Unraveling an Organic Soluble Precursor-Based Low-Temperature Synthetic Strategy to Impurity-Free Pristine and Transition Metal Doped Lead Apatites.

Doping of hydroxyapatites has garnered considerable interest, as it enables the tuning of the material's intrinsic properties. However, synthesizing hydroxyapatites and their doped variants is highly challenging, as the synthesis demands high temperature and complex, multi-step reaction conditions. Hence, we propose a soft, one-step synthetic approach to develop single-phase lead hydroxyapatite (Pb-HA), Pb₁₀(PO₄)₆(OH)_2, and transition metal-doped lead hydroxyapatites (TM-doped Pb-HA), Pb_10-xM_x(PO₄)₆(OH)₂ (x ≃ 0.5 to 1.0) (M = Cu, Co, or Mn) through a low-temperature hydrothermal decomposition route under neutral conditions. A newly synthesized 1D lead phosphate polymer [Pb(μ-dtbp)₂]_n (1) (dtbp = di-tert-butylphosphate) has been used as the metal-organic precursor for different lead phosphate phases by employing both solvothermal and solid-state thermal decomposition pathways. Hydrothermal decomposition of 1 in the presence of required stoichiometric amounts of an additional lead precursor, PbO, and transition phosphates/metal oxides (MO) at 140 °C gave phase-pure Pb-HA and TM-doped Pb-HA. The associated magnetic and electronic property analysis revealed that all the synthesized materials display paramagnetic behavior, and they are wide-gap n-type semiconductors. More pertinently, this mild, versatile route offers improved control over the metal-to-ligand ratio compared to existing methods and can be adapted to introduce other divalent transition metals into hydroxyapatite frameworks.