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.     

Evidence for collective excitations in superconducting tin whiskers

Based on the assumption that a phase-slip center in a clean quasi-one-dimensional superconductor excites a collective oscillation, the time-averaged value of the electrochemical potential of quasiparticles is calculated. At larger distances from the phase-slip center, swings below (or above) the electrochemical potential _p of the Cooper pairs. This makes it possible to understand the unexpected results of previous measurements.     

Study of the zero-field magnetic ordering, charge fluctuation and trapping in the oxo-bridged heterometallic acetylacetonate complex Fe3YO6R3[Y11(C5O2H7)33]; (R = C5H7)

The Mössbauer, magnetic susceptibility and EXAFS data for the oxo-bridged heterometallic acetylacetonate Fe₃YO₆R₃[Y₁₁(C₅O₂H₇)₃₃] (R = C₅H₇) are analyzed in terms of a bound-to-free model describing the transition from the state of delocalized valence, denoted Fe_deloc ^(3–)+, in the magnetically disordered paramagnetic complex at 300 K to the states of localized valence, denoted Fe_loc ²⁺ and Fe_loc ³⁺, in the magnetically ordered complex at 4.2 and 77 K.     

Low-temperature specific heat of YBa2Cu3O7, YBa2Cu3O6, Y2BaCuO5, YBa3Cu2O7, BaCuO2, and CuO

We have measured the low-temperature specific heat (1.3T20 K) and the dc magnetic susceptibility (100T250 K) of eight samples of the high-T _c superconductor Y _x Ba_3–x Cu₃O_7– (x=0.9, 1.0, 1.1) and of two samples of nonsuperconducting YBa₂Cu₃O₆₊. We have also performed specific heat measurements on the possible impurity phases: YBa₃Cu₂O₇, Y₂BaCuO₅, CuO, and BaCuO_2+x . The superconducting samples all have a nonzero, sample-dependent linear term * and an upturn inC/T at very low temperature. We show that this anomalous behavior is at least partly due to the presence of a small amount (1%) of BaCuO_2+x impurity phase in the measured samples. This is evidenced by the correlation between * and the Curie component of the susceptibility, which is proportional to the amount of paramagnetic impurities.     

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.     

Radiofrequency size-effect measurements of the electron scattering frequency in cadmium

Precise parallel- and tilted-field radiofrequency size-effect measurements of the temperature dependence of the electron scattering frequency v(T) have been made on symmetric orbits on the first-, second-, and third-band Fermi surface sheets in samples with normals 11\-20 and 10\-10. The limiting point measurements on the third-band lens near 0001 provide the clearest evidence for a T ² contribution to v(T) that is the right order of magnitude for electron-electron scattering in cadmium. In parallel field measurements on orbits on the first and second bands (including a broken orbit) we find v(T) T ² + T ³. On these orbits the values for are 5–20 times larger than for the limiting point and other orbits on the third band. The temperature dependence of v(T\> 2 K) on extremal, limiting point, and open orbits on the second- and third-band Fermi surface sheets can be well accounted for by a simple plane wave model for electron-phonon intersheet scattering. This contribution to v(T) turns on approximately as exp (–T _t /T) above T _t /10, where T _t is the minimum gap temperature on the orbit for intersheet scattering by quasi-transversely polarized phonons. The fitted gap temperatures as well as the other parameters of the plane wave model agree well with the known dimensions of the Fermi surface of cadmium. While clear evidence is lacking, we note that this intersheet scattering model can also be used to explain the large T ² coefficients obtained for the first- and second-band orbits, where, in fact, one has gap temperatures T _t smaller than 1 K.Supported by the Fonds National Suisse de la Recherche Scientifique.     

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.     

