Beryllium Single Crystals Research Articles

Double-Quantum Transitions in the Resonance Depolarization ofB12

Double-quantum transitions have been observed in the resonance depolarization spectrum of $^{12}\mathrm{B}$ implanted in a single-crystal beryllium host. The effect is observed at large depolarizing fields and gives a line unshifted by quadrupolar interactions.

Investigation of X-Ray Plasmon Scattering in Single-Crystal Beryllium

X-ray scattering studies in single-crystal beryllium reveal for the first time an anisotropy in both the plasmon dispersion and linewidth. By comparing the data with random-phase-approximation-type theory which includes band structure, we can begin to separate the contributions from the lattice and from the true many-body interactions to the temporally and spatially dependent response of an interacting electron gas at metallic densities.

Diffusion creep by dislocation climb in beryllium and Be-Cu single crystals

High temperature creep of beryllium and Be-Cu alloy (10 wt pct Cu) single crystals com-pressed along the -c axis was shown to proceed by pure climb of -c dislocations (Burgers vector [0001]). Experimental results can be explained if we assume that -c dislocation loops grow in the basal planes. The activation energy for the climb of the -c dislocations is found to exceed the activation energy for self diffusion by 10 ±5 kcal/mole for both beryllium and Be-Cu. This leads us to think that thec dislocation climb rate is controlled by the processes of vacancy emission or absorption at jogs rather than by lattice diffusion.

Parametric acoustic transmitting arrays : Muir, T.G., Willette, J.G. 52 (November 1972) 1481

The correlation of structural anisotropy with normal spectral emissivity has been investigated experimentally and theoretically. Measurements include data on the two major crystallographic faces of pyrolytic graphite, pyrolytic boron nitride and single crystal beryllium. The results were obtained at temperatures near 800°C over a wavelength range from visible to near i.r. (0.60 to 11 μ) in both purified hydrogen and argon atmospheres. Pyrolytic graphite C-faces deposited at higher temperatures exhibit generally lower normal spectral emissivity (0.60 to 11 μ) corresponding to an increase in basal plane absorption as the deposition temperature increases. A further increase in basal plane absorption upon extreme annealing results in the lowest normal spectral emissivity of C-face pyrolytic graphite. This highly annealed C-face pyrolytic graphite exhibits a normal spectral emissivity dispersion which is close to the theoretically predicted curve of C-face single crystal graphite. Pyrolytic boron nitride in its lattice absorption region (λ ≳ 2.60 μ) exhibits a normal spectral emissivity of the A-face which is greater than that of the C-face. This corresponds to the greater absorption in the basal plane than in the prismatic plane. Single crystal beryllium in its free-carrier intraband absorption region (λ ≳ 2.50 μ) exhibits a normal spectral emissivity of the A-face, (1010), which is greater than that of the C-face, (0001). Thus, absorption is greater in the basal plane (E→ ⊥ c-axis) than in the prismatic plane (E→ ⊥ c-axis) corresponding to an inverse relationship of normal spectral emissivity to absorption in the intraband region.

Beryllium 100 ns acoustic delay line

A beryllium single crystal is used to fabricate an acoustic delay line. The sputtered ZnO transducers are deposited on the (0001) surfaces. A delay of 110 ns is obtained in the range 1000–2000 MHz with an insertion loss of about 50 dB and spurious responses below 70 dB.

Aging of beryllium single crystals

Aging of beryllium single crystals

The anisotropy in the compton profile of magnesium

Abstract The Compton profiles of magnesium were measured in three directions: with the x-ray scattering vector along the c axis, along the a axis and along the bisector of the a and c axes. The profiles are free-electron-like but indicate some concentration of electron momentum density in the basal plane. As in previous measurements on polycrystalline magnesium, there is a significant high-momentum tail above the Fermi momentum indicative of electron–electron correlation effects. Comparison with previous measurements on beryllium single crystals indicates that the anisotropy in the valence electron profile is greater in magnesium than in beryllium (10% at the peak for magnesium versus ∼4% for beryllium). No band wave function calculations in momentum space are available for comparison.

