Low-temperature Grüneisen gamma of II–VI semicoductor ZnS

Abstract

The theoretical study of low-temperature lattice thermal expansion of the II–VI semiconductor ZnS is attempted. The generalized Grüneisen gammas of the elastic waves propagating in different directions with respect to the [001] crystallographic axis of ZnS are calculated using the second- and third-order elastic constants. The values of mode Grüneisen gammas γ _j are determined and found generally positive except from γ ₂ at θ = 25° to θ = 65°. The low-temperature limit of the Grüneisen gamma $\ifmmode\expandafter\bar\else\expandafter\=\fi{\gamma }$ is determined and compared with experimental values. Using this $\ifmmode\expandafter\bar\else\expandafter\=\fi{\gamma },$ we calculated the Brugger gamma γ ^Br and hence the low-temperature volume lattice thermal expansion γ _L. It is expected that the volume expansion is positive down to absolute zero for ZnS.