Vol. 7, No. 24 7.
ABSTRACTS OF PAPERS TO APPEAR IN
LATTICE DYNAMICS OF MAGNESIUM STANNIDE AT ROOM TEMPERATURE R.J. Kearney, University of Idaho, Moscow, Idaho 83843, and T.G. Wonton and R.E. Schmunk Idaho Nuclear Corporation, Idaho Falls, Idaho 83401
construct unitary transformation matrices U which will be used to (3) block diagonalize the dynamical matrix D.
to determine the frequency-wave vector phonon dispersion relation of Mg2Sn at room tempera-
The results obtained here are generally applicable to other fluorite structure crystals as well as Mg2Sn. Received 24 July 1969 Revised 23 October 1969
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Received 24 July 1969 Revised 23 October 1969
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APPLICATION OF GROUP THEORY TO THE LATTICE DYNAMICS OF MAGNESIUM STANNIDE R.J. Kearney, University of Idaho, Moscow, Idaho 83843, and T.G. Wonton and R.E. Schmunk, Idaho Nuclear Corporation, Idaho Falls, Idaho 83401
FORMATION AND STRUCTURE OF ‘ CENTERS G. J. Dienes, Brookhaven National Laboratory, Upton, New York, R.D. Hatcher, Queens College, Flushing, New York and R. Smoluchowski, Princeton University, Princeton, New Jersey The theoretically predicted crossections
for the formation of H’ -centers out of H-centers in KC1 and KBr and for the trapping of H-centers at Na impurities are in good agreement with the values obtained experimentally by Itoh. Two H-centers joined along a [110] direction can have nine possible configurations. Their energies have been calculated using a somewhat simplified model with the result that in the lowest state the two H-centers are perpendicular to each other and lie in a (001) plane. In the highest state they are co-linear.
Group theoretical techniques have been applied to an analysis of the lattice dynamics of Mg2Sn along directions of high symmetry and at certain points in the Bnillouin zone. Matrix representations have been constructed for the symmetry elements in the group of the wave vector. These representations have been used to:
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(1) determine the classification of the phonon modes for a given q, (2) construct projection operators to determine the form of the eigenvectors for the atomic motions and from these
Neutron inelastic scattering has been used
ture along the [00~], [~C0] and [~~] symmetry directions. The frequency of the infrared active optical mode was found to be 5.56 x 1012 sec~ in excellent agreement with infrared absorption measurements. Slopes of the acoustic modes were in good agreement with elastic constant data. Both rigid ion and shell models have been least squares fit to the experimentally measured frequencies. A satisfactory fit to the experimental data was obtained with 9 and 10 parameter shell models, but no satisfactory fit was found for the 7 parameter rigid ion model. The best fitting model was used to calculate the vibration frequencies along the [1~0] direction in addition to the directions for which measurements were made.
J. PHYS. CHEM. SOLIDS
Received 8 August 1969 Revised 30 October 1969
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SOME OBSERVATIONS ON THE LUMINESCENCE OF ,6- Ga2O3 G. Blasse and A. Bnil, Philips Research