Electron diffraction study of superlattices and orientation variants in Ca3SrAl6SO16

Samples having the nominal composition of Ca₃SrAl₆SO₁₆ were sintered at 1380 °C and analysed by electron diffraction. The frequent appearances of forbidden and satellite reflections in this compound imply the presence of a number of basal and nonbasal superlattices so that the microstructure of this cement clinker was characterized by various superstructures including one-, two- and even three-dimensional superstructures along the 0 0 1, 1 1 0, 1 1 2, 1 1 4 or 2 2 1, 0 1 3 and 1 2 3 directions with repeat periods of two or three times of that of basic one, respectively, and intergrowth of these. Various domain structures with 90°, 120° and 48.2°, etc., orientation relationships were also detected in these superstructures and the total number of these orientation variants related to the symmetry elements lost in the process of phase transformation, can be predicted according to the conclusions of Van Tendeloo and Amerlinckx, or they are equal to the number of those unique planes in the matrix.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Agglomeration problems in the formation of FeSi2 from Fe-Si thin-film couples

The agglomeration process that occurs during annealing of thin Fe films (<200 nm) on Si substrates has been studied. Agglomeration occurred on uncapped films prior to silicide formation. Capping layers of SiO₂, or more appropriately Si-SiO₂, have been used to minimize agglomeration effects. Continuous thin films of -FeSi₂ have been grown on 11 1 and 100 oriented substrates. Preferred growth of (202) and (220) suicide planes on 111 Si has been obtained, while preferential growth was not observed on 100 Si.     

Deformation of single crystals of gallium arsenide

Deformation of single crystals of gallium arsenide is reported in bend and tension up to 1000° C whilst maintaining stoichiometry in an arsenic atmosphere. Surface defects and impurity segregation are shown to be dislocation sources. The dislocation density is low enough, however, to show large yield drops which are analysed in detail. Strains of 39% are possible. The activation energy for dislocation movement is increased by heat-treatment owing to an increase in point defect population.Electron microscopy shows that the predominant slip systems are {111} 110 and the majority of dislocations have b=a/2 110, the axes lying along 110 and 112 directions. Sub-cell formation occurs with sub-boundaries lying along 110 directions.     

Microstructure and crystallographic texture of rolled polycrystalline Fe3Al

An imperfectly B₂ ordered Fe₃Al aggregate was cast, thermomechanically hot rolled and finally annealed at 870 K. Subsequently, the specimen was rolled at 800–830 K to a strain of 80%. The microstructure and the crystallographic texture of the rolled polycrystalline sample was investigated within the range =20–80%. The microstructure consisted of flat, elongated grains. In numerous grains straight slip lines were detected. Even after =80% recrystallization was not observed. The rolling texture of Fe₃Al considerably deviates from that of non-ordered body centered cubic (b.c.c.) alloys and pure b.c.c. metals. The {111}uvw texture fibre (7-fibre) was very pronounced, while the {hkl}110 fibre (-fibre) was very weak. The {112}110 orientation which represents the strongest texture component in non-ordered b.c.c. alloys did not occur at all. The textures are discussed in terms of the {110}111, {112}111, {112}111 and {123}111 slip systems. The contribution of crystallographic slip of the various types of potential slip systems was simulated by means of the Taylor theory.     

A transmission-electron-microscopy study of a face-centred-cubic phase in an Al-Li-Cu-Mg-Zr alloy

Icosahedral T₂ phases can form either by solid-state precipitation or during solidification in Al-Li-Cu-Mg alloys. The T₂ phase forming during solidification can transform to an R phase at high annealing temperatures. The T₂ phase forming by solid-state precipitation coexists with the Y phase, which has a face-centred cubic (f.c.c.) structure with lattice parameter a2.0 nm and can form microtwins with the twin plane of (111). The orientation relationships between the C phase and the T₂ phase are: i¯5Y0 1 1, Y1 1 3; i¯3Y1 1 1, Y1 2 3, Y1 1 5; Y2 3 5; i2Y0 1 1, Y1 1 1, Y1 1 2, Y1 1 3, Y1 1 5.     

