Evaluation of the Fourth‐Order Elastic Constants of NaCl‐Structure Alkali Halide Crystals

Abstract

All the fourth-order elastic constants are calculated for 16 alkali halide crystals with NaCl structure using Lundqvist's three-body potential energy expression. I n addition to long-range Coulomb interactions the short-range overlap repulsive interactions are considered between firstand second-nearest neighbours as well as the van der Waals dipole-dipole and dipole-quadrupole interactions. Values of the fourth-order elastic constants calculated in the present study are used to deduce the first pressure derivatives of the third-order elastic constants and second pressure derivatives of the second-order elastic constants for the crystals under investigation. The results are discussed and compared with available experimental data.Alle elastischen Konstanten vierter Ordnung fur 16 Alkalihalogenidkristalle mit NaCI-Struktur werden mit dem Lundqvistschen Ausdruck fur die Dreikorperpotentialenergie berechnet. Zusltzlich zu den langreichweitigen Coulomb-Wechselwirkungen werden sowohl kurzreichweitige abstoSende Uberlappungswechselwirkungen zwischen niichsten und ubernachsten Nachbarn als auch van der Waals-Dipol-Dipol-und Dipol-Quadrupol-Wechselwirkungen beriicksichtigt. Die Werte der berechneten elastischen Konstanten vierter Ordnung werden benutzt, urn die ersten Ableitungen der elastischen Konstanten dritter Ordnung nach dem Druck und die zweiten Ableitungen der elastischen Ilonstanten zweiter Ordnung nach dem Druck fur die untersuchten Kristalle abzuleiten. Die Ergebnisse werden diskutiert und mit erhiiltlichen Werten verglichen. l )

Anharmonic properties of rocksalt structure solids

“…Since the contribution from third-and fourth-order coupling parameters to many anharmonic properties are of the same order of magnitude, the knowledge of FOECs is Table 8. Some theoretical results [51,52] are also shown. Due to non-availability of experimental data, the comparison is not made.…”

“…This is why, recently [42][43][44][45]49,50,[53][54][55][56][57], there have been several attempts to determine the elastic constants of higher order, particularly for alkali halide crystals, using theoretical [7,8] techniques. The FOPDs and SOPDs of the SOECs of alkali cyanides, sodium and potassium halides are presented in Table 9 along with experimental [26,39,41,58-60] and theoretical [51] data. On comparison, one may state that the present results are in well agreement at a great extent.…”

“…Experimental values of SOPD are available corresponding to 300 K. The good agreement between theoretical and experimental values supports the validity of the present work. The FOPDs of the TOECs of alkali cyanides, sodium and potassium halides are presented in Table 10 along with theoretical [51] data. On comparison, one may state that the present results are in well agreement at a great extent.…”

Thermoelastic behaviour of orientationally disordered NH4Br

“…The expressions for TOECs and FOECs are taken from Ref. [33]. The TOECs and FOECs obtained from ETSM are listed in Table 3.…”

Temperature Dependence of Fourth‐Order Elastic Constants of Alkali Halide Crystals

“…Expressions ( Expressions for these linear combinations represented by y$$) have been given by equations (10) to (12) in [7]. Calculated values of yit) are compared with experimental data in Table6.…”