Structural response of A2TiO5 (A = La, Nd, Sm, Gd) to swift heavy ion irradiation

Different compositions of orthorhombic A2TiO5 (A = La, Nd, Sm, Gd) have been irradiated with swift Xe ions (1.47 GeV). Systematic analysis of the structural modifications induced by ion track formation was completed using transmission electron microscopy, synchrotron X-ray diffraction, and Raman spectroscopy. Significant radiation-induced amorphization occurred, but the size of the amorphous regions within the tracks decreased as smaller cations (higher Z) occupied the A-site. This decrease in the amorphous domain size is attributed primarily to epitaxial recrystallization of a disordered phase at the outer edge of the tracks, the stability of which is related to the ratio of the ionic radii of the A- and B-site (B = Ti) cations. While similar ion track recrystallization phenomena have been observed in pyrochlores of varying composition, A2TiO5 is unique in that the disordered phase is not a high-temperature polymorph, suggesting kinetic control of the radiation-induced transformation.