in the temperature ranges of 83-198 and 198-300 K.     

Electrophysical Properties of ZnAs 2 and CdAs 2 at Hydrostatic Pressure up to 9 GPa

Specific electroresistance and Hall coefficient on oriented ZnAs 2 and CdAs 2 single crystals in the region of room temperatures at hydrostatic pressure up to 9 GPa were measured. In p -ZnAs 2 specific electroresistance falls for one order of magnitude with the increase of pressure, and Hall coefficient falls for two orders in magnitude, and at P =7 GPa specific electroresistance and Hall coefficient come out to a saturation. Under mentioned conditions the phase transition in investigated p -ZnAs 2 samples was not observed, in all probability it occurs under the pressure P >10 GPa. Two groups of n -CdAs 2 samples oriented on [1 0 0] and [0 0 1] directions were investigated. The reversible structural phase transition was observed in investigated n -CdAs 2 samples at P =5.5 GPa from the dependencies of specific electroresistance 𝜌 ( P ) and Hall coefficient R H ( P ). On the basis of the values of concentrations and mobilities before and after phase transition a conclusion was made that semiconductor-semiconductor transition takes place in n -CdAs 2 . Maxima that earlier weren't observed, were detected on dependencies 𝜌 ( P ), R H ( P ) at P =1.8 GPa and at P =3 GPa.     

Electrical properties of (PBS)0·59TiS2 crystals at high pressures up to 20GPa

Abstract

The measurements of thermoelectric power S and resistance p at high pressure synthetic diamond anvils cell were performed for (PbS)0·59TiS2 and TiS2 crystals. The phase transition was found at P?;2GPa accompanied by descend of ρ and |S| for (PbS)o·59TiS2. This transition is connected with structural change of PbS fragment from pseudocubic cell to orthorombic one and as consequence, with change of the electron concentration in Tis2-layers. From the electronic structure calculations for TiS2, the semiconductor-metal transition occurs at pressure P ≥ 4 GPa. Experimentally at this pressure range the decrease of ρ(P) was observed for (PbS)0·59TiS2 crystals.     

Raman studies of the high pressure effects in high Tc superconductors

Abstract

The effect of a hydrostatic pressure (up to 6GPa) on the Raman spectra of YBa₂Cu₃O_x(x = 6.5 and overdoped) single crystals is investigated in the temperature range 77-300 K in connection with all available data in the literature for the other oxygen concentrations. All five strong modes (4A_g+1B_1g) are examined for both oxygen doping and compared with previously published results. From the systematic investigation of the phonon spectral characteristics with the application of pressure, the formation or disappearance of the phases is examined. The results provide a spectroscopic support for the changes induced by the hydrostatic pressure on the chain ordering and the corresponding phases.     

Effect of chemical substitution and oxide additives on the Tc behaviour of the oxide superconductor,Bi4Sr3Ca3Cu4O16

Studies on the superconductivity behaviour of pure and doped (Pb,TI) Bi₄Sr₃Ca₃Cu₄O₁₆ phases are reported. Effect of oxide additives PbO, BaPbO₃ and BaBiO₃ has also been examined. Results show that an oxygen treatment at 600°C for 12 h during the final stages of the synthesis has the beneficial effect of sharpening the T_c ^zero of the 4334 Bi-composition. Pb and TI substitution has only a marginally beneficial effect on the T_c , though it is not definitely known whether substitution is actually occurring in the system. PbO as an additive raises the T_c ^zero to 89 K, whereas other additives do not basically affect the properties of the 4334 system.     

Melting curve of NaCl0.5Br0.5 up to 4.5 GPa

Abstract

The melting curve of NaCl_0.5Br_0.5 has been measured under pressure up to 4.5 GPa. The melting temperatures of Ag and NaCl have been used to determine the pressure in the sample at its melting temperature.     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Fe3O4薄膜的电输运及光诱导特性研究

用脉冲激光沉积法在(111)Si衬底上成功制备了高度择优取向的Fe₃O₄薄膜.电阻-温度关系表明Fe₃O₄薄膜的Verwey转变(T_V)约在122 K,低温段(T_V)输运特征满足Mott变程跳跃模型,高温段(T>T_V)为小极化子输运.激光作用下的光电导实验发现,在整个温区表现为光致电阻率减小,而且低温段的电阻变化率比高温段要大很多.分析认为Fe₃O₄薄膜的光致电阻率变化主要与激光激发t_2g电子的转移有关. 关键词： 3O₄薄膜')" href="#">Fe₃O₄薄膜 小极化子 光诱导特性     

Effects of RE2O3 (RE = Tm, Sc, Yb) addition on the superconducting properties of ErBa2Cu3Oy

