Abstract
A new betaine compound, (CH 3) 3NCH 2COO·C 4O 4H 2, has been synthesized. The substance crystallizes at ambient temperature with space group Pc2 1 b. Accordingly, it is pyro- and piezoelectric. Elastic, optic, and dielectric investigations have shown that betaine squarate under-goes a continuous ferroelastic transition at T c ≈ 52.7 K. However, there are two, symmetrically independent, elastic shear compliances, s 55 and s 66, which display an anomalous temperature dependence. The divergence of s 55 at T c leads to the elastic instability, and the spontaneous shear strain e 5 s is considered the order parameter. Preliminary Raman-scattering results indicate that the transition is driven by an optic soft mode.
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