V-V Dimerization and Magnetic State of Cobalt Ions in Ilmenite-Type CoVO3.

The nature of chemical bonds determines the electronic and magnetic properties of compounds. A metal-metal bonding (V-V dimer) and its effect on the magnetism of ilmenite-type CoVO3 were studied. Polycrystalline CoVO3 samples were synthesized using a high-pressure synthesis method. Crystal structure refinement revealed that V-V dimers exist at temperatures below 550 K in the vanadium layers. Co2+ in CoVO3 exhibits an S = 3/2 state, whereas a Jeff = 1/2 state was reported in ilmenite-type CoTiO3. The existence of V-V dimers reduces the structural symmetry (from R3 to P1), which can change the magnetic ground state.

Cation Dimerization in a 3d1 Honeycomb Lattice System.

In one-dimensional systems with partially filled valence bands, simultaneous changes occur in the electronic states and crystal structures. This is known as the Peierls transition. The Peierls transition (cation dimerization) in VO2, which has a quasi-one-dimensional structure, is well-known, and its mechanism has been extensively discussed. Honeycomb lattices exhibit the Peierls instability owing to their low dimensionality. However, cation dimerization is rare in the 3d1 honeycomb lattice system. Here, we perform an in-depth examination of the V-V dimerization (formation of V-V direct bond) in ilmenite-type MgVO3, which is a 3d1 honeycomb lattice system. A ladderlike pattern was observed in the V-V dimers through synchrotron X-ray experiments at temperatures below 500 K. This dimerization was accompanied by a magnetic-to-nonmagnetic transition. Moreover, a valence bond liquid phase may exist at 500-600 K. Our results reveal the behavior of the valence electrons in the 3d1 honeycomb lattice system.

Size-dependent thermochromism through enhanced electron-phonon coupling in 1†nm quantum dots.

1 nm CuO quantum dots (QDs) were produced in size-controlled super-micropores of a silica matrix. The reversible color change of the QDs from pale blue to deep green was clearly observed in a wide temperature range from 298 to 673 K. This particular thermochromism is ascribed to an enhanced bandgap shift depending on temperature with a strong electron-phonon coupling in the confined space of the 1 nm QDs.