Intermediate surface reactions to obtain nanocrystalline PbTe via high-energy milling

To elucidate how surface and gaseous phases interact each other to induce chemical reactions, X-ray photoelectron spectroscopy (XPS) analyses were carried out on powders as milling took place. An acute analysis of data acquired by the XPS-technique allowed us to find a series of well-defined chemical transitions from precursors to the stoichiometric PbTe phase. By coupling, theoretical and experimental data a self-consistent model was developed.Initially, the process manifested itself as an oxidation stage and secondly as a reducing process. In agreement with a thermodynamic evaluation of free energy of phases traced during milling, chemical transitions were traced as Te2+ to Te6+ in oxidation reactions. If high oxygen potential prevails in the milling system subsequently Pb2+ evolves to Pb4+. On the other way, high valence oxides like Pb4+ or Te4+ were reduced to Pb2+ and Te2−. However, the last transition an asymmetric transformations was identified as non-stoichiometric phases.

Figure optionsDownload as PowerPoint slideHighlights
► Pb–O–Te ternary system presents three major reaction stages.
► Gas–solid reactions are the kinetic contributors that promote greater rates of transformation.
► A comprehensive model based on dynamical equilibria will be proposed.
► Non-stoichiometric phases have to be expected to see as amorphous reaction products.