Bismuth Single Crystals Research Articles

Size Effect and Temperature Dependence of the Electrical Resistance in Bismuth Single Crystals of High Perfection

AbstractBi single crystals of high perfection (having extremely high resistance ratios r4.2 = ϱ290 K/ϱ4.2 K) are grown by the mould growing method. In these crystals, the thickness dependence of the resistance ratio r4.2 and the temperature dependence of the electrical resistance are investigated in a temperature range between 2 and 77 K. In the range of the diffusion size effect, a markedly different behaviour is found to occur in the thickness dependence of the two crystal orientations investigated (j ‖ C3; j ‖ C2). An anisotropy of the slope of the T2‐terms is detected in the temperature dependences of the electrical resistance in the temperature interval from 2 to 16 K.

Optical fiber sensor for the measurement of electric field intensity and voltage (OPSEF)

Abstract An optical fiber sensor for measuring high electric field intensity and voltage, which utilizes the electro-optic effect of bismuth silicone oxide single crystal, has been developed successfully, and the fundamental characteristics have been evaluated. The electric field intensity distribution inside the coaxial electrodes has been measured with this sensor. The measured results are in agreement with the theoretical values.

Preferred growth of bismuth single crystals

AbstractThe results of the study of the factors influencing the orientation of the (111) cleavage plane of bismuth are presented. It has been observed that at high purity the growth rates and temperature gradients do influence the orientation whereas at low purities no such influence is observed.

Temperature Dependence of the Magnetic Susceptibility of Bismuth

The magnetic susceptibility of bismuth single crystals is measured in the trigonal-binary plane over a wide temperature range from 90 K to 540 K. Moreover, we get a function to express the observed values at any temperature, assuming that the temperature dependence of the energy gap dominates the susceptibility of bismuth. All coefficients of this function are determined by using a feast squares fitting method. Then we can evaluate the energy gap at any temperature; for example, the values of energy gaps at 0 K are 18 meV and 193 meV at the L-point and at the T-point in the Brillouin zone, respectively. They are nearly compatible with other experimental results.

Investigation of the electromechanical effect in twinning of bismuth crystals in the temperature range 77?530�K

A study was made of the influence of high-density current pulses on twinning of bismuth single crystals by a concentrated load at temperatures of 77–530° K. Twinning was stimulated by current pulses throughout the investigated temperature range and at high temperatures these pulses widened the interval of twinning temperatures. The electroplastic effect in twinning appeared most clearly at low temperatures. The temperature dependences of the quantitative characteristics of twinning had three regions in which there were considerable differences in the qualitative pattern of the distribution of twins originating from indentations.

OPSEF: an optical sensor for measurement of high electric field intensity

An optical sensor for measurement of high electric field intensity by means of the electro-optic effect in single-crystal bismuth silicon oxide has been successfully developed and the fundamental characteristics measured. By use of this sensor, the electric field intensities between parallel and coaxial electrodes have been measured.

Critical Resolved Shear Stresses of Two Slip Systems in Bismuth Single Crystals

The temperature and strain rate dependences of the critical resolved shear stress of bismuth single crystal are investigated by compression tests for two slip systems, (111) <11̄0> and {001} <1̄1̄0>, over the temperature range from 77 K to 538 K. From the results the activation energy U0 and the activation volume of dislocation motion for each slip system are determined. They are 0.1 eV and 2×10-19 cm3 for the (111) <11̄0> slip system, 0.4 eV and 0.06×10-19 cm3 for the {001} <1̄1̄0> slip system, respectively. It is concluded that for the (111) <11̄0> slip system the main obstacle to moving dislocations is the forest dislocation, and for the {001} <1̄1̄0> slip system the Peierls potential controls the slip mechanism.

Adsorption and condensation of bismuth on tungsten

The bismuth-tungsten system was studied by means of field emission microscopy. The average work function changes induced by the bismuth adsorption were measured for different amounts of adsorbed bismuth. It was found that the adsorption of bismuth changes the work function of tungsten only slightly. The penetration of bismuth into the tungsten substrate was observed. The growth of bismuth single crystals was studied when bismuth was deposited with a rate of about 6 monolayers per minute onto the tungsten substrate and kept at 470 K. Bismuth single crystals with two-fold symmetry occurred most often on the (100) tungsten planes. On the (111) tungsten plane bismuth crystals with three-fold symmetry were observed. An explanation of the observed phenomena is proposed.

