PHYSICAL-PROPERTIES OF PHTHALIC-ACID AND OF 8 SALTS OF PHTHALIC-ACID WITH MONOVALENT CATIONS

Single crystals of phthalic acid, of the orthorhombic hydrogen phthalates of Li, Na, K, Rb, Cs, Tl, NH4 and of neutral sodium phthalate 3.5-hydrate have been grown from aqueous solutions. The structurally related group of the hydrogen phthalates of Na, K, Rb, Cs, Tl and NH4 behave quite similar in respect to thermal expansion, dielectric and elastic properties. From the elastic behaviour of the hydrated Li and Na phthalates the contribution of water of crystallization to the mean elastic stiffness could be estimated. Ammonium hydrogen phthalate exhibits an unexpected large negative thermal expansion along a2. In the potassium and rubidium salts strong pyroelectric and piezoelectric effects could be detected. TlHC6H4(COO)2 possesses a longitudinal piezoelectric effect d111 and a transverse piezoelectric effect d122 about 17 and 14 times, respectively, larger than d111 of alpha-quartz.