Effects of swift heavy ion irradiation on the structure of Er2O3-doped CeO2

In order to simulate the effects of burnable poison doping on the fission fragment damage of UO₂ nuclear fuels, Er₂O₃-doped CeO₂ pellets were irradiated with 200 MeV Xe¹⁴⁺ ions. The irradiation effect was measured by means of X-ray diffraction (XRD). The expansion of lattice and the disordering of atomic arrangement due to the irradiation become more remarkable with increasing the concentration of the Er₂O₃ dopant.     

Swift heavy ion irradiation induced nanoparticle formation in CeO2 thin films

Nanoparticle formation in the, rf-sputtering grown, polycrystalline CeO₂ thin films is achieved by the swift heavy ion (SHI) irradiation. Crystal structure and phases present in the as-grown and irradiated thin films are investigated by the X-ray diffraction (XRD) measurements. Irradiation induced formation of spherically shaped nanostructures, on the film surface, is confirmed by the atomic force microscopy (AFM). The Raman spectra of the irradiated samples show increased line-width and peak position shifting in the Raman active mode (F_2g) of CeO₂, indicative of the nanocrystallization in the irradiated CeO₂ thin films. Formation of nanostructures in the irradiated samples is also briefly discussed in the light of ion energy and energy loss mechanisms.     

Effect of swift heavy ion irradiation on structural, optical and electrical properties of Cd2SnO4 thin films

Transparent conducting cadmium stannate thin films were prepared by spray pyrolysis method on Corning substrate at a temperature of 525 °C. The prepared films are irradiated using 120 MeV swift Ag⁹⁺ ions for the fluence in the range 1 × 10¹² to 1 × 10¹³ ions cm⁻² and the structural, optical and electrical properties were studied. The intensity of the film decreases with increasing ion fluence and amorphization takes place at higher fluence (1 × 10¹³ ions cm⁻²). The transmittance of the films decreases with increasing ion fluence and also the band gap value decreases with increasing ion fluence. The resistivity of the film increased from 2.66 × 10⁻³ Ω cm (pristine) to 5.57 × 10⁻³ Ω cm for the film irradiated with 1 × 10¹³ ions cm⁻². The mobility of the film decreased from 31 to 12 cm²/V s for the film irradiated with the fluence of 1 × 10¹³ ions cm⁻².     

Electronic sputtering of Gd3Ga5O12 and Y3Fe5O12 garnets: Yield, stoichiometry and comparison to track formation

The results of present paper have shown that sputtering of yttrium iron garnet (Y₃Fe₅O₁₂) under swift heavy ions in the electronic energy loss regime is non-stoichiometric. Here we are presenting additional experimental results for gadolinium gallium garnet (Gd₃Ga₅O₁₂) as target. The irradiations were performed with different ions (⁵⁰Cr (589 MeV), ⁸⁶Kr (195 MeV) and ¹⁸¹Ta (400 MeV)) impinging perpendicularly to the surface. As earlier, the sputtering yield was determined by collecting the emitted gadolinium and gallium atoms on a thin aluminium foil, placed upstream above the target and analyzing the Al catcher by Rutherford backscattering. Also for Gd₃Ga₅O_12, the emission of Gd and Ga is non-stoichiometric. Sputtering appears above a critical electronic stopping power of S_th = 11.6 ± 1.5 keV/nm, which is larger than the threshold for track formation, in agreement with other amorphisable materials. In addition, the angular distribution of the sputtered species was measured for Y₃Fe₅O₁₂ and Gd₃Ga₅O₁₂ using 200 MeV Au ions impinging the surface at 20° relatively to the surface. For the two garnets the ratio of Y/Fe (and Gd/Ga) varies with the angle of emitted species and the stoichiometry seems to be preserved only for an emission perpendicular to the surface.     

Ion guiding through capillaries in uncoated Al2O3 membranes

We made an experimental study on ion guiding through capillaries in uncoated Al₂O₃ membranes using a variety of ions such as O¹⁺, O³⁺, and O⁶⁺. The incident energy was varied within the range of 30-150 keV. The results were compared with others using coated PET and Al₂O₃ capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q_∞ seems to exist in our experiment.     

