摘要:

We have systematically investigated the influence of the three parameters (temperature of sintering, lead content, and duration of the sintering) on the growth of the (2:2:2:3) phase in ceramics of nominal composition Bi2−xPbxSr2Ca2Cu3O10−x/2, and have determined the compositions and thermal conditions leading to ceramics withTc≊110 K and containing more than 95% of this phase. We show that this result can be obtained by usual calcination near 880°C in air, without recurring to the introduction of excess in the constituants, providing that intermediate grinding are effected, in order to reactivate the formation of the (2:2:2:3) phase which otherwise saturates for long durations of sintering. The suitable nominal compositions (0.3≤x≤0.4) correspond to those that yield inside the grains a lead content in the vicinity of the limit of solubility for lead. From the results of the preceding investigations and of experiments effected on lead‐substituted single crystals of the (2:2:1:2) phase, we have clarified the role played by lead, at the microscopic level, in the enhancement of the formation of the (2:2:2:3) phase. The inferred role is the establishment of strong bonding between the slabs which are the buildings blocks of the structure of the superconducting phases, these slabs being almost independent in the lead‐free compounds. The origin of the stronger bonding is discussed.

ISSN:0021-8979    

DOI:10.1063/1.346534

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

X‐ray diffraction data of Bi1.4Pb0.6Sr2Ca2Cu3.6O10+xsamples show a sharp change near the annealing temperature of 845 °C. Below this temperature a solid solution of (Ca0.867Sr0.133)2PbO4is formed and prolonged annealing leads to transformation of the 2212 phase to the 2223 phase. Above this temperature, Ca2PbO4is formed, and prolonged annealing leads to an irreversible transformation of both the 2212 phase and the 2223 phase to the 2201 phase.

ISSN:0021-8979    

DOI:10.1063/1.346535

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducting YBa2Cu3O7−&dgr;thin films with surface roughness Ra∼20 A˚ have been successfully prepared by either rf or dc magnetron sputtering. The substrate temperature was kept at 600–670 °C during deposition and a subsequentinsituplasma oxidation treatment was performed at 480–520 °C. The films deposited on single‐crystal SrTiO3(100) exhibited zero resistance at 91 K and had the critical current density of 3×106A/cm2. In this paper we describe the influences of fabrication conditions on film superconductivity.

ISSN:0021-8979    

DOI:10.1063/1.346536

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We show here that cerium and gallium‐doped dysprosium iron garnet (Ce,Ga:DylG) sputtered films may have widely varying magnetic properties that are functions of the predeposition sputtering system base pressure. A Ga site preference model that qualitatively accounts for these differences is introduced and is seen to agree with previously reported experimental results on the Ga site distribution and kinetics in liquid phase epitaxial and flux grown garnet films. Furthermore, we show strong evidence that indicates that the large Faraday rotation in highly doped Ce‐substituted sputtered garnet films is not solely ascribable to Ce+3intraorbital transitions as has been suggested for low concentration Ce:YIG. On the contrary, it is seen that the Faraday rotation in our materials increases almost exclusively in the near‐infrared region as the Ce+4/Ce+3ratio increases. It appears that this effect is largely due to an enhanced tetrahedral sublattice contribution to the Faraday rotation.

ISSN:0021-8979    

DOI:10.1063/1.346537

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The analysis of the canting model theory up to the fourth order, including the in‐plane contribution to the total anisotropy, is presented. The origin of the first‐order magnetization process (FOMP) is well explained in terms of competing anisotropies. The fourth‐order terms are essential for the presence of a FOMP; in fact, computer simulations, with only second‐order terms, show regular magnetization curves, and the representation, in terms of equivalent single sublattice anisotropy constantK@B|i, explains the origin, from the competition, of the high‐order terms, but they are not strong enough to produce FOMP transitions. An analysis of the effects of each parameter in the energy expression is given, in particular the behavior of the magnetization curves and the evolution of the easy cone are studied. An analytical expression for the anisotropy field and of the energy instability at zero field (origin of easy cone) has been derived. As an application of the model, an analysis of the magnetization curves, in hard direction of single crystals of PrCo5, Nd2Fe14B, and Pr2Fe14B is given; the good agreement with experimental results shows that the above model explains well the origin of the spin reorientation and of the FOMP transitions observed in these compounds.

