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1.
We study experimentally the local chemistry and atomic structure of heterophase interfaces on an atomic scale. In this work, the heterophase precipitate/matrix interfaces of small molybdenum nitride precipitates in an -iron matrix are investigated on a subnanometer scale by 1-dimensional atom-probe field-ion microscopy (1D-APFIM) and 3-dimensional atom-probe microscopy (3DAPM). Molybdenum nitride precipitates are generated by annealing Fe- 2 at.% Mo- X, where X = 0.4 at.% Sb or 0.5 at.% Sn, at 550°C, in an ammonia/hydrogen atmosphere. Internal nitridation at this temperature produces thin, coherent platelet-shaped molybdenum nitride precipitates. 1D-APFIM selected area analyses are efficient in determining the composition of the precipitates and it is found that a possible Sn or Sb segregation at coherent matrix/precipitate interfaces is either nonexistent or below the detection limit of 1D-APFIM. 3DAPM analyses, however, provide significantly better counting statistics and detect a small, but significant segregation of Sb at the matrix/precipitate interface with a Gibbsian interfacial excess of 0.30 ± 0.15 nm–2. This is in distinct contrast to the segregation behavior of Sn or Sb at the interfaces of semicoherent coarse precipitates produced by internal nitridation at 600°C, for which much larger Gibbsian interfacial excesses of Sn or Sb, up to 7 ± 3 nm–2, have been measured. In contrast, the thin platelets are either coherent or have significantly fewer misfit dislocations than is geometrically necessary for a full compensation of the lattice parameter misfit between precipitate and matrix. This demonstrates that Sn or Sb segregation with an appreciable Gibbsian interfacial excess is related to the presence of misfit dislocations at the interfaces of the coarse precipitates.  相似文献   

2.
An alternative methodology to analyze Gibbsian segregation at heterophase interfaces with transmission electron microscopy (TEM) is presented and discussed. In this approach the actual concentration of the segregating element in a monolayer at the interface is obtained. This is in contrast to line scans or maps where the concentrations determined are a convolution of the concentration profiles with the electron probe and where for general interfaces the deconvolution problem can not be solved accurately. This is possible because the present approach uses explicitly the information offered by hetero-interfaces. The method is tested on the possible segregation of indium and gallium dissolved in a Cu matrix to interfaces between MnO precipitates and the Cu matrix. The occurrence of indium segregation is clearly demonstrated and the In concentration in the terminating Cu monolayer at the parallel {111} Cu/MnO interface is determined to be 15 ± 3 at.%, whereas the average In concentration in the Cu matrix is 3.8 ± 0.4 at.%. Further it was found that indium effectively blocks gallium segregation towards the oxide side of the interface. On the other hand, the presence of gallium does not influence the segregation of indium. Explanation for the gallium segregation at the oxide side relies on a thin spinel type Ga x Mn y O4, which reduces the misfit at the metal-oxide interface.  相似文献   

3.
Surface segregation studies of Sn and Sb in Cu(1 0 0)-0.14 at.% Sn-0.12 at.% Sb ternary alloy, have been done by making use of Auger Electron Spectroscopy. The method of Linear Temperature Ramp (LTR) was employed, whereby the sample was heated and cooled linearly at a constant rate. The positive heating rate showed both a kinetic segregation profile, as well as a narrow equilibrium segregation region, at higher temperatures. The equilibrium segregation profile was extended by cooling the sample. Sn was first to segregate to the surface due to its higher diffusion coefficient, mainly from a smaller activation energy ESn. Sb, due to its higher segregation energy, eventually replaced Sn from the surface. The modified Darken model was used to simulate the profile yielding the following segregation parameters: Do(Sn) = 6.3 × 10−6 m2/s, Do(Sb) = 2.8 × 10−5 m2/s; ESn = 175.4 kJ/mol, ESb = 186.3 kJ/mol; , ; ΩCu-Sn = 3.4 kJ/mol, ΩCu-Sb = 15.9 kJ/mol and ΩSn-Sb = −5.4 kJ/mol.  相似文献   

4.
The technique of NMR on oriented nuclei has been applied to127Sb to measure the magnetic dipole moment of the127Sb ground state. Resonant destruction of gamma-ray anisotropy from127Sbg (I =7/2+) has been observed at 139.6(2) MHz forB app=0.30(1) T andat 138.7(1) MHz forB app=0.25(1) T. The deduced magnetic moment is ||=2.697(6) µN.  相似文献   

5.
6.
During 350 keV Ar+ irradiation at 77K, laser-deposited Fe–Ag multilayers first show stress relaxation and demixing processes at the interfaces followed by grain coarsening and a supersaturation of the bcc -Fe phase with Ag due to ballistic mixing. At high fluence, the fcc -Fe(Ag) phase (a=3.65 Å) is formed, which can be explained by either chemically guided ballistic short-range relocations or by the occurrence of thermal spikes, where all atoms possess sufficient energy to allow collective structural rearrangements, but only during such a short time that a decomposition due to long-range diffusion is suppressed.  相似文献   

