Electronic states of one-dimensional binary crystals

Electronic states of one-dimensional binary crystals

vi ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS 20. DETERMINATION OF CATION VALENCES IN Cu2Fe~Sn’~S4 BY MOSSBAUER EFFECT AND MAGNETIC SUS...

231KB Sizes 0 Downloads 12 Views

vi

ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS

20.

DETERMINATION OF CATION VALENCES IN Cu2Fe~Sn’~S4 BY MOSSBAUER EFFECT AND MAGNETIC SUSCEPTIBILITY MEASUREMENTS M. Eibschütz, E. Hermon and S. Shtrikman (Department of Electronics, The Weizmann Institute of Science, Rehovoth, Israel)

The ambiguity in the cation valencies of Cu2FeSnS4 was resolved by Mossbauer effect studies in Fe ~ and in Sn~and verified by magnetic susceptibility measurements.2 +The Sn4 cation ~S valencies were found to be Cu2”Fe 4.

(Received 6 February 1967) (Revised 25 AprIl 1967) 21.

COLOR CENTER GROWTH CURVES IN CALCITE W. Medltn

Growth of color density has been measured as a function of X-ray dose in a number of natural calcite single crystals. Measurements were made by irradiating at 77 CK and recording absorbance change in one of the principal absorption bands while heating to 750°K. At this temperature, all color has been removed by thermal bleaching which occurs in four stages near 350, 500, 600 and 680°K. Growth curves were obtained by measuring absorbance change during each thermal bleaching stage as a function of irradiation time, The growth curves are interpreted in terms of free charge capture by trapping centers. Results are consistent with a mechanism in which only electrons are free to migrate to capture centers and holes are immobile. Another possible mechanism is radlolytic decomposition of the CO ion which Is discussed briefly, -

Thermoluminescence produced during each thermal bleaching stage gives glow peaks whose area Is proportional to absorbance change. This relation has been used to interpret thermoluminescence growth curves in limestones and synthetic calcite precipitates in terms of color center growth. Results show that limestones behave like natural crystals but synthetic calcite behaves quite differently. This difference is attributed to effects of U and Th alpha activity In natural samples. (Received 24 March 1967)

22.

Vol. 5, No. 6

ABSOLUTE THERMOELECTRIC POWER OF VANADIUM-IRON ALLOYS BETWEEN 100 AND 600°K K. Schroder and M. Yessik (Department of Chemical Engineering and Metallurgy, Syracuse University, Syracuse, N.Y.)

The absolute thermoelectric power S of vanadium rich vanadium iron alloys with up to 45 at % iron was measured between 100°K and 600°K with a differential technique. S was usually temperature independent between 300 and 500°K. 8, if plotted as a function of composition for different approximately linearly temperatures, with composition increased from a value between 0 and 2 p. V/ °Kfor pure vanadium toa maximum between 12 and 15p.V/°Kfor alloys with about 26 at % iron. A further increase of iron concentration decreased S nearly linearly to negative values of about -7p.V/°K, for the alloy with 45 at % iron, except for the ferromagnetic state. (Received 21 November 1966) (Revised 20 March 1967) 23.

CATION MIGRATION IN TETRAGONAL SPINELS (MgMn2O4 R. Manaila

Previous data concerning the high-temperature cation migration in tetragonal MgMn2O4 were worked out by means of a generalized migration law. The energy of migration was found to depend strongly on A, in a rather nonlinear way. The experimental e (A ) values agree well with some lattice-energy calculations, relying upon structural data. 24.

ELECTRONIC STATES OF ONEDIMENSIONAL BINARY CRYSTALS Davison, Ling and Ghosh

The MO- LCAO method has been used, in; conjunction with the tight-binding approximation, to examine the volume and surface states of A2 B, A3 B and A2 B2 linear crystals. The electronic energy spectrum for each type of binary crystal has been analysed. The energies of the volume states lie in bands separated by forbidden energy gaps, whose widths depend on the crystal composition. For a given crystal, the number of volume bands equals the number m of atoms in the elementary cell, while the maximum number of surface levels is 2m. The surface levels lie outside the bands and their position and number are governed by existence

Vol. 5, No. 6

ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS

equations which have been derived. When m is odd It is possible for surface levels to occur in all of the gaps while, if m is even, it is impossIble for surface levels to occur in some of the gaps. 25.

A BOX MODEL OF ALKALI HALIDE CRYSTALS P.A. Sysi6 ( Department of Physics, University of Helsinki)

The model introduced In author’s first paper [Ann. Acad.Sci. Fenn.A VI 110 (1962)] has been developed further, both tIi~6ietically and technically, It is based on the assumption that each ion is moving in its own, practically impenetrable sphere (or cube) in a constant coullombic potential. Then the eigenvalues of the Hamiltonian are easily found and the only experimental crystal parameter needed is the lattice constant d. Validity of the theory has been tested by comparing the computed values of the binding energy E, the molar heat C,, the coefficient of volume expansion a, and the adiabatic cornpressibility K, to the experimental ones; the mean I %t deviations are, respectively, 4.4%, 5. 1%, 16. 8% and 34. 3%. The results are rather promising, so that this model seems to be worthy of further research. (Received February (Revised 216 April 1967)1967)

vii

positive in view of thermoelectric power measurements. These results confirm Lyons’ assumption of generation mechanism of charge carriers in anthracene crystals, and, furthermore, they reveal more generally the extrinsic character of carrier generation through acceptor centers which are produced under the influence of light and oxygen In the surface. (Received 25 October 1966) (Revised 21 February 1967) 27.

HALL COEFFICIENT AND TRANSVERSE MAGNETORESISTANCE IN HgTe AT 4.2 AND 77°K T. C. Harman, J. M. Honig and P. Trent (Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts, 02173)

Using a computer optimization routine, it was ascertained that magneto-Hall and magnetoresistance data for HgTe at 4. 2°Kcould 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 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. (Received 2 March 1967)

26.

EXTRINSIC PROCESS OF CARRIER GENERATION IN ANTHRACENE CRYSTALS S. Sakai, M. Yoskith, S. Tanaha, H. Mitsudo and Y. Ooshika (Faculty of Science, Kwansei Gakuifl University, Nishinomiya, Japan)

As a result of ultraviolet irradiation in the presence of oxygen, photo- and dark-conductivity and thermoelectric power are enhanced, but the intensity of fluorescent emission is enfeebled. The shape of the spectral-response curve ~f photo-conductivity is similar to the first fundamental absorption band, but the excitation spectrum of fluorescence shows an opposite tendency, I. e., photoconduction and fluorescence are considered to be mutually competing processes. Before and after the irradiation, the photocurrent Is linear to the intensity of incident light, the activation energy of dark conductivity does not change, and the sign of majority carriers is

28.

BAND STRUCTURE, DEFORMATION POTENTIALS AND EXCITON ~ATES IN SOLID XENON M. H. Reilly (Department of Physics and Astronomy, University of Rochester, Rochester, New York)

The relativistic band structure, deformation potentials, and effective masses for solid xenon are found by the orthogonalized plane wave method. This is supplemented by the tight-binding method, for comparison, and for the determination of certain valence band energies and effective masses. The problem of determining a suitable one-electron potential Is discussed, and a new potential for insulators is developed, critically compared with other potentials, and used in the calculations. For comparison, results are also obtained with other potentlals, and these are Interpreted. Certain