T. Gödecke

Investigation of the AlMgSi system by experiments and thermodynamic calculations

Abstract The enthalpies of formation and fusion as well as the heat capacity of Mg 2 Si were measured calorimetrically. The Al corner of the AlMgSi ternary system was investigated by DTA and optical micrography. A few points of the solvus of the Al(f.c.c.) solid solution were determined by dilatometry. The results of these experiments, together with literature data, were used to redetermine a complete set of analytical descriptions of the Gibbs energies of all stable phases of the AlMgSi system.

Zur struktur der mischung Nickel-Germanium

Zusammenfassung Das Phasendiagramm Ni-Ge wurde teilweise neuuntersucht. Die Kristallstrukturen von Ni 5 Ge 2 , Ni 2 Ge(r), Ni 5 Ge 3 und Ni 19 Ge 12 wurden analysiert. Die Ergebnisse werden diskutiert vom Standpunkt des Zwei-Elektronenkorrelationen-Modells.

Konstitution einiger mischungen des platins mit b-elementen (B = Sn, Sb, Te)

Abstract The phase diagrams of the systems Pt-Sb, Pt-Sn-Sb, Pt-Te have been partially investigated by thermal analysis and X-ray diffraction, and several new phases have been found. The structures of Pt3Sb2, PtSn1.3Sb0.7, PtSnSb, PtSn1.2Sb1.8, PtTe, Pt3Te4, Pt2Te3 have been analysed. The structures are discussed in terms of assumptions regarding the spatial correlation of the electrons.

Über die mischungen palladium-thallium und platin-thallium

Zusammenfassung Die Phasendiagramme Pd-Tl und Pt-Tl wurden ausgearbeitet. Die noch unbekannten Kristallstrukturen von Phasen in diesen Legierungssystemen wurden analysiert. Die Phasen Co6GaGe3 und Fe3Ge2(r) sind isotyp zu Pd13Tl9, und Pt3In2 ist isotyp zu Pt3Tl2. Die Bindung in den Strukturen wird diskutiert.

Stable and metastable phase equilibria of the In-Se system

The In-Se phase diagram was redetermined using DTA, x-ray analysis, optical microscopy, TEM, and scanning electron microscopy. In9Se11 and In5Se7 are stable phases at stoichiometric composition and βIn2Se3 was observed at 59.6 at % Se. ΒIn2Se3 decomposes at 198 °C into γIn2Se3 and In5Se7. Alloy melts between 33 and 54 at.% Se exhibit a strong tendency for undercooling. Between 50 and 60 at. % Se, the InSe, In6Se7, or In2Se3 phases solidify directly from the undercooled melt, and the formation of In5Se7 and In9Se11 is suppressed while applying cooling rates between 2 to 10 K/min. The respective undercooled states and metastable phase equilibria are provided.

Die zustandsdiagramme Silber-Germanium-Silizium Und Gold-Germanium-Silizium

Zusammenfassung Durch thermische Analysen und metallographische Untersuchungen sind die Schmelzgleichgewichte der Systeme Silber-Germanium-Silizium und Gold-Germanium-Silizium ermittelt worden. Kennzeichnend ist in beiden Fallen eine Rinne der binaren eutektischen Kristallisation, die sich zwischen den Eutektika der binaren Randsysteme Silber-Germanium und SilberSilizium bzw. Gold-Germanium und Gold-Silizium durch das ternare Gebiet erstreckt. Im System Ag-Ge-Si fallt die Temperatur der binaren eutektischen Konzentration kontinuierlich vom Randsystem Ag-Si zum Randsystem Ag-Ge ab, wahrend sie im System Au-Ge-Si bei etwa 78 At.-% Au und x Ge x Si = 2 3 ein Minimum durchlauft. Die Schmelzgleichgewichte werden im Zusammenhang mit den Bedingungen fur eine amorphe Erstarrung diskutiert.

Phase and Interface Stability Issues in Chalcopyrite-Based Thin Film Solar Cells

How stable are Cu(In,Ga)Se{sub 2} solar cells? CuInSe{sub 2} is known also as an ionic Cu conductor and the Cu-In-Se system has a rich phase diagram. Two stability-related problems are treated from a thermodynamic point of view: (a) Cu migration, (b) phase segregation. The authors show how Cu migration imparts self-stabilization on the system. Based on recently reported results on the room temperature phase diagram of CuInSe{sub 2}, they explain why an overlayer of an ordered vacancy compound (OVC) is not to be expected to appear as a separate phase, even though the surface composition corresponds to that of the I-III{sub 3}V{sub 5} OVC compound.

Phase Equilibria at Internal Interfaces of Icosahedral Al–Mn–Pd

Highly faceted microholes (voids) in icosahedral Al-Mn-Pd quasicrystals form during annealing at temperatures between 750 and 830°C via classical Ostwald ripening. The specimens were single-phase icosahedral with a composition of Al 71 Mn 9 Pd 20 . If such a specimen containing voids is cooled to room temperature with a constant cooling rate of typically 0.6 to 5 K/min, the facets of the voids are frequently found to be decorated by a different material. The decorations have typically a morphology similar to fractals. Specimens rapidly quenched after isothermal heat treatments around 830°C never showed similar decorations. By X-ray microanalysis in a scanning electron microscope it has been found that this decoration material is considerably poorer in Al-content that the icosahedral phase, namely: Al 60 Mn 10 Pd 30 . Accordingly, these decorations are precipitations at the surfaces of voids inside a single-phase icosahedral matrix. This implies that these decorations are formed at the void surfaces bya diffusion induced local equilibrium. The local equilibrium can be understood on the basis of the equilbrium results in a single icosahedral phase.