摘要:

The interaction of ultrasonic phonons with charge carriers in nearly intrinsic InSb via deformation potential and piezoelectric coupling mechanisms has been investigated at 296 K in magnetic fields of 0 to 11 kOe and over a frequency range of 10 to 200 MHz. The single crystal InSb wasptype with an average acceptor concentration of (1.45±0.05)×1016cm−3. The experiment permitted an ultrasonic determination of the electron and hole mobilities. The values obtained were &mgr;n0= (58 000±4000) cm2V−1sec−1and &mgr;p0= (720±80) cm2V−1sec−1. Values of the deformation potential and piezoelectric coupling constants obtained were |Cn+Cp| = (5.8±0.4) eV ande14= | 0.076±0.010 | C/m2.

ISSN:0021-8979    

DOI:10.1063/1.1660591

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Light diffraction by an acoustic surface strain wave in fused quartz was observed in the Debye‐Sears limit. An acoustic surface wave has both compressional and shear strains. It is possible to observe and distinguish the diffraction of light caused by the two different strains since the diffracted beam polarization due to the shear strain is rotated 90° from the incident polarization. In the experiment performed 2.5% of the incident energy was diffracted into a single order. Light diffracted by both the compressional and shear strains was clearly identified.

ISSN:0021-8979    

DOI:10.1063/1.1660592

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Paramagnetic vanadium‐phosphate and molybdenum‐phosphate glasses have been studied using electron‐spin resonance and nuclear magnetic resonance. These glasses were nominally 80% MO:20% P2O5, where MO denotes the transition‐metal oxide. The electron‐spin‐resonance results showed a strongly exchanged, narrowed interaction with V4+/V5+and Mo5+/Mo6+ratios and line shapes which were independent of temperature over the range 77°–300°K. Since the conductivity is nonlinear in this temperature range, the result is direct evidence that the mobility is temperature dependent and that the average paramagnetic‐site is unchanged over this temperature range. The nuclear magnetic resonance of51V and31P in the glasses verifies the assumption of exchange narrowing. The51V quadrupole coupling (1.5 MHz) and spin‐lattice relaxation time (T1<500 &mgr;sec) were temperature independent over the 77°–300°K range. The31P resonances in each of the glasses also had temperature‐independent properties. For the molybdenum glass the linewidth was 0.45 G andT1=300 msec. For the vanadium glass the corresponding numbers were 1.4 G and <500 &mgr;sec. The results are compared in part with previously published values.

ISSN:0021-8979    

DOI:10.1063/1.1660593

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The resistivity of a sample is given by &rgr;=VI−12&pgr;sF, whereVis the voltage,Iis the current,sis the voltage contact separation, andFis a correction factor appropriate to the sample geometry. Correction factors are found for the cases of parallelepiped samples with (1) nonequidistant point contacts symmetrically located on the top face, and (2) point voltage contacts symmetrically located on the top face and point current contacts centered on the end faces. In studies of these cases, curves are given for determining the geometries which give, between the voltage contacts, current densities directed parallel to the sample length. Although in the development it is assumed that the resistivity is homogeneous and isotropic and that there is no magnetic field present, a discussion is given on the applicability to anisotropic resistivity and low magnetic fields. Experimental verification is given.

ISSN:0021-8979    

DOI:10.1063/1.1660594

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The low‐temperature electrical resistivity in thin plates has been theoretically examined. It is shown that the bulk relaxation time &tgr;iis a reasonable approximation to describe the impurity scattering. In constrast, the low‐temperature phonon‐electron interaction is not properly described by the bulk thermal relaxation time &tgr;p. Nevertheless, expressions have been obtained for the Fermi function in thin plates correct to first order in &tgr;i/&tgr;p≪1. The predicted temperature‐dependent resistivity obtained is smaller than the results predicted by Fuchs, which are also given explicitly in this limit for the first time. In the limit of very low temperatures and very thin plates a temperature dependence of resistivity greater than the bulk value, but ⅔ that obtained by Fuchs, is predicted. These results are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1660595

