Size effects in a ferroelectric NH4IO3.

The temperature dependences of the linear permittivity ε' and the harmonic coefficient γ of composite materials obtained by introducing the ferroelectric NH₄IO₃ into the porous Al₂O₃ alumina matrix with a pore diameter of 60 nm are studied. It is found that the phase transition is smeared out and the Curie temperature shifts to the low-temperature region ΔT ∼ 25 K. The results obtained are consistent with the Ising model and are discussed within the framework of the phenomenological Landau theory. [ABSTRACT FROM AUTHOR]