SPP 1415 Subproject - Phase relations and kinetics of phase formation of non-equilibrium-solids of pnicogens and chalcogens - Mechanisms of structure formation, synthesis and characterization of element allotropes and compounds

Basic data for this project

Description

In this project, different methods are summarized in the EnPhaSys-concept: quantum chemical modeling and determination of the energy landscape of investigated systems, analysis of phase formation, and inorganic solid state synthesis. This concept is applied to determine the thermodynamic relations of metastable and stable phases, the kinetics of phase formation and transformation of allotropes and compounds of pnicogenes and chalcogenes, and the processes of nucleation and seed growth of the non-equilibrium phases.Three sub-projects are to be processed:A) Mechanisms of phase formation and transformation of allotropes of Phosphorus and Arsenic; investigation of nucleation and seed growth processes by using in-situ-NMR, in-situ-neutron diffraction, and gas phase analysisThis partial project shall fully clarify the thermodynamic relations of allotropes of the elements phosphorus and arsenic. The mechanisms of phase formation and transformation of allotropes are to describe, and the effect of mineralization is to elucidate. Complementary investigations of the kinetics of phase formation by time dependent, isothermal pressure measurements, solid state and gas phase NMR spectroscopy, and powder neutron diffraction of the crystalline phases growth supply information on the identification of formation mechanism and on the nucleation and seed growth processes of the allotropes.B) Identification of metastable and stable candidates showing polymorphism of polyanionic phases MX2 and MXY (X, Y = P, As, Se, Te) and their directed synthesisOrdering phenomena and thus the relations of polymorphism of binary and ternary compounds MX2 and MXY consisting of polyanionic substructures with dumbbells X-X and X-Y shall be investigated. By using the EnPhaSyn concept there is the potential of ordering the polymorphic phases by thermodynamic stability and directing the synthesis in a systematic way depending on different phase stabilities.C) Investigation of order-disorder phenomena of ternary intermetallic LAVES phases; determination of stability criteria of ordered, partially ordered, and disordered phases; directed synthesisTernary LAVES phases commonly exist with random distribution of components and therefore show distinct disordering. Besides these obviously stable phases a plethora of ordered compounds of various compositions is conceivable. It is aim of the project to determine their stabilities and to analyze the phase formation. Based on the discovery of the new representative of ordered LAVES phases, A4B7B‘, by the EnPhaSyn concept, more ordered metastable transition metal - arsenic compounds shall be synthesized. A comparison of the stabilities and the conditions for directed growth of phases of different ordering is intended.