Heavy ion irradiation effects in the rare-earth sesquioxide Dy2O3

Polycrystalline pellets of the rare-earth sesquioxide Dy₂O₃ with cubic C-type rare-earth structure were irradiated with 300 keV Kr²⁺ ions at fluences up to 5 × 10²⁰ Kr/m² at cryogenic temperature. Irradiation-induced microstructural evolution is characterized using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). In previous work, we found a phase transformation from a cubic, C-type to a monoclinic, B-type (C2/m) rare-earth structure in Dy₂O₃ during Kr²⁺ ion irradiation at a fluence of less than 1 × 10²⁰ Kr/m². In this study, we find that the crystal structure of the top and middle regions of the implanted layer transform to a hexagonal, H-type (P6₃/mmc) rare-earth structure when the irradiation fluence is increased to 5 × 10²⁰ Kr/m²; the bottom of the implanted layer, on the other hand, remains in a monoclinic phase. The irradiation dose dependence of the C-to-B-to-H phase transformation observed in Dy₂O₃ appears to be closely related to the temperature and pressure dependence of the phases observed in the phase diagram. These transformations are also accompanied by a decrease in molecular volume (or density increase) of approximately 9% and 8%, respectively, which is an unusual radiation damage behavior.     

γ辐照联合H_2O_2处理污泥滤液的研究

采用60 Coγ射线辐照处理污泥滤液,通过对比处理前后化学需氧量(COD)、紫外可见吸光度和浑浊度的变化,研究了辐照处理中初始pH、初始H2O2浓度和吸收剂量对污泥滤液处理效果的影响。结果表明:在相同吸收剂量和初始H2O2浓度条件下,酸性条件更利于CODCr的降低;γ辐照联合H2O2处理存在显著协同效应,吸收剂量为18.75kGy、初始H2O2浓度为2mmol/L时,污泥滤液CODcr去除率达70.4%,浑浊度下降94.9%。     

Clarification of high density electronic excitation effects on the microstructural evolution in UO2

In order to understand the properties of ion tracks and the microstructural evolution under accumulation of ion tracks in UO₂, 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions irradiation examinations have been done at a tandem accelerator facility of JAEA-Tokai, and it has been observed the microstructure by means of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) in CRIEPI.Comparison of the diameter of ion tracks between UO₂ and CeO₂ under irradiation with 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions at room temperature clarify that the sensitivity on high density electronic excitation of UO₂ is much less than that of CeO₂. By the cross-sectional observation of UO₂ under irradiation with 210 MeV Xe¹⁴⁺ ions at 300 °C, elliptical changes of fabricated pores that exist till ∼6 μm depth and the formation of dislocations have been observed in the ion fluence over 5 × 10¹⁴ ions/cm². The drastic changes of surface morphology and inner structure in UO₂ indicate that the overlapping of ion tracks will cause the point defects, enhance the diffusion of point defects and dislocations, and form the sub-grains at relatively low temperature.     

Ion beam analysis of partial lithium extraction of LiMn2O4 by chemical delithiation

Lithium manganese oxide, LiMn₂O₄, has been studied by many research groups. This material is a great candidate to be used as positive electrode in rechargeable lithium-ion batteries because of its low cost, abundant precursors and non-toxicity. LiMn₂O₄ has a spinel Fd-3m structure and shows a reversible extraction and insertion of lithium ions that is one of the most important characteristic of positive electrodes in rechargeable batteries.In this work, LiMn₂O₄ samples were synthesized by solid state reaction. A partial lithium removal was performed on this system by chemical delithiation using HCl aqueous solutions at different concentrations. Six partial-extracted compounds were obtained and characterized by Ion beam analysis (IBA) in order to obtain the Li concentrations. X-ray diffraction (XRD) and Rietveld analyses were also performed. A rigorous study of lithium contents is critical to analyze the structure properties of these compounds and samples production parameters. The IBA method used in this work was the analysis of energy spectra of elastic backscattered (EBS) proton from Mn, O and Li nuclei and the α-particles energy from the ⁷Li(p,α)⁴He nuclear reaction (NR).     

Application of combined neutron diffraction and impedance spectroscopy for in-situ structure and conductivity studies of La2Mo2O9

In-situ neutron diffraction combined with AC impedance spectroscopy was applied successfully to investigate the correlation between crystal structure and electrical properties of the La₂Mo₂O₉ oxide ion conducting electrolyte material. Neutron diffraction patterns were collected as a function of temperature while the AC impedance spectra were recorded simultaneously using a modified sample environment to monitor the conductivity change of the sample. A close relationship between unit cell parameters and the bulk conductivity was observed, confirming that the oxygen transport is dependent on the lattice structure. With the transition from the low temperature alpha to the high temperature beta phase, expansion of the crystal structure makes more space available for oxygen transport, leading to a dramatic increase of the ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future.     

