Materials science - Displaced by radiation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62871/1/445161a.pd

Cross-sectional transmission electron microscopy study of 1.5 MeV Kr+Kr+ irradiation-induced amorphization in α-quartz

Cross-sectional and high-resolution transmission electron microscopy (XTEM and HRTEM, respectively) have been used to characterize ion-beam-induced amorphization of α-quartz irradiated with 1.5 MeV Kr+Kr+ ions at room temperature. The accumulation of damage and the growth of the amorphous layers in quartz were studied as a function of ion fluence up to 1.7×10141.7×1014 ions/cm2.ions/cm2. An amorphous band was first observed at the peak displacement damage range, and this region increased in width with increasing ion fluence. These results demonstrate that direct displacement damage by nuclear collision is more efficient than ionization processes in inducing amorphization in quartz. At lower fluences ( ⩽ 1.7×1013(⩽1.7×1013 ions/cm2),ions/cm2), the damage profile observed by XTEM is in excellent agreement with the distribution of displacement damage predicted by TRIM calculations. At higher fluences, the range of the amorphous band measured by XTEM exceeds the depth predicted by TRIM. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69882/2/JAPIAU-84-8-4204-1.pd

Electronic structure and energetics of tetragonal SrCuO 2 and its high-pressure superstructure phase

First-principles calculations have been used to investigate the electronic structure and energetics of the simple tetragonal SrCuO 2 ( P 4/ m m m ) and its high-pressure tetragonal superstructure ( P 4/ m m m ). Based on the calculations, the high-pressure phase is metastable as compared with the low pressure tetragonal phase, with an energy difference of 0.13 eV per SrCuO 2 formula unit. The energy barrier to the transition from the superstructure to the simple tetragonal structure is 0.24 eV at 7 GPa; thus, high temperatures are required to synthesize the latter. Among the possible structural configurations resulting from the partially occupied oxygen site in the superstructure phase, the most stable structure has a space group ##IMG## [http://ej.iop.org/images/0953-8984/23/46/465503/cm401032ieqn3.gif] {$P\bar {4}m 2$} , reduced from that of the simple tetragonal structure P 4/ m m m . The detailed analysis of the electronic band structures of the simple tetragonal and superstructure phases suggests that the out-of-plane buckling of the O atoms in the superstructure leads to significant decrease in the O p–Cu d orbital overlap, allowing the energy of the system to be lowered, which is necessary for the structural stability. An understanding of the electronic structure and energetics of the high-pressure superstructure phase and its relation to the simple tetragonal phase provides a basis for exploring the physical properties of the infinite layer, high- T C superconductor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90783/1/0953-8984_23_46_465503.pd

Nanodomains of pyrochlore formed by Ti ion implantation in yttria-stabilized zirconia

The microstructural evolution of a single crystal of yttria-stabilized zirconia (YSZ) implanted with Ti has been studied by cross-sectional transmission electron microscopy (TEM). The implantation of 180 keV Ti ions to a dose of 1×1017 ions/cm21×1017ions/cm2 was completed at room temperature. After annealing at 1100 °C in an Ar atmosphere for 2 h, a phase transition from the fluorite structure of ZrO2ZrO2 to an isometric pyrochlore structure-type, A2B2O7,A2B2O7, occurred due to cation ordering. High-resolution TEM revealed nanodomains of pyrochlore, Y2(TixZr1−x)2O7,Y2(TixZr1−x)2O7, with a ≅ 10.24±0.05 Å.a≅10.24±0.05Å. The nanodomains of the pyrochlore phase, embedded within the YSZ fluorite substrate, occurred in a depth range from 45 to 105 nm below the surface, which corresponds to Ti concentrations from ∼10 to ∼15 at. %. The nanoscale pyrochlore precipitates and the YSZ matrix have a completely coherent orientation. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70072/2/APPLAB-80-23-4327-1.pd

Effects of fission product accumulation in cubic zirconia

Yttria stabilized cubic-zirconia (YSZ) is a promising candidate material for both inert matrix fuel and waste form based on its high solubility for actinides, high chemical durability and its reported exceptional stability under radiation. Because the incorporation of fission and other transmutation products during burnup may significantly affect the radiation response and the chemical durability of cubic zirconia, the solubility and mobility of the fission product nuclides in the inert matrix fuel at high temperatures (reactor fuel conditions) and low temperatures (repository conditions) are important. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87572/2/95_1.pd

Radiation effects in uranium-niobium titanates

Pyrochlore is an important actinide host phase proposed for the immobilization of high level nuclear wastes and excess weapon plutonium.[1] Synthetic pyrochlore has a great variety of chemical compositions due to the possibility of extensive substitutions in the pyrochlore structure.[2] During the synthesis of pyrochlore, additional complex titanate phases may form in small quantities. The response of these phases to radiation damage must be evaluated because volume expansion of minor phases may cause micro-fracturing. In this work, two complex uranium-niobium titanates, U3NbO9.8U3NbO9.8 (U-rich titanate) and Nb3UO10Nb3UO10 (Nb-rich titanate) were synthesized by the alkoxide/nitrate route at 1300 °C under an argon atmosphere. The phase composition and structure were analyzed by EDS, BSE, XRD, EMPA and TEM techniques. An 800 KeVKr2+800KeVKr2+ irradiation was performed using the IVEM-Tandem Facility at Argonne National Laboratory in a temperature range from 30 K to 973 K. The radiation effects were observed by in situ TEM. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87573/2/403_1.pd

Comparison of Ion-Beam Irradiation Effects in X2YO4 Compounds

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65948/1/j.1151-2916.1999.tb02246.x.pd

Direct evidence of N aggregation and diffusion in Au+Au+ irradiated GaN

A surface amorphized layer and a buried disordered structure were created in gallium nitride (GaN) irradiated using 1.0 MeV1.0MeV Au+Au+ ions to fluences of 25 and 70 Au+/nm270Au+∕nm2 at room temperature. Bubbles of N2N2 gas within both the amorphized and disordered GaN are formed. A gradient profile with a lower N concentration in the amorphized region is observed, which provides direct evidence of N loss by diffusion in the Au+Au+ irradiated GaN. These results are important to understanding the amorphization processes in GaN and may have significant implications for the design and fabrication of GaN-based devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87811/2/021903_1.pd

X-ray photoelectron spectroscopy study of irradiation-induced amorphizaton of Gd2Ti2O7Gd2Ti2O7

The radiation-induced evolution of the microstructure of Gd2Ti2O7,Gd2Ti2O7, an important pyrochlore phase in radioactive waste disposal ceramics and a potential solid electrolyte and oxygen gas sensor, has been characterized using transmission electron microscopy and x-ray photoelectron spectroscopy. Following the irradiation of a Gd2Ti2O7Gd2Ti2O7 single crystal with 1.5 MeV Xe+Xe+ ions at a fluence of 1.7×1014 Xe+/cm2,1.7×1014Xe+/cm2, cross-sectional transmission electron microscopy revealed a 300-nm-thick amorphous layer at the specimen surface. X-ray photoelectron spectroscopy analysis of the Ti 2p2p and O 1s1s electron binding energy shifts of Gd2Ti2O7Gd2Ti2O7 before and after amorphization showed that the main results of ion-irradiation-induced disorder are a decrease in the coordination number of titanium and a transformation of the Gd–O bond. These features resemble those occurring in titanate glass formation, and they have implications for the chemical stability and electronic properties of pyrochlores subjected to displacive radiation damage. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71018/2/APPLAB-79-13-1989-1.pd