A reversible wetting transition in strontium titanate and its influence on grain growth and the grain boundary mobility

• Published in: Acta materialia Vol. 101; pp. 80 - 89
• Main Authors: Rheinheimer, Wolfgang, Bäurer, Michael, Hoffmann, Michael J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2015
• Subjects: Abnormal grain growth; Anisotropy; Constants; Grain boundaries; Grain boundary mobility; Grain growth; Kinetic grain boundary shape; Microstructure; Oxidation; Reducing atmospheres; Strontium titanates; Wetting; Wetting transition; Abnormal grain growth; Grain boundary mobility; Kinetic grain boundary shape; Anisotropy; Wetting transition
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2015.08.069

[Display omitted] The impact of the oxygen partial pressure on grain growth in high purity strontium titanate is evaluated by observing microstructures, the grain growth constant k and the relative mobility of strontium titanate. The microstructures indicate a reversible wetting transition between 1460°C and 1500°C. The wetting second phase is titania-rich and free from any detectable solutes. Exaggerated grain growth was found close to the wetting transition and is explained by a temperature dependent anisotropy of the grain boundary mobility in conjunction with a high mobility of wetted grain boundaries. The grain growth constant in reducing atmosphere shows two transitions at 1350°C and at 1460°C. At the first transition the grain growth constant decreases with temperature. A strong increase of k with temperature at the second transition is attributed to the wetting transition. The relative grain boundary mobility of different orientations ({100}, {110}, {111}, and {310}) was measured in oxidizing and reducing atmosphere by observing the growth of oriented single crystals into polycrystals. At 1550°C in reducing atmosphere the wetting liquid phase enhances the mobility by a factor of ∼10 compared to oxidizing atmosphere. Additionally, the atmosphere changes grain growth kinetics: in oxidizing, but not in reducing atmosphere growth stagnation occurs for long dwell times.