摘要:

Studies of the EPR of dilute Mn2+in CsPbCl3have been carried out over the temperature range 77°–340°K. Crystalline phase changes as indicated by changes in the Pb site symmetry were evident at 320°K (46.5°C) and 185°K. The first of these has been reported previously while the latter is apparently a new observation. Between 185° and 320°K, the EPR spectra can be assigned to two and possibly four crystallographically equivalent sets of magnetically inequivalent sites, the spectra of theith set derivable from the spin HamiltonianHi=g&bgr;H·S+Di[Sz2−13S(S+1)]+Ei(Sx2−Sy2)+16ai(Sx4+Sy4+Sz4)+ASzIz+B(SxIx+SyIy).Typical values of the crystal field parameters are:A= −87.5 G,B= −86.5 G, anda≈1 G; all sensibly temperature independent, whileDandEare temperature dependent. For example at 195°K,D1,2,3,4=45 G andE1= −E2=7.2 G,E3=6.4 G, andE4= −5.0 G. BothDandEtend continuously to zero at 320°K. Thus, the individual site symmetries are evidently orthorhombic and the overall crystal symmetry is apparently orthorhombic or nearly so. Some discussion of possible crystal space groups is included.

ISSN:0021-8979    

DOI:10.1063/1.1657345

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Ta&sngbnd;Al2O3cermet thin films were produced by diode sputtering. Cathodes were fabricated by powder techniques, plasma spraying and as mechanical composites. Film compositions of 1–20 wt% Al2O3produced resistivities of 250 to 25 000 &mgr;&OHgr;·cm and TCR's of +100 to −450 ppm/°C, respectively. The films showed good thermal stability and could be anodized. Electron microscopy and x‐ray analyses suggest a film structure consisting of long columnar grains of bcc Ta, approximately 100 Å in diameter, surrounded by Al2O3. A quantitative analysis is made of tunneling currents in an idealized film. Resistivity‐composition and resistivity‐temperature data are explained in terms of this analysis. The height of the Al2O3barrier between grains is estimated to be 0.23 eV for an effective electron mass of 1/9. Barrier thicknesses are estimated at 15–30 Å.

ISSN:0021-8979    

DOI:10.1063/1.1657346

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

New experimental results on the dc electrical conductance, between room temperature and 250°C, of potassium azide single crystals and pellets and potassium azide doped with barium azide are described. These data have been interpreted as involving cation current carrying species. Numerical values for the enthalpy of migration and enthalpy of defect pair formation are deduced. These are, respectively &Dgr;h1=0.79±0.05 andh=1.43±0.05. Isothermal dc conductance data are also presented and imply that the charge carriers are involved in the thermal decomposition processes of KN3.

ISSN:0021-8979    

DOI:10.1063/1.1657347

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

If an obstacle exists in the vicinity of the free surface of a half‐space and a stress field is applied in such a manner that dislocations are pushed towards the obstacle, an array of dislocations then piles up into an equilibrium distribution against the obstacle. The distributions of dislocations are obtained by the Wiener‐Hopf technique for the edge and screw dislocations. The total strength of dislocations (Burgers vector multiplied by the number of dislocations) distributed in the distanceLis calculated as 0.92&pgr;(1−v)&sgr;AL/Gfor edge dislocations and 2&sgr;AL/Gfor screw dislocations, whereG, vare the shear modulus and Poisson ratio respectively and &sgr;Ais the applied stress. The result can be applied to crack problems. The above two numbers for the total strength of dislocations give the crack openings at the free surface for the extensional mode and the antiplane shear mode of fracture, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1657348

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The annealing behavior of Cu‐8.5 at.% Ge filings has been studied by means of x‐ray diffraction. The shifts in the positions of the powder pattern peaks from deformed and partially annealed samples can be accounted for by stacking faults and changes in the layer spacings at the stacking faults. No evidence was found for extrinsic faulting. Isothermal annealing treatments in the range 180°–240°C showed that the deformation stacking faults annealed out in a two‐stage process. The first stage was associated with recovery while a kinetic study showed the second stage to be connected with recrystallization. The rms microstrains obtained by Fourier analysis techniques annealed out in a manner similar to the stacking faults. The particle size as determined by Fourier analysis remained constant during isothermal annealing until the recrystallization stage where it increased sharply. Analysis of the peak asymmetries during annealing showed that the number of twin faults remained constant at the value for the cold‐worked state until the recrystallization stage where a small increase occurred followed by a rapid decrease toward zero.