Depth profiling of Al2O3 + TiO2 nanolaminates by means of a time-of-flight energy spectrometer

Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al₂O₃ + TiO₂ nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements ⁶³Cu, ³⁵Cl, ¹²C and ⁴He ions with energies ranging from 0.5 to 10 MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5 nm individual layer thickness.     

烧绿石(La1-yNdy)2Zr2O7模拟固化241Am的晶体结构稳定性研究

为研究²⁴¹Am在La₂Zr₂O₇烧绿石中的固化行为及其对烧绿石晶体结构稳定性的影响,实验选用Nd作为²⁴¹Am的模拟物,采用Sol-喷雾热解法合成了(La_1-yNd_y)₂Zr₂O₇（0.0≤y≤1.0）系列样品,并借助X射线衍射和振动光谱手段对样品的晶体结构稳定性进行了研究。实验结果表明：随着Nd掺杂量的增加,O48f位置参数x_48f和I₍₁₁₁₎ /I₍₂₂₂₎均呈规律性增大,Raman谱逐渐展宽,IR谱发生蓝移,所有结果均证实用Nd不断替换La将导致烧绿石晶体结构有序化程度逐渐降低。另外,实验发现掺杂量y≈0.8是烧绿石晶体结构发生几何相变的逾渗阈值,超过该阈值有序的烧绿石结构将发生突变进而加速向无序萤石结构转变,该实验结果可为(La_1-yAm_y)2Zr2O7固溶体的结构稳定性研究提供参考。     

Study of the magnetic modifications of Fe3O4 ferrite thin films induced by 2.03 GeV Kr ions irradiation

The effect of 2.03 GeV Kr²⁶⁺ ions irradiation on antiphase boundaries (APBs) of polycrystalline Fe₃O₄ ferrite thin films has been investigated. The structure, magnetic and electrical transport properties of samples were characterized. The initial crystallographic structure of the Fe₃O₄ remains unaffected after Kr-ion irradiation, but the magnetic and electrical transports properties are sensitive to swift heavy ions (SHI) irradiation and exhibit different behaviors depending on the Kr-ion fluence range. The energy deposition is mainly due to the electronic energy loss (S_e) and the large value of energy transferred induces an unusual density of defects, stress and heat annealing effect in the samples, which can affect on the arrangement of magnetic moments and APBs density strongly. On the basis of our observations we conclude that the production, accumulation and free of the defects and stress induced by SHI irradiation is more dominant in the case of the magnetic and electrical transport properties modifications of the Fe₃O₄ thin films.     

Structure and morphology of ion irradiated Au nanocrystals in SiO2

We have investigated the effect of ion irradiation on the structure and morphology of Au nanocrystals (NCs) fabricated by ion beam synthesis in a thin SiO₂ layer on a Si substrate. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements show a significant drop in the average Au–Au coordination, as well as a loss of medium and long range order with increasing irradiation dose. Small angle X-ray scattering (SAXS) measurements reveal a concomitant reduction in average NC size. These observations are a consequence of structural disorder and collisional mixing induced by the irradiation. The observed reduction in average Au–Au coordination by EXAFS differs significantly from that estimated from the average NC sizes evaluated using SAXS. This behavior can be explained by the dissolution of Au NCs into the SiO₂ matrix. A significant bond-length contraction indicates that part of this material forms small Au clusters (dimers, trimers, etc.) during irradiation that cannot be detected by SAXS. Combining the results from SAXS and EXAFS measurements, we estimate the volume fraction of such clusters.     

