Keiji Yada

Application of lattice imagery to radiation damage investigation in natural zircon

High-, intermediate-, and low-type zircon crystals of natural origin were investigated using a 1,000 kV high-resolution electron microscope. The lattice images obtained successfully for high zircon were in good accordance with computer simulated ones, and 1.5 Å separations, the nearest distance between zirconium atoms projected along the a axis, were clearly resolved under a certain instrumental condition. The images of fission tracks and surrounding areas show nearly perfect lattice images and that within the fission tracks, with a width of 20 ∼ 30 Å and length of ca. 1,000 Å, the structure is heavily disordered, almost amorphous; that both sides of the tracks the lattices are displaced or dislocated, and that in the area adjacent to the tracks, bright and dark spot images occur, corresponding to vacancies and their interstitial atoms. In low zircon, the structure is completely destroyed to show an entirely amorphous state, whereas an intermediate type consists of domains of the order of 50 ∼ 100 Å across with nearly regular lattices, along whose boundaries strongly disordered areas with widths of few tens of angstroms appear, but the relative orientations of the neighbouring domains are almost continuous. Thus a whole process of metamictization is visualized on a lattice scale. Metamictization proceeds principally by the formation of fission tracks, the direct result of fast movement of nuclear particles; recoil nuclei therefrom seem to play a less important role in the destruction of the structure.

Radiation induced lattice defects in natural zircon (ZrSiO4) observed at atomic resolution

Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO2 thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated.

Thermal Transformation of Talc as Studied by Electron-Optical Methods

The thermal decomposition of a fibrous talc was studied by transmission electron microscopy (TEM) and selected-area electron diffraction (SAD). Small changes in the lengths of a and b unit-cell parameters were noticeable at 500°C, but the talc laths did not change morphologically until 800°C. At this temperature striations began to appear in the TEM image, and the talc SAD reflections began to develop faint satellite streaks. At 900°C the striations appeared to be crystallites, and reflections of orthorhombic enstatite were noted. Both TEM and SAD evidence showed that the enstatite crystallites were formed in three orientations corresponding to the three pseudohexagonal a axes of the talc. Thus, triple superposition of the electron diffraction pattern at the three equivalent angles explains the high symmetry star-shaped pattern. At 1000° to 1100°C the enstatite crystallites were shorter and thicker, and the streaks in the SAD pattern were nearly absent. Above 1200°C only one orientation of the enstatite crystallites was found. Noncrystalline regions were also detected at 900°C and became progressively scarce at 1000° and 1100°C. They were not detected at 1200°C. At 1300°C cristobalite was detected in some SAD patterns. The crystallographic axes and unit-cell parameters of the talc and enstatite were also topotactically related as follows: at (5.3 A)//ce (5.2 A); bt (9.16 A)//be (8.8 A); d(001)t (18.84 A)//ae (18.2 A). These results are compatible with an inhomogeneous decomposition mechanism as proposed by earlier workers.The thermal decomposition of a fibrous talc was studied by transmission electron microscopy (TEM) and selected-area electron diffraction (SAD). Small changes in the lengths of a and b unit-cell parameters were noticeable at 500°C, but the talc laths did not change morphologically until 800°C. At this temperature striations began to appear in the TEM image, and the talc SAD reflections began to develop faint satellite streaks. At 900°C the striations appeared to be crystallites, and reflections of orthorhombic enstatite were noted. Both TEM and SAD evidence showed that the enstatite crystallites were formed in three orientations corresponding to the three pseudohexagonal a axes of the talc. Thus, triple superposition of the electron diffraction pattern at the three equivalent angles explains the high symmetry star-shaped pattern. At 1000° to 1100°C the enstatite crystallites were shorter and thicker, and the streaks in the SAD pattern were nearly absent. Above 1200°C only one orientation of the enstatite crystallites was found. Noncrystalline regions were also detected at 900°C and became progressively scarce at 1000° and 1100°C. They were not detected at 1200°C. At 1300°C cristobalite was detected in some SAD patterns. The crystallographic axes and unit-cell parameters of the talc and enstatite were also topotactically related as follows: at (5.3 Å)//ce (5.2 Å); bt (9.16 Å)//be (8.8 Å); d(001)t (18.84 Å)//ae (18.2 Å). These results are compatible with an inhomogeneous decomposition mechanism as proposed by earlier workers.ResumoA decomposição térmica de um talco fibroso foi estudada por microscopia eletrônica de trans-missão (MET) e por difração eletrônica de área selecionada (SAD). Foram observadas ligeiras modificações nos comprimentos dos parâmetros da cela unitária aeba 500°C, mas as ripas de talco não apresentaram transformações morfológicas até 800°C, quando estriações começaram a aparecer nas micrografias e a desenvolver reflexões satélites em forma de traços muito tênues. A 900°C as estriações puderam ser caracterizadas corno cristalitos e começaram a aparecer reflexões de enstatita ortorrômbica. As evidências obtidas por MET e SAD mostraram que os cristalitos de enstatita foram formados em três orientações correspondentes aos três eixos a pseudohexagonais do talco; assim a tripla superposição do diagrama nos très ângulos equivalentes explica a alta simetria do diagrama em forma de estrela. Entre 1000° e 1100°C os cristalitos se tornaram mais curtos e mais grossos, e os traços no diagrama SAD quase desapareceram; acima de 1200°C apenas urna direção dos cristalitos de enstatita foi encontrada. Regiões não cristalinas foram detectadas a 900°C se tornando progressivamente mais raras entre 1000° e 1100°C e desaparecendo a 1200°C. A 1300°C pôde ser detectada a cristobalita em alguns diagramas de SAD. Os eixos cristalográficos e os parâmetros das celas unitárias do talco e da enstatita são relacionados corno se segue: at (5.3 Å)//ce (5.2 Å); bt (9.16 Å)//bt (8.8 Å); d(001)t (18.84 Å)//ae (18.2 Å). Os resultados do presente trabalho são compatíveis com um mecanismo de decomposição como aquele proposto por Taylor e por Brindley.

