Electron Poor Materials Research Group
EPMRG
Central idea
Complex structured semiconductors from “diluting” the abrupt metal-nonmetal transition in the Periodic Table when going from group III (13) to group IV (14) elements
Central questions:
What are (feasible) compositions, structures, bonding motifs (mechanisms of band gap opening) of such semiconductors? Properties?
-SiB3
Refractory semiconductors (boron, (B-C), B-Si, B-Ge)
Thermoelectric semiconductors (Zn-Sb, Al-Si, Al-Ge)
Larger band gaps (> 1 eV)
Narrow band gaps (< 0.5 eV)
Common features: complex crystal structures (various forms of disorder, large unit cells)
→ low (lattice) thermal conductivity
Electron poor bonding patternsCharge density/bonding analysis
Boron: bonding patterns, ground state?
-B28 High pressure modification (Dubrovinski, van Smaalen)
-B12 (not completely conclusive)
-boron (disordered)
Synthesis of and -boron crystals by using metal fluxes (Pt, Pd, Ni)Low temperature crystallization of -boron?
ZnSb
B-Si
-SiB3
Zn2Sb2 rhomboid ring: multi center bonded entity (4e4c)
Si42+
B122-
B-Si
-SiB3
-SiB3
Disordered, complex
B-Ge
empty
SiB6
Al-Si Al-Ge
empty, but metastable phases are knownempty
Theory
- Modeling of B-C, B-Si, B-Ge, Al-Si, Al-Ge systems
- Polarity of frameworks, quantification of polarity, distinction to Zintl phases?
Zn-Sb Zn-Te Zn-Se
Mg-Sb
Li-Sb
-Support of experimental bonding (charge density) analysis
- Modeling of properties
- Universal transition (structures & bonding patterns) between group 13&14?
Old (and safe) stuff:
- Zn5Sb4In2: high temperature structures and properties
- ZnSnSb2-2InSb: detailed property determination around MI transition
New synthesis activities
Everything leading to new III-IV combinations
Oxidation of Zintl phases- Hydrogenations - HCl, Cl2, Br2, I2- (ionic liquids)- amalgamations
NaSi, NaGe, NaSnLiSi, LiGe, Li7Ge12LiBCLi-Al-Si, Li-Al-GeLi(A)-B-Si, Li(A)-B-Ge (Hillebrecht)
High-pressure B-Si, B-Ge