Phenomenological theory of antiferroelectricity and ferroelectricity applied to NaNbO3 and the system KNbO3–NaNbO3

Abstract

Cross has applied the Kittel‐Devonshire phenomenological treatment of ferroelectricity and antiferroelectricity to NaNbO₃ and the system NaNbO₃–KNbO₃. Recent experimental work has shown that the low‐temperature form has rhombohedral symmetry with space group R3c, and that therefore this phase is a ``line ferroelectric'', rather than a ``cone ferroelectric'' with canted polarization, as had been supposed by Cross. The amendments to the phenomenology are discussed, and it is shown that the agreement with observation is improved using the correct low‐temperature form.