Mechanical relaxation of 4 wt% Y2O3-ZrO2 tetragonal single crystals

The mechanical relaxation was examined by a resonance piezoelectric method for a 3.5 wt % Y₂O₃-ZrO₂ polycrystal and 4 wt% Y₂O₃-ZrO₂ tetragonal single crystals with orientations in the 100 and 111 directions. The relaxation was observed for the 111-oriented crystal, but not for the 100-crystal. The results indicated that the relaxation was active only for the elastic compliance, S₄₄, and inactive for (s ₁₁–s ₁₂). The amplitude of the anelastic relaxation measured for the polycrystalline and the 111-crystal body was 4.2 × 10^–12 m²N^–1 and 6.7×10^–12 m² N^–1, respectively. An observed broad relaxation peak suggested that complex processes exist even in single crystals.     

Thermal Conductivity of the Four-Leg Spin-Ladder System La2Cu2O5 Single Crystal

We have investigated the magnetic susceptibility, , and the thermal conductivity, , in magnetic fields for the four-leg spin-ladder system La₂Cu₂O₅ single crystal. The in a magnetic field parallel to the ladder exhibits a kink at 130 K in correspondence to the magnetic ordering. The along the ladder exhibits a peak at 25 K and a shoulder at 14 K, which are probably related to the thermal conductivity due to magnons, _magnon, and that due to phonons, _phonon, respectively. The perpendicular to the ladder, on the other hand, exhibits only one broad peak related to _phonon. The observed large anisotropy of has been explained based upon the anisotropy of _magnon.     

Texture study of two molybdenum shaped charge liners by neutron diffraction

The textures of two different conical shaped liners, fabricated by the same forging processes from arc-cast and powder-sintered ingots, were investigated by using neutron-diffraction measurements and three-dimensional orientation-distribution-function (ODF) analysis. The major textures of both liners could be described by the (1 1 1) uv w and (1 0 0) u v w type. The two liners had essentially identical texture at the 8 cm position (measured from the base of the cone) with strong sheet-type texture components, i.e. (1 1 1) ¯1 0 1, (1 1 1) ¯1 1 0 and (1 0 0) 0 1 1. However, the dominant textures at the 3 cm positions were 1 1 1 and 1 0 0 fibre textures with the fibre axes oriented parallel to the normal direction in both liners. A strong cube texture was observed at the 3 cm position of the arc-cast liner but it was not observed for the powder-sintered liner. The arc-cast liner had a generally higher degree of texture than the powder-sintered liner.     

Flux motion in anisotropic type-II superconductors nearH c 2 with arbitrary vortex orientation

Flux motion in anisotropic type-II superconductors near H_{c 2} is studied in the framework of the time-dependent Ginzburg-Landau (TDGL) theory for the case that the average flux densityB is oriented in an arbitrary direction relative to the principal axes of the sample. The linearized TDGL equation for a uniformly translating order parameter is solved and expressions for all elements of the flux-flow resistivity tensor _ij (including the off-diagonal Hall elements) are obtained. The diagonal elements _ii show the angular scaling property that _ii(B) = _ii(B/H_{c 2}(, ø)), whereas the Hall elements _ij (i j) have additional angular dependences that are not contained in H_c2. For the case that the normal state Hall elements _ij ⁽ⁿ⁾ B _k with i j k, the ratios _ij/ _ij ⁽ⁿ⁾ are functions of B/H_c2 (, ) only.     

Phase decomposition of liquid-quenched β-type Ti-Cr alloys

Phase decomposition behaviour of liquid-quenched (bcc) type Ti-Cr alloys was investigated by means of transmission electron microscopy and hardness measurements. It was found that decomposition of to ₁ (Ti-rich, bcc) + ₂ (Ti-lean, bcc) takes place in the intermediate composition range of the Ti-Cr system. This experimental result proves the theoretical prediction made by Menon and Aaronson, but the observed ₁ + ₂ two-phase field expands towards higher temperatures than the predicted binodal line. The coherent ₁ + ₂ two-phase state exhibits the so-called 100 modulated structure and it was concluded that the formation of such a structure is a result of spinodal decomposition of the -phase. We obtained time-temperature-transformation (TTT) diagrams of -type Ti-30, 40 and 50 at % Cr alloys. A typical sequence of structural change is coherent ₁ + ₂ incoherent ₁ + ₂ incoherent ₁ + ₂ + grain boundary precipitates stable state of + TiCr₂ or + TiCr₂. Not all the states in the above sequence appear, depending on alloy composition, liquid-quenching rate and ageing temperature.     