7.
The magnetic hyperfine field B hf for Cd in the Heusler alloy Pd2MnSn at the site of chemically introduced Ag has been investigated by PAC following the decay of 111Ag. Sign and temperature dependence of B hf have been determined. Comparison of the result B hf(T=0)=+8.0(1) T with earlier data and ab-initio band structure calculations leads to the conclusion that the Ag activity has been incorporated at the Mn site.  相似文献   

8.
9.
Based on thermodynamic analysis of interfacial segregation, the segregation enthalpy H o of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface and the solid solubility limit X infI sup* at temperature T and can be written as In this equation, the structural dependence of interfacial segregation is contained in H *() which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [Tln(X infI sup* )] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [Tln(X infI sup* )]max. The parameter v>0 represents the relationship between the activity a infI sup* of a solute at the bulk solid solubility limit in a given matrix and X infI sup* , a infI sup* =(X infI sup* ) v , and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of -iron, the averaged value was determined. Values of H *() range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of -iron.  相似文献   

10.
Ag grain boundary (GB) diffusion was measured in the Cu-0.2at%Ag alloy in a wide temperature range from 473 to 970 K. The direct measurements of Ag GB diffusivity D alloy gb under conditions of the Harrison C regime revealed that D alloy gb is almost identical to D pure gb determined earlier for Ag diffusion in high-purity Cu (Divinski, Lohmann, and Herzig, 2001). The penetration profiles determined in the Harrison B regime showed a complex, multi-stage shape. This diffusion behavior can be rationalized assuming that besides GBs significantly covered by segregated Ag atoms, some fraction of GBs remains almost free from Ag atoms in the studied temperature interval. The total amount of pure GBs drastically decreases with decreasing temperature. This hypothesis was proven by measurements of Ag GB diffusion in Cu near 5 bicrystals, which allowed us to analyze in detail the non-linear segregation of Ag in Cu GBs.  相似文献   

11.
Solid-phase transformations at different annealing temperatures in Mn/Bi (Mn on Bi) and Bi/Mn (Bi on Mn) films have been studied using X-ray diffraction, electron microscopy, and magnetic measurements. It has been shown that the synthesis of the α-MnBi phase in polycrystalline Mn/Bi films begins at a temperature of ~120°C and the Mn and Bi layers react completely at 300°C. The resulting α-MnBi(001) samples have a large perpendicular magnetic anisotropy (K u ? 1.5 × 107 erg/cm3) and a coercive force H > H C ~ 3 kOe. In contrast to Mn/Bi, the ferromagnetic α-MnBi phase in Bi/Mn films is not formed even at annealing processes up to 400°C and Mn clusters are formed in a Bi melt. This asymmetry in phase transformations occurs because chemosorbed oxygen existing on the surface of the Mn film in Bi/Mn films suppresses a solid-phase reaction between Mn and Bi. The analysis of the results obtained implies the existence of new low-temperature (~120°C) structural transformation in the Mn–Bi system.  相似文献   

12.
In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge2Sb2Te5 (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5 m. After the programming signals of more than 2×106 cycles were repeatedly applied to the device, the high-resistance memory state (reset) could not be rewritten and the cell resistance was fixed at the low-resistance state (set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than 1×1010 cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming.  相似文献   

13.
The observation of NMR signals from 55Mn nuclei in Mn2Sb has been reported. A temperature variation study of the domain and domain wall signals in Mn2Sb confirms that the magnetization is aligned parallel to the c-axis at temperatures higher than 240 K and that it is in the basal plane below 240 K. The temperature dependence of the anisotropy in the hyperfine field at the Mn(I) and Mn(II) sites has been determined.  相似文献   

14.
We report successful fabrication of Ag doped Hg:1223 films by reacting Ba2Ca2.3Cu3.3Oz(Agy): y=0, 0.02, 0.025, 0.05, 0.1 and 0.2 precursors deposited by spray pyrolysis on SrTiO3 (100) substrates, in controlled Hg+Pb ambient, in an evacuated sealed quartz tube at 820 °C for 4 h. The effects of AgNO3 addition on the superconducting properties of Hg/(Pb):1223 films are studied. The addition of low concentration of silver e.g. y≈0.025 results in a slight increase in Tc (R=0) from 125 to 126 K and the dc critical current density (Jc) decreases with the increasing Ag in Hg(Pb):1223 (Agy) films. The microstructural details exhibit the curious characteristics of spiral like features for lower concentrations of silver i.e. up to y=0.05. These improvements are believed to be due to the liberation of oxygen through the dissociation of AgNO3 at higher temperature and passivation of weak link effects through the segregation of silver at these grain boundaries. The addition of silver content y≥0.05 resulted in the decrease in transition temperature. The Jc is observed to decrease steadily with increasing Ag content. The microstructural features, e.g. spiral are also found to deteriorate with increasing silver content. The deterioration in superconducting properties at high Ag content is believed to be mainly due to the formation of Ag-Hg amalgam.  相似文献   

