Ionization-induced effects in amorphous apatite at elevated temperatures
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Manabu Ishimaru and Yoshihiko Hirotsu The Institute of Scientific and Industrial Research, Osaka University, Osaka 567-0047, Japan
Mikio Higuchi Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan (Received 21 September 2007; accepted 27 December 2007)
Electron-beam-induced effects in preamorphized Sr2Nd8(SiO4)6O2 were investigated in situ using transmission electron microscopy with 200-keV electrons at temperatures ranging from 380 to 780 K. Within the electron-irradiated area, epitaxial recrystallization was observed from the amorphous/crystalline interface toward the surface, with the rate of recrystallization increasing as temperature increased from 380 to 580 K. Structural contrast features (i.e., O deficient amorphous material), as well as recrystallization, were observed outside of the irradiation area at temperatures from 680 to 780 K. Ionization-induced processes and local nonstoichiometry induced by oxygen migration and desorption are possible mechanisms for the electron-beaminduced recrystallization and for the formation of the structural contrast features, respectively.
I. INTRODUCTION
Electron-beam (e-beam) irradiation using transmission electron microscopy (TEM) is an important technique to study radiation effects of materials. In particular, e-beam irradiation is known as a direct method to simulate the effects of ionization and electronic excitations from -particles and ␥-rays in reasonable laboratory time periods.1,2 When target materials are irradiated with energetic electrons, two primary events may occur: (i) displacements of target atoms by knock-on damage, and (ii) production of electron-hole pairs by ionization processes. If knock-on damage plays an important role, the irradiated materials often transform from crystalline to amorphous by the accumulation of point defects as reported in Si3 and SiC.4 On the other hand, ionizationinduced processes have been known to promote the recovery of knock-on damage by enhancing the mobility of point defects in some ceramic materials such as Ca2La8(SiO4)6O2, Al2O3, MgAl2O4, MgO, and SrTiO3.5–7
a)
Address all correspondence to this author: e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on reviews and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/jmr/policy.html DOI: 10.1557/JMR.2008.0114 962 J. Mater. Res., Vol. 23, No. 4, Apr 2008 http://journals.cambridge.org Downloaded: 17 Mar 2015
Ionization-induced recovery processes can be dramatically enhanced above a certain threshold ionization rate as revealed in the cases of e-beam and high-energy ion irradiations in SiC.8,9 A recent result for e-beam irradiation of ion-beam-induced amorphous Sr2Nd8(SiO4)6O2 at room temperature reveals that epitaxial recrystallization is induced by ionization processes.10 In the current study, the temperature dependence of the ionizationinduced processes in amorphous Sr2Nd8(SiO4)6O2 were investigated. II. EXPERIMENTA
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