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.     

Deformation in spinel

Stoichiometric MgAl₂O₄ spinel was deformed in compression at temperatures from 1790 to 1895 C and the dislocation structures analysed by transmission electron microscopy. {1 1 1}1 1 0 slip was observed on both the primary and cross-slip systems, and there was much secondary slip as well; all six 1 1 0 Burgers vectors were present in electron micrographs. This secondary slip leads to very high work-hardening rates, approximately/70 at 1790 C, where is the shear modulus. Since it is known that deformation in nonstoichiometric (alumina-rich) spinel crystals occurs by {1 1 0}1 1 0 slip, the electrostatic and geometric aspects of 1/4 110 dislocations moving on {1 1 1} and {1 1 0} planes are considered in some detail. It is porposed that the octahedral cation vacancies present in non-stoichiometric spinel diffuse to dislocations during deformation and thus favour {1 1 0} slip.     

Relationship between deposition and recrystallization textures of copper and chromium electrodeposits

The 100, 111 and 110 textures of copper electrodeposits obtained from copper sulfate baths changed to the 100, 100 and textures, respectively, after recrystallization. The textures of chromium electrodeposits obtained from the standard Sargent bath remained unchanged after recrystallization. The results are in agreement with the prediction of the strain energy release maximization model, in which the recrystallized grains orient themselves so that their minimum elastic modulus direction can be parallel to the absolute maximum internal stress direction due to dislocations in the non-recrystallized grains.     

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.     

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.     

Preparation of rod-shaped BaTiO3 powder

Rod-shaped BaTiO₃ powder particles have been prepared from rod-shaped TiO₂ ·nH₂O and BaCO₃ in molten chloride. The morphology of BaTiO₃ particles was studied referring to the effects of the chemical species of the starting titanium compound, amount of chloride, particle size of the titanium compound and reaction conditions, and the preparation condition of rod-shaped BaTiO₃ has been determined: i.e., large TiO₂ ·nH₂O particles were heated at 700°C in molten salt with an equal amount of BaTiO₃. This condition was effective in suppressing the formation of BaTiO₃ by a solution-precipitation process as well as the deformation of either TiO₂ ·nH₂O or BaTiO₃, which are responsible for the formation of equiaxed BaTiO₃ particles. The obtained rod-shaped BaTiO₃ particles had a cubic symmetry. Electron diffraction analysis showed that the following topotactic relation is retained; 0 1 0_{potassium tetratitanate} 0 1 0_{hydrated titania} 1 0 0_anatase 1 0 0_{barium titanate}     

A Monte Carlo Study of Disorder in the High Pressure Mixed Crystal N2-Ar

In order to obtain a better notion of the experimental results in our laboratory, Monte Carlo calculations have been performed of the N ₂-Ar crystal on the N ₂-rich side, in the p-T region where the and phases exist in pure N ₂. Considering the enthalpy, the system prefers the Ar atoms to be located on the sphere positions. The * phase is present for mixtures down to but is most likely metastable. The *-* transition shifts to lower temperatures with decreasing . The 2 ^nd order transition within the phase continues to exist to even smaller . In contrast to the * -* transition, the transition temperature for the 2 ^nd order transition does not shift to lower temperatures. For a mixture of it is within 5 K from the pure 2 ^nd order transition at a pressure of 7.0 GPa.     

On the mechanism of feathery crystallisation of aluminium

The growth of twinned crystals of aluminium on solidification is discussed with reference to the structure of the growing tip. It is shown that one must differentiate between two types of 112 growth directions in the twin boundary. Normally, all the tips grow in the same type of 112 growth direction and this particular type may give the tip a favourable shape, possibly by producing a sharp edge. If a tip is growing in a less favourable 112 direction, the favourable type can be established by the twins changing sides. This is observed to occur regularly in the continuous casting method according to Hunter. The re-entrant edge mechanism is not supported by the present results.