CU(OH)(2) - A NEW FERROELECTRIC

The crystal structure of Cu(OH)(2), recently redetermined at room temp erature by Oswald, Reller, Schmalle & Dubler [Acta Cryst. (1990), C46, 2279-2284], is shown to satisfy the structural criteria for ferroelec tricity. The Cu2+ ion at 295 K is displaced 0.131 Angstrom from the mo st likely paraelectric atomic arrangement, allowing the prediction to be made that the ferroelectric Curie temperature is T-c = 343 K. This prediction is in excellent agreement with an earlier report of a rever sible structural transition at 325-335 K in Cu(OH)(2). The presence of a lambda-shaped anomaly in the heat capacity at about 335 K has been confirmed, and a dielectric anomaly is also observed at similar temper atures over a wide frequency range; the frequency dependence is disper sive, owing at least partly to ionic conductivity. The prediction is h ence verified, and Cu(OH)(2) is demonstrated experimentally to be a ne w ferroelectric.