Irradiation effects on microstructure change in nanocrystalline ceria – Phase, lattice stress, grain size and boundaries

Abstract

Moll, S.; Namavar, F.; and Weber, W.J., "Irradiation effects on microstructure change in nanocrystalline ceria -Phase, lattice stress, grain size and boundaries" (2012 AbstractWith a wide variety of applications in numerous industries, ranging from biomedical to nuclear, ceramics such as ceria are key engineering materials. It is possible to significantly alter the materials functionality and therefore its applications by reducing the grain size to the nanometer size regime, at which point the unique varieties of grain boundaries and associated interfaces begin to dominate the material properties. Nanocrystalline films of cubic ceria deposited onto Si substrates have been irradiated with 3 MeV Au + ions at temperatures of 300 and 400 K to evaluate their response to irradiation. It was observed that the films remained phase stable. Following a slight stress relief stage at low damage levels, the overall lattice is extremely stable up to high irradiation dose of $34 displacements per atom. The grains were also observed to undergo a temperature-dependent grain growth process upon ion irradiation. This is attributed to a defect-driven mechanism in which the diffusion of defects from the collision cascade is critical. Formation of dislocations that terminate and stabilize at symmetric grain boundaries may be the limiting factor in the grain growth and overall energy reduction of the system. Utilizing ion modification, possible improvement of the adhesion of thin films and reduction of the probability of detrimental effects of stress-induced problems are discussed.

Effect of grain size and microstructure on radiation stability of CeO2: an extensive study

“…3 shows that up to 3 Â 10 12 ions per cm 2 , the most intense (111) peak broadens, however with little change in d-values (or 2y). Similar behaviour was also observed by Ishikawa et al 3 and Edmondson et al; 22 it has been stated that such kind of behaviour is accompanied with the break in peak symmetry after irradiation. However, a very careful observation of the XRD patterns indicates that peaks are becoming asymmetrical.…”

Ion‐Beam‐Induced Chemical Mixing at a Nanocrystalline CeO2–Si Interface

“…The reduction in size, from the macroscopic to the nanoscopic, results in the enhancement of many materials properties, including electrical and ionic conductivity, and radiation tolerance . This phenomenon is due to the high number of unique interfaces that exist in nanocrystalline systems . As a potential high‐ k dielectric material in semicondutor devices, ceria (CeO 2 ) may be deposited in a nanocrystalline form onto a silicon substrate and subsequently ion irradiated to electrically dope the device.…”

The role of electronic energy loss in ion beam modification of materials

“…Synergistic effects 28 56 (E < 0.5 MeV), the transfer of energy to atomic nuclei (nuclear 57 energy loss) dominates, leading to the displacement of atoms via 58 elastic scattering collisions between atomic nuclei in ballistic colli- 59 sion cascades. For high energy ions exceeding $1 MeV per nucleon 60 (MeV/u), particularly for swift heavy ions (E > 50 MeV), electronic 61 energy loss dominates, leading to intense local ionization that 62 can cause damage production [6], track formation [7] or damage 63 recovery [8], and the formation of long, straight ion tracks with 64 nanometer diameters by swift heavy ions has been exploited in a 65 range of nanoscience applications [9,10].…”

“…The grain growth in ceria results in an increase in Snapshots (projections along the [0 0 1] axis) of ion track evolution in Si simulated using the 2T-MD model for an electronic stopping power of 50 keV/nm [48]. Due to the scale, the individual atoms are not visible; thus, the amorphous regions appear as darker areas.symmetric grain boundaries[58]. In the nanocrystalline zirconia, 472 the cubic structure is stable to high irradiation doses (>30 dpa); 473 however, faster grain growth is observed at 160 K compared to 474 400 K[59].…”