Serpentine minerals hydrothermally synthesized and their microstructures

Abstract Serpentine minerals were synthesized from the 2Mg 2 SiO 4 (natural olivine)+3H 2 O system under various conditions for periods of 30 min to 30 days to investigate: (1) the influence of pH and other additives, (2) the influence of the reaction temperature and (3) the behavior of the initial stage of serpentinization. Growth patterns and structures of the synthesized products were examined by means of X-ray, electron diffraction and lattice imaging electron microscopy.

Thermal transformation of chrysotile studied by high resolution electron microscopy

Thermal transformation of chrysotile from Uruaçu District, state of Goiás, Brazil, heated in dry conditions at temperatures from 600°C to 1300°C was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Up to 600°C, no morphological or SAD pattern changes were observed. At 600°C, the fibrils were still crystalline with the characteristics of the clinochrysotile. In addition, a new fringe system of 10–15 Å spacings appeared sporadically parallel to the 7.3 Å fringes of chrysotile. Areas of these extra fringes seem to constitute favorable sites for the nucleation of forsterite. At 650°C, forsterite nuclei appeared inside the nearly amorphous fibrils in the shape of patches consisting of flaky crystallites. At 700°C the chrysotile structure had disappeared; the new spots present in the SAD pattern were indexed as those of forsterite. Between 800–900°C the crystallinity of the patches was clearly demonstrated. From the lattice images in the patches, topotactic relations between chrysotile and forsterite were analyzed. At 1000°C very tiny grains of enstatite were formed mixed with forsterite grains. The SAD pattern is complex due to the coexistence of forsterite, enstatite, and silica-rich amorphous areas. From 1100°C to 1300°C the tridimensional growth of enstatite was promoted. The present results support the topotactic relations between chrysotile and forsterite found by X-ray analysis although differences up to several degrees may exist when these phases are observed microscopically. Evidence suggesting a topotactic growth between forsterite and enstatite was also obtained.РезюмеС помощью электронной микроскопии высокой разрешающей способности и электронной дифракции выбранной зоны (ДВЗ) изучалось термальное превращение хризотила из района Ураку, штат Гойас, Бразилия, нагреваемого в сухом виде до температур от 600°С до 1300°С. При нагревании до 600°С не наблюдалось ни морфологических изменений, ни измененний картины ДВЗ. При 600°С фибриллы оставались кристаллическими с характеристиками клинохризотила. Кроме того, появилась новая система полос с промежутками 10–15 Å, спорадически параллельная 7,3 Å полосам хризотила. Зоны этих дополнительных полос по-видимому являются благоприятными местами для образования центров кристаллизации форстерита. При 650°С центры кристаллизации форстерита появились внутри почти аморфных фибрил в форме включений, состоящих из чешуйчатых кристаллитов. При 700°С исчезла хризотиловая структура; новые пятна, появившиеся на картине ДВЗ были определены как пятна форстерита. Между 800°С и 900°С отчетливо была видна кристалличность этих пятен. По изображениям решеток в пятнах анализировались топотактические отношения между хризотилом и форстеритом. При 1000°С сформировались очень маленькие зерна энстатита, смешанные с зернами форстерита. Картина ДВЗ сложная из-за сосуществования форстерита, энстатита и богатых кремнеземом аморфных зон. От 1100°С до 1300°С происходил трехмерный рост энстатита. Полученные результаты подтверждают топотактические отношения между хризотилом и форстеритом, которые были обнаружены рентгеноструктурным анализом, хотя различия до нескольких градусов могут существовать, когда