摘要:

A molecular‐orbital energy‐level diagram is constructed and used to interpret the metal‐ionLII,IIIx‐ray emission and absorption spectra from the oxides, nitrides, carbides, and borides of titanium and vanadium. It is shown that the MO model provides a more accurate description of the experimental results than did the ionic model and crossover transition theory. Specific electronic transitions are assigned to spectral components. Anomalous emission peaks which fall on the low‐energy side of the mainLIIIband are found to originate in molecular orbitals which are primarily associated with ligand 2pand 2slevels.

ISSN:0021-8979    

DOI:10.1063/1.1659472

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The narrow‐beam mass‐attenuation coefficients of helium and hydrogen were measured at 5.895 keV. AK&bgr;‐filtered55Fe source of Mn x rays, a set of collimators, and a low‐energy sodium iodide counter were used with a high‐pressure gas chamber. Photon intensities were measured with and without gas in the chamber. The measured coefficients are 0.416±0.017 cm2/g for He and 0.400±0.016 cm2/g for H2. These numbers are compared with theoretical predictions of this parameter.

ISSN:0021-8979    

DOI:10.1063/1.1659473

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Diffraction effects due toa/8[110](11¯0)‐anda/6[111](1¯1¯2)‐typestacking faults anda/2[111](11¯0)‐anda/2[111](1¯1¯2)‐typeantiphase boundaries in &bgr;‐brass structures have been considered. The stacking faults broaden both the fundamental and the superstructure peaks, while only the latter class is affected by the antiphase boundaries. The magnitude of broadening, for the two stacking faults, varies from one reflection to another as well as among different orders of the same reflection leading to strong anisotropy in the particle sizes derived from the broadened peaks. When different orders of the same reflection are broadened differently by faulting, the measured particle size anisotropy is found to depend on the fault type as well as on the manner in which strain contributions are removed from the total broadening. Several strain correction procedures have been considered and expression for particle size due to faulting for each case is given. The effects of the two stacking faults differ in several ways. For example, while the (211) fault broadens all fundamental orders of a reflection to the same extent, the broadening due to (110) generally increases with the order of the reflection. Allpowderreflections along [111], however, are unaffected by the (110) faulting. These and other differences in the broadening behavior lead to quite dissimilar particle size anisotropies for the two stacking faults. Among other stacking faults that may also occur in &bgr;‐brass structure, thea/6[111](11¯0)‐anda/6[111](3¯21)‐typefaults predict particle size anisotropies identical to that for thea/6[111](1¯1¯2)fault. Thea/3[1¯1¯1¯](1¯1¯2)‐typefault, on the other hand, broadens the fundamental reflections to the same extent as thea/6[111](1¯1¯2)fault, but it affects the superstructure peaks differently; on this basis it is possible to distinguish between these two fault types from their diffraction effects. In addition to broadening, the stacking faults also lead to small peak shifts of varying magnitudes and directions which, in the case of powder peaks, occur only when there are spacing changes at the faults, but the relative shifts of the various powder peaks due to the (110) and (211) faults are similar; the same is also true of the antiphase boundaries

ISSN:0021-8979    

DOI:10.1063/1.1659474

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The defect substructure in cold‐worked &bgr; AlNi intermetallic has been examined by means of x‐ray diffraction. The broadenings exhibited by the fundamental and superstructure powder peaks were analyzed in terms of contributions from inhomogeneous strain and planar faults on the 211 and 110 planes. No account was taken of possible contributions from microtwinning. The analysis shows that the pattern of particle size anisotropy exhibited by &bgr; AlNi can be satisfactorily accounted for in terms of certain concentrations ofa/8[110](11¯0)‐anda/6[111] (1¯1¯2)‐typestacking faults, with the former predominating. Possible contribution froma/3[1¯1¯1¯] (1¯1¯2)‐typestacking faults, however, was found to be negligible. Similarly antiphase boundaries were also not found to be important in the cold‐worked structure of stoichiometric AlNi.

