Crystallization characteristics of yttria-stabilized zirconia/hydroxyapatite composite nanopowder

Yttria-stabilized zirconia (YSZ)/hydroxyapatite (HAp) composite nanopowder was synthesized using a chemical precipitation and calcination process. Each YSZ/HAp gel powder showed an averaged particle size of ∼ 50-100 nm and it was dried and calcined for crystallization. The crystallization characteristics of each powder were analyzed using X-ray diffraction (XRD) and quantitative analyses were performed on each phase using quantitative XRD (Q-XRD). The formation of β-tricalcium phosphate (β-TCP) was controlled changing the Ca/P ratio in HAp phase and also YSZ content in the composite nanopowder. It was revealed that β-TCP content showed a minimum value at Ca/P ratio of ∼ 1.73 and at YSZ content of 10 wt%, respectively. The mechanism of increased β-TCP content with Ca/P ratio lower than 1.73 and increased β-TCP content with YSZ content was explained as Ca-deficiency due to the Ca-diffusion into t-ZrO₂ crystals to form a solid solution, which was confirmed analyzing the lattice parameter change of t-ZrO₂ crystals. The composite nanopowder with Ca/P ratio of 1.77 showed formation of CaO crystals, resulting in the increase in β-TCP content.