ANOTHER PATTERN OF INCOMMENSURATE MODULATION IN A SUBSTANCE LIKE AMMONIUM ROCHELLE SALT - ITS RELATIONSHIP TO INCOMMENSURATE FERROELECTRICITY

In general, when one set of unmodulated transition parameters is given, then corresponding to it, not only one but some nonequivalent sets of modulated transition parameters are possible, and hence so many different patterns of incommensurate modulation of the crystal are possible. Concerning a substance like ARS as an example, another pattern than that in the previous paper [JPSJ 44 (1978) 1248] is presented. The two patterns give different consequences. (It is assumed for simplicity that incommensurate modulation may occur only along the x axis.) In the present case, the gap index is found to be 2. The number of possible incommensurate phases is 3. These phases, despite being incommensurate along the x axis, are all ferroelectric with their Ps along the y axis, the z axis and a general direction, respectively. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.