Phase lead determined growth of 〈100〉 — textured germanium crystallites in eutectic Ag?Ge alloys

Al Si type eutectics (Al Si, Ag Si, Ag Ge, Zn Ge) form 〈100〉 — textured eutectic dendrites of the semiconductor phase when a certain growth rate R and liquid temperature gradient G are held. The spacings of these eutectic dendrites λ follow the relationship: λ = (r_λ ≈︁ 0.2; g ≈︁ 0.5). The exponents of this relationship can be explained by the model of phase lead determined growth. This model is based on the consideration of the analogy to dendrite growth. The Al Si type eutectics have geometrically similar morphologies for determined G^x/R-relations (x = 1.25 in the case of Ag Ge) and the relation λ²R = const. is valid. In this paper the Ag Ge eutectic will be discussed in close detail.     

Microstructure and spacings of directionally solidified metal-semiconductor eutectic alloys

Directionally solidified metal-semiconductor eutectic alloys, representing nonfacetted facetted eutectics, show a variety of microstructures caused by the great differences in semiconductor volume fraction (Zn Ge 7,8 %; Ge ZrGe₂ 98.6 %), the influence of growth rate and temperature gradient at the solid-liquid interface. The Al Si, Ag Si, Ag Ge, Zn Ge, Cu₃Si Si, NiGe Ge, CoGe₂ Ge, Mn₃Ge₂ Ge, FeGe₂ Ge, Mn₁₁Si₁₉ Si, Cu₃Ge Ge, Ge TiGe₂ and Ge ZrGe₂ eutectics habe been investigated. The following three models are applicable for the calculation of the spacings as a function of growth rate and temperature gradient at the solid-liquid interface to certain microstructures: diffusion-determined growth, branchinglimited growth and phase-lead-determined growth.     

On the morphology of <100>-textured Germanium Crystallites in Zn—Ge Eutectic Alloy

Different geometry parameters for the cross-like germanium crystallites (eutectic dendrites) of the Zn-Ge eutectic alloys unidirectionally solidified have been related to the growth rate R and liquid temperature gradient G using linear regression analysis. It has been found that for eutectic dendrite spacing λ, balk length d and balk thickness b follow the relationship of the type w = C_wR^−rwG^−gw; C_w is a constant. The spacing relationship of eutectic dendrites (r_λ = 0.21; g_λ = 0.48) shows a similarity with published experimental and theoretical results on primary dendrite arm spacing (r_λ = 0.25; g_λ = 0.5). It has been shown in terms of a profile ration λ/d that for geometrical similar morphologies the relationship λ²R = const. is valid.     

Metallurgically grown Schottky junction in directionally solidified eutectic Ag–Si alloys

Metallurgically grown M(metal)–S(semiconductor) phase boundaries in directionally solidified Ag Si alloys were investigated relative to their behaviour as Schottky junctions. By the aid of point contacts I/V characteristics have been measured which correspond to these ones of Schottky diodes. The Si crystallites were proved to be n-doped. Reverse breakdown voltages of 8 … 24 V are not incompatible with the purity of the used materials. In forward direction the value of diode factor n = 1.1 … 5 shows the existence of several current flow mechanisms. In order to be able to interpret the characteristics it is necessary to have exact information on the specific resistivity of the Si crystallites and on the content of grain boundaries and dislocations in silicon. Beyond that the complicated shape of Si crystallites prevents the necessary determination of the interface size.     

Sattructural changes during post-ageing of an Al?Zn (15 at.%) alloy at 100 °C studied by positron annihilation,small angele X-ray scattering and microhardness measurements

The positron lifetime τ, the shape parameter of the Doppler-broadened annihilation line S, the microhardness H_V and the Guinier radii r_G are studied in dependence on the ageing time during isothermal ageing of an Al Zn (15 at.%) alloy at 100 °C following a pre-ageing at R.T. for 1 h after the quench. Weak effects in H_V and r_G are interpreted by a transformation of spherical Guinier-Preston zones into ellipsoidal ones. At an ageing time of 10⁴s H_V decreases strongly while r_G starts to increase more rapidly. This behaviour is explained by the transformation of coherent GP zones into semicoherent α′_R-particles. Incoherent part of the α′_R-particle-matrix interface are able to localize positrons resulting in a strong increase of τ and S. The characteristic parameters τ and S of the coherent defect-free GP zones and of the semicoherent α′_R-particles are estimated. It is concluded that positrons can be used as a very sensitive tool in detecting the transformation of coherent particles into semicoherent or incoherent ones.     