фазы наблюдаются под микроскопом. Получены также доказательства топотактических отношений между форстеритом и энстатитом при их развитии.ResümeeThermische Transformationen von Chrysotil vom Urauçu Distrikt, Staat von Goiás, Brasilien, erhitzt unter trockenen Bedingungen bei Temperaturen von 600°C bis 1300°C, wurde mittels Elektronenmikroskopie mit hohem Auflösungsvermögen und Elektronenbeugung ausgewählter Flächen (SAD) untersucht. Bis 600°C wurden keine Unterschiede in Morphologie oder SAD Bildern gesehen. Bei 600°C waren die Fäserchen immer noch kristallen mit den Eigenschaften des Klinochrysotil. Außerdem erschien sporadisch, parallel zu den 7,3 Å Rändern von Chrysotil, ein neues Randsystem mit Netzabständen von 10–15 Å. Die Flächen dieser extra Ränder scheinen günstige Plätze für die Kembildung von Forsterit zu ergeben. Bei 650°C erschienen Forsteritkeme in den fast amorphen Fasern als Flecken, die aus schuppigen Kristallen bestehen. Bei 700°C war die Chrysotilstruktur verschwunden; die neuen Flecken in den SAD Bildern wurden als Forsterit katalogisiert. Zwischen 800–900°C wurde die Kristallinität der Flecken deutlich demonstriert. Aus den Gitterabbildungen in den Flecken wurden topotaktische Verwandtschaften zwischen Chrysotil und Forsterit analysiert. Bei 1000°C wurden sehr kleine Körner von Enstatit gemischt mit Forsteritkömchen geformt. Das SAD Muster ist wegen der Koexistenz von Forsterit, Enstatit und silika-reichen, amorphen Flächen komplex. Von 1100°C bis 1300°C wurde das dreidimensionale Wachstum von Enstatit gefördert. Die vorliegenden Resultate unterstützen die topotaktischen Verwandtschaften zwischen Chrysotil und Forsterit, welche durch Röntgenanalyse gefunden wurden, obwohl etliche Grade Unterschiede existieren können, wenn die Phasen mikroskopisch untersucht werden. Beweise, welche ein topotaktisches Wachstum zwischen Forsterit und Enstatit vorschlagen, wurde auch erhalten.RésuméLa transformation thermale de chrysotile du District d’Urauçu, état de Goiás, Brézil, chaufée sous des conditions sèches, de 600°C à 1300°C, a été étudiée par microscopie électronique à haute résolution et par diffraction électronique de régions sélectionnées (SAD). Aucun changement morphologique ou de clichés SAD n’a été observé jusqu’à 600°C. A 600°C, les fibrilles étaient encore cristallines avec les caractéristiques de clinochrysotile. De plus, un nouveau système de franges d’espacements 10–15 Å a apparu sporadiquement, parallèle aux franges 7,3 Å de chrysotile. Les régions de ces franges nouvelles semblent constituer des sites favorables pour la nucléation de forstérite. A 650°C, des nuclei de forstérite apparaissent à l’intérieur des fibrilles quasi amorphes en la forme de plaques constituées de cristallites floconneuses. A 700°C la structure de chrysotile avait disparu, les nouvelles tâches présentes dans le cliché SAD étaient classées comme étant celles de forstérite. Entre 800–900°C, la cristallinité des plaques était clairement démontrée. Des relations topotactiques entre la chrysotile et la forstérite ont été analysées à partir des images du réseau cristallin dans les plaques. A 1000°C, de très petits grains d’enstatite ont été formés, mélangés avec les grains de forstérite. Le cliché SAD est complexe à cause de la coexistence de forstérite, d’enstatite et de régions amorphes riches en silice. De 1100°C à 1300°C, la croissance en 3 dimensions d’enstatite a été promue. A présent, les résultats soutiennent les relations topotactiques entre la chrysotile et la forstérite trouvées par analyse aux rayons-X, quoique des différences jusqu’à plusieurs degrés peuvent exister lorsque les phases sont observées au microscope. Certaines preuves suggérant une croissance topotactique entre la forstérite et l’enstatite ont aussi été obtenues.

