Amorphization of cubic zirconia by caesium-ion implantation

Stabilized cubic zirconia is a promising candidate material for use as an inert fuel matrix for 'burning' excess Pu in light-water nuclear reactors. Zirconia is also considered to be an excellent nuclear waste form for direct geological disposal. Both applications are based on zirconia's high solubility for actinides, high chemical durability and high stability under irradiation. We report the first evidence of solid-state amorphization of yttria-stabilized cubic zirconia (YSZ) by 400keV Cs-ion implantation to 1 x 10²¹ ions m^-2 at room temperature. Amorphization of YSZ is caused by the large size incompatibility and low mobility of Cs ions in the YSZ structure, reflecting a relatively low solubility of Cs in YSZ. Nevertheless, the Cs concentration at which amorphization of YSZ occurred (about 8at.%) is well above the value that will typically be reached in an inert fuel matrix.     

A comparative study of Sr-doped LaMnO3 synthesised via solid-state reaction and sol–gel methods

ABSTRACT

This work deals with the synthesis of hole-doped La_1-xSr_xMnO₃ (x?=?0.25 and 0.33) perovskite via two different ways, namely a solid-state reaction method and a sol–gel process. Various properties of the samples have been investigated and compared by means of different techniques, namely X-ray diffraction (XRD), temperature-dependent resistivity measurements in the temperature range 25–300?K using a closed cycle refrigerator and vibrating sample magnetometry (VSM). All samples have orthorhombic crystal symmetry and an irregular variation in unit-cell volume with increase in Sr content. The average crystallite size was determined from the XRD data and found to lie in the range 19–22?nm. Metal–insulator transitions (MIT) were observed in all the samples via low-temperature electrical characterisations. The magnetic measurements confirm that the magnetisation does not saturate for the 25% Sr doped samples up to the available field of 10?kOe. The magnetic response also supports the interpretation of XRD and resistivity data. The obtained results are explained on the basis of double-exchange and super-exchange mechanisms.     

Irradiation-induced amorphization of graphite: A dislocation accumulation model

We present a kinetic model to explain irradiation-induced phenomena in graphite up to a high dose of amorphization. We attribute the origin of amorphization to the accumulation of dislocation dipoles instead of a disordered region assumed in a previous model by Niwase. Calculated results for the change in a sample dimension up to amorphization and the Raman intensity ratio in a low-damage range compare favourably with the experimental results, revealing the existence of a barrier inhibiting the mutual annihilation of an interstitial and a vacancy.     

Atomistic study of structural fluctuations during radiation-induced amorphization in the ordered intermetallic compound NiTi

We have carried out an atomistic study of electron-induced amorphization of an ordered intermetallic compound NiTi by means of in-situ high-resolution high-voltage electron microscopy observations and molecular dynamics simulations. Both theoretical and experimental results show that metastable nanometre-size atomic clusters form and disappear during irradiation, so that a spatiotemporal fluctuation under amorphization is induced. Mean-lifetime measurements of these clusters demonstrate that high-energy particle irradiation provides a useful tool to study dynamic fluctuations of the local atomic structure in the non-equilibrium open systems.     

On the stability of 𝛃-SiC with respect to chemical disorder induced by irradiation with energetic particles

X-ray diffraction measurements of changes in the long-range structural orderof 𝛃-SiC thin films have been performed during irradiation with energetic ions atlow temperature. The decrease in both the chemical and the topological order wasanalysed in situ using the superstructure (002) and the fundamental (004)reflections of the zincblende-type structure, in a dose range up to completeamorphization. The data indicate that the crystalline-to-amorphous transitionis a continuous process rather than a sudden collapse of a defective crystalstructure and that, in contrast with previous assumptions, 𝛃-SiC remains stablewith respect to amorphization up to a high degree of chemical disorder.     

Solid-phase epitaxy of implanted silicon at liquid nitrogen and room temperature induced by electron irradiation in the electron microscope

Abstract

Electron-beam-induced solid-phase epitaxy (SPE) has been obtained on cross-sections of implanted Si layers, by in situ irradiation in the electron microscope, with electrons of energies of 200, 250 and 300 keV, at both room and liquid-nitrogen temperature. The, absence of a transition from SPE to layer-by-layer amorphization (which is observed during ion-beam irradiation on decreasing the temperature below a certain critical value) and the athemal nature of the electron-induced crystallization process below room temperature, indicate that, although elastic displacement is the basic mechanism of both processes, the models which describe ion-beam-induced epitaxy in the temperature range 200≤T≤400°C cannot be extrapolated to explain the results of electron irradiation below room temperature.     