Rheological behaviour of lamellar eutectic Al?Al2?Cu elaborated by induction heating

This paper presents solutions to the experimental problems encountered in the elaboration of lamellar Al Al₂Cu or fibrous Al Al₃Ni eutectic samples using the Bridgman technique. The objective is to prepare samples for use in mechanical tests. The investigation of the elaborated structures of Al Al₂Cu (orientation, grain selection, shape of the solid-liquid (S.L.) interface, interlamellar spacing λ…) can then be used to confirm the predicted behavior. Creep tests under constant applied stress σ (from 2 to 5 · 10⁷ N/m²) at temperatures from 300 to 450 °C show:

• – that a stationary state exists (with constant strain rate )
• – the influence of an imperfect orientation
• – the existence of a Bailey-Norton creep law = kσⁿ. This law leads to the possiblity of finding a constitutive equation for high temperatures tests.

     

Growth of Ge1—xSix (x= 0 to 0.5) Single Crystals by a Zone Melting Method

Ge_1—xSi_x graded crystals with 0 < x < 0.66 were grown by a zone melting method in a double ellipsoid mirror furnace. They have a diameter of 9 mm and grown lengths between 27 and 80 mm. Single crystalline regions reached a maximum Si concentration of 50 at%, determined by EDX and ECP measurements. Starting with a Ge seed, a defined concentration profile was obtained by a wedge-shaped arrangement of the feed material. The concentration profiles could be predicted by a simulation program.     

An EPR Study of Scapolite

In single crystals of scapolite from two different localities, three paramagnetic centres are detected by electron paramagnetic resonance (EPR): 1. One isotropic singlet with g_iso = 2.005; 2. One triclinic singlet with g‖ = 2.005 ± 0.001 and g⟂= 2.009; 3. One triclinic sextet with g‖= 2.005 ± 0.001, g⟂ = 2.011; A‖ = 85.4 × 10⁻⁴ cm⁻⁴, A⟂ = 85.3 × 10⁻⁴ cm⁻¹. Centres 1 and 2 can be attributed to colour centres as they are bleached after annealing. Centre 3 can be due to Mn²⁺ (only the central M_s = ± 1/2 transition is observable) most likely substituting for Ca²⁺ The site symmetry must be triclinic but due to Al, Si disorder and mixed Na, Ca composition the different components from magnetically non-equivalent sites are averaged out for many orientations.     

An X-ray diffraction refinement of the crystal structure of natural tetragonal analcime (NaAlSi2O6. H2O)

An X-ray diffraction analysis was performed on a single crystal of natural tetragonal analcime: (Na_0.99K_0.01)/(Al_1.05Si_2.02) O₆/0.99 H₂O, space group I 4₁/acd, a = 13.726(2) Å, c = 13.684(1) Å, V = 2578.1 ų, Z = 16, D_obs = 2.26. Refinement of 260 independent reflections yields R = 0.028 (R_w = 0.033). The mean Si(Al) O distance is 1.636 Å and tetrahedral angle is 109.35°. The framework of tetragonal analcime is topologically the same as the cubic modification.     

The structure of Tetraphenyl Imidodiphosphate,C24H21NO6P2

M_r = 481.24, monoclinic, P 2₁/c, a = 12.009(3), b = 12.305(5), c = 18.993(7) Å, β = = 122.1(1)⁰, V = 2377.2(6) ų, D_x = 1.349 Mgm⁻³, Z = 4. Final R = 0.051 for 2690 independent reflections excluding those with |F₀| < 4 σ(F₀). Intensities were measured with an automatic diffractometer. The two phosphoryl oxygen atoms are in trans position. The acidic hydrogen atom is bonded at the nittogen atom. The molecules form dimers connected by N H … O intermolecular hydrogen bonds. Results are compared with those of the structure of tris(tetraphenylimidodiphosphato)ytterbium (III).     