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The defect structure induced in Al‐6.5‐at.% Zn upon quenching consisted of homogeneously nucleated dislocation loops, helical dislocations developed from screw dislocations, the latter being introduced by two different processes. The defect structure also contained perfect loops converted from helical dislocalocations and faulted dislocation loops whose nucleation was enhanced by vacancies generated by quench deformation. Based on experimental evidence, a model is presented explaining the formation of a row of perfect dislocation loops from a single helical dislocation. The interrelation of the various types of induced defects is shown by correlating their formation with the aid of vacancy mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.1660596

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The dislocation‐associated energy of subgrains in a lattice‐parameter (concentration) gradient is calculated using two‐dimensional isotropic elasticity and neglecting almost all subgrain‐subgrain interactions. The subgrains are rectangular and are bounded by regular arrays of pure edge dislocations with Burgers vector normal to the gradient. These boundaries are either lattice‐parameter step boundaries or tilt boundaries. The energy per unit volume normalized by &mgr;/4&pgr;(1−&ngr;) isR−1[2&agr;−1+ln(b/2&pgr;&rgr;0)−&agr; ln&agr;−(1−&agr;)ln(1−&agr;)−&agr; ln(QH/R)−(1−&agr;)ln(H/R)]+(H2/12R2){8(1−&agr;)tan−1Q+(1−4&agr;)Q+[(3−6&agr;+3&agr;2)Q−(1−4&agr;+3&agr;2)Q3]ln(1+Q−2)+[3&agr;2Q+(9&agr;2−6&agr;)Q−1]ln(1+Q2)},where &rgr;0is the dislocation core radius,bis its Burgers vector, &agr; is the fraction of dislocations in tilt boundaries,bHis the height of the subgrain (parallel to the concentration gradient),Qis its length to height ratio,bRis its relaxed radius of curvature due to its lattice parameter gradient, &mgr; is the shear modulus, and &ngr; is Poisson's ratio. Two low‐energy regimes are identified: first at lowH, highQ, and &agr;=0, the lattice‐step boundary regime; second at highH, lowQ, and &agr;=1, the tilt boundary regime. The latter appears to be slightly lower in energy.

ISSN:0021-8979    

DOI:10.1063/1.1660597

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

For a very restricted range of situations, earlier work has shown that the exact equilibrium positions of discrete dislocations in a planar array may be obtained analytically, in the sense that they are given by the zeros of classic polynomial functions satisfying certain second‐order differential equations; at the same time analytic expressions have been derived for the stresses acting on obstacle dislocations. This paper explores the various models that evolve as a consequence of applying an appropriate coordinate transformation to the most general situation hitherto considered, and the range of application of the analytical approach is thereby extended.

ISSN:0021-8979    

DOI:10.1063/1.1660598

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Exact expressions for the displacement and stress components of a dislocation parallel to a⟨110⟩axis in a cubic crystal have been derived. For⟨110⟩/{112}and⟨110⟩/{111}dislocations, the stress components &sgr;xx(y=0), &sgr;yy(y=0), and &sgr;xy(x=0) are found to be nonzero. It was shown that &sgr;xy≠0 atx=0 has no effect on the stability of a vertical wall of edge dislocations. The energy factorKwas computed for the dislocations in bcc, fcc, and diamond‐cubic crystals. By comparison, the elastic energy of an edge dislocation on the {110} slip plane in bcc crystals is generally less than that on the {112} slip plane. The differences, however, are very small except in a few cases of highly anisotropic crystals such as Li, K, Na, and &bgr;‐brass.

ISSN:0021-8979    

DOI:10.1063/1.1660599

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The development of cell structure during room‐temperature tensile deformation of beyllium oriented for prism slip was studied by a combination of a new x‐ray diffraction technique (synergy method) and transmission electron microscopy. It was convenient to divide the development of the cell structure into three stages. In stage one, dislocations moving on the prism plane pulled out small segments of dislocations lying on the basal plane to form long dipoles and numerous pinched‐off loops. During the second stage, dense dislocation clusters developed which became interconnected by dislocation tangles. The final stage consisted of the formation of well‐developed cell walls with regular hexagonal networks of dislocations. The striking feature of all the stress‐strain curves was the low work‐hardening rate extending up to &egr;=15% strain. The low work‐hardening rate was ascribed to nucleation and propagation of new slip bands into hitherto undeformed volumes of the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1660600

出版商:AIP    

年代:1971

数据来源: AIP