Ion tracks and microstructures in barium titanate irradiated with swift heavy ions: A combined experimental and computational study

• Published in: Acta materialia 2013-12, Vol.61 (20), p.7904-7916
• Main Authors: Jiang, W., Devanathan, R., Sundgren, C.J., Ishimaru, M., Sato, K., Varga, T., Manandhar, S., Benyagoub, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Atomic Physics; Barium titanate; Exact sciences and technology; Ion track; Metals. Metallurgy; Molecular dynamics simulation; Physics; Swift heavy ion irradiation
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2013.09.029

Tetragonally structured barium titanate (BaTiO3) single crystals were irradiated using 635MeV 238U+ ions to fluences of 1×107, 5×1010 and 1.4×1012ionscm−2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ∼10nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ∼22keVnm−1. Molecular dynamics simulations show an amorphous track of ∼1.2nm in radius under thermal energy deposition at 5keVnm−1; the radius increases to ∼4.5nm at 20keVnm−1. A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ∼8.4nm due to thermal recrystallization if electron–phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates.