Static Relaxation Time Research Articles

Regularities of behavior of temperature dependences of resistivity of crystals of solid solutions (Bi-=SUB=-2-x-=/SUB=-Sb-=SUB=-x-=/SUB=-)Te-=SUB=-3-=/SUB=- (0<x<2)

It is shown that the change in the resistivity of crystals of solid solutions (Bi2-xSbx)Te3 (0<x<2) p-type in the temperature range preceding the onset of intrinsic conductivity is due not only to a change in the static relaxation time, the behavior of which in the temperature range from 80 to 300 K is determined mainly by carrier scattering on the vibrations of the crystal lattice, but also by changing the concentration of light holes. The latter is a consequence of the transition of charge carriers from the subzone of heavy holes to the subzone of light holes, as a result of which the concentration of light holes, which make the main contribution to electrical conductivity, decreases with increasing temperature. As a consequence, the plasmon energy proportional to the concentration of charge carriers also decreases with increasing temperature, and the energy of this transition, comparable to the plasmon energy, increases. In this regard, crystals (Bi2-xSbx)Te3 have a specific feature due to the convergence of the plasmon energy and the interband transition, which creates conditions for increasing the intensity of the electron-plasmon interaction. Keywords: thermoelectric materials, bismuth and antimony tellurides, resistivity, interband transitions, plasma of free charge carriers.

Закономерности поведения температурных зависимостей удельного сопротивления кристаллов твердых растворов (Bi-=SUB=-2-x-=/SUB=-Sb-=SUB=-x-=/SUB=-)Te-=SUB=-3-=/SUB=- (0<x<2)

It is shown that the change in the resistivity of crystals of solid solutions (Bi2-xSbx)Te3 (0<x<2) p-type in the temperature range preceding the onset of intrinsic conductivity is due not only to a change in the static relaxation time, the behavior of which in the temperature range from 80 to 300 K is determined mainly by the scattering of carriers on oscillations crystal lattice, but also by changing the concentration of light holes. The latter is a consequence of the transition of charge carriers from the subzone of heavy holes to the subzone of light holes, as a result of which the concentration of light holes, which make the main contribution to electrical conductivity, decreases with increasing temperature. As a consequence, the plasmon energy proportional to the concentration of charge carriers also decreases with increasing temperature, and the energy of this transition, comparable to the plasmon energy, increases. In this regard, crystals (Bi2-xSbx)Te3 have a specific feature due to the convergence of the plasmon energy and the interband transition, which creates conditions for increasing the intensity of the electron-plasmon interaction. Keywords: thermoelectric materials, bismuth and antimony tellurides, resistivity, interband transitions, plasma of free charge carriers.

Flow Rates Using Nuclear or Electron Paramagnetic Resonance Techniques with Applications to Biological and Chemical Processes

The equations for measuring flow rates are derived using NMR and EPR relaxation time determinations. Several experimental procedures are discussed. One method of measurement depends upon the difference between static relaxation times and the apparent relaxation time of materials flowing through the observation region. Another procedure utilizes saturated or inverted spins as a ``tracer'' to measure flow rates. These schemes may readily be applied to blood flow velocity measurements in humans or animals, or to mineral and chemical flow rate determinations. The advantage of this spin resonance flowmeter is that the flow channel is not disturbed. Thus blood flow velocities are readily measured without the necessity of breaking the skin.