Torsional mode frequency and elastic anisotropy in alkali vermiculites

The torsional mode frequency _t in Cs_1–xRb_x-Vermiculite has been determined using an angular force constant model and a virtual crystal approximation. The sensitivity of _t has been examined with respect to the force constants between the Kagome' oxygen frame and the interlayer cations. These force constants were used to calculate the longitudinal elastic constants, C₁₁ and C₃₃ and are consistent with the observed elastic anisotropy in related layer silicates. The observed nonlinear x-dependence of the torsional mode frequency in ternary systems can be related to the polarizability of the interlayer cations (Cs⁺,Rb⁺).