Preparation of functional metal nanoparticles embedded mullite composite powders by solid solution reduction

Abstract

The mullite composite powders with embedded Fe and Ge nanoparticles were individually prepared through the reduction of Al_5.4Fe_0.6Si₂O₁₃ and Al₁₂Si_3.75Ge_0.25O₂₆ solid solution. The complete reduction of Fe³⁺ cation in solid solution is realized by hydrogen at 1200°C for 1 h. The magnetic properties of composite powders such as hysteresis loops and magnetization versus temperature were measured using SQUID. The Fe nanoparticles with the particle size around 10 nm embedded in mullite grain show the superparamagnetic behavior with the blocking temperature around 50 K. The mullite composite powders with Ge nanoparticles have strong room temperature photoluminescence (PL) at 561, 610, 676, 713 and 787 nm, respectively. The highest photoluminescence intensity was observed in the sample reduced at 500°C for 3 h. Based on the analysis of XPS and Raman spectra, it is clear that the PL phenomenon is derived from the formation of embedded Ge clusters with the average size of around 1-2 nm in mullite composite powders. It is proved that the multi-functional mullite nanocomposites with functional metal nanoparticles can be prepared through the selective reduction of designed solid solutions.