Early Transition Metal Arsenides, Germanides and Gallides

Mixed early transition metal compounds, in particular ternary calcogenides and pnictides, stabilized by differential fractional site occupation are a steadily growing class of materials. These compounds combine mixed site occupation on the metal sites (substitution among the transition metals) with strong variations of the observed fractional site occupations at crystallographically independent sites and thus represent a special class of entropically stabilized materials. For a better understanding of the factors involved in the stabilization of this group of materials, much additional work is to be done. This includes the synthesis and characterization of new ternary compounds and solid solutions stabilized by differential fractional site occupation as well as the detailed investigation of chemical bonding employing band structure calculations and the thermodynamic modeling of the observed internal distribution equilibria. A better understanding of the mechanisms governing the site preferences among the different transition metals should lead to the possibility to predict differential fractional site occupation in a more quantitative way. The exploratory synthesis and structural characterization of compounds and solid solution phases in the systems M- M`-A, with M and M` are early transition metals (in particular Zr, Hf, Nb and Ta) and A = Ga, Ge or As will be the main goal of the current project. Experimental work will include the application of various high temperature methods for sample preparation, the structure determination by single crystal X-ray diffraction and the refinement of powder diffraction data. New compounds will be investigated in detail for substitution mechanisms and site preferences connected with the partial ordering phenomena. The application of theoretical tools will be focused on the improvement of site preference prediction based on electronic structure calculations and the estimation of the connected driving forces employing thermodynamic models.

Mixed early transition metal compounds, in particular ternary calcogenides and pnictides, stabilized by differential fractional site occupation are a steadily growing class of materials. These compounds combine mixed site occupation on the metal sites (substitution among the transition metals) with strong variations of the observed fractional site occupations at crystallographically independent sites and thus represent a special class of entropically stabilized materials. For a better understanding of the factors involved in the stabilization of this group of materials, much additional work is to be done. This includes the synthesis and characterization of new ternary compounds and solid solutions stabilized by differential fractional site occupation as well as the detailed investigation of chemical bonding employing band structure calculations and the thermodynamic modeling of the observed internal distribution equilibria. A better understanding of the mechanisms governing the site preferences among the different transition metals should lead to the possibility to predict differential fractional site occupation in a more quantitative way. The exploratory synthesis and structural characterization of compounds and solid solution phases in the systems M- M`-A, with M and M` are early transition metals (in particular Zr, Hf, Nb and Ta) and A = Ga, Ge or As will be the main goal of the current project. Experimental work will include the application of various high temperature methods for sample preparation, the structure determination by single crystal X-ray diffraction and the refinement of powder diffraction data. New compounds will be investigated in detail for substitution mechanisms and site preferences connected with the partial ordering phenomena. The application of theoretical tools will be focused on the improvement of site preference prediction based on electronic structure calculations and the estimation of the connected driving forces employing thermodynamic models.