We investigated the effects of added Tm₂O₃, Sc₂O₃, and Yb₂O₃ on the superconducting properties of sintered Er123 samples. Tm₂O₃ addition caused the least T_c degradation, exhibiting a T_c above 90 K even for 17 vol% addition. Samples with added Sc₂O₃ maintained a T_c at above 90 K up to an addition of 7.2 vol%, while Yb₂O₃-containing samples showed a monotonic decrease in T_c with increased vol% of added Yb₂O₃. Tm₂O₃-containing samples exhibited a slight increase in J_c(0.1 T)/J_c(0) and had constant J_c values even for 17 vol% addition. XRD and SEM results indicate that the Tm₂O₃ is very stable in the superconducting matrix.     

纳米结构CoxFe3-xO4多孔微球的磁性及交换偏置效应研究

用乙二醇为溶剂,用三氯化铁、二氯化钴和醋酸铵为起始反应试剂,通过溶剂热反应首次合成了纳米结构Co_xFe_3-xO₄多孔微球.用X射线衍射仪(XRD)、透射电子显微镜(TEM)和扫描电子显微镜(SEM)表征样品的结构和形貌,结果表明,所制备的单分散Co_xFe_3-xO₄多孔微球为立方多晶结构,其直径约300 nm,是由约30 关键词： xFe_3-xO₄')" href="#">Co_xFe_3-xO₄ 多孔微球 磁性 交换偏置效应     

Directional behavior of nuclear quadrupole resonance in YBa2Cu3O6

Powder samples of YBa₂Cu₃O₆ were magnetically aligned and the anisotropies in the systems were studied by means of Cu(1) nuclear quadrupole resonance (NQR) in the absence of external magnetic fields. Our room temperature measurements of the NQR lineshapes and the spin–lattice and spin–spin relaxation times as a function of the aligning magnetic field indicate that full microscopic alignment can be achieved by using a magnetic field of about 4.7 T, for which doublet line patterns arising from a hyperfine splitting were observed.     

Infrared investigation of benzene to 30 GPa transformation to a polymer

Abstract

After a pressure cycle to 30 GPa, benzene transforms to a white solid which can be recovered at ambient. Results obtained from infrared spectroscopy and other physico-chemical methods show that the recovered solid is a highly cross-linked polymer. The molecular structure of benzene is very likely completely altered by the transformation.     

Hydrostatic pressure study of the structural phase transitions and superconductivity in single crystals of (Ba1−xKx)Fe2As2 (x=0 and 0.45) and CaFe2As2

We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe₂As₂, BaFe₂As₂, and (Ba_0.55K_0.45)Fe₂As₂, by means of measurements of electrical resistivity (ρ) in the 1.8-300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe₂As₂ and BaFe₂As₂ (lightly doped with Sn) display structural phase transitions near 170 and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba_0.55K_0.45)Fe₂As₂ is superconducting for T<30 K. The effect of pressure on BaFe₂As₂ is to shift the onset of the crystallographic transformation down in temperature at the rate of ~−1.04 K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba_0.55K_0.45)Fe₂As₂ is to shift the onset of superconductivity to lower temperatures at the rate of ~−0.21 K/kbar. The effect of pressure on CaFe₂As₂ is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P<5 kbar. However, higher pressures bring about another phase transformation characterized by reduced-resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (H_c2) data in (Ba_0.55K_0.45)Fe₂As₂ and CaFe₂As₂ are discussed.     

Electrical conductivity in magnesium-doped Al2O3 crystals at moderate temperatures

Abstract

AC and DC electrical measurements between 273 and 800 K were used to characterize the electrical conductivity of Al₂O₃: Mg single crystals containing [Mg]⁰ centers. At low fields contacts are blocking. At high fields, electrical current flows steadily through the sample and the I–V characteristic corresponds to a directly biased barrier with a series resistance (bulk resistance). AC measurements yield values for the junction capacitance as well as for the sample resistance, and provide reproducible conductivity values. The conductivity varies linearly with the [Mg]⁰ concentration and a thermal activation energy of 0.67 eV was obtained, which agrees very well with the activation energy previously reported for the motion of free holes.     

Microstructures and microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm³, a dielectric constant (ε_r) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τ_f) of −86 ppm/°C were obtained for La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

Optoelectronic properties of GaAs1−xPx alloys under the influence of temperature and pressure

This work is concerned with the dependence of the electronic energy band structures for GaAs_1−xP_x alloys on temperature and pressure that is based on local empirical pseudo-potential method. The band structures of GaAs_1−xP_x alloys were calculated in the virtual crystal approximation using the EPM which incorporates compositional disorder as an effective potential.