15.
The effect of colloidal dispersion of silver on the luminescent properties of Eu (III) complex with pyridine-3,5-dicarboxylic acid (PyDC) was investigated. The luminescence from Förster type europium complex was enhanced several times with the presence of Ag colloid and the enhancement factor showed Ag concentration dependence. The observed enhancement effect was discussed in view of surface-enhancement effect and optical absorption due to surface plasmon resonance, both arising from excitation of surface plasmon polariton. The coordination structure around Eu (III) ion was also affected with the presence of Ag colloid, which induced the change in the intensity ratio between two emission bands of 5 D 0 7 F 1 and 5 D 0 7 F 2 transitions of Eu (III) ion.  相似文献   

16.
Interfaces of solid state bonded Si3N4ceramics with Fe and Fe-(5, 10, 15 wt%)Cr alloy interlayers inArgon for 1 h at 1100°, 1200° and 1300°C have beencharacterized by electron probe microanalysis (EPMA) and transmissionelectron microscopy (TEM). Smooth interfaces with no evidence ofreactions products resulted when bonding at 1100°C. However, theinteraction between the ceramic and the metal increased at higherbonding temperatures and Cr-contents. In all samples Si and N fromthe ceramic dissolve and diffuse in the metal interlayer, whereas thesintering additives of the ceramic remain inactive.Low Cr-content (5%) interlayers resulted in the formationof an interfacial zone composed of two sublayer structures; adjacentto the ceramic was a thin one containing the sintering aids ofSi3N4 and fine precipitates of Fe3Si and -Fe4N in a bcc-Fe matrix. The second was thicker and includedfine Fe3Si,-Fe4N and-Fe2N precipitates in abcc-Fe matrix. The bond region with high Cr-content interlayersincluded three sublayer structures. The first one next to the ceramicwas a bcc-Fe matrix containing sintering aids, fine dispersedFe3Si and-Fe4N, and CrN. The secondsublayer was similar but without any segregants from the ceramic. Thethird one, finally had a lamellae structure of Cr2N/bcc-Fe and the Fe matrix contained also-Fe4N.The interactionbetween the ceramic and the metal interlayer is believed to becontrolled by the solution rate of N in the alloy foils.  相似文献   

17.
By internal oxidation of AgMg- and PdMg-alloys small precipitates ofMgO are formed within the Ag- or Pd-matrix. Thetotal area of the metal/oxide interface produced this way becomes severalsquare meters in one cubic centimeter of metal. Segregation of oxygen at theinterface is determined by desorption of gaseous oxygen for theAg/MgO-interface and by trapping of hydrogen for the Pd/MgO-interface. At673 to 873 K the oxygen coverage of the Ag/MgO boundary does not obey aLangmuir-McLean relation. At the highest oxygen pressure of105 Pa O-coverage reached a maximum value of about2.2·1014 O-atoms/cm2. The average freeenthalpy of segregation is about -70 kJ/mol O. The results are interpretedin terms of a structural model, where the interface contains vacancies inthe terminating oxygen (111)-plane of MgO. Segregation, i.e., filling of thevacancies with oxygen from solid solution, leads to the formation of a twodimensional silver oxide. For Pd/MgO condition were less favorable andoxygen segregation can be determined indirectly by irreversible hydrogentrapping. Oxygen segregation does not occur if the sample is rapidlyquenched from 1273 K by drooping it into liquid nitrogen. In order tounderstand the kinetics of segregation, the diffusion coefficient of oxygenwas determined in Pd by measuring solubility and permeability. Measuredvalues can be described by the following relationD = 2.3;10 -3 exp[-12,300/T] cm2/s.  相似文献   

18.
The transport properties and magnetoresistance of half-Heusler CoNb1−xMnxSb (x=0.0-1.0) alloys have been investigated between 2 and 300 K. In this temperature range, a metallic conductivity has been observed for the alloys with higher (x=1.0) and lower (x=0.0-0.2) Mn contents. However, the middle Mn content alloys (x=0.4-0.8) exhibit non-metallic conductive behavior. Their temperature dependence of resistivity undergoes a Mott localization law ρ=ρ0exp(T0/T)p (p=1/4) rather than a thermal excitation regime ρ=ρ0exp(Ea/kT) at low temperature (). The localization can be attributed to atomic and magnetic disorder. Resistivity peaks from 25 to 300 K were also observed for these alloys. Magnetotransport investigation reveals that these resistivity peaks result from localization effect as well as spin-disorder scattering.  相似文献   

19.
20.
55Mn nuclear magnetic resonance experiments are reported on a series of fully strained epitaxial La(2/3)Ca(1/3)MnO3 thin films on SrTiO3. We have found evidence of multiple phase segregation into ferromagnetic metallic and nonmetallic regions as well as regions that are nonferromagnetic and insulating. These insulating regions are mainly located close to interfaces and may have a significant impact on the performance of spin-tunnel devices. As a result of phase segregation, the ferromagnetic coupling within the metallic regions is depressed. This accounts for the reduction of the Curie temperature and conductivity in nanometric thin films.  相似文献   

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