Effect of Bi and Ti substitutions for Na and Nb on ferroelectric properties of oriented (Bi4.5+xNa0.5−x)(Ti2xNb2−2x)WO15 compounds

(Bi_4.5+xNa_0.5−x)(Ti_2xNb_2−2x)WO₁₅ (BNTNW) compounds were synthesized and their ferroelectric properties were characterized. The X-ray powder diffraction patterns of the compounds revealed that they have a single phase over the whole composition range. The linear variations of the lattice parameters with composition indicate the formation of solid solutions, resulting in a reduction in the orthorhombicity of the compounds. The remnant polarization of the BNTNW decreased from 8.5 to 5.1 μC/cm² with increasing x, which may be related to the orthorhombicity of the compounds. By using hot forging, an oriented BNTNW compound at x = 0 was obtained. Strong reflections from (0 0 l) were observed for sample // in which the measurement direction is parallel and the orientation factor of such sample was approximately 0.72. A remarkable increase in the remnant polarization (P_r) of the compound was observed for the sample ⊥ in which the direction of applied pressure is perpendicular to the measurement direction; the highest P_r value was 18 μC/cm².