Structure-Property Relationships in Solid Solutions of Noncentrosymmetric Aurivillius Phases, Bi4-xLaxTi3O12 (x=0-0.75)

Solid solutions of the noncentrosymmetric (NCS) Aurivillius phases, Bi4-xLaxTi3O12 (x = 0, 0.25, 0.50, 0.75), have been synthesized through standard solid-state reactions and structurally characterized by powder X-ray and neutron diffractions. These materials crystallize in the orthorhombic space group B2cb (No. 41) and exhibit layered perovskite structures with both (Bi2O2)(2+) fluorite-like units and [A(n-1)B(n)O(3n+1)](2-) (n = 3) blocks. As the amount of La3+ cations increases, the polarization arising from the Bi3+ positions, especially the A sites of the perovskite units, continuously decreases in the reported materials. Powder second-harmonic generation (SHG) measurements on Bi4-xLaxTi3O12 using 1064 nm radiation revealed frequency-doubling efficiencies ranging from 200 to 50 times that of alpha-SiO2. Converse piezoelectric measurements resulted in d(33) values of 19 and 13 pm V-1 for Bi4Ti3O12 and Bi3.5La0.5Ti3O12, respectively. The magnitudes of the SHG efficiency and piezoelectric response are strongly dependent on the asymmetric coordination environment attributable to the lone pairs on Bi3+. Structure-property relationships along with the influence of the doped foreign cation on the associated NCS properties are discussed.