Charging effect on the HRTEM imaging of small MgO crystals

Abstract It is reported that lattice fringes appearing in the profile image of the (100) surface of a small MgO crystal observed from the [001] or [011] direction by a high-resolution conventional transmission electron microscope show strange bending at the corners of the crystal. In order to interpret this bending of fringes on the surface, a charging effect is introduced into the contrast simulation with the multi-slice method. Contrasts simulated on the assumption of three types of charge distribution are compared with actual micrographs. It is found that the bending of fringes can be explained by the charging effect, that is, lattice fringes are observed as being bent even if the atomic arrangement is not distorted. The seriousness of the effect of charging on imaging does not depend on the density of charge, but on the total amount of additive charges in the whole of the crystal. The calculated images that include the effects of defocus and aberrations of the electron lenses are much more sensitive to the charging effects than the calculated intensity distributions at the exit surface of the crystal.

Direct Observation of Crystal Imperfections in KCl Single Crystal by Electron Microscope

The processes of change of a thin KCl single crystal due to electron irradiation were observed by means of an electron microscope and electron diffraction. It was found that under weak electron irradiation loop structures first appeared and then disappeared showing a lot of small bright specks over the whole crystal. In this stage, each diffraction spot had streaks in 〈100〉 directions. Under intense electron irradiation bright squares appeared initially without the appearance of loop structures. In this stage, the diffraction pattern was a perfect net‐like pattern. It was found that by using the replica technique, loop structures and large squares appeared in the crystal, and also that by using the dark‐field image method the contrast of loop structures and bright squares was due to Bragg reflection, which had resulted from the formation of voids and cubic cavities in the crystal, respectively. From the experimental results, the mechanism of coagulation of vacancies in KCl crystal with electron irradiatio...

