Ordered Arrangement of Oxygen in the Interstitial Solid Solution of Zirconium-Oxygen System

The crystal structure of interstitial solid solution of zirconium-oxygen system was investigated by means of X-ray, electron and neutron diffraction on specimens in the composition range between 11 and 27 at% O. The specimens were prepared by melting appropriate mixtures of zirconium metal and zirconium dioxide in an arc-furnace. In addition to a superstructure found by Holmberg and Dagerhamn in the composition ZrO_y (0.33 has an intermediate structure in which the arrangement of oxygen atoms is basically described as ABCBCACAB... stacking with nine layers period. The actual distribution of oxygen in specimens is not ideally regular as mentioned above, but contains rather high degree of stacking disorder

Twin Structures Associated with Ordering in Evaporated Thin Films of Cu_<60>Au_<40>

Electron diffraction and microscopic observations were made on twin structures associated with ordering in single crystalline films of Cu_Au_ prepared by vacuum evaporation. Crystallographic relationships of the twinned region in the ordered phase were determined with respect to the disordered cubic phase. The twin plane was parallel to {101} of the tetragonal CuAu I. It was usually found in slowly cooled specimens that the twin plane was normal to the film surface, and thus the c-axis of CuAu I in the twin lamellae was lying in the film plane making an angle of about 2°with the principal axis of the original cubic phase. The results are discussed in comparison with the observations of previous workers

Long Period Superstructures with Hexagonal Symmetry in the Cu-Sb Alloys near 20 at.%Sb

Crystal structures of two hexagonal phases in Cu-Sb alloys have been studied by means of X-ray and electron diffraction as well as electron microscopy. A new long period superstructure with space group P6_3/mmc is found in the range 16-19 at.%Sb (ε phase), which is essentially an anti-phase modulation derived from the hexagonal ordered structure of the Ni_3Sn (DO_) type. The super-period of atomic order in the close packed plane is nearly seven times the nearest neighbor distance and decreases with increasing e/a. The image of the super-period is directly observed with an 1 MV electron microscope. A similar long period superstructure is established for the neighboring phase (ε\u27) around 21 at.%Sb. The stabilization mechanism of the two superstructures is interpreted in terms of the interaction of the Fermi surface with the super-zone faces

Ageing Characteristics of Cu-Be-Al Alloys

The ageing characteristics of the Cu-Be-Al ternary alloys, containing 9～11 at% Be and 6～9 at% Al, were studied by means of hardness and tensile tests, optical and transmission electron microscopy, X-ray and electron diffraction, and calorimetric measurements. The investigation was done mainly on the specimen containing 9.07 at% Be and 9.05 at% Al, which was initially quenched from 800℃, where the two phases (α and β) are in equilibrium, and then aged at 340℃ for various periods. The changes in various properties during ageing were due to the precipitation in the α phase and the decomposition of the β phase, both of which terminated in the equilibrium state, (α+γ). The most hardened state attained by 1.5hr ageing was attributed to the formation of G. P. zones in the α phase and the decomposition of the β phase into the α and intermediate phases. The crystallographic orientation relations between the matrix and these phases in the course of the ageing process were determined. Finally the age-hardening of the alloys was briefly discussed

Long-Period Stacking Order of Oxygen Atoms Dissolved in α-Zirconium near the Composition ZrO_<1/3>

Ordered arrangements of oxygen atoms dissolved in α-zirconium near the stoichiometric composition ZrO_ have been investigated by means of electron diffraction and dark-field electron microscopy. The arrangements of oxygen atoms are specified as the long period stacking sequences of the interstitial layers of octahedral sites normal to the c axis of the h.c.p. lattice. Eight kinds of the stacking variants of the oxygen layers are found in the composition range from 24 to 26 at. % O in the order of 8H (71), 5H (41), 12R (31)_3, 7H (3121), 10H (131131), 9R (21)_3, 12H (13111131) and 14H (1131111311) or (1311111131). These stackings become irregular by quenching from about 600℃

