Dopant diffusion and segregation of iron in a near 45° (100) twist grain boundary in SrTiO 3

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Abstract Dopant segregation is a key contributor to interfacial stability and the macroscopic physical properties of polycrystalline materials. Near 45° (100) twist grain boundaries were diffusion bonded either from Fe‐doped SrTiO 3 single crystals, or nominally undoped single crystals after a thin film of iron was deposited onto the single crystal surface prior to diffusion bonding. After diffusion bonding, scanning transmission electron microscopy characterization detected increased Fe signals from the grain boundary cores of both types of bicrystals. Fe enrichment occurred either by segregation from the doped single crystals or by dopant out‐diffusion into the bulk away from the deposited layer. Quantitative energy dispersive X‐ray spectroscopy experiments identified that the grain boundary prepared after Fe deposition was characterized by much higher dopant enrichment compared to the case after diffusion bonding of two doped single crystals. Additional thermal annealing of the bicrystal formed after iron layer deposition caused a decrease in iron enrichment approaching the excess observed for the diffusion‐bonded doped single crystals. The experimental results demonstrate that, dependent on the method of doping, extended thermal annealing of bicrystals may be necessary after diffusion bonding to achieve equilibrium grain boundary excess quantities.

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