Structural Changes during Post-Ageing of an Al-Zn (15 at.%) Alloy between 125 °C and 215 °C

The structural changes going on in an Al Zn (15 at.%) alloy postaged between 125 °C and 215 °C after pre-ageing between 20 °C and 90 °C (till start r_s = (20…︁ 55) Å are obtained) were followed by means of XSAS-investigations. The main results are the following:

• 1 An increase of r_s does not favour the growth of the precipitates during the reversion treatment.
• 2 At later reversion times the happening is obviously independent of the pre-history of the samples.
• 3 The integral intensity is decreasing with increase of T_rev, but the mean distance (d)-size (r_G) relation between the precipitates is not changed remarkably up to T_rev ≈ 200 °C in the early reversion stage.

Conclusions from this behaviour are drawn.     

Co-crystal structures of 2,4-diamino-6-phenyl-1,3,5-triazine – 4-chlorobenzoic acid/4-methoxybenzoic acid: Synthesis,structural and Hirshfeld surface analysis

The co-crystal structure of 2,4-diamino-6-phenyl-1,3,5-triazine with 4-chlorobenzoic acid/4-methoxybenzoic acid molecules are explain the link between the dimension and shape of their hydrogen-bonded assembly. The co-crystal structure of 2,4-diamino-6-phenyl-1,3,5-triazine with 4-chlorobenzoic acid/4-methoxybenzoic acid forming a cyclic R₂²(8) ring motif via N–H?O and O–H?N hydrogen bonding interactions, to form a supramolecular heterosynthon. In both the co-crystal structures, self-association of 2,4-diamino-6-phenyl-1,3,5-triazine moieties are connected via N-H^….N base pairs with cyclic R₂²(8) motif form a supramolecular homosynthon. In co-crystal II, the centrosymmetrically paired methoxy group of 4-methoxy benzoic acid form a supramolecular homosynthon via weak intermolecular C-H^….O hydrogen bonds, generating R₂²(6) ring motif. Both the co-crystal structures are stabilized by weak aromatic π-π and C—Cl???π stacking interactions. Hirshfeld surface and fingerprint plots were used to study the intermolecular interactions both of the crystal structures.     

X-ray diffraction studies of glasses in the systems Na2OMeOSiO2 (MeMg,Zn, Ca,Ba)

X-ray diffraction studies of glasses in the following ternary systems have been made: Na₂OMgOSiO₂, Na₂OZnOSiO₂, Na₂OCaOSiO₂ and Na₂OBaOSiO₂. The following heavy atom substitutions have been used: Ag for Na and Ge for Si. The changes in the electron radial distribution curves resulting from AgNa replacement can be explained as amplifications of relatively well-defined NaSi distances, which are nearly the same in all the glasses investigated. The GeSi substitution causes changes which can be explained on the basis of isostructural GeSi substitutions.     

Crystal and molecular structure of N-(Diethylaminothiocarbonyl)-N′-phenyl-benzamidine

The crystal structure of the title compound has been determined by X-ray diffractometer data collected on a CAD-4 diffractometer. C₁₈H₂₁N₃S crystallizes monoclinic, space group P 2₁/n with a = 8.939(1) Å, b = 18.992(3) Å, c = 10.416(2) Å, β = 97.29(2) Å and Z = 4. Least-squares refinement gave a value of R = 0.107 for 2647 observed reflections. The molecule has a configuration which can be described best by Z, E′ and exists in the tautomeric enamine form. The molecules form infinite chains connected by intermolecular N—H … S interactions, with H … S distances of 2.46 Å.     

