Pulsed X-ray induced transient absorption in LiNbO3, TiO2:LiNbO2, and MgO:LiNbO3 at 1061nm

Characteristics of pulsed X-ray induced transient absorption at 1061 mm have been determined for LiNbO₃, TiO₂:LiNbO₃, and MgO:LiNbO₃. The addition of the dopants TiO₂ and MgO reduces the induced absorption significantly. The two materials, LiNbO₃ and TiO ₂:LiNbO₃, decay with an approximate 1/t^1/4 time dependence for the time interval 0.01 to 8 ms. After 8 ms, the decay rate for LiNbO₃ is faster than 1/t^1/4, and the decay rate for TiO₂:LiNbO₃ is slower than that initial rate. A low-intensity absorption which lasts for about 20 μs is observed for the MgO:LiNbO₃. Peak radiation induced absorption coefficients for LiNbO₃, TiO₂:LiNbO₃, and MgO:LiNbO₃ have been determined     

EXAFS studies of thermal annealing effects on the local environment of erbium implanted in LiNbO3

X-ray absorption spectroscopy (XAS) has been applied to the study of thermal annealing effects on the local environment of erbium ions implanted at 300 keV (2 × 10¹⁶ ions/cm²) in LiNbO₃. The radial distribution functions change dramatically as a function of temperature and duration of annealing in air. The best simulations of the shells surrounding Er have been obtained with the Nb and Li site positions for Er after annealing at 500°C for 20 h and 1100°C for 100 h, respectively. Moreover, a shared site (Li, Nb) has to be considered after high temperature annealing for 20 h.     

Ion beam enhanced etching of LiNbO3

Single crystals of z- and x-cut LiNbO₃ were irradiated at room temperature and 15 K using He⁺- and Ar⁺-ions with energies of 40 and 350 keV and ion fluences between 5 × 10¹² and 5 × 10¹⁶ cm⁻². The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He⁺-irradiation of z-cut material at 300 K provokes complete amorphization at 2.0 dpa (displacements per target atom). In contrast, 0.4 dpa is sufficient to amorphize the LiNbO₃ in the case of Ar⁺-irradiation. Irradiation at 15 K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400 nm thick amorphous layers were generated via multiple irradiation with He⁺- and Ar⁺-ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40 °C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80 nm min⁻¹. The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO₃ are discussed.     

Amorphization and recrystallization of the ABO3 oxides

Single crystals of the ABO₃ phases CaTiO₃, SrTiO₃, BaTiO₃, LiNbO₃, KNbO₃, LiTaO₃, and KTaO₃ were irradiated by 800 keV Kr⁺, Xe⁺, or Ne⁺ ions over the temperature range from 20 to 1100 K. The critical amorphization temperature, T_c, above which radiation-induced amorphization does not occur varied from approximately 450 K for the titanate compositions to more than 850 K for the tantalates. While the absolute ranking of increasing critical amorphization temperatures could not be explained by any simple physical parameter associated with the ABO₃ oxides, within each chemical group defined by the B-site cation (i.e., within the titanates, niobates, and tantalates), T_c tends to increase with increasing mass of the A-site cation. T_c was lower for the Ne⁺ irradiations as compared to Kr⁺, but it was approximately the same for the irradiations with Kr⁺ or Xe⁺. Thermal recrystallization experiments were performed on the ion-beam-amorphized thin sections in situ in the transmission electron microscope (TEM). In the high vacuum environment of the microscope, the titanates recrystallized epitaxially from the thick areas of the TEM specimens at temperatures of 800–850 K. The niobates and tantalates did not recrystallize epitaxially, but instead, new crystals nucleated and grew in the amorphous region in the temperature range 825–925 K. These new crystallites apparently retain some ‘memory' of the original crystal orientation prior to ion-beam amorphization.     

