^1,2Patrick Cordier et al. (>10)
The Astrophysical Journal, 1005, 87
Open Access Link to Article [DOI: 10.3847/1538-4357/ae71bd]
¹Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207—UMET—Unité Matériaux et Transformations, F-59000 Lille, France
²Institut Universitaire de France, 1 rue Descartes, F-75005 Paris, France

Olivine is one of the most abundant silicate minerals in cosmic environments, occurring largely in amorphous form in the interstellar medium before crystallizing within protoplanetary disks. The kinetics and mechanisms governing this transition are central to understanding the thermal and chemical evolution of silicate dust. To investigate these processes at high spatial and structural resolution, we conducted an in situ transmission electron microscopy study on amorphous olivine thin films produced by pulsed laser deposition. Structural and chemical evolution during heating was monitored using selected-area electron diffraction, pair distribution function analysis, automated crystal orientation mapping, electron energy-loss spectroscopy, and aberration-corrected high-resolution transmission electron microscopy. The amorphous material begins to chemically reorganize at ∼400 °C, where Fe²⁺ is oxidized to Fe³⁺ and nanoscale crystallites—presumably hematite—form within the glassy matrix. These crystallites appear to act as nucleation sites that promote subsequent olivine crystallization. Full crystallization occurs near 800 °C, yielding grains 50–150 nm in size. These observations provide direct nanoscale evidence for iron-assisted nucleation in amorphous olivine and offer constraints on the temperatures and pathways governing the crystallization of interstellar and protoplanetary silicate dust.