Interface characterization of a β-SiC whisker-Al composite

The nature of the interface, the orientation relationship of -SiC whisker (-SiC_w)-Al combination, and the misfit dislocation structures at the -SiC_w-Al interfaces in a -SiC_w-Al composite have been observed by a high-resolution transmission electron microscopy (HRTEM). It was shown that quite a good bonding between the whisker and the aluminium was achieved due largely to the lattice match between SiC and aluminium at the interfaces. The orientation relationship between the whisker and the aluminium was {002}_SiC{111}_Al; 110_SiC110_Al. The interface was clean, faceted and semicoherent. The misfit dislocation cores were located in the whisker side away from the -SiC_w-Al interfaces.     

Defects on TiBiTe2 single crystals

Single crystals of rhombohedral TiBiTe₂ examined by transmission electron microscopy consist of large areas separated by {100}- and {110}-type twins. By measuring the rhombohedral angle from the splitting of diffraction patterns in the twin areas, we calculated the residual strain which remained after the transformation O_h D _3d, ranging from 1.2 to 12.2 %. Dislocations with Burgers vector (a/2) 1¯10 were mobile and the main slip system was (111) 1¯10. Planar defects with complex - fringe contrast were also observed.     

1 : 2 Long-range ordering and defect mechanism of WO3-doped perovskite Ba(Mg1/3Ta2/3)O3

The nature of the B-site cation ordering and the associated defect process necessary to stabilize the ordered domains were investigated using the WO₃-doped BaMg_1/3Ta_2/3O₃ BMT system as a typical example of BaB_1/3B_2/3O₃-type complex perovskites. It was shown that only the 1 : 2 long-range ordering of the B-site cation existed in both undoped and WO₃-doped BMT perovskites. The atomic defect mechanism associated with the stoichiometric 1 : 2 long-range ordering was systematically investigated. It is concluded that the substitution of W⁶⁺ for Ta⁵⁺ in the WO₃-doped BMT enhances the degree of the 1 : 2 long-range ordering and produces the positively charged W _Ta sites with a concomitant generation of tantalum vacancies V_Ta and mobile oxygen vacancies V _O for the ionic charge compensation.     

Atom positions in the R-phase unit cell in TiNi shape memory alloy

A crystallographic analysis of the atom positions in the unit cell of the R-phase of the TiNi shape memory alloy has been performed. In addition to a homogeneous shape change the atoms are found to shuffle in the [111]_B2 and –211_B2 directions during the B2 to R-phase transformation. The origin of these shuffles is found to be a complex interaction between 1101–10 transverse acoustic and 111 longitudinal acoustic soft phonon modes.     

Magnetic Properties of High-Resistivity CdTe〈In〉 and CdTe〈Cl〉 Crystals

The magnetic susceptibility of high-resistivity CdTeIn and CdTeCl crystals was measured between 4.2 and 300 K. The susceptibility was found to vary anomalously with temperature. Below 50 K, all the samples were paramagnetic. The observed anomalies are interpreted in terms of donor–acceptor pairs formed by native defects and dopant or uncontrolled impurity atoms. The effect of doping on the 300-K is related to the Van Vleck paramagnetic contribution resulting from the local electric fields of X_i–V _Cdand In_i–V _Cddefect complexes. In CdTeCl, this contribution is insignificant.     

Photosensitive Centers in CdTe〈Ge〉, CdTe〈Sn〉, and CdTe〈Pb〉

The spectral and temperature dependences of photoconductivity in CdTePb crystals under band-gap and combined excitation were studied at photon energies in the range 0.53–1.7 eV and temperatures from 80 to 300 K. The high photosensitivity of the crystals and the observed IR and temperature quenching of photoconductivity indicate that, just as in CdTeGe and CdTeSn, the recombination processes in CdTePb are dominated by deep centers with drastically different capture cross sections for electrons and holes. Some parameters of the centers are determined. The results suggest that the likely defect species responsible for the high photosensitivity of CdTePb is an acceptor complex consisting of a Cd vacancy and a metal (Ge, Sn, Pb) ion on the Cd site: (V ^2– _CdM⁺)^–/0.     

Anisotropy in the hardness and friction of calcium fluoride crystals

Anisotropy in the Knoop indentation hardness and the friction of diamond cones on calcium fluoride crystals has been investigated at experimental temperatures from 20 to 300° C. It is shown that the directions of minimum and maximum indentation hardness, on the (001) plane, are 110 and 100 respectively whilst the 1¯10 are harder than the 11¯2 directions on the (111) plane. Also, the sliding friction in the (001) plane is greatest in the 110 directions and least in the 100 and, on the (111) cleavage plane, [¯1¯12] sliding leads to higher friction than [11¯2]. The nature of anisotropy, for both hardness and friction measurements, does not change over the experimental temperature range covered in this work. Observations on the resultant deformation are made and these anisotropic properties are explained in terms of the effective resolved shear stresses developed on the {100} 011 primary slip systems at all experimental temperatures.     