Pulsed Ettingshausen cooling in bismuth

The Ettingshausen cooling in single-crystal bismuth was investigated using pulsed currents far in excess of the equilibrium value. At 80K, transient cooling of nearly five times the equilibrium value was observed using rectangular current pulses. By using ramp-shaped pulses even larger transient cooling was observed. The authors suggest that this phenomenon may be due to the localised nature of the generation and recombination of the carriers at the sample surface.

Charge carrier drift velocity in a finite bismuth single crystal

The drift velocity of charge carriers in a bismuth single crystal with crossed electric and magnetic fields (E⊥H) is calculated numerically. The real structure of the Fermi surface and electric fields perpendicular to the current density vector, produced within a finite specimen, are considered. Results obtained agree well with observations of the transition of bismuth into the phonon generation regime under the condition cE/Hs≈0.5.

Giant negative phonon drag thermopower in pure bismuth

In contrast with previous reports, an important negative phonon drag hump is observed in a large binary bismuth single crystal. Without questioning the theory, this result is compared with the existing data showing the extreme sensitivity of phonon drag to size in the liquid helium range. This, together with the marked anisotropy of the transport properties, should be taken into account to explain the apparent discrepancy between the published experimental data. It is suggested that the phonon drag hump is negative for an infinite sample.

Emissivities of arsenic, antimony, and bismuth single crystals

Emissivities of arsenic, antimony, and bismuth single crystals

Measurements of Equilibrium Vacancy Concentration in Bismuth

Precision measurements of macroscopic (dilatometric) thermal expansion Δ L / L 0 and microscopic (X-ray) thermal expansion Δ d / d 0 have been carried out on bismuth single crystals (99.9999%) along both a and c directions in the temperature range between 50° to 260°C. The equilibrium defect concentration was obtained as a function of temperature by assuming the primary defects to be monovacancies. The concentration of vacancies is 6.17×10 -4 at the melting point, and the formation energy and entropy of a monovacancy are 0.35 eV and 0.3 k , respectively. The ratios of the expansion arising exclusively from the creation of defects to the true thermal expansion of the ideal lattice without any thermal generation of vacancies are 2.0% and 0.53% at the melting point for the a and c directions, respectively.

Low-temperature plasticity of bismuth single crystals

A study is made of the effect of temperature on strain hardening and slip propagation in bismuth at 4.2, 77.3, 130, and 293°K. At low temperatures the dependence of deforming stress τ on shear strain ϵ is exponential, and no relaxation of the flow stress τ0 is observed. The temperature dependence of the flow stress τ0(T) is nonmonotonic, with a maximum at 130−160°K. The magnitude of the relative shear in the slip bands increases by a factor of around 10 as T decreases from 293 to 4.2°K, although τ0 at this temperature is the same. A theoretical description of low-temperature strain hardening of bismuth is given using an exhaustion model of slip-band sources. The distribution function of the number of sources over start stress is recovered through the form of the curve τ(ϵ) and data on the width of the slip bands and their relative shear. At low temperatures nucleation of dislocation loops on heterogeneities is nonactivational in nature. It is shown that the mean velocity of dislocations at the flow point in bismuth increases with decreasing T from 293 to 4.2°K. The nature of the nonmonotonic dependence τ0(T) is discussed.

Heat conduction in bismuth-antimony alloy single crystals between 4.2 and 300 K

Thermal conductivity measurements in the temperature range 4.2–300 K on three single crystals of bismuth containing 1.77, 3.2, and 9.33 at % antimony, respectively, are reported. In the low-temperature region, a change from purely phonon-phonon scattering process to a predominantly impurity scattering process was observed with the increase of antimony concentration. In the high-temperature region, the analysis of the results shows the dominance of the electronic contribution over the phonon contribution to the total thermal conductivity, though the latter is not negligible. Individual contributions to total electronic thermal conductivity were calculated, using the equation formulated by Price, for the sample containing 9.33 at % antimony. The agreement between (K E)calc and (K E)exp = K − KL seems to be quite satisfactory up to about 200 K.

