김성운 교수

The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi(0.5)Sb(1.5)Te3 (bismuth antimony

We report a metallic state in a nanostructured porous crystal 12CaO x 7Al2O3 by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping ( approximately 2 x 10(21) cm(-3)), which was achieved by a thermal treatment in Ti metal vapor at approximately 1100 degrees C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator-meta

Solvated electrons persist in high-temperature melts and quenched melts of a calcium aluminum oxide.

A room temperature (RT) stable electride was realized by thermally annealing an insulating 12CaO·7Al2O3 (C12A7) single crystal in a calcium metal vapor. Here we report a simple and direct method for synthesizing polycrystalline C12A7 electride (C12A7:e-); the solidification of a “melt” in a reducing atmosphere and the crystallization of a “glass” with an oxygen-deficient composition in a vacuum. The carbon-related anion (C22-) presumably serves as the template for the formation of the C12A7 phas

Over the last decade, experimental studies supported by theoretical calculations have demonstrated that 12CaO · 7Al2O3 (C12A7), a typical electrical insulator, could be converted into an electro-active functional material, such as a metallic conductor with a low work function but chemical inertness and superconductivity, at low temperatures. These properties were realised by successful heavy electron doping into positively charged sub-nanometre-sized cages inherent to the crystal structure throu

Thermoelectrics, which transports heat for refrigeration or converts heat into electricity directly, is a key technology for renewable energy harvesting and solid-state refrigeration. Despite its importance, the widespread use of thermoelectric devices is constrained because of the low efficiency of thermoelectric bulk alloys. However, boundary engineering has been demonstrated as one of the most effective ways to enhance the thermoelectric performance of conventional thermoelectric materials su

Structural defects often dominate the electronic- and thermal-transport properties of thermoelectric (TE) materials and are thus a central ingredient for improving their performance. However, understanding the relationship between TE performance and the disordered atomic defects that are generally inherent in nanostructured alloys remains a challenge. Herein, the use of scanning transmission electron microscopy to visualize atomic defects directly is described and disordered atomic-scale defects

Electrides are ionic compounds in which electrons act as anions. These compounds are expected to have interesting properties arising from their exotic structure. The fatal drawbacks of the thermal and chemical instability of organic electrides were resolved by the synthesis of a room temperature (RT) stable electride using single crystalline 12CaO.7Al2O3 (C12A7) with a nanoporous structure and the chemical treatments for a long duration. However, an innovative fabrication method is obviously req

Electron carriers were generated in refractory oxide 12CaO·7Al 2 O 3 (C12A7) through a thermal treatment in a reducing CO/CO 2 atmosphere, and the reduction process was thermodynamically analyzed. Electrical‐conductive C12A7, which had an electron concentration of ∼8 × 10 19 cm −3 and an electrical conductivity of ∼4 S/cm at 300 K, was obtained by extracting free O 2− ions in sub‐nanometer‐sized cages in the C12A7 lattice and leaving electrons behind. The enthalpy for this substitutive reaction