Shell Model Calculation of Thermal Expansion of Alkali Halides and Magnesium Oxide

Haridasan

Physica Status Solidi (b)

1980

on the occasion of his 75th birthdayThe perturbation approach of Achar and Barsch is employed to work out the mode gammas and the thermal expansion of CaF,. A shell model similar to that of Axe is employed. The pressure dependent dynamical matrix components are computed using the available data on the pressure derivatives of the elastic constants and the mode gammas of the long wavelength optical phonons. The modified moments of the phonon density of states are also computed. These results agree fairly well with the experimental values reported by Baily and Yates and the previously reported work of Ruppin.Das Storungsverfahren von Achar und Barsch wird benutzt, um die Modengamma und die thermische Ausdehnung in CaF2 zu betrachten. Verwendet wird ein Schalenmodell Lhnlicher Art, wie das von Axe. Die druckabhangigen dynamischen Matrixkomponenten werden mit erreichbaren Werten der Druckableitungen der elastischen Konstanten und den Modengamma der langwelligen optischen Phononen berechnet. Die modifizierten Momente der Phononenzustandsdichte werden ebenfalls berechnet. Diese Ergebnisse stimmen ziemlich gut mit experimentellen Werten iiberein, die von Baily und Yates und kiirzlich von Ruppin berechnet wurden.

Section: Moments Y ( N )supporting

confidence: 82%

Mode Gammas and Thermal Expansion of CaF₂

Haridasan

Physica Status Solidi (b)

1980

Geophysical Journal of the Royal Astronomical Society

“…Chang & Barsch (1973) concluded that for single-crystal spinel, the first assumption is bad. Based on Achar & Barsch (1971) and Barsch & Achar (1972), Chang & Barsch concluded that the second assumption in Anderson's derivation is valid for T E 6/2. In short, (39) holds in the form 6 ( g~) oc C, for T 2 -P 2 independent of assumptions regarding Gruneisen parameters.…”

Section: Results and Comparison With Other Experimentsmentioning

confidence: 99%

Temperature Dependence of Single-Crystal Spinel (MgAl2O4) Elastic Constants from 293 to 423°K Measured by Light-Sound Scattering in the Raman-Nath Region

Liu

Schock

Anderson

2007

The temperature dependence of single-crystal elastic constants of synthetic stoichiometric MgAl,O, spinel has been measured by the light-sound scattering technique in the Ramaii-Nath region. The crystal is set into forced vibration by a single crystal LiNbO, transducer coupled to one crystal face. A He-Ne Laser beam is diffracted by the stress-induced birefringence inside the crystal. The diffraction angle is determined from the distance between two spots exposed on a photographic plate by the first order diffracted beams as measured by a microdensitometer. The sound wavelength inside the crystal is then inferred from the laser diffraction angle. Combining the sound wayelength with the measured transducer frequency, the velocity inside the crystal is determined typically to a precision of 0-05 per cent. In this method, the measurement of velocity is not dependent on either the determination of sample length or on phase shifts at sample-transducer interface. Velocities of four pure modes, L/[OOI], T/[001], L/[110], and T/[llO](P/[lTO] are measured in the temperature range between 293 and 423 OK. A linear temperature dependence is fit to the data by a least square method. Values obtained at 25 "C from this linear fit are V,[OOl] = 8.869+0.013kms-l, V,[001] = 6.5666+0*0055 km s-l,

Physica Status Solidi (b)

Dispersion Relations of Mode Grüneisen Parameters in Rubidium Halides

Jex

1974

Dispersion relations of microscopic mode Griineisen parameters have been cnlcalated from a n evaluation of a shell model to third order. Leading terms such as the anhnrnionic shellshell interaction between first and second neighbours and Coulomb contril)ut,ions are taken into account. In t,he phonon dispersion curves breathing terms are included. The thermal expansion and mean Griineisen constants of RbF, RbCI. RbBr, and RbI are analysed with this model. Die Dispersionsreliitionen der mikroskopischen Griineisen-Parameter von RbF, RbC1, RbBr und R b J nurden aus eineni anharmonisch erweiterten Schalenniodell berechnet. Als Hnuptbeitrage wcrden die anharmonische Schale~Srhale-Weclisel~irknng z\vischen crsten und zweiten Gitternachbarn rind die Coiilonib-Beitrage berucksichtigt. Das RIodcll fur die Gitterdynamik enthalt auDerdem die ,,breat,hing"-8nteile. Die niikroskopischen Griineisen-Parameter der Rabidiumhalogenide werden mit experinlentellen Dat.en ails opt,ischen, Ultra~chall-und Ne~itronenmessungen verglichen. Der lineare thermische Ausdehnungskoeffizient und der mittlere ~riineisen-Parxmeter werden ebenfalls analysiert.