Ultrasonic studies on bismuth single crystals

Abstract Studies of ultrasonic velocities and attenuation are carried out in bismuth single crystals along the trigonal axis and perpendicular to the trigonal axis and the results are interpreted in terms of the changes in carrier concentration with change of direction. Temperature dependence of ultrasonic attenuation is also reported.

Neodymium ion environment in germanate crystals and glasses

Absorption and fluorescence spectra are presented for neodymium-doped alkali germanate and bismuth germanate glasses and crystals. Narrower spectral components and a shift in intensity distribution toward shorter wavelengths for the composite bands corresponding to the principal neodymium absorption and fluorescence transitions are observed as the radius of the glass modifier ion is increased (Li +Na +K +). These changes in component band width and intensity distribution become more pronounced as the concentration of large radius modifier ion is increased, and result in effectively narrower widths for the fluorescent bands involved in laser emission. Optical spectra for neodymium in a sodium germanate single crystal show broad bands characteristic of those of glasses. Electron microprobe scans reveal non-uniform distribution and clustering of neodymium in alkali germanate crystals. Narrow, temperature sensitive bands similar to those of neodymium in other crystals are found for single crystal and polycrystalline neodymium-doped bismuth germanate, while the glass exhibits broad bands. Substitutional replacement of Bi 3+ with Nd 3+ in the bismuth germanate crystal lattice is indicated from the optical spectra but the environment of neodymium in crystalline sodium germanate appears to have only short-range order. The difficulty encountered in introducing neodymium into substitutional positions in alkali germanate crystals may result from the charge difference between neodymium and the alkali cations as well as the oxygen: germanium ratio of these compounds, which favors glass network formation rather than crystallization.

Magnetic focusing of electrons and holes in bismuth

The electron and hole focusing effects in a magnetic field predicted by Pippard have been observed in bismuth. Two interlocking superconducting combs were evaporated onto the surface of a bismuth single crystal. The resistanceR(H) between the combs was measured with a superconducting voltmeter as a function of the magnetic fieldH applied parallel to the teeth of the combs. A local minimum in the resistance was observed when the magnetic field focused electrons or holes in extremal orbits between the teeth of different combs. A similar effect was observed when the combs were replaced by two parallel superconducting strips. In this case the dependence ofR(H) onH was in good qualitative agreement with the calculation of Goncalves da Silva on a model whose Fermi surface was topologically equivalent to that of bismuth. From the values ofH at which the minima occurred we have deduced estimates forD xe andD ze , the diameters of the principal electron ellipsoid along the binary and trigonal axes. We findD xe =(0.94±0.03)×10 −2 A −1 andD ze =(1.35±0.04)×10 −2 A−1. These values lie somewhat below other values in the literature. This discrepancy may occur because each minimum inR(H) occurs at a field slightly belowH 0, whereH 0 is the field for which the diameter of the extremal electron trajectory is equal to the separation of the superconducting strips.

Low-field galvanomagnetic effect of bismuth from 80 °K to 300 °K

The low-field galvanomagnetic tensor elements of single-crystal bismuth have been measured in the temperature region from 80°K to 300°K. From the experimental data, the electron and hole transport parameters are calculated and found to be in good agreement with those of the recent work by Michenaud and Issi. The electron concentration deduced from the measured magnetoresistivity coefficients does not agree with the theoretical calculation at higher temperature based upon the charge neutralization condition. The concentration-dependence on different electron band structure models and the effect of impurities are also briefly discussed.

Bismuth titanate-ferroelastic distortion and domain studies

Abstract The monoclinic shear distortion in single-crystal bismuth titanate has been measured directly by an optical-reflection technique. The shear angle is ∼1.45 min at room temperature and has a negative temperature coefficient. The shear distortions at domain walls were measured in an interference microscope. These and other electrical-mechanical measurements indicate that ferroelectric-ferroelastic coupling in bismuth titanate is relatively small.