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