Piezoelectric and Elastic Properties of Orthorhombic LiH2PO3 and LiH2PO4

Single crystals of LiH₂PO₃ and LiH₂PO₄, both of space group symmetry Pna2₁, with dimensions up to 40 mm were grown from aqueous solutions by controlled evaporation. Pyroelectric, dielectric, piezoelectric, elastic and thermoelastic properties were studied by standard methods. The static piezoelectric constants d₃₃₃ exceed d₁₁₁ of α-quartz by only a factor 2. The pyroectric effects reach 3 times and 7 times, respectively, that of tourmaline. The mean elastic stiffness of the phosphite is 13% smaller than that of the phosphate, a phenomenon also observed in the corresponding sodium and potassium salts.