Sample shape influence on the antiferroelectric phase transitions in dipolar systems subject to an external field

A continuous change in the macroscopic shape of a sample from a needle through a sphere to a plate is shown to greatly affect phase transitions in Ising dipolar systems. The first- and second-order phase transition lines with critical and tricritical points appear, coexist, and disappear on the phase diagram with varying sample shape. The values of the shape-dependent depolarization factor corresponding to the changes in the phase diagram are identified.