Magnetic breakdown in beryllium

Despite the several experimental and theoretical studies that have been devoted to the investigation of the Fermi surface of beryllium, certain problems remain elusive in connection with the behavior of the electrons in beryllium single crystals. Only recently, for example, has magnetic breakdown in beryllium been investigated in detail, although its onset in fields of 50 kOe was discovered as far back as 1963.1'2 Beryllium is well known as one of the lightest of the elements; it has a low atomic number, and its atoms have only four electrons. Elements of this nature exhibit good agreement between the theoretical calculations of the Fermi surface and the experimental data. Metallic beryllium has relatively few carriers in the conduction band and, accordingly, a low density of carrier states at the Fermi level. Beryllium also has a small electron heat capacity; the coefficient associated with the linear term of its heat capacity has a value ~ = 0.4 x 10 -4 cal/mole • deg2. 3 Beryllium is a metal characterized by a high Debye temperature, which, according to Ref. 3, is equal to (1480 _+ 16)°C. The end result of the low density of states of the electrons and high Debye temperature is that a number of quantum effects are far more pronounced in beryllium than in most other metals. This feature renders beryllium a useful and fascinating medium for the investigation of such effects as magnetic breakdown. It has proven feasible in beryllium, for example, to study magnetic breakdown over a wide range of temperatures and to observe the socalled "thermal" breakdown effect) '4 A fair number of papers have been written to date on the subject of magnetic breakdown (see, e.g., the survey in Ref. 5), but a great many striking characteristics of this intriguing effect have not been unequivocally explained and are in need of further study. As the magnetic fields in which measurements are possible are increased, new possibilities are opened up for the investigation of magnetic breakdown, which is rapidly becoming one of the most interesting problems of the modern physics of l~etals. Another absorbing facet of magnetic breakdown is that it is one of many phenomena in which coherent quantum effects are strongly manifested. The study of various relevant factors and how they influence magnetic breakdown is there-

Compton Scattering and Electron Momentum Density in Beryllium

Compton-scattered x-ray spectra were measured for three orientations of a beryllium single crystal. The reduced profiles were analyzed in terms of the electron momentum distribution. Observed anisotropies can be explained qualitatively in terms of the geometry of the Fermi surface and are in qualitative agreement with earlier positron and x-ray data. The present results show high-momentum components among the valence electrons which are not revealed in the positron experiment nor accounted for by available calculations. In the process of reducing the data to obtain the momentum distribution of the valence electrons, detailed consideration was given to the effects of binding upon the Compton scattering by the core electrons.

Compton Scattering and Electron Momentum Density in Beryllium

Compton-scattered x-ray spectra were measured for three orientations of a beryllium single crystal. The reduced profiles were analyzed in terms of the electron momentum distribution. Observed anisotropies can be explained qualitatively in terms of the geometry of the Fermi surface and are in qualitative agreement with earlier positron and x-ray data. The present results show high-momentum components among the valence electrons which are not revealed in the positron experiment nor accounted for by available calculations. In the process of reducing the data to obtain the momentum distribution of the valence electrons, detailed consideration was given to the effects of binding upon the Compton scattering by the core electrons.

On steady-state diffusional creep

Abstract Introduction of the effective stress for climb and a periodic internal stress field in Nabarro's model for diffusional creep modifies the original derivation in such a way that the creep rate varies with the applied stress as [sgrave]a m , where m can be very large. The role of climb is often underestimated in high temperature deformation, as is also suggested by creep experiments on beryllium and magnesium single crystals stressed in compression along the c axis.

Symmetry in Raman scattering from the optical phonon in single crystal beryllium

We have measured the polarization of the Raman active optical mode of the single crystal, beryllium, at room temperature. To our knowledge, this is the first such measurement for a single crystal metal. We find the Raman tensor to obey the symmetry laws as outlined for a transparent insulator. After presentation of the experimental techniques and results, a discussion is given relating the symmetry results to the theory of Raman processes in metals.

Deformation of beryllium single crystals under hydrostatic pressure

Tensile tests on beryllium single crystals under hydrostatic pressure up to 15 kbar showed a 0.7% kbar−1 decrease of the critical resolved shear stress for the prismatic slip {1010} 〈1120〉. The critical resolved shear stress for the basal slip {0001} 〈1120〉 remained constant. Compression tests in the c-axis direction gave a lower limit for the critical resolved shear stress for the pyramidal slip {1122} of 15 kbar whereas fracture occured along a plane close to (1124) for stresses as high as 35 kbar.

The effect of anisotropy on emissivity

The correlation of structural anisotropy with normal spectral emissivity has been investigated experimentally and theoretically. Measurements include data on the two major crystallographic faces of pyrolytic graphite, pyrolytic boron nitride and single crystal beryllium. The results were obtained at temperatures near 800°C over a wavelength range from visible to near i.r. (0.60 to 11 μ) in both purified hydrogen and argon atmospheres. Pyrolytic graphite C-faces deposited at higher temperatures exhibit generally lower normal spectral emissivity (0.60 to 11 μ) corresponding to an increase in basal plane absorption as the deposition temperature increases. A further increase in basal plane absorption upon extreme annealing results in the lowest normal spectral emissivity of C-face pyrolytic graphite. This highly annealed C-face pyrolytic graphite exhibits a normal spectral emissivity dispersion which is close to the theoretically predicted curve of C-face single crystal graphite. Pyrolytic boron nitride in its lattice absorption region ( λ ≳ 2.60 μ) exhibits a normal spectral emissivity of the A-face which is greater than that of the C-face. This corresponds to the greater absorption in the basal plane than in the prismatic plane. Single crystal beryllium in its free-carrier intraband absorption region ( λ ≳ 2.50 μ) exhibits a normal spectral emissivity of the A-face, (1010), which is greater than that of the C-face, (0001). Thus, absorption is greater in the basal plane ( E → ⊥ c- axis ) than in the prismatic plane ( E → ⊥ c- axis ) corresponding to an inverse relationship of normal spectral emissivity to absorption in the intraband region.

