Generalized Gruneisen parameters of elastic waves in lithium niobate and its low-temperature thermal expansion

The generalized Gruneisen parameters of elastic waves propagating in different directions in lithium niobate are calculated from the measured second- and third-order elastic constants. There are a large number of longitudinal acoustic gammas that are negative. Some of the transverse elastic gammas are also negative, in particular when the crystal is strained parallel to the trigonal axis. The Brugger gammas are evaluated and the low-temperature limit of the Gruneisen gamma is calculated using the procedure of Ramji Rao and Srinivasan. ovγL has the value 0.65 for lithium niobate. ovγ∥Br(0) has a low value of 0.03, indicating a small thermal expansion coefficient parallel to the trigonal axis, which is corroborated by the thermal expansion measurements of Zhdanova et al. © 1975 Plenum Publishing Corporation.