Piezoelectric, electro-optic, dielectric, elastic and thermoelastic properties of hexagonal Cs₂S₂O₆, LiClO₄.3H₂O, LiClO₄.3D₂O, and Ba(NO₂)₂.H₂O

Complete tensor sets of piezoelectric, electro-optic, dielectric, elastic and thermoelastic properties were measured on hexagonal Cs₂S₂O₆, LiClO₄. 3H₂O, LiClO₄. 3D₂O, and Ba(NO₂)₂. H₂O. The space-group symmetry of Cs₂S₂O₆ and Ba(NO₂)₂. H₂O has been definitely established, by X-ray work in combination with the measurement of polar properties, to be P6₃mc and P6₁ (P6₅), respectively, contrary to earlier X-ray determinations. LiClO₄. 3H₂O and LiClO₄. 3D₂O possess almost identical physical properties, with the exception of density and density-dependent properties. The very small differences correspond to those observed in other hydrates and deuterates. Most components of the piezoelectric and electro-optic tensors do not exceed the effective values of other crystals already in technical use. However, an exceptionally strong longitudinal piezoelectric effect is observed in Cs₂S₂O₆ (d₃₃₃ = - 41 e.s.u, dyn^-1, electromechanical coupling coefficient k_t = 0.25), which together with other favourable acoustic and optical properties supports the application of this new material for acousto-optical devices in the high-frequency range.