Thermal stability of nanocrystalline fcc and hcp Ni(Si) synthesized by mechanical alloying of Ni90Si10

The thermal stability of nanocrystalline fcc and hcp Ni(Si), obtained by mechanical alloying of Ni₉₀Si₁₀, has been studied. The allotropic transformation from fcc to hcp Ni(Si) is accompanied by a volume expansion of 8.6% and is observed when fcc Ni(Si) reaches a critical crystallite size of 10nm. The hcp phase transforms to stable fcc Ni(Si) at 573K. It has been identified that the lattice distortion in nanometre-sized crystallites from the equilibrium configuration and the decrease in the interfacial energy with grain refinement act as self obstacles in controlling the grain growth of nanocrystalline materials.     

Stress-corrosion cracking in YBa2Cu3O7−x ceramic superconductor

Abstract

Thin-foil transmission electron microscopy specimens of orthorhombic YBa²Cu³O^7?x subjected to residual elastic strains have shown slow crack growth in an atmosphere with low moisture content. Microcracks, initiated by amorphization at the strained edges, propagate alternately along (110) twin boundaries and (001) stacking faults, where strain energy is accumulated locally. The formation of carbon-rich amorphous layers along the strained lattice planes, followed by residual stress-assisted crack propagation, resembles stress-corrosion cracking in this ceramic superconductor.     

Cluster-ion bombardment studies to reveal the amorphization mode in strained Si0.8Ge0.2

Radiation damage caused by cluster ions of different sizes is predicted to be distinctly different if materials follow disparate phenomenological models of amorphization, namely overlap and direct amorphization methods. Determination of an amorphization model for a crystalline solid can be accomplished based on its radiation response to cluster sizes of bombarding ions. In the present study, we use this approach and apply it to study radiation damage in Si_0.8Ge_0.2 caused by Ag _n clusters with the number of atoms in a cluster, n, taking values from 1 to 4. The displacements measured by using channeling Rutherford backscattering spectrometry show size-enhanced damage accumulation, which is in good agreement with the atomistic detail obtained by molecular dynamics simulations. Our studies suggest that strained SiGe, a material known to have poor radiation tolerance, follows the overlap model rather than the direct amorphization model.     

Perspectivas actuales en Psicología de la Religión

Resumen

El objetivo del trabajo radica en llevar a cabo una revisión sobre el estado actual de las investigaciones rejerentes a los aspectos psicosociales de la religión.

Se comienza planteando los problemas que ello extraña: escaseZ de investigaciones rigurosas, connotaciones ideológicas de los planteamientos y estrategias, diversas y contrapuestas acepciones de términos elementales, etc.

Se aborda la polémica que ba enfrentado a psicólogos y teólogos, que, a pesar de su poca operatividad, ha supuesto un foco de interés.

Se analiza la multidimensionalidad de las actitudes religiosas, aportaciones realizadas al respecto y los instrumentos de medida que han gomado de mayor predicamento.

Se concluye con la exposición panorámica de las investigaciones actuales más relevantes sobre el tema, señalando cómo se han ocupado básicamente de correlacionar las actitudes religiosas o la religiosidad con diversas variables de personalidad, como autoritarismo, neuroticismo, autoestima, etc.     

Transformation of Shockley into Frank stacking faults in a ZnS 0.04 Se 0.96 /GaAs (001) heterostructure

We report the transformation of Shockley partial dislocations (PDs) into Frank PDs in lattice-matched ZnS 0.04 Se 0.96 /GaAs(001) as investigated by transmission electron microscopy. The ZnS 0.04 Se 0.96 layers, with a nominal thickness of 70 nm, were grown on GaAs(001) by metal-organic chemical vapour deposition at 350°C. We mainly find stacking-fault pairs on the (111) and planes that are bound by Shockley PDs with Burgers vector . Different reactions are observed between PDs taking place in situ in the electron microscope, leading to the transformation of Shockley PDs into Frank PDs with and stacking faults on the or planes.     

Hacia las máquinas conscientes

Resumen

Se propone un bosquejo de teoría para el estudio del fenómeno de la consciencia desde un punto de vista unificador—natural y artificial—basado en el análisis de la mente como un fenómeno de control. Se incluye una justificación de la investigación en consciencia artificial no como imitación mecánica de la consciencia natural, sino por las propiedades de que puede dotar a un sistema técnico. Se describe la evolución no biomimética de las estructuras básicas de control y se analizan las estrategias más actuales para el desarrollo de máquinas conscientes.     

Pensamiento,argumentación y significado

Resumen

El objetivo de este trabajo es el de realizar una exploración teórica que conecte los tres conceptos que configuran el título del mismo. Se revisa someramente alguna de la investigación psicológica más destacada sobre procesos de argumentación. Se contraponen los resultados de esos estudios con la perspectiva normativa acerca de la discusión racional. Se presenta la teoría de la relevancia como una aproximación pragmática al significado. Y finalmente se formula una sugerencia teórica sustantiva: que la teoría de la relevancia puede constituir una fuente teórica para aproximarse al estudio de los efectos cognitivos de la argumentación.     