Thermal transformation of antigorite as studied by electron-optical methods

The thermal transformation of a Brazilian antigorite heated dry from 600° to 1300°C, was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Below 600°C, the antigorite particles did not change morphologically or crystallographically, as evidence by the presence of the superlattice in the SAD patterns and lattice images. At 650°C, traces of antigorite remained, although the superlattice structure had disappeared and the first indications of forsterite formation were observed in the same SAD. Diffraction patterns of the transition phases showed various topotactical relationships between antigorite and forsterite. At 800°C, the crystallization to forsterite was much more pronounced. At 900°C, the individual particles retained their original shapes, but they were actually pseudomorphs, for their SAD patterns showed only forsterite. Between 1000° and 1300°C various topotactical relationships were observed. Although the overall transformation to forsterite appears to be similar for both chrysotile and antigorite, the transformation of antigorite took place at a slightly higher temperature (~50°C) with a larger number of topotactical relationships than for chrysotile. Enstatite was formed at 1300°C, but it was impossible to determine the topotactic relations between enstatite and forsterite, which was possible with chrysotile.РезюмеТермическая трансформация Бразилийского антигорита, нагретого в сухом состоянии от 600° до 1300°С, исследовалась при помощи сильно разрешающего электронного микроскопа и диффракции электронов на выбранных поверхностях (ДЭП). Ниже 600°С частицы антигорита не изменялись морфологически или кристаллографически, что было подтверждено присутствием супер-решетки в образцах ДЭП и образах решетки. При 650°С остались следы антигорита, хотя структура супер-решетки исчезла, и первые следы образования форстерита наблюдались в том же самом ДЭП. Образцы диффракции переходных фаз указывали на различные топо-тактические отношения между антигоритом и форстеритом. При 800°С кристаллизация форстерита была более видна. При 900°С индивидуальные частицы сохраняли начальную форму, но они были псевдоморфными, потому что их образцы ДЭП показали только форстерит. Различные топотактические отношения наблюдались между 1000° и 1300°С. Хотя трансформация в фостерит является подобной для обоих, антигорита и хризотила, трансформация антигорита происходила при немного большой температуре (~50°С) с большим числом топотактических отношений, чем для хризотила. Энстатит формировался при 1000°С, но определение топотактических от-ношений между энстатитом и форстеритом (как в случае хризотила) было невозможно. [Е.О.]ResümeeDie thermische Umwandlung von brasilianischem Antigorit, der trocken auf 600°–1300°C erhitzt wurde, wurde mittels hochauflösender Elektronenmikroskopie und Feinbereichselektronendiffraktion (SAD) untersucht. Unter 600°C veränderten sich die Antigoritteilchen weder morphologisch noch kristallographisch, wie durch die Anwesenheit von Überstrukturen in SAD-Diagrammen und in Gitterbildern bestätigt wird. Bei 650°C waren noch Spuren von Antigorit vorhanden, obwohl die Überstrukturen verschwunden waren, und die ersten Anzeichen einer Forsteritbildung im gleichen SAD-Diagramm beobachtet wurden. Die Diffraktionsdiagramme der Übergangsphasen zeigten verschiedene topotaktische Beziehungen zwischen Antigorit und Förstern. Bei 800CC wurde die Kristallisation viel ausgeprägter. Bei 900°C hatten die einzelnen Teilchen noch ihre ursprüngliche Form, doch waren sie in Wirklichkeit Pseudomorphosen, da ihre SAD-Diagramme nur mehr Forsterit zeigten. Zwischen 1000° und 1300°C wurden verschiedene to-potaktische Beziehungen beobachtet. Obwohl die endgültige Umwandlung in Forsterit für Chrysotil und Antigorit gleich zu sein scheint, findet die Umwandlung von Antigorit bei etwas höheren Temperaturen (um etwa 50°C) und mit einer größeren Zahl von topotaktischen Beziehungen statt als die von Chrysotil. Enstatit wurde bei 1300°C gebildet, aber es war unmöglich, die topotaktischen Beziehungen zwischen Enstatit und Forsterit zu bestimmen, wie es im Fall von Chrysotil möglich war. [U.W.]RésuméLa transformation thermique d’une antigorite brésilienne chauffé au sec de 600°C à 1300°C a été étudiée par microscopie à électrons à resolution élevée et par diffraction d’électrons de region sélectionnée (SAD). Sous 600°C, les particules d’antigorite n’ont changé ni morphologiquement ni cristallographiquement, comme le met en evidence la présence du supertreillis des clichés SAD et des images de treillis. A 650°C, il restait des traces d’antigorite, quoique la structure du supertreillis avait disparu et les premières indications de la formation de forsterite avaient été observées dans le même SAD. Les clichés de diffraction des phases de transition ont montré des rapports topotactiques entre l’antigorite et la forsterite. A 800°C, la cristallisation en forsterite était beaucoup plus prononcée. A 900°C, les particules individuelles avaient gardé leurs formes d’origine, mais elles étaient en fait des pseudomorphes, car leur clichés SAD n’ont montré que de la forsterite. Entre 1000°C et 1300°C, des rapports topotactiques variés ont été observés. Quoique la transformation générale en forsterite semble être similaire pour la chrysotile et l’antigorite, la transformation en antigorite s’est produite à une température plus élevée (~50°C) avec une quantité plus élevée de rapports topotactiques que pour la chrysotile. De l’enstatite a été formée à 1300°C, mais il était impossible de determiner les rapports topotactiques entre l’enstatite et la forsterite, ce qui était possible avec la chrysotile. [D.J.]

Image reconstruction from an in-line X-ray hologram with intensity distribution constraint

An image reconstruction method for in-line soft X-ray holography is presented. The image is reconstructed by a Fresnel phase-retrieval algorithm using a constraint on the intensity distribution. Experimental results show that the introduction of the intensity constraint is effective for eliminating artifacts such as a twin-image.

Effect of crystalline properties on coercive force in iron acicular fine particles

Crystallographic properties and their size dependence in acicular fine particles of iron prepared by reduction fromα-FeOOH were investigated by transmission electron microscopy and compared with magnetic properties. Although both larger particles with an average needle length of 0.5μm and smaller ones of 0.2μm length have single domain configuration, the former are crystal lographicaIly polycrystalline while the latter are single crystal with a [100] axial orientation, an easy magnetization direction of iron. The coercive force, principally yielded by external shape anisotropy, is higher in smaller particles in spite of their inferior axial ratio. The intrinsic magnetocrystalline anisotropy is inferred to be the most responsible to give rise to this further increase of coercive force. The experimentally obtained values of magnetic properties are also compared with the theoretical estimation, which results semi-quantitatively in good accordance.