Klaus W. Richter

Reinvestigation of the binary FeSb phase diagram

Abstract The binary iron-antimony phase diagram was reinvestigated using thermal analysis, and the phase boundaries of the NiAs(B8)-type phase Fe1 + tSb were fixed by support of a pseudo-isopiestic vapor pressure method.

Redetermination of iron dialuminide, FeAl2

The crystal structure of iron dialuminide [Corby & Black (1973). Acta Cryst. B29, 2669-2677] has been redetermined on a single crystal synthesized from the elements by arc melting. The compound crystallizes in the triclinic space group P-1 with 19 atoms per unit cell, one Fe site being on an inversion centre. The crystal structure can be described as an inclusion-plus-deformation derivative of the orthorhombic YPd(2)Si structure type.

Contact materials for III–V semiconductors: phase equilibria of InSb in the ternary system In–Ni–Sb

Abstract The In–Ni–Sb phase diagram was investigated in the compositional region of the compound semiconductor InSb. The phase equilibria were established in two isothermal sections at 440 and 300°C, respectively, by means of EPMA and X-ray diffraction. Using DTA experiments, six invariant ternary phase reactions were identified and a complete reaction scheme was constructed in the respective composition area. The B8 1 -type phase Ni 1± x Sb and the B8 2 -type ζ -phase in the Ni–In system were found to form a continuous solid solution which was studied in detail at 900°C. The lattice parameters of the ternary phase Ni 1± x (Sb y In 1− y ) ( ζ -phase) were determined as a function of composition along a section connecting the two binary melting point maxima.

NiAi1.74Al0.26 and NiSi1.83Ga0.17: Two materials with perfect lattice match to Si

We report on the preparation and characterization of two materials based on cubic NiSi2 (CaF2-type, cF12, Fm3m) that show no lattice mismatch to Si and are thus promising materials for perfect epitaxial films grown on silicon. The perfectly lattice-matched materials are special compositions within the extended solid solution phases NiSi2−xAlx and NiSi2−xGax with x=0.26 for Al and x=0.17 for Ga, respectively. The variations of bulk lattice parameters with the composition were studied by means of x-ray diffraction and the melting behavior of the solid solution phases was investigated by differential thermal analysis. Both phases are thermally stable up to temperatures around 1000 °C. Phase diagram investigations show that the respective phases are in thermodynamic equilibrium with pure silicon. The electrical conductivity of NiSi2−xAlx and NiSi2−xGax was studied on selected bulk samples between 4.2 and 300 K. Both materials show metallic behavior with specific room-temperature resistivities between 23 and ...

Phase relationships in the ternary Ga-Ni-Sb system

Abstract Undesirable chemical reactions between metal contacts and a semiconductor substrate may be prevented by selecting metallization layers which are in thermodynamic equilibrium with the substrate. In order to determine the reaction products resulting from the formation of the Ni–GaSb contact, phase equilibria in the Ga–Ni–Sb system have been established experimentally at 500, 600 and 900°C. For the compound semiconductor GaSb negligible solid solubility of Ni was measured both at 500 and 600°C. In an attempt to clarify the existence of the ternary ϵ-phase in this system, a number of alloys with various compositions were prepared, equilibrated, and examined by XRD, EPMA, and optical microscopy. In addition, the variation of the lattice parameters of the ϵ-phase was determined as a function of composition at 900°C; the results are discussed in terms of the filling of the different lattice positions of the hexagonal unit cell.

On the stability of hexagonal Ge7Nb10

Abstract Our studies on the Ge–Nb system reveal the existence of a hexagonal compound with the composition Ge 7 Nb 10 that is stable with respect to disproportionation and which was found to crystallize in the space group P6 3 /mmc . A hexagonal phase of the approximate composition Ge 3 Nb 5 has been mentioned by different authors but has been commonly regarded as C- or N-stabilized and therefore not included in the binary phase diagram. A single crystal X-ray study of the compound revealed a Mn 5 Si 3 -type based structure where half of the 2b interstitial positions are filled with Ge. X-ray powder diffraction studies and electron probe microanalysis were used to determine the composition ranges of the phases. Various experiments were carried out in order to confirm the thermodynamic stability of this compound and to rule out stabilization by hetero-elements. These studies included the use of different starting materials, different sample preparation techniques and different annealing procedures. The results show strong indications, that Ge 7 Nb 10 is formed as a binary phase which is stable with respect to disproportionation and should therefore be included in the binary phase diagram.

