Porous Li-Na-K niobate bone-substitute ceramics: Microstructure and piezoelectric properties

Disc specimens of a porous ceramic, lithium sodium potassium niobate (Li_0.06Na_0.5K_0.44)NbO₃, were prepared using ammonium oxalate monohydrate or poly(methyl methacrylate) as pore-forming agent, and made piezoelectric using a modified polarizing method to preserve biocompatibility. Scanning electron microscopy showed a bicontinuous 3-3 structure of interconnected pores 150-250 µm in size. The piezoelectric constant (d₃₃) and electromechanical coupling coefficient (Kp) are discussed as a function of porosity and pore shape: d₃₃ fitted the theoretical expectation for shape factor K_s = 1, while Kp was approximately constant (~ 0.23) for porosity of 15-45 vol.%. 50 vol.% AOM gave the highest porosity (~ 45%) without decline of the value of Kp whilst maintaining mechanical integrity. Such materials show promise for use as a piezoelectric composite bone substitute.