Crystal Structure and Ferroelectricity of Lithium Niobate Crystals

The origin of the ferroelectricity in lithium niobate (LN) crystals is studied using the viewpoint of crystal chemistry. On the basis of the crystallographic characteristics of LN crystals, Pauling's third rule and the bond-valence sum model are employed to study the relationship between the crystal structure and the ferroelectricity of LN crystals. The origin of the ferroelectricity in such ferroelectric crystals as LN can be ascribed to the face sharing octahedra along the c-axis of the crystal. The difference between both Li+- and Nb5+-sublattices is quantitatively studied by putting a +5 valence cation at both sublattices, i.e., by substituting Nb5+ for Li+, and by substituting Ta5+ for Nb5+, respectively. Ferroelectric properties of the substituted LN crystals with the crystal formulae [Li1−5x Nb x □4x ]NbO3 and Li[Nb1−y Ta y ]O3 are quantitatively studied on the basis of corresponding crystallographic characteristics. The present results show that the Li+-site is a sensitive sublattice in the LN crystallographic frame, and possesses the much stronger effect on the ferroelectricity of LN crystals, while the Nb5+-site only has a relatively weak effect on the crystal ferroelectricity. This work presents us a new sight on the ferroelectric materials designing.