Damage distributions in LiNbO3 crystal induced by MeV F tilted implantations

X-cut LiNbO₃ crystals have been implanted by 0.8, 1.0 and 1.2 MeV F⁺ tilted at angles of 15°, 45° and 60° with doses of 5 × 10¹⁴, 7 × 10¹⁴ and 5 × 10¹⁴ ions/cm², respectively. The Rutherford backscattering (RBS)/channeling technique was used to investigate the induced damage distributions. The damage profiles were deconvoluted from the measured spectra after considering the energy spread due to the different stopping power of channeled and nonchanneled ions. Good agreements were obtained between the measured damage profiles and the calculated defect profiles by TRIM'90 (transport of ions in matter, version 1990), except that the measured damage concentration was enhanced in the near-surface region. Information on the lateral and longitudinal damage spread in LiNbO₃ crystals was obtained from the damage profiles induced by tilted ion implantations and compared with TRIM'90 calculation.     

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.     

Argon irradiation damage at a Cu/Al2O3 interface for different alumina structures

The evolution of damages at a Cu/Al₂O₃ device interface after Ar⁺ irradiation, depending on alumina structure, and the effect of surface roughness on sputtering have been studied. A polycrystalline Cu/Al₂O₃ bilayer and polycrystalline Cu on amorphous alumina were irradiated with 400 keV Ar⁺ ion beam at doses ranging from 5 × 10¹⁶ to 10¹⁷ Ar⁺/cm² at room temperature. The copper layer thicknesses were between 100 and 200 nm. RBS analysis was used to characterize the interface modification and to deduce the sputtering yield of copper. The SEM technique was used to control the surface topography. A RBS computer simulation program was used to reproduce experimental spectra and to follow the concentration profile evolutions of different elements before and after ion irradiation. A modified TRIM calculation program which takes into account the sputtering yield evolution as well as the concentration variation versus dose gives a satisfactory reproduction of the experimental argon distribution. The surface roughness effect on sputtering and the alumina structure influence at the interface on mixing mechanisms are discussed.     

Low-temperature diffusion in inert-gas bombarded Al2O3

Previous work on diffusion in inert-gas bombarded Al₂O₃ has revealed the presence of four diffusion processes, of which two take place well below the temperatures for self-diffussion, one agrees with self-diffusion, and one occurs at temperatures well above those for self-diffusion. The present work serves to explore in greater detail the two low-temperature processes. It is shown that the first, which is found in -Al₂O₃, Al(OH)₃, and γ-Al₂O₃beginning at about 100° C, is consistent with a range of ΔH's of 28 to 50 kcal/mole. The mechanism of the process is hinted at by the fact that it overlaps the temperatures both for Al(OH)₃decomposition and for point-defect motion in -Al₂O₃; the correlation with point defects is believed, however, to be the more significant. The second process, which is found only in -Al₂O₃ beginning at 500–650° C, implies an essentially single ΔH lying between 69 and 79 kcal/mole. It was suggested previously by Matzke and Whitton on the basis of electron diffraction that the process could be attributed to the amorphous-crystalline transition of -Al₂O₃. Further aspects of low-temperature diffusion in Al₂O₃ were revealed by comparing autoradiographs of specimens of -A₂O₃which were bombarded to various doses and then either heated to 850° C or immersed in unheated 12N NaOH. Thus regions exposed to a high dose and which would be expected to be amorphous, had an increased sticking factor, a greater tendency to lose gas during heating, and an enhanced chemical reactivity.     

Investigation of Stable Al2O3 Scale on Fe-Al Aluminized Coating for Tritium Barrier