ISSN:0021-8979    

DOI:10.1063/1.1657349

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Diffraction contrast profiles have been calculated using the two beam approximation for a thin crystal foil which contains a spherical void. The influence of the foil thickness, foil orientation, void radius, and void depth on the total contrast, a combination of both the strain contrast due to distortion of the foil by the void and the thickness contrast due to the absence of scattering material within the void, was examined, the lengths being expressed in units of &xgr;g*=&xgr;g(1+w2)−1/2wherew=Sg&xgr;gwithSgthe deviation from the exact Bragg condition and &xgr;gthe extinction distance. Maximum strain contrast occurs for the profiles of both beams at depthsd*= (N/2)&xgr;g*(Nan integer); the black and white sides of these profiles alternate as the depth changes by 1/2&xgr;g*. The amplitude of the strain contrast is maximum at thicknessest*=N&xgr;g*and (N+1/2)&xgr;g*for the scattered beam and the transmitted beam respectively. In either case, the inbetween thicknesses give a smaller strain contrast for which the white sides of the profiles are suppressed for voids within an extended region of the foil. This region of small amplitude is centered on the midplane of the foil forw=0, but shifts for only the scattered beam toward the entrance (exit) surface aswincreases positively (negatively); a much larger amplitude can then occur near the opposite surface. Although the strain contrast for either beam is largest for void radiusR0*=1/4&xgr;g*, the thickness contrast atw=0 dominates the image of the void at this and larger radii. ForR0*≲1/16&xgr;g*, the strain contrast, when maximum, becomes the dominant image forming mechanism. As the foil is rotated away from the exact Bragg condition,w≠0, the thickness contrast can firstly become quite small compared to the strain contrast even atR0*=1/4&xgr;g*, but upon further rotation it predominates once again as in the casew=0 while showing an image of opposite character to the former case.

ISSN:0021-8979    

DOI:10.1063/1.1657350

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The integrated Bragg intensities of the (111) reflections of perfect crystal Ge and Si have been measured with a higher accuracy than heretofore. Ge was measured using x‐ray wavelengths of 0.56 and 1.54 Å, and Si using 1.54 Å. Comparison of the scattering factors so obtained with those measured previously by the same method or by the Pendello¨sung fringe method leads us to the conclusion that there is not a systematic difference between the two methods, as has been suggested. We find that the reflectivity in the wings of the Bragg peak is much lower than the calculated value, and this effect would have to be taken into account if accuracies of the order of 0.1% are envisaged. We also measured Si (222) and found results in agreement with other reflection measurements, but not with recent transmission measurements.

ISSN:0021-8979    

DOI:10.1063/1.1657351

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An extension of the method for calculating the shapes of diffracting planes from the shape of the observed Laue spots is described in this paper. The method can be used for determining the shapes of the Laue spots diffracted from ideally perfect and deformed sets of planes. The method has been applied for calculating the shapes of several Laue spots by considering the planes to be ideally perfect. The calculated shapes are then compared with the shapes observed on Laue photographs.

ISSN:0021-8979    

DOI:10.1063/1.1657352

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The cylindrical antenna is potentially useful as a probe for studying the properties of any material in which it is immersed. Examples of possible media are the earth, plasmas, and organic tissues. Such applications presuppose a knowledge of the detailed behavior of the currents and charges along an antenna in a medium with very general properties. In this paper the integral equation for the current along a highly conducting center‐driven cylinder of length 2hand radiusawhen immersed in a homogeneous isotropic medium is solved analytically and simple, and quite accurate formulas are obtained for the distribution of current, the distribution of charge, and the admittance. The lengths 2hmay range from zero to over a wavelength; the radiusais assumed to satisfy the conditiona≪h. The real effective conductivity of the medium may extend from zero to arbitrarily large values, the real effective permittivity from large negative values (as in certain plasmas) to large positive values (as in ordinary dielectrics like water).

ISSN:0021-8979    

DOI:10.1063/1.1657353

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The problem of the interaction of obliquely incident microwaves with a plasma column which is moving uniformly in the axial direction is treated analytically. An arbitrary polarization for the incident plane wave is assumed. Two methods in solving this problem are presented. Extensive numerical results for the scattered energy in the backward and broadside directions and the angular distribution of the scattered energy are obtained for various interesting ranges of the parameters involved. It is found that cross‐polarized field components are induced even at normal incidence when the plasma medium is moving with respect to the observer and that cross‐polarized field components disappear at an incident angle &thgr;0=sin−1(vz/c), where vzis the velocity of the moving plasma andcis the speed of light in vacuum when the plasma column is imbedded in free space.

ISSN:0021-8979    

DOI:10.1063/1.1657354

出版商:AIP    

年代:1969

数据来源: AIP