ISSN:0021-8979    

DOI:10.1063/1.346538

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermal processing of InP at temperatures above 500 °C is indispensable in the growth and device fabrication of InGaAsP alloy semiconductors for optoelectronic and microwave applications. Incongruous loss of P at these temperatures creates native defects and their complexes. The presence of such defects modifies the electrical and optical properties of the material resulting in poor device performance. In addition, native defects play a significant role in dopant diffusion which is a topic of current interest. We have measured deep‐level photoluminescence (PL) on undoped InP after heat treatments at 500 and 550 °C in an open‐tube processing system in different protective environments of powder InP, and Sn‐InP melt together with an InP cover. In this paper we shall present the PL results which have bearing on the question of defects. We find that (1) the Sn‐InP melt provides better protection in preserving the overall luminescence in InP; (2) the deep‐level PL related to defects has at least two components in the virgin samples, viz., MnIn, and band C, which is a native defect complex related toVP; (3) a new defect appears in samples heated in a P‐deficient environment; and (4) the enhancement in the deep‐level luminescence intensity after heat treatment can be attributed to the excess defect concentrations existing under nonequilibrium conditions of an open‐tube processing environment.

ISSN:0021-8979    

DOI:10.1063/1.346539

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photocurrent spectroscopy is used to investigate the properties of the CdHgTe (CMT)/anodic oxide /electrolyte junction. The anodic oxide growth follows the high‐field growth mechanism and the positive photocurrent response is found to originate from a thin layer close to the CMT/anodic oxide interface. The spectral response of this photocurrent indicates that the oxide is amorphous with a band gap of 2.8 eV. This value is considerably lower than has been previously reported. Electron photoemission also occurs at the CMT/anodic oxide interface, with an apparent threshold energy of ∼2.08 eV.

ISSN:0021-8979    

DOI:10.1063/1.346540

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new theoretical model for electrical conduction in polycrystalline silicon under optical illumination is introduced to investigate the effect of grain size, illumination level, temperature, and grain‐boundary scattering effect on the carrier mobility and resistivity of polycrystalline silicon by considering the variation of grain‐boundary space‐charge potential barrier height (Vg) with these parameters. This theory is based on the assumption that the grain‐boundary scattering effect on carrier transport is represented by a rectangular potential barrier with a constant width of 20 A˚ and height &fgr;. It is found that this barrier cannot be completely eliminated by lowering the temperature, while the barrierVgcan be removed in some cases, especially when the illumination level is very high and the grain size is large. Our theory predicts that the carrier mobility is approximately proportional to the temperature in the temperature range 100–125 K and approximately proportional toT−2/5between 125 and 200 K. Computations show that the dependence of resistivity and carrier mobility of illuminated polysilicon on grain size is large at small grain sizes and at low temperatures and illumination levels.

ISSN:0021-8979    

DOI:10.1063/1.346541

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Transmission and reflection measurements in the energy range 0.5–1 eV have been performed on thin CoSi2films grown by molecular‐beam epitaxy on Si(111). For film thicknesses above 200 A˚, the transmission factor decreases exponentially with film thickness, with an optical attenuation length of 180 A˚ nearly independent of photon energy. Deviations from this law for film thicknesses below 200 A˚ are explained by reflection effects. These data, supplemented by reflection measurements, can be fitted by theoretical calculations of the transmission and reflection factors, thus leading to the determination of the CoSi2optical indexes. The energy dependence of the real and imaginary indexes is found to be consistent with the Drude model. Some interesting aspects of this intraband absorption either in ultrathin films or at low temperature are presented.

ISSN:0021-8979    

DOI:10.1063/1.346542

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The previously determined optical properties of SrB4O7;Sm2+make this compound a possible better pressure calibrant than ruby, particularly when used at elevated temperatures. Moreover, it can be used with the same experimental devices. In fact, SrB4O7;Sm2+displays an intense emission line which is a nondegenerated singlet,5D0−7F0, at 685.41 nm in the same spectral range as ruby, 694.22 nm. In the present study, its shift with pressure has been calibrated with the shift of the ruby R1line up to 60 GPa and has also been recorded to over 100 GPa. No phase transition of SrB4O7;Sm2+was found at least up to 108 GPa. The pressure profiles in the diamond anvil cell have been established at 60 and 105 GPa. In addition, the bulk modulus of SrB4O7;Sm2+, B0=170 GPa, has been determined from x‐ray diffraction experiments up to 27 GPa. An analytical expression for the shift of the wavelength with pressure is derived and applications to ruby and strontium borate are given.

ISSN:0021-8979    

DOI:10.1063/1.346543

出版商:AIP    

年代:1990

数据来源: AIP