It is well known that α-Al₂O₃ phase has stablility performance, high permeation reduction factor and good resistance performance in liquid LiPb, which is considered as the reference tritium barrier coating in future fusion reactor. In order to study the formation mechanism of stable α-Al₂O₃ scales on fusion structure material, the oxidation behavior of Fe-Al aluminized coating on China Low Activated Martensitic （CLAM） steel was investigated under the oxygen partial pressure from 1 Pa to 20 kPa at the temperature of 940-980 ℃. The Al₂O₃ scales were analyzed by thermogravimetric analysis meter, grazing angle X-ray diffractometer, glow discharge spectrometer, focused ion beam and transmission electron microscope. A single continuous Al₂O₃ scales with the maximum thickness of about 2 000 nm was formed on the diffusion Fe-Al aluminized layer. Thermogravimetric analysis results show that the higher oxidation rate constant is achieved while increasing the oxygen partial pressure, and then oxidation rate constant decreases. The phase transformation of Al₂O₃ scales on the surface of Fe-Al aluminized coating was studied during different oxidation time ranges from 3 min to 180 min. The metastable γ-Al₂O₃ and α-（Al0.948Cr0.052）₂O₃ phases is formed in the earlier oxidation process and finally transformed to stable α-Al₂O₃ phase. The features of the transient α-（Al0.948Cr0.052）₂O₃（113） and α-Al₂O₃（113） were detected by GXRD and then confirmed by focused ion beam and transmission electron microscope.     

基于铌酸银的耐高温放射性碘吸附剂的制备及性能

通过机械混合法制备了一种基于铌酸银(AgNbO_3)的耐高温放射性碘吸附剂(AgNbO_3/Al_2O_3)。和常规载银吸附剂(Ag/Al_2O_3)相比,AgNbO_3/Al_2O_3吸附剂的吸附性能更为稳定;特别是在650℃以上时,其对放射性碘的去污因子远高于常规载银吸附剂。表征测试结果表明,该吸附剂结构稳定性良好,可耐受较长时间的高温。热重测试和高温脱附试验等结果表明,碘化银在AgNbO_3/Al_2O_3吸附剂表面稳定性的提高是该吸附剂在高温时吸附性能更佳的主要原因,其将来有望用于核事故中的应急处置。     

Synthesis and sintering of Li2SnO3

As one of candidates for solid blanket materials of fusion reactors, lithium stannate Li₂SnO₃ was synthesized by precipitation of a complex, lithium hexahydroxystannate Li₂Sn(OH)₆, and its thermal decomposition. In order to get single-phase precipitates Li₂Sn(OH)₆, aqueous solution SnCl₄ had to be added slowly to LiOH aqueous solution. Decomposition of Li₂Sn(OH)₆ to Li₂SnO₃ proceeded in two steps, abrupt release of about two molecules of water around 200° C and gradual release of remaining water above 260° C. The grains of Li₂SnO₃ obtained at 800° C were porous, consisting of small primary particles of about 0.2 μm size. For the pellets prepared from these porous grains under 20 and 100 MPa, the density saturated to a value of 1.8 and 2.4 g/cm³ within two days at 1000° C, corresponding to the porosity of 64 and 52%, respectively. The porous nature of the original Li₂SnO₃ grains was found to be kept even after 1000° C treatment for a week. For the pellet prepared by ground Li₂SnO₃ under 200 MPa, remarkable sintering was observed at 1000° C; density increased rapidly and became close to theoretical density (7% porosity) after four days. The product Li₂SnO₃ synthesized by the present process has advantages in terms of manufacturing, handling and possibly tritium recovery of the blanket.     

活性UO3制备技术研究

为提高UO₃活性、降低铀转化生产成本,以硝酸铀酰溶液为原料、丙烷燃烧产生的高温气体为热源,采用高压喷雾技术制备了高活性UO₃粉末。探讨了硝酸铀酰溶液中的铀浓度和反应温度对UO₃活性的影响,并分析了高压喷嘴结构对UO₃粉末粒度分布的影响。实验结果表明,在反应温度400 ℃、反应压力-100 Pa等控制条件下,采用雾化干燥技术制备的UO₃比表面积可达18 m²/g,粉末粒径在15～50 μm之间,说明制备的UO₃活性较好。其原因是高温高速气流与雾化液滴横向接触时,不仅发生了高速气体对液滴的撕裂作用,也存在高温条件下水气化导致液滴破裂的过程。同时也显示该工艺具有潜在的工业应用价值。     

Interactions of slow H, H2, and H3 with thin carbon foils

Interaction processes resulting from the transit of incident 2–30 keV H⁺, H⁺₂ and H⁺₃ through 1.2 to 2.5 μg cm⁻² carbon foils are investigated by examining the charge state and angular scatter distributions of atomic and molecular species that exit the foils. A comparison of the scatter distributions of exiting H⁺₂ and H⁰ from incident H⁺₂ and H⁺₃ show that the atomic components of transmitted molecules scatter independently from foil atoms. For a given foil thickness, the measured fractions of H⁺₂ from incident H⁺₂ and H⁺₃ are inversely proportional to the square of the angular scatter half-width.     

