Research Highlight

Electronic Excitations Transform Structure of Ceramics

Electron-spin density distribution for crystalline Gd2Ti2O7 with 1.6% electronic excitations prior to amorphous transformation. Electronic excitations lead to charge redistributions, indicated by yellow spheres/ellipsoids, located primarily on oxygen atoms (small orange spheres). Large spheres are Gd & Ti atoms; O vacancies, VO, are small spheres with blue cores.

Ab initio molecular dynamics calculations reveal that electronic excitations induce a structural instability that transforms Y2Ti2O7, Gd2Ti2O7 and Sm2Ti2O7 with the pyrochlore crystal structure to an amorphous state. This work demonstrates the critical role local electronic excitations have on the structural stability of ceramics, and improved understanding will lead to more radiation- tolerant materials and novel approaches to modifying the structures and properties of ceramic surfaces, films and coatings for nuclear, electronic, magnetic, optical, catalytic and thermal-barrier applications.

Normally, radiation-induced amorphization is a high-energy process caused by local melting due to thermal spikes created by atomic collision cascades or extreme ionization; however, this work demonstrates that localized electronic excitations make the transformation to an amorphous state easier. In these pyrochlore structures, excitation of the oxygen 2p electrons creates an instability of the structure that decreases the temperature for the crystalline-to-amorphous transformation as the concentration of electronic excitations increases: from the melt temperature for no electronic excitations to room temperature for electronic excitation concentrations of 1.4% for Gd2Ti2O7 and Sm2Ti2O7 and 1.6% for Y2Ti2O7.

H. Y. Xiao, W. J. Weber, Y. Zhang, X. T. Zu, and S. Li, “Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study,” Scientific Reports 5, 8265 (2015).  DOI: 10.1038/srep08265

 

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