Effect of thermal spike energy created in CuFe2O4 by 150 MeV Ni swift heavy ion irradiation

Effects of 150 MeV Ni¹¹⁺ swift heavy ion (SHI) irradiation on copper ferrite nanoparticles have been studied at the fluences of 1 × 10¹¹, 1 × 10¹², 1 × 10¹³, 1 × 10¹⁴ and 5 × 10¹⁴ ions/cm². The XRD pattern shows the irradiation fluence dependant preferential orientation. Scanning electron microscope analysis displays fine blocks of material for pristine while partial agglomeration on irradiation. Notably, a large number of holes are present at the fluence of 5 × 10¹⁴ ions/cm². The magnetization measurements performed in these samples exposes that the coercivity and remanence magnetization value increases due to the magnetocrystalline anisotropy up to the fluence of 1 × 10¹³ ions/cm². At 1 × 10¹⁴ ions/cm² fluence, the induced thermal energy overcomes the magnetocrystalline anisotropy constant and causes a decrease in coercivity and remanence values. The saturation magnetization decreases up to the fluence of 1 × 10¹³ ions/cm² and then it increases for further irradiation. The change of crystalline orientation observed from XRD, the creation of holes from SEM and the change in magnetic properties are discussed on the basis of electro-phonon coupling and it invokes the thermal spike theory.     

Structural stability of Cu nanocrystals in SiO2 exposed to high-energy ion irradiation

Cu nanocrystals (NCs) were synthesized in SiO₂ by ion implantation and thermal annealing. Annealing at two different temperatures of 950 °C and 650 °C yielded two different nanocrystal size distributions with an average diameter of 8.1 and 2.5 nm, respectively. Subsequently the NCs were exposed to 5.0 MeV Sn³⁺ ion irradiation simultaneously with a thin Cu film as a bulk reference. The short-range atomic structure and average NC diameter was measured by means of extended X-ray absorption fine structure (EXAFS) spectroscopy and small angle X-ray scattering (SAXS), respectively. Consistent with the high regeneration rate of bulk elemental metals, no irradiation induced defects were observed for the reference, whereas the small NCs (2.5 nm) were dissolved as Cu monomers in the matrix. The latter was attributed to irradiation-induced mixing of Cu, Si and O based on dynamic binary collision simulations. For the large NCs (8.1 nm) only minor structural changes were observed upon irradiation, consistent with a more bulk-like pre-irradiation structure.     

Nanoparticles of Al2O3:Cr as a sensitive thermoluminescent material for high exposures of gamma rays irradiations

Aluminum Oxide (Al₂O₃) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from γ-rays of ¹³⁷Cs. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of γ-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al₂O₃:Cr nanoparticles might be used for the dosimetry of food and seed irradiations.     

N-TiO2 nanoparticles embedded in silica prepared by Ti ion implantation and annealing in nitrogen

Room-temperature Ti ion implantation and subsequent thermal annealing in N₂ ambience have been used to fabricate the anatase and rutile structured N-doped TiO₂ particles embedded in the surface region of fused silica. The Stopping and Range of Ions in Matter (SRIM) code simulation indicates a Gaussian distribution of implanted Ti, peaked at ∼75 nm with a full width at half maximum of ∼80 nm. However, the transmission electron microscopy image shows a much shallower distribution to depth of ∼70 nm. Significant sputtering loss of silica substrates has occurred during implantation. Nanoparticles with size of 10-20 nm in diameter have formed after implantation. X-ray photoelectron spectroscopy indicates the coexistence of TiO₂ and metallic Ti in the as-implanted samples. Metallic Ti is oxidized to anatase TiO₂ after annealing at 600 °C, while rutile TiO₂ forms by phase transformation after annealing at 900 °C. At the same time, N-Ti-O, Ti-O-N and/or Ti-N-O linkages have formed in the lattice of TiO₂. A red shift of 0.34 eV in the absorption edge is obtained for N-doped anatase TiO₂ after annealing at 600 °C for 6 h. The absorbance increases in the ultraviolet and visible waveband.     

Vacuum plasma etching of 1 wt% La2O3 dispersed tungsten

Vacuum plasma etching of 1 wt% La₂O₃ doped tungsten alloy surfaces were carried out to refine the surface morphology for enhancing its bonding characteristics with copper for fusion reactor components. Three different gas compositions containing argon with zero, 14.3 and 25 vol% hydrogen were used to carry out the plasma etching from 30 to 120 s on the given samples. Mitutoyo surface roughness (R_a) measurement, FORM TALYSURF and scanning electron microscopy (SEM) were employed to measure the changes in the surface roughness. Plasma etching with 14.3 vol% hydrogen mixture was found to be the best in micro-roughening the alloy surface. The maximum increase of 44% in R_a value was obtained with this gas mixture, when etched for 90 s.