Phase equilibria in the ternary Ga–Pt–Sb system

Abstract The phase relationships of GaSb in the ternary system Ga–Pt–Sb were studied within an isothermal section at 500°C by means of X-ray diffraction (XRD) and electron probe micro analyses (EPMA). Ternary phase reactions were determined using differential thermal analyses (DTA) in the platinum-poor area of the phase diagram. All experimental phase diagram data were combined to construct a complete reaction scheme (Scheil diagram) in the investigated composition area and the liquidus surface was derived based on the results of the DTA measurements.

New Iminodiacetate–Thiosemicarbazone Hybrids and Their Copper(II) Complexes Are Potential Ribonucleotide Reductase R2 Inhibitors with High Antiproliferative Activity

As ribonucleotide reductase (RNR) plays a crucial role in nucleic acid metabolism, it is an important target for anticancer therapy. The thiosemicarbazone Triapine is an efficient R2 inhibitor, which has entered ∼20 clinical trials. Thiosemicarbazones are supposed to exert their biological effects through effectively binding transition-metal ions. In this study, six iminodiacetate-thiosemicarbazones able to form transition-metal complexes, as well as six dicopper(II) complexes, were synthesized and fully characterized by analytical, spectroscopic techniques (IR, UV-vis; 1H and 13C NMR), electrospray ionization mass spectrometry, and X-ray diffraction. The antiproliferative effects were examined in several human cancer and one noncancerous cell lines. Several of the compounds showed high cytotoxicity and marked selectivity for cancer cells. On the basis of this, and on molecular docking calculations one lead dicopper(II) complex and one thiosemicarbazone were chosen for in vitro analysis as potential R2 inhibitors. Their interaction with R2 and effect on the Fe(III)2-Y· cofactor were characterized by microscale thermophoresis, and two spectroscopic techniques, namely, electron paramagnetic resonance and UV-vis spectroscopy. Our findings suggest that several of the synthesized proligands and copper(II) complexes are effective antiproliferative agents in several cancer cell lines, targeting RNR, which deserve further investigation as potential anticancer drugs.

Fractional site occupation of Hf5−xNbxGe4: crystallographic investigation and thermodynamic modeling

Abstract The binary compound Hf 5 Ge 4 (structure type Sm 5 Ge 4 , oP 36, Pnma ) was found to form an extended ternary solid solution Hf 5− x Nb x Ge 4 with 0⩽ x ⩽3.8. This solid solution was investigated by X-ray diffraction employing powder- as well as single crystal methods. Structure refinements at several different compositions within the phase revealed strongly preferred site occupation by Nb at the three crystallographically independent metal sites of the Sm 5 Ge 4 -type structure yielding an almost stepwise substitution mechanism of the two transition metals. Chemical bonding and site occupation are discussed on the basis of extended Huckel calculations performed on Hf 5 Ge 4 , and site volumes (Dirichlet domains) as well as atomic orbital occupations (site potentials) are correlated with the observed substitution mechanism. A thermodynamic model based on the compound energy formalism was developed in order to link the observed substitution mechanism to thermodynamic properties (Gibbs energies) of the different sublattices formed by the crystallographically independent sites.

Thermodynamic investigations in the lanthanum–cadmium system

An isopiestic vapor pressure method was developed which allows vapor pressure measurements in systems containing elements that are air and/or moisture sensitive. With this method, cadmium vapor pressures were determined for the intermetallic compound La13Cd58 and the neighboring two-phase field with LaCd 2 between about 750 and 1020 K. From these, activities and partial molar enthalpies were derived, and integral Gibbs energies of formation were obtained by a Gibbs–Duhem integration. It was found that the compound La13Cd58 shows some non-stoichiometry extending between about 79 and 81.5 at.% Cd. The enthalpy of formation of La13Cd58 was determined by a calorimetric