Deformation and recrystallization textures of copper single crystals and bicrystals

Recrystallization textures in rolled copper specimens have been investigated so as to elucidate the mechanisms of cube texture formation. The specimens are single crystals with the orientations corresponding to the main components of the rolled textures, such as {112}111,{110}112, etc. and bicrystals consisting of such oriented crystals. The cube texture was not observed in any single crystal specimens, but observed in only two bicrystal specimens with {112}/111{100}001 and {110}112/{100}001 orientations. The formation of cube texture seems to require the existence of a cube oriented region in the deformed state, and the favourable oriented matrix to allow the growth of such nuclei.     

A texture formation mechanism during electrodeposition

The texture of electrodeposited iron foil has been measured. It was observed that the deposited iron foil had a {110} uvw type texture. If a sufficiently strong magnetic field was applied along the deposited layer during the deposition process, a {110} 001 texture developed from the initial {110} uvw texture, with the 001 axis parallel to the direction of the applied field. An attempt has been made to explain the mechanism of texture development, as well as the effect of the magnetic field during the deposition process.     

Electron microscope study of domains in PbZrO3

The domains in lead zirconate, PbZrO₃, can be classified as two types: The type I domains with the orientation relationship [001]_A//[001]_B, (200)_A//(040)_B and the type II domains with the orientation relationship form of 001_A//210_B, {200}_A//{122}_B.     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

Size-strength effects in sapphire and silicon nitride whiskers at 20° C

Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers. The sapphire whiskers were of 0001, 1¯120, 10¯10, and 10¯11 orientations, while the silicon nitride whiskers were 0001, 11¯20, and 10¯13. Tensile strengths were in the range 45 to 1500 kg/mm², and deformation was found to be purely elastic. The tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations. These empirical equations have been used to deduce possible fracture nucleation mechanisms. It is concluded that, in the case of 0001 sapphire whiskers, fracture nucleation may be due to dislocation pile-ups or interactions, while in the other cases a Griffith flaw mechanism is probably applicable.     

The effect of substrate surface nature on texture formation in nickel oxide

X-ray diffraction was used to study the influence of surface finishing on polycrystalline nickel and its modification with ultra-fine dispersions of CeO2 on crystallographic texture development in NiO scales, grown at 1073 K in 760 torr oxygen for time periods up to75 h. Ni substrate characterized by 100 023 texture and surface with an atomic structure revealed by chemical polishing led to the formation of NiO with 100 013 texture, indicating an epitaxial growth.After applying CeO2 on the Ni surface prior to the oxidation, no essential changes in NiO texture were detected. When the Ni surface was deformed by mechanical polishing, NiO exhibited a fibre texture with a major component of 110 oriented along the growth direction. The presence of CeO2 on this substrate changed the dominant fibre axis to 100. The texture data are discussed in terms of the oxide microstructures and their growth kinetics. In particular, for CeO2-modified NiO scales with complex depth structure, the possible contribution of individual sublayers to the overall measured texture is estimated.     

Dislocation structures in Zr3Al-based alloys

Transmission electron microscopy has been used to investigate dislocation structures in deformed binary and ternary Zr₃Al-based alloys. In the binary alloy deformed at temperatures between 293 and 673 K the dislocations in the Zr₃Al phase consisted of a/31 1 2-type partial dislocations bounding superlattice intrinsic stacking fault on {1 1 1} planes. The {111} a/31 1 ¯2 stacking fault energy was approximately 2mJ m^–2 at 673 K. In binary specimens deformed between 873 and 1073 K cube slip predominated. Dislocations consisted mainly of a/2 1 1 0 pairs separated by antiphase boundary. For this temperature range the {1 0 0} a/201 1 antiphase boundary energy was between 30 and 45 mJ m^–2. Alloying with niobium or titanium was found to increase the {111} a/31 1¯2 stacking fault energy and thus increase the propensity for antiphase boundary-type dissociation.