Pb Stabilization by a New Chemically Durable Orthophosphate Phase: Insights into the Molecular Mechanism with X-ray Structural Analysis
Ying Zhou, Jiliang Zhang, Changzhong Liao, Ting‐Shan Chan, Ying‐Rui Lu, Yu‐Chun Chuang, Chung‐Kai Chang, Kaimin Shih
Abstract
The rapid progression of piezoelectric technology and the upgradation of electronic devices have resulted in a global increase in Pb-based piezoelectric ceramic materials. In this study, the feasibility of incorporating Pb into a PbZr(PO4)2 double orthophosphate structure was evaluated by investigating the interaction mechanism of the perovskite with phosphate. The unique combination of X-ray absorption spectroscopy, selected area electronic diffraction, and Pawley refinement revealed that Pb was incorporated into a hexagonal structure and tetra-coordinated with oxygen in the phosphate-treated product. The chemical durability was enhanced through the structural alterations via Zr–O–P and Pb–O–P bond linkages. The stable phase encapsulating both Pb and phosphate showed effectiveness not only in stabilizing Pb but also in inhibiting P release as a secondary pollution risk within a wide pH range (1 ≤ pH ≤ 13). Despite the excellent chemical durability of the robust PbZr(PO4)2 crystalline phase, the increased Ti doping amounts at the Zr site resulted in a slight decrease in the lattice parameters and further enhanced the Pb stabilization effect through the formation of PbZrxTi(1–x)(PO4)2 solid solutions. This study demonstrates that the newly robust crystalline structure, developed through a well-designed thermal treatment scheme, provides an effective strategy for the treatment of Pb frequently encountered in electronic wastes.