Low temperature peculiarities of thermal expansion of laminated crystals

Low-temperature peculiarities of thermal linear expansion coefficient (TLEC) of laminated crystal are investigated experimentally and theoretically. Dilatometric and dielectric measurements of highly anisotropic CsDy(MoO4)2 with laminated structure and with structural phase transition within low temperature (Tcr=42K) range are carried out within 4.2-300K temperature range. Portions of curve with negative value of TLEC are determined for some directions at T <or approx. Tcr. It is shown theoretically that the observed membrane effect is caused only by the presence of interatomic interaction high anisotropy. Is is shown that in highly anisotropic crystals with increase of bending rigidity the membrane effect is suppressed. The presented theory allows to explain negative values of TLEC, high by absolute value and observed during the experiment at temperatures close to Ter