热-水-力-化学耦合作用下Ca0.86Nd0.14Ti0.86Al0.14SiO5固溶体的化学稳定性

以CaCO₃、Nd₂O₃、TiO₂、SiO₂、Al₂O₃为原料,用固相法制备掺钕榍石固溶体（Ca_0.86Nd_0.14Ti_0.86Al_0.14SiO₅）。采用PCT法进行浸泡实验,借助X射线衍射（XRD）、扫描电镜（SEM）、电感耦合等离子体发射光谱（ICP-OES）等分析手段,研究掺钕榍石固溶体在热 水 力 化学（THMC）耦合作用下的化学稳定性。结果表明,在pH值为5～9、温度150～200 ℃、压强0.476～1.554 MPa的耦合作用下,Ca_0.86Nd_0.14Ti_0.86Al_0.14SiO₅固溶体具有良好的化学稳定性;pH值、温度（压力）对Ca_0.86Nd_0.14Ti_0.86Al_0.14SiO₅固溶体中Si⁴⁺、Al³⁺、Nd³⁺的归一化浸出率无明显影响;Ca²⁺在200 ℃（1 554 MPa）时的抗浸出性能较150 ℃时的好;在浸泡初期（1～21 d）Ca²⁺在pH值为9时的抗浸出性能优于pH值为5和7时的,浸泡后期（28、42 d）3种溶液中固溶体的Ca²⁺抗浸出性能趋于一致;Ti⁴⁺在pH值为9时的抗浸出性能较pH值为5和7时的好。     

Ion implantation doping and electrical conductivity enhancement of C60 films

Pristine C₆₀ films sublimed onto sheet mica were implanted with 20 keV K⁺ ions and I⁺ ions at doses of 1.0 × 10¹⁶/cm², 3.0 × 10¹⁶/cm² and 5.0 × 10¹⁶/cm², and with 20 keV Ar⁺ ions at a dose of 5.0 × 10¹⁶/cm². The distributions of dopants were studied using Rutherford backscattering spectrometry (RBS). The temperature dependence of sheet resistivity of the films was investigated applying a four-probe system. It was proposed that the conductivity enhancement of K⁺ implanted C₆₀ films was due to the implanted ions in the films, while for I⁺ implanted C₆₀ films, both implanted I⁺ ions and irradiation effects of the ions contributed to the enhancement of conductivity.     

Effect of forming gas anneals on the photoluminescence from nanocrystalline silicon formed by Si implantation into SiO2 matrix

The blue region of the room temperature photoluminescence spectrum from Si nanocrystallites formed in SiO₂ by Si⁺ ion implantation has been observed for the first time after annealing in a forming gas (10% H₂ + 90% N₂) ambient. Thermally grown SiO₂ on Si substrates were implanted with a dose of 2 × 10¹⁷ Si⁺ cm⁻² at energies of 200 keV and 400 keV. For reference purposes, quartz silica was implanted also with the same dose of 200 keV Si⁺ ions. The implanted samples were annealed in nitrogen and forming gas at 900°C for 3 to 180 min. Both the SiO₂ and quartz samples exhibited luminescence at about 380 nm which was weak, but detectable, before annealing. During extended anneals in forming gas, the intensity increased by a factor of about 2 above that recorded after a nitrogen anneal but the peak position was unchanged. The intensity was greater in samples annealed in forming gas which is due to the additional hydrogen. It would seem that this blue luminescence originates from new luminescent centres in the matrix caused by the Si⁺ ion implantation.     

