J. M. Honig

Resistivity and Magnetic Order in Ti2O3

Electrical resistivities of pure and vanadium‐doped single crystals of Ti2O3 have been measured as a function of applied magnetic field strength and temperature. The anomalous high‐temperature increase in electrical conductivity has been confirmed. It is argued that the symmetry of Ti2O3 leads naturally to a two‐band model having bandwidths and an energy separation between band centers that are sensitive to the crystallographic axial ratio c/a. With this model, the change in conductivity with temperature can be adequately described on the basis of known variations in the c/a ratio with temperature. The vanadium‐doped samples are good p‐type conductors and exhibit a negative magnetoresistance at low temperatures. With a model of inelastic scattering at trace impurities carrying a localized magnetic moment, it is possible to describe the negative magnetoresistance of vanadium‐doped samples provided the total, local (applied plus intrinsic) magnetic fields are within a few gauss of the applied field. It is c...

Theory of Galvano-thermomagnetic energy conversion devices. I. Generators

Using phenomenological equations in partially inverted form, the operation of galvano-thermomagnetic generators has been analyzed for six different modes of operation. The efficiency, figure of merit, and geometry optimization have been investigated. The two-dimensional temperature distribution prevailing in a device arm is also briefly analyzed. For the “longitudinal” case where heat flow and current are colinear in a transverse field, Hz, the mathematical relations conform to the standard theory, except that the transport coefficients depend on Hz. In the “transverse” case where heat flow, current, and magnetic field are mutually perpendicular, new expressions are obtained for the figure of merit and device efficiency. Furthermore, in the latter case the optimal operating conditions are those in which both device arms are made of the same material. The results are discussed in the light of some existing experimental data.

Hall coefficient and transverse magneto-resistance in HgTe at 4·2°k and 77°k

Abstract Using a computer optimization routine, it was ascertained that magneto-Hall and magnetoresistance data for HgTe at 4·2°K could be fitted by a three-carrier model involving two sets of electrons and one set of holes. This quantitative examination of the number and types of carriers establishes the occurrence of off-axis maxima [see Fig. 1(d)] associated with the inverted band structure model for HgTe. Under special crystal growth conditions the electron Hall mobility at 4·2°K of HgTe exceeded 640,000 cm2/V-sec.

Galvano-thermomagnetic effects in semiconductors and semi metals—III. The standard and kane band models

Abstract A general theory of transport for a band of spherical symmetry in k -space was developed in a prior paper. Using three special functions for the dependence of energy on wave number vector (the parabolic band, the Kane band for energy gap small or large compared to the spin-orbit splitting), the six basic galvano-thermomagnetic transport coefficients (GTMTC) have been determined in terms of specific transport integrals which must be evaluated numerically. Simple analytic expressions for the GTMTC have been obtained in certain limiting cases. It is of special interest that the parametric dependence of the Nernst coefficient on the scattering index is sensitive to the band curvature.

Theory of Galvano-Thermomagnetic Energy Conversion Devices. II. Refrigerators and Heat Pumps

Following the procedure of an earlier paper (Port I) the maximum temperature difference, coefficient of performance, figure of merit, optimum current and voltage, and the optimization conditions were obtained for galvano-thermomagnetic refrigerators and heat pumps under a variety of operating conditions. It is shown that the coefficients of performance of refrigerators and heat pumps differ by unity. Upper bounds are placed on the transverse figure of merit and a brief discussion of the main features of the theory is given.

Galvano‐Thermomagnetic Phenomena. IV. Application to Anisotropic Adiabatic Nernst Generators

Tensor components have been derived for the matrix relating entropy flux and gradient of electrochemical potential to gradient of temperature and electrical current. The entries have been specified in terms of six basic galvano‐thermomagnetic transport coefficients; the Casimir—Onsager reciprocity conditions have been utilized to reduce the number of independent coefficients. These relationships have also been employed to extend the Bridgman—Heurlinger identities to anisotropic materials. Using these equations along with the phenomenological relations, the characteristics for galvano‐thermomagnetic Nernst generators operating under adiabatic conditions have been formulated. The results are compared with the equations which are valid for the isothermal case.

The electrical properties and band structure of doped LaInO3

Abstract Theoretical arguments suggest that LaInO 3 might be a narrow-band semiconductor rather than an ionic insulator. Experimental measurements of resistivity show that at lower temperatures the doped material behaves like a p-type extrinsic semiconductor, and at higher temperatures, like an intrinsic material with a gap energy of 2.2 eV. The Seebeck coefficient changes from positive to negative values with rising temperature slightly above the range of temperature in which the system shifts from the extrinsic to the intrinsic regime. These findings are interpreted in terms of an elementary band model.

Performance Characteristics of Thermomagnetic Devices Involving Graded Mass and Gap. I. Generators

The theory pertaining to operating characteristics of thermomagnetic generators with graded mass and gap has been developed using the fundamentals of irreversible thermodynamics. On introducing transport theory and a considerable number of simplifying assumptions, analytic results were obtained for the efficiency of such devices in terms of the transport coefficients evaluated at the hot junction temperature. The numerical results have been compared to those obtained with materials of constant bandgap and to calculations performed by the method of averaged parameters. The advantages of using a graded gap material for energy conversion are pointed out.