# Sequential crystallization pathways in apatite–wollastonite glass-ceramics via spray pyrolysis

## TL;DR

This paper introduces a new method to control the crystallization of bioceramics, enabling precise design for medical applications.

## Contribution

A scalable spray pyrolysis technique enables deterministic phase control in apatite–wollastonite glass-ceramics.

## Key findings

- Spray pyrolysis creates homogeneous precursors for predictable phase formation.
- Three-stage crystallization is revealed via temperature-controlled sintering.
- A quantitative phase-temperature map is established for targeted biomedical applications.

## Abstract

The clinical performance of next generation bioceramics requires precise control over their multi-phase composition, a goal often unachievable with conventional synthesis routes that lead to stochastic crystallization. Here, we establish a deterministic processing-structure paradigm for apatite–wollastonite glass-ceramics (AWGCs) by using a scalable spray pyrolysis technique to create atomically homogeneous amorphous precursors. By systematically controlling the sintering temperature (700–1100 °C), we decouple the kinetic and thermodynamic drivers of phase formation. High-resolution XRD with Rietveld analysis reveals a predictable, three-stage evolution; kinetically driven hydroxylapatite nucleation (<800 °C), followed by a thermodynamic crossover to a whitlockite-dominant regime (900–1000 °C), and finally the diffusion-controlled growth of mechanically robust wollastonite (>1000 °C). This work presents the first quantitative, predictive map for this system, enabling the rational design of AWGCs with bespoke phase assemblages for targeted biomedical applications, from bioactive coatings to load-bearing implants.

A predictive phase-temperature map reveals sequential crystallization of apatite–wollastonite glass-ceramics, advancing rational design of bioceramics.