Thermodynamic studies on Cs4U5O17(s) and Cs2U2O7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs₄U₅O₁₇(s)+Cs₂U₂O₇(s)+Cs₂U₄O₁₂(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δμ(O₂) (kJ/mol) (±0.5)=−272.0+0.207T (K). The differential thermal analysis showed that Cs₄U₅O₁₇(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs₄U₅O₁₇(s) was calculated from the above oxygen potentials and can be given by, Δ_fG⁰ (kJ/mol)±6=−7729+1.681T (K). The enthalpy measurements on Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, (H⁰_T−H⁰₂₉₈), in J/mol for Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) can be represented by, H⁰_T−H⁰_298.15 (Cs₄U₅O₁₇) kJ/mol±0.9=−188.221+0.518T (K)+0.433×10⁻³T² (K)−2.052×10⁻⁵T³ (K) (368 to 905 K) and H⁰_T−H⁰_298.15 (Cs₂U₂O₇) kJ/mol±0.5=−164.210+0.390T (K)+0.104×10⁻⁴T² (K)+0.140×10⁵(1/T (K)) (411 to 860 K). The thermal properties of Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were derived from the experimental values. The enthalpy of formation of (Cs₄U₅O₁₇, s) at 298.15 K was calculated by the second law method and is: Δ_fH⁰_298.15=−7645.0±4.2 kJ/mol.     

高温低氧条件下膨润土添加碳酸钠和菱铁矿试验研究

为探究处置库高温低氧条件下,添加剂对膨润土-北山水体系化学性能的影响,开展了膨润土-北山水体系中添加菱铁矿和碳酸钠的试验研究。研究了体系pH值和Eh值、胶体zeta电位和黏度、膨润土中可交换阳离子和矿物成分以及液相离子成分随碳酸钠和菱铁矿添加量的变化。结果表明,90 ℃低氧条件下膨润土中添加碳酸钠不仅可使体系的pH值维持在7.84～8.99,而且膨润土中可交换Na⁺升高至60 mmol/100 g,有效阻止了钠基膨润土向钙基膨润土的转化,同时增强了胶体的稳定性;添加菱铁矿可使体系的Eh值降低至-124 mV,并维持在还原状态;碳酸钠和菱铁矿的加入对膨润土矿物成分无很大影响。最终得出高温低氧条件下,增强膨润土化学缓冲性能的膨润土、碳酸钠、菱铁矿的最佳质量配比为400∶12∶160。     

Na_2O/Al_2O_3摩尔比对模拟高放废液硼硅酸盐玻璃固化体结构和性能的影响

研究了Na2O/Al2O3摩尔比(n)对模拟高放废液硼硅酸盐玻璃固化体结构和性能的影响。利用红外光谱分析了不同Na2O/Al2O3摩尔比时硼硅酸盐玻璃固化体的结构变化,并用溶解速率法(DR)和全谱直读等离子发射光谱(ICP-OES)表征了所制备出固化体的化学稳定性。结果表明:在研究组分范围内,当n1.0时,硼硅酸盐玻璃固化体结构中Al以[AlO4]四面体的形式存在,但[BO3]三角体的量较大;随着Na2O/Al2O3摩尔比的增加(n=1.0),固化体结构中[BO3]三角体向[BO4]四面体转变,Al仍以[AlO4]四面体的形式存在,固化体结构稳定性增加;Na2O/Al2O3摩尔比继续增加(n=1.5或2.0),固化体成分中由于Al含量已很少而使[AlO4]含量过少,对固化体结构网络致密性的影响起主要作用,且此时成分中存在过多的碱金属离子在结构中起断网作用,玻璃固化体网络结构变疏松。在Na2O/Al2O3摩尔比为1.0时,玻璃固化体有相对较佳的结构稳定性和化学稳定性,浸泡56d后的失重速率为10-9 g/(cm2·min)数量级,且浸出液中各浸出离子的平均浓度最低。