The effect of temperature on the hardness anisotropy of beryllium single crystals

The effect of orientation on hardness of beryllium single crystals, in the range of room temperature to 400° C, has been studied using Knoop and Vickers indenters. The variation of Knoop hardness anisotropy with temperature is related to the alternation of deformation modes. The asymmetry of Vickers impression is also explained on the basis of deformation around impressions. There is good agreement between the deformation markings around impressions and the orientation factors for each deformation system.

The tensile deformation of overaged copper-1.8 wt.% beryllium single crystals

The tensile deformation of overaged copper-1.8 wt.% beryllium single crystals

The microstrain behavior of beryllium single crystals

The room temperature microstrain behavior of zone-refined single crystal beryllium has been examined as a function of prestrain. Crystals oriented for basal slip were deformed in simple tension (prestrains ≤0.09) and by low frequency cyclic compression (prestrains ≤0.40). The friction stress was determined from the energy dissipated in generating closed hysteresis loops as a function of forward plastic strain and maximum stress amplitude. The corresponding dislocation substructures were characterized by transmission electron microscopy. The friction stress T f associated with forward plastic strain amplitudes ≤5 × 10 −5 is low and in the range 0.02 – 0.13 kg·mm −2, with no significant effect of prestrain; a large fraction of T f is due to dislocation-impurity interaction so that the actual lattice friction stress on the basal plane is extremely small. Closed hysteresis loops exist at stress amplitudes up to the macroscopic flow stress level with corresponding forward plastic strain amplitudes as high as 2 × 10 −3. Under these conditions, a much higher friction stress T f(2) ~ 1 kg · mm −2 is measured. Cyclic compression eliminates the region of easy glide (Stage I) in beryllium and raises the flow stress. Differences in behavior in tension and cyclic compression, and the independence of T f with prestrain, have been related to the associated dislocation substructures.

Slow-Neutron Inelastic Scattering from Beryllium Powder

The inelastic scattering of slow neutrons by a sample of beryllium powder has been measured using the Materials Testing Reactor phased-chopper velocity selector. Data were obtained at incident neutron energies of 0.040, 0.0415, 0.070, and 0.10 eV and at room temperature for a sample which had a transmission of 87%. The data were converted to partial differential cross sections and to the scattering-law presentation $S(\ensuremath{\kappa}, \ensuremath{\hbar}\ensuremath{\omega})$. In contrast to previous measurements, the scattering-law presentation of the data displays considerable structure which correlates directly with the interference condition for coherent scattering. Factors which contribute to the observed structure include the structure factor for neutron-phonon interactions and the phonon dispersion relation itself. Data from this experiment are compared with the dispersion relation for single-crystal beryllium and the calculated frequency distribution of beryllium.

Tensile deformation of beryllium single crystals in various orientations between 25°C and 600°C

Single crystals of predetermined orientation have been grown from the melt by a floating zone technique using “seeds” to nucleate the required orientation. The crystals have been prepared from vacuum cast and extruded electrolytic flake of the highest commercial purity available. The level of purity obtained is 99.83% and the critical resolved shear stress for basal (0001) slip has been measured in tension from 25°C to 600°C, in crystals which have deformed only by basal (0001) slip. The critical resolved shear stress for (0001) slip remains constant at 750 p.s.i. in the temperature range 300° to 600°C and increases only × 5 in the range 300° to —196°C. This small rise in critical resolved shear stress contrasts markedly with that found for (101̄0) slip, which increases by × 9 in the same temperature range from ~ 1,500 to 13,000 p.s.i. By comparison with similar work 2 on metal 99.0% purity, it is concluded that increasing purity reduces the critical resolved shear stress for both (0001) and (101̄0) slip throughout the temperature range 25° to 600°C by ~ × 2. It is suggested that the independence of critical resolved shear stress for both (0001) and (101̄0) slip with temperature in the range 300° to 600°C implies that the beryllium lattice is hardened by increasing its solute concentration.

MTR phased chopper velocity selector

The Materials Testing Reactor (MTR) velocity selector consists of a pair of Fermi-type phased choppers and a pair of rotating collimators. The four rotors are driven at identical speeds up to 5225 rpm by four hysteresis synchronous motors. With the appropriate angular phase difference established between the choppers and the collimators, bursts of monoenergetic neutrons are selected from the MTR's Maxwellian flux. Phase instability broadens the initial neutron burst by only 12%, as demonstrated by actual measurements of time distributions. The monochromatic neutrons produced by the selector are used in measuring inelastic scattering cross sections by means of time-of-flight equipment. Intensities per time channel are sufficient to give reasonable statistics in a 24 hour run. Wavelength resolutions between 2% and 8% are realized. The paper describes the layout and characteristics of the velocity selector in detail, and discusses problems associated with backgrounds and time and intensity calibrations. Inelastic scattering data taken on samples of methane gas and on a beryllium single crystal are displayed and analyzed to show the counting rates and background levels achieved with the selector, and to demonstrate the versatility possessed by this type of monochromator.