Millimetre-sized hollow spheres of lead zirconate titanate by a sol-gel method

Hollow spheres of lead zirconate titanate (PZT) [chemical formula Pb(Zr_0.52Ti_0.48)O₃)], with outer diameter of 1–2 mm and a wall thickness of about 100 m, were fabricated by gellation of a PZT sol inside solid polymer spheres and then burning the polymer out. Monomodally sized polyacrylamide spheres, with diameter 1.40–1.90 mm, were soaked in a PZT sol, prepared by dissolving Pb(NO₃)₂, zirconiumn-butoxide and titanium isopropoxide inN, N-dimethylformamide. The absorbed sol was then gelled beneath the surface of the polymer sphere by the action of NH₃. Upon calcination of the spheres at 850 °C for 4 h in air, hollow spheres of pure PZT perovskite phase (as identified by X-ray diffraction patterns) were obtained. The density of the hollow spheres was 1.13gcm^–3, while that of the wall of the spheres was 3.10g cm^–3. The scanning electron microscopic examination of the broken spheres showed that the inner surface of the spheres contained rib-like structures, which provided strength to the hollow spheres. The planar coupling factor,k_p, of six hollow spheres, placed at a close-packed arrangement in a plane, was 0.22, indicating the possibility of fabrication of low-density transducer arrays.