Amorphization under fracture surface in hydrogen-charged and low- temperature tensile-tested austenitic stainless steel

ABSTRACT

The microstructure just below the fracture surface in hydrogen-charged stable austenitic SUS 316L stainless steel, which was subjected to a low strain rate tensile test at ?70°C, was studied by a combination of the focused-ion-beam method and transmission electron microscopy. An amorphous region with a chemical composition almost identical to that of the polycrystalline region was found under the lath-like structure on the fracture surface, although no deterioration of tensile properties by hydrogen appeared. In the amorphous region, band-like regions with wavy contrasts were observed, which were often accompanied by cracks at the boundaries. The presence of the amorphous region with band-like regions implies that amorphization occurred due to high-density vacancies accompanied by agglomerations of excess vacancies in the hydrogen-charged SUS 316L stainless steel that was tensile-tested at low temperatures.     

Movement of Pt markers in MgO during a solid-state reaction

The effectiveness of Pt in marking the initial location of heterophase boundaries between two reactants in a thin-film solid-state reaction is discussed. The Pt markers were produced by dewetting a continuous Pt film at elevated temperatures, thus forming an array of small isolated particles. These particles can then serve as fine-scale markers for tracking the motion of interfaces. The thin-film diffusion couples with Pt markers were used, in this study, to investigate the effect of an applied electric field on a spinel-forming reaction. The reacted diffusion couples with Pt markers were analysed using both transmission and scanning electron microscopy. Analysis of the diffusion couples showed that the Pt markers could be affected by, or themselves affect, the reaction process. The interface between the Pt marker and surrounding oxide matrix plays an important role in the reliability of Pt as an effective marker.     

Limitaciones y sesgos en el procesamiento de la información: más allá de la teoría del «hombre como científico»

Resumen

En el presente trabajo se discute la pertinencia de considerar a los seres humanos como procesadores eficientes de información. Se efectúa una revisión de los sesgos y errores que las personas habitualmente cometen en sus análisis de la realidad. Se revisan las deficiencias observables en las personas cuando efectúan juicios sobre las relaciones entre dos sucesos (juicios de contingencia), juicios de probabilidad sobre la aparición de un fenómeno dado y, por último, juicios sobre relaciones causa-efecto en contextos sociales (atribuciones causales). Se analizan las posibles consecuencias que, para la vida cotidiana, pueden tener tales limitaciones y se proponen algunas estrategias para remediar o eliminar estos errores cognitivos.     

Mecanismos atencionales en autismo de alto nivel de funcionamiento cognitivo: una revisión del estado de la cuestión

Resumen

Se revisan los planteamientos y resultados de los trabajos que evalúan el funcionamiento atencional en personas con trastorno del espectro de autismo (TEA), particularmente en el subgrupo de personas con nivel alto de funcionamiento cognitivo.

Se señalan los resultados convergentes de los diversos estudios, analizando algunas de las contradicciones entre los resultados obtenidos, así como sus posibles causas y, por último, se destaca la utilidad de los estudios de la atención en este grupo desde un punto de vista conceptual, diagnóstico y clínico.     

Solubility criterion for sequential disordering in metal-metal multilayers upon solid-state reaction

An n-body Ni-Ti potential is derived and applied in a molecular dynamics simulation to study the maximum supersaturated solubility of the terminal solid solutions and solid-state reaction in a Ni/Ti bilayer. It reveals that during interfacial reaction of the Ni/Ti bilayer the Ti lattice reaches its maximum solubility by dissolving Ni earlier than Ni does through dissolution of Ti, which results in a sequential disordering of first Ti and then Ni, although Ti has a higher melting point than Ni. In the Ni-Zr, Ni-Mo and Ni-Ta systems, however, the Ni lattice collapses more rapidly because it reaches a maximum solubility earlier than its partners, which have higher melting points than Ni. A solubility criterion is thus relevant for all the above cases; the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction.     

Algunas cuestiones sobre el desarrollo del lenguaje de referencia mental: los problemas de los niños con el lenguaje de estados mentales

Resumen

En este artículo se revisan algunas cuestiones sobre el desarrollo del lenguaje de referencia mental. Se presentan y analizan algunos trabajos sobre la comprensión de los niños de las propiedades de factividad y de certidumbre, así como sus problemas con la distinción entre significado literal y pretendido. También se analizan las relaciones entre el desarrollo del lenguaje mentalista y el desarrollo del proceso de lecto-escritura. Se analizan los resultados en el marco de los modelos de inferencia mentalista de ‘teoría de la mente’.     

Algunas cuestiones sobre el desarrollo del lenguaje de referencia mental: los problemas de los niños con el lenguaje de estados mentales

Resumen

En este artículo se revisan algunas cuestiones sobre el desarrollo del lenguaje de referencia mental. Se presentan y analizan algunos trabajos sobre la comprensión de los niños de las propiedades de factividad y de certidumbre, así como sus problemas con la distinción entre significado literal y pretendido. También se analizan las relaciones entre el desarrollo del lenguaje mentalista y el desarrollo del proceso de lecto-escritura. Se analizan los resultados en el marco de los modelos de inferencia mentalista de ‘teoría de la mente’.