Ultrasonic wave propagation in rare-earth monochalcogenides

Abstract

Abstract:The ultrasonic attenuation in thulium monochalcogenides TmX (X =S, Se and Te) has been studied theoretically with a modified Mason's approach in the temperature range 100 K to 300 K along 100 , 110 and 111 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second-and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.

Temperature Dependent Anharmonic Properties of Lead Chalcogenides

“…In view of its simplicity, it appears to be reasonably successful in explaining the basic features of materials. The versatility of this model is further witnessed from its successful applications to explain the semiconducting behaviour [33], nonlinear properties as variation of temperature [1,3,21,34] acoustical parameters of solids [5,19,32,33,35], etc. The theoretical predictions generally show good agreement with measured data for almost all of them.…”

“…However, in view of the rigorous derivations and heavy calculations involved in these models, the degree of agreement achieved is not very encouraging since the same can be obtained from present theory which is relatively much simpler and easily adaptable for calculations. The applicability of present model has been tested by several workers by calculating lattice anharmonicity in LiH and LiD [30], ultrasonic attenuation in metals [3], chalcogenides [5,19,31] and zinc blende structure solids [32]. In view of its simplicity, it appears to be reasonably successful in explaining the basic features of materials.…”

“…This is why, recently, there have been several attempts [1][2][3][4][5][16][17][18][19][20] to determine the elastic constants of higher order using experimental and theoretical [1,16,20] techniques. In this paper, the second-and third-order elastic constants at room temperature for lead chalcogenides are shown in Table I together with values calculated by other workers [9].…”

“…Only few [5,6,16,19] of them are taken into account in the temperature dependence of these properties. Comparison data on pressure derivatives of SOECs have been reported for all the solids under study and are included in Table III [5,19]. The experimental data for FOPDs of SOECs, which are related to the TOECs, have been available for PbTe and are included in Table III for the sake of comparison.…”

“…These expressions are easily applicable [2,3] to determine the higher order elastic constants and related properties at temperature near melting point. Nowadays, determination of anharmonic properties at high temperatures [1][2][3][4][5][6] is of common interest, therefore, we have used these expressions to evaluate the second-, third-and fourth-order elastic constants (SOECs, TOECs and FOECs), the first-order pressure derivatives (FOPDs) of SOECs and TOECs, second--order pressure derivatives (SOPDs) of SOECs and partial contractions of lead chalcogenide crystals crystallising in the NaCl-structure. Since the thermal effects contribute significantly, the temperature dependence of elastic constants is much more sensitive to the short-range interactions.…”