ISSN:0021-8979    

DOI:10.1063/1.1659475

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Glide velocity measurements were made on isolated screw and 60° dislocations in silicon for the temperature range 775°–925°C. The x‐ray topographs which were used to reveal dislocation displacements also gave qualitative information concerning the early stages of dislocation multiplication in highly perfect silicon crystals. Freshly generated dislocations were more mobile than aged dislocations. Pinning points which were tentatively attributed to thermal jogs developed along the lines. The pinning point spacing decreased with increasing temperature as would be expected for a jog formation energy of 1.2 eV. Heating to above 1000°C effectively immobilized all the dislocations present in the crystal. On subsequent loading at 825°C, no motion took place until the stress was high enough to cause catastrophic multiplication when a segment of dislocation did break away. This resulted in the formation of heavy bands of slip. For fresh dislocations the temperature dependence of velocity was analyzed on the basis of a kink pair nucleation and kink propagation model. The measured activation energy for motion of both 60° and screw dislocations was 1.8±0.3 eV.

ISSN:0021-8979    

DOI:10.1063/1.1659476

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Electrical breakdown in single crystals of NaCl, NaCl+MnCl2, KCl, and KCl+SrCl2is studied in the temperature range 100°–320°C. Two types of breakdown are distinguished and detailed study is given to that type in which no strong dependence of the breakdown strength on the time of application of voltage is found. ``Intrinsic''‐type mechanisms would appear to be involved, but the nature of breakdown and of the prebreakdown current is such as to suggest that space‐charge effects, if present, are not primarily of ionic origin as has been previously suggested.

ISSN:0021-8979    

DOI:10.1063/1.1659477

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Parallel field excitation of piezoelectric plates has been analyzed with a matrix method, and the admittance of the plate is derived. This formulation affords the definition of coupling factor to each of three vibrational modes, which is shown to be modified by the antifield effect due to the induced charges on major surfaces of the plate in case of anisotropic crystals. In contrast to the perpendicular field excitation case, the resonant frequencies in this case are odd multiples of the fundamentals and the antiresonant frequencies are determined as solutions of a transcendental equation. The validity of the derived equations is confirmed by comparing measured and calculated frequency constants of lithium tantalate single crystal.

ISSN:0021-8979    

DOI:10.1063/1.1659478

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The cubic‐tetragonal phase transformation in V3Si and Nb3Sn has been investigated dynamically with optical and x‐ray techniques. For Nb3Sn a simple shear on the {110} ⟨11¯0⟩ completely describes the lamellar morphology in the tetragonal state. The lamellar structure and associated shear are concluded to arise from an accommodation of internal stresses and are a result of, not a mechanism for, the transformation. All our observations are consistent with a continuous transformation from the cubic to tetragonal state with no evidence of hysteresis or the coexistence of the two phases.

ISSN:0021-8979    

DOI:10.1063/1.1659479

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A kinetic theory of the anomalous energy spread in electron beams is given which is based on a new method of solving the nonlinear Vlasov equation. Basically we assume that the thermal velocity of the electrons is small compared to their drift velocity. The energy spread is caused by noise fed into the beam from the electron gun. The theoretical relationships are in agreement with the experiments.

ISSN:0021-8979    

DOI:10.1063/1.1659480

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A numerical study is reported of the equations describing the steady state of a column of thermal plasma that is heated inductively by a radio‐frequency axial magnetic field. The electric and thermal conductivities and the specific radiation of the plasma are taken to be given functions of the temperature. A numerical technique is described which yields self‐consistent solutions for given values of the input parameters, these being the frequency and the number of ampere turns per unit length of the driving solenoid, and the radius of the tube. Typical results are shown for an argon plasma at atmospheric pressure.

ISSN:0021-8979    

DOI:10.1063/1.1659481

出版商:AIP    

年代:1970

数据来源: AIP