Interstitial Order-Disorder Transformation in the Ti-O Solid Solution. IV. : A Neutron Diffraction Study

Interstitial order-disorder transformation regarding oxygen atoms dissolved in alpha-titanium has been studied by neutron diffraction on single crystals in the range from 17 to 28 at% O. Occupation probabilities of the oxygen atoms in the octahedral interstitial sites are determined quantitatively with the variation of composition and temperature. The change of the long-range order with increasing temperature reveals a two-step process attributed to the disordering of the oxygen atoms. The static displacement of the titanium atoms parallel to the c-axis increases almost linearly with the oxygen concentration. The results are compared with the previous works in Parts I, II and III

Superstructure and Order-Disorder Transformation of Interstitial Oxygen in Hafnium

Crystal structure and phase transition in the hafnium-oxygen system containing 10-20 at% O have been studied by means of electron, neutron and X-ray diffraction and calorimetry as well. The oxygen atoms occupy the octahedral holes in h.c.p. metal lattice and two types of interstitial superstructures are found at the hypo- and hyper-stoichiometric composition HfO_ and HfO_ below 430℃. The lattice constants of the hexagonal supercells are respectively a=√, c=3c_0 and a=√, c=2c_0, where a_0～3.2A and c_0～5.1A are those of the metal lattice. The oxygen sublattices are described in terms of the stacking sequence of interstice layers parallel to the close-packed planes of the metal atoms, which varies continuously from A□B□C□…for HfO_ to A□B□…for HfO_. The concentration dependence of the ordered structures is interpreted in terms of strain ordering

An Ordered Structure of Au_5Sn (Metallurgy)

A new ordered structure of Au_5Sn is determined by X-ray and electron diffraction using single crystals. The unit cell of the hexagonal superstructure contains 15 Au and 3 Sn atoms, having the lattice constants a=√3 a_0 and c=3c_0, where a_0～2.94A and c_0～4.78A are those of the fundamental hcp cell. The closest interatomic distance of Sn-Sn pairs is √3 a_0～5.1A, and the displacement of gold atoms from the ideal close packing is evaluated as 0.03_7A. The ordered phase transforms to the disordered hcp phase (ζ) at 195℃, and a revised phase diagram of the region of 10-20 at%Sn is proposed

Study on Anti-Phase Domains in Cu_3Au by Means of Electron Diffraction and Electron Microscopy

It has been confirmed by electron diffraction that anti-phase domains in Cu_3Au giving rise to diffuse superlattice reflections grow up during isothermal annealing below the transition temperature of order-disorder, evaporated films of nearly stoichiometric compositions being used. This fact means that anti-phase domains in Cu_3Au are not in an equilibrium state unlike the so-called periodic anti-phase structure. Electron-microscopic images of domain boundaries of alloy films with 26 atomic per cent gold have been observed. These images also confirm the isothermal growth of domains. The irregular configuration of domain boundaries as observed by Fisher and Marcinkowski in electropolished specimens of Cu_3Au has been confirmed also in the evaporated films. It is concluded, however, that some correction should be made on the domain distribution of Cu_3Au suggested by these authors, on the basis of dark field images of electron micrographs formed by different kinds of superlattice reflection in the present study. The correct distribution is that in which the occupation of nearest neighbor positions by gold atoms is avoided as far as possible

Confirmation of Existence of Cu_3Au II Using Thin Films

The results are summarized in Table 1. Electron diffraction patterns and (110) dark field electron micrographs were taken from the specimen with 31 at. % Au annealed at 350℃. In diffraction patterns, clear splittings of superlattice reflections characteristic of the periodic anti-phase structure were observed. Satellite spots around fundamental reflections were also observed. Any deviation from cubic symmetry could not be recognized in this diffraction pattern. Domain size was estimated to be ten times the unit cell. In electron micrographs, parallel lines with regular spacing were clearly observed. The spacing was about 40A, in agreement with the domain size estimated from diffraction patterns. These results are considered to confirm essentially the X-ray results obtained by Scott. It is noted that the periodic anti-phase structure was not found in the alloys with excess of copper