Meijuan Yu

We report remarkably enhanced thermoelectric performance of Te doped Cu2Se in mid-temperature range. Through ball-milling process followed by spark plasma sintering (SPS), nanoscale Cu2Te clusters were embeded in the matrix of Cu2Se, inducing a drastic enhancement of thermoelectric performance by reducing the thermal conductivity without degrading the power factor. A large ZT value of 1.9 was achieved at 873 K for Cu2Se1.9Te0.1 which is about 2 times larger than that of the pure Cu2Se. The nanoscale heat management by Cu2Te nano-clusters in superionic conductors opens up an avenue for thermoelectric materials research.

The thermoelectricity of Fe doped Ca ₃ Co ₄ O ₉ is tuned by nanoscale structural heterogeneity, as unveiled by X-ray absorption spectroscopy and density functional theory.

The superionic behavior of cubic δ-phase Bi₂O₃, a metastable phase at high temperature, is of great interests from both scientific and technological perspectives. With the highest ionic conductivity among all known compounds, the δ-phase Bi₂O₃ possesses promising applications in solid-oxide fuel cells. Previous investigations pointed out the α to δ- phase transition occurs during the heating process, as supported by the X-ray and Neutron diffraction experiments. Through in situ measurements of the long-range order structure and the local structure by X-ray powder diffraction and X-ray absorption spectroscopy, we investigated the evolution of the structures under different temperatures. Both techniques provided ample evidence that the existence of meta-stable β-phase are crucial for forming the defective fluorite cubic δ phase. Our finding suggested that the phase transition from tetragonal β-phase to δ-phase is an influencing factor for the generation of the oxygen-ion pathways.

The local configurations around metal ions in metalloproteins are of great significance for understanding their biological functions. Cu²⁺/histidine (His) is a typical complex existing in many metalloproteins and plays an important role in lots of physiological functions. The three-dimensional (3D) structural configurations of Cu²⁺/His complexes at different pH values (2.5, 6.5, and 8.5) are quantitatively determined by x-ray absorption near-edge structure (XANES). Generally Cu²⁺/His complex keeps an octahedral configuration consisting of oxygen atoms from water molecules and oxygen or nitrogen atoms from histidine molecules coordinated around Cu²⁺. It is proved in this work that the oxygen atoms from water molecules, when increasing the pH value from acid to basic value, are gradually substituted by the O_carboxyl, N_am, and N_im from hisitidine molecules. Furthermore, the symmetries of Cu²⁺/His complexes at pH 6.5 and pH 8.5 are found to be lower than at pH 2.5.

The layered oxyselenide BiCuSeO system is known as one of the high‐performance thermoelectric materials with intrinsically low thermal conductivity. By employing atomic, nano‐ to mesoscale structural optimizations, low thermal conductivity coupled with enhanced electrical transport properties can be readily achieved. Upon partial substitution of Bi³⁺ by Ca²⁺ and Pb²⁺, the thermal conductivity can be reduced to as low as 0.5 W m⁻¹ K⁻¹ at 873 K through dual‐atomic point‐defect scattering, while a high power factor of ≈1 × 10⁻³ W cm⁻¹ K⁻² is realized over a broad temperature range from 300 to 873 K. The synergistically optimized power factor and intrinsically low thermal conductivity result in a high ZT value of ≈1.5 at 873 K for Bi_0.88Ca_0.06Pb_0.06CuSeO, a promising candidate for high‐temperature thermoelectric applications. It is envisioned that the all‐scale structural optimization is critical for optimizing the thermoelectricity of quaternary compounds.

The performance of Ge doped In ₂ O ₃ thermoelectric materials is enhanced via band structure engineering and phonon suppression.

Metalloporphyrins are networking molecules with strong internal N–H hydrogen bonds that may be used to substitute a metal ion inside a porphyrin ring, forming a metallo complex. The understanding of electronic structures and charge dynamics of porphyrin based molecular architectures is mandatory to clarify biological functions, catalytic processes, and opto-electrical responses in which these molecules are involved. We present here a systematic analysis of the electronic structures and the charge dynamics of two different iron-porphyrins (i.e. protoporphyrin IX and meso-tetraphenylporphine) with different functional architectures. We investigated these prototypical porphyrins and their μ-oxo-dimer derivatives by means of Fe K-edge X-ray Absorption Near-Edge Spectroscopy (XANES) combined with theoretical calculations. The electronic structure, namely the partial projected density of states and the polarization components were discussed in terms of orbital hybridizations among metal and local ligands. Data show that hydrogens are electron donors while the central metal irons accept electrons. Moreover, the metal axial ligands exhibit different electron behaviors: donors for Cl in prototypical porphyrins and acceptors for O in μ-oxo-dimer derivatives. Actually, the charge dynamics are affected by local metal ligands, but also strongly depend on the mid-range atomic ordering of the porphyrins network. The charge dynamics, evaluated from the self-consistent local potential, is associated with charge transfer mechanisms involving interactions with the axial ligands as well as with the substituents. The quantum chemical topology analysis of the electron localization function (ELF) has been used to identify the distribution of the electron pairs. They are localized around Cl atoms regardless of porphyrin configurations. Charge dynamics and electron localization are fundamental information for a deep understanding of the role of porphyrin and porphyrin-like molecules in a wide range of molecular biophysical mechanisms and in materials science processes.

Numerous studies suggested carbon nanotubes (CNTs) as a type of promising sorbent for heavy metals from water and explained the sorption mechanism mainly by oxygen-containing functional groups on CNT surfaces but neglected the potential role of metal catalyst residues in CNTs. This is a first study showing that metal impurities could dominate the sorption of one type of commercially available CNTs (P-CNTs) for Pb(II) from water, which will help to understand and guide environmental applications of CNTs as a sorbent. Sorption capacity of P-CNTs (27.3 mg g⁻¹) for Pb(II) was much higher than that of the water-washed P-CNTs (W-CNTs, 4.7 mg g⁻¹). SEM-EDS and ICP-MS analyses showed that both P-CNTs and W-CNTs contained metal impurities (mainly Co and Mo) which released into the solutions during the sorption, especially P-CNTs. XAFS examination and precipitation experiments demonstrated that PbMoO₄ formation between Pb(II) and CNT-released MoO₄²⁻ and subsequent precipitation in the sorptive solutions was the dominant mechanism for the apparent sorption of Pb(II) by P-CNTs.