Structures of Azomethine Imines of the Pyrazolidone-(3)-type, (III) The Structure of 1-[Anthryl-(9)-methylene]-pyrazolidone-(3)-betaine

C₁₈H₁₄N₂O, Pbca, a = 19.541(4) Å, b = 14.800(2) Å, c = 9.572(3) Å, Z = 8, U = 2768.3 ų, D_x = 1.32 g cm⁻³, μ(MoKα) = 0.93 cm⁻⁻¹, crystal size 0.5 × 0.2 × 0.1 mm, colourless. Final R = 0.077 for 1177 independent reflections excluded those with |F₀| < 8 σ(F₀). The intensities were measured with an automatic diffractometer. The azomethine imine unit of the molecule has a geometry in approximate agreement with a polymethinic electron structure. The conjugation of the azomethine imine unit with the anthryl unit is only small. The anthryl ring and the five membered pyrazolidone ring include a dihedral angle of 65.4°. The main intermolecular forces are C–H … N hydrogen bridges.     

Electrical and optical properties of CuGaTe2

The electrical and optical properties of CuGaTe₂ single crystals were investigated by resistivity and Hall effect measurements in the temperatur range T = 77… 300 K and optical transmission measurements in the temperature range T = 20… 300 K at photon energies hν = 1.15…1.50 eV. All samples were p-type conducting due to shallow acceptors with ionization energies E_A1 ≈︁ 10⁻³ eV and concentrations N_A1 ≈︁ p = (2…4). 10¹⁸ cm⁻³. The absorption spectra could be described by simultaneous consideration of acceptor - to - conduction band transitions with E_A2 = 360 meV and N_A2 ≈︁ 10²² cm⁻³ and valence band - to - conduction band transitions with E_G = 1.24 eV at room temperaure. The temperature coefficient of the fundamental edge is dE_G/dT = −4.0. 10⁻⁴ eV/K. The results are discussed with regard to some general trends found in the Cu-III–VI₂ compounds.     

Chemical Effects at the Deposition of Germanium onto Yttrium-Iron-Garnet Single Crystals

At the deposition of Ge onto YIG-crystals by uhv-evaporation a sharply limited temperature T_st was found with no further deposition above this point. Several experimental facts suggest the following model: incoming Ge atoms pick out oxygen atoms from the substrate and reevaporate as GeO. The step temperature T_st is defined by an equilibrium of the incoming Ge vapour rate, r_Ge, and the GeO evaporation rate. For r_Ge = 3 monolayers/sec we found T_st = 510°C.     

Study of the complex vibrational spectra of natural mesolite

The vibrational spectra of the natural zeolite, mesolite (locality Akureyri-Island) were measured in the infrared (200—400 cm⁻¹) and the far infrared — FIR (40—400 cm⁻¹) regions: the infrared reflectance (200—1400 cm⁻¹) and Raman scattering (50—3600 cm⁻¹) spectra of the polycrystalline material were also measured. The Schimanouchi GCCC, BGLZ, and LSMA programs were used to calculate the force constants and vibrational frequencies of the Si O, Al O, O H, cation-oxygen, O Si O, O Al O, H O H bonds and libration of H₂O and Si(Al) O Si on the basis of the symmetry coordinates. The KKK-1 program (Petzelt, Kroupa) was used to calculate the dispersion curves of the complex refractive index for both parts of the complex dielectric permittivity in the whole measured wavenumber region. The bands in the spectra were assigned to the vibrations of the individual bonds and structural groups of the mesolite on the basis of theoretical calculations.     

Optical absorption of Fe3+ Ion in LiF crystals

The absorption spectrum of LiF—Fe³⁺ single crystals was investigated at liquid nitrogen temperature. Six new absorption bands, unobserved earlier in other works, were found, which were located at 11 200, 16 000, 22 700, 27300, 30 500, and 41 900 cm⁻¹. The spectrum was interpreted in the cubic cristalline field approximation with D_q = 1397 cm⁻¹, B = 657 cm⁻¹, C = 3226 cm⁻¹. Above mentioned bands were assigned to the transitions from a ground state ⁶A_1g to the levels ⁴T_1g(G), ⁴T_2g(G), ⁴A_1g(G) (⁴E_g), ⁴E_g(D), ²T_1g(F), and ⁴T_1g(F), respectively.