Phase Relations and Crystal Structures in the Ternary Systems Sr‐{Ag, Au}‐{Si, Ge}

Abstract

Abstract. Phase equilibria in the isothermal sections of the ternary systems Sr-{Ag,Au}-{Si,Ge} were determined in the (Si) or (Ge) rich part up to 33.3 at % Sr after annealing at 700°C (Sr-{Ag,Au}-Ge) or 800°C (Sr-{Ag,Au}-Si). Tentative liquidus projections were constructed for the Si,Ge-rich part of all the four phase diagrams. These systems are characterized by a series of ternary compounds, exhibiting in some cases extended homogeneity regions at a constant Sr content. Compounds in the Si,Ge-rich region essentially form along two sections: at 33.3 at % Sr (AlB 2 -family) and at 20 at % Sr (BaAl 4 -family of structure types). The crystal structures of the novel equilibrium phases were derived by X-ray single crystal diffraction:

Order and disorder in the modulated phase hp‐Mg9Ge5.1

“…Thus, the observation is compatible with a monotropic (irreversible) phase transition. After the heating cycle, X‐ray powder diffraction data exhibit only diffraction lines of thermodynamically stable (anti‐)CaF 2 ‐type Mg 2 Ge( cF 12) [2–5,8] and Ge( cF 8) [18–20] . Thus, the experiments are consistent with a decomposition of Mg 9 Ge 5.1(2) at 496(5) K and atmospheric pressure confirming that the compound is a metastable high‐pressure phase at ambient pressure.…”

“… Differential scanning calorimetry measurement of the high‐pressure phase Mg 9 Ge 5.1(2) at ambient pressure. The effect at 496(5) K is attributed to the exothermal decomposition into CaF 2 ‐type Mg 2 Ge [2–5,8] and diamond‐type germanium [18–20] …”

“…The effect at 496(5) K is attributed to the exothermal decomposition into CaF 2type Mg 2 Ge [2][3][4][5]8] and diamond-type germanium. [18][19][20] . The given directions refer to the unit cell of an Er 3 Ru 2 -type arrangement [21] which is indicated in white.…”

Structure variations within RSi2 and R 2Si3 silicides. Part II. Structure driving factors

“…The +II oxidation state [e(R) = 2] of the alkaline earth metals as well as of Eu and Yb is a special case and represents an ionic state with full charge transfer of the outer valence shells. For this group, a [Si 6 ] 10À ring was reported (von Schnering et al, 1996;Cardoso Gil et al, 1999;Peter et al, 2013;Zeiringer et al, 2015), which corresponds to 34 electrons and a nominal charge of À1.67 for Si, see x3.6.5. We already discovered that this configuration only arises for the divalent R elements in combination with the noble metals Ag and Au.…”

BaAl4 derivative phases in the sections {La,Ce}Ni2Si2–{La,Ce}Zn2Si2: phase relations, crystal structures and physical properties

“…This idea comes from the fact that an alloy with stoichiometric composition CeNi 2 Si 2 does not show any changes in the powder diffraction spectra in the as-cast state, and after annealing at 1000°C for 4 days. An example of structural evolution at a constant temperature can be found in the Sr-Au-Ge system 38 …”