Melting and homogeneity in germanium–silicon alloys and a modified micro-manufactured assembly for stable high pressure and temperature measurements

Odling

et al. 2015

Angew Chem Int Ed

Alloy and nitride solid solutions are prominent for structural, energy and information processing applications. There are frequently however barriers to making them. We remove barriers to reactivity here using pressure with a new synthetic approach. We target pressures where the reasons for cubic endmember nitride instability can become the driving force for cubic nitride solid solution stability. Using this approach we form a novel rocksalt Mg0.4 Fe0.6 N solid solution at between 15 and 23 GPa and up to 2500 K. This is a system where, neither an alloy nor a nitride solid solution form at ambient conditions and bulk MgN and FeN endmembers do not form, either at ambient or at high pressure. The new nitride is formed, by removing endmember lattice mismatch with pressure, allowing a stabilizing redistribution of valence electrons upon heating. This approach can be employed for a range of normally unreactive systems. Mg, Fe and enhanced nitrogen presence, may also indicate a richer reaction chemistry in our planets interior.

mentioning

confidence: 99%

Creating Reactivity with Unstable Endmembers using Pressure and Temperature: Synthesis of Bulk Cubic Mg_0.4Fe_0.6N

Odling

et al. 2015

Angew Chem Int Ed

“…Furthermore, the melting points are virtually identical at 17 GPa, which serves as an additional barrier against segregation (Figure ). In contrast, at ambient pressure, despite the four criteria for solid solution being formally fulfilled, the more than 500 K melting point difference between Si and Ge leads, in actuality, to profound segregation effects. This makes extended homogeneous solid solution formation extremely difficult, especially on the Ge-rich side, because of the larger segregation coefficients for Ge-rich compositions. , The impetus for synthesis and promise of obtaining technologically important, tunable novel solid solutions are reinforced by a host of recent experiments and calculations on the preparation, stability, and optoelectronic properties of Si and Ge phases. − Pure Ge obtained at ambient pressure from above 10–12 GPa is tetragonal ( P 4 3 2 1 2) and is calculated to exhibit a direct band gap …”

Section: Introductionmentioning

confidence: 96%

Dense Si_xGe_1–x (0 < x < 1) Materials Landscape Using Extreme Conditions and Precession Electron Diffraction

Koch‐Müller

et al. 2014

Inorg. Chem.

High-pressure and -temperature experiments on Ge and Si mixtures to 17 GPa and 1500 K allow us to obtain extended Ge-Si solid solutions with cubic (Ia3) and tetragonal (P4(3)2(1)2) crystal symmetries at ambient pressure. The cubic modification can be obtained with up to 77 atom % Ge and the tetragonal modification for Ge concentrations above that. Together with Hume-Rothery criteria, melting point convergence is employed here as a favored attribute for solid solution formation. These compositionally tunable alloys are of growing interest for advanced transport and optoelectronic applications. Furthermore, the work illustrates the significance of employing precession electron diffraction for mapping new materials landscapes resulting from tailored high-pressure and -temperature syntheses.

“…An XRD pattern from a sample extracted from a pellet, also indexed to the cubic rocksalt ${Fm\bar 3m}$ structure with the bulk Mg 0.4 Fe 0.6 N composition, is shown in Figure 5. In contrast to the 15 to 23 GPa experiments, in an ambient and four lower pressure experiments to 3 GPa and 1500 K on magnesium, iron, iron nitride, nitrogen and sodium azide containing mixtures (see also the Supporting Information containing more detailed experimental description) using tube furnace, piston cylinder22 (Helmholtz Centre Potsdam) and MAX80 press23 (DESY, Deutsches Elektronen Synchrotron, Hamburg) devices, only iron, iron nitride, magnesium, magnesium nitride and magnesium oxide result.…”

mentioning

confidence: 99%

Creating Reactivity with Unstable Endmembers using Pressure and Temperature: Synthesis of Bulk Cubic Mg_0.4Fe_0.6N

Odling

et al. 2015

Angewandte Chemie

Alloy and nitride solid solutions are prominent for structural, energy and information processing applications. There are frequently however barriers to making them. We remove barriers to reactivity here using pressure with a new synthetic approach. We target pressures where the reasons for cubic endmember nitride instability can become the driving force for cubic nitride solid solution stability. Using this approach we form a novel rocksalt Mg0.4Fe0.6N solid solution at between 15 and 23 GPa and up to 2500 K. This is a system where, neither an alloy nor a nitride solid solution form at ambient conditions and bulk MgN and FeN endmembers do not form, either at ambient or at high pressure. The new nitride is formed, by removing endmember lattice mismatch with pressure, allowing a stabilizing redistribution of valence electrons upon heating. This approach can be employed for a range of normally unreactive systems. Mg, Fe and enhanced nitrogen presence, may also indicate a richer reaction chemistry in our planets interior.