Cu1.5SeyTe1-y (y = 0.2-0.7): A Series of Narrow Band Gap Semiconductors with Low Thermal Conductivity at Ambient Temperature.

Coinage metal chalcogenides offer ideal prerequisites for high thermoelectric performance and sensor applications, with their usually low lattice thermal and high electrical conductivity, as well as small band gaps. In the solid solution Cu1.5SeyTe1-y we synthesized phase pure materials with y = 0.2-0.7 and characterized them concerning selected physical properties. X-ray crystal structure determination was performed for two representatives of the solid solution, Cu1.5Se0.3Te0.7 and Cu1.5Se0.5Te0.5. The entire series crystallizes cubically, in space group Pm3̅n. No structural changes are observed between room temperature and the synthesis temperature of 723 K. The conductivity measurements and Seebeck coefficients of Cu1.5Se0.3Te0.7 and Cu1.5Se0.5Te0.5 indicate that the two representatives are narrow band gap semiconductors (Eg 0.06-0.08 eV). Both compounds show positive Seebeck coefficients and reasonably low thermal conductivities at moderate temperatures. Cu1.5Se0.5Te0.5 is characterized by a bulk modulus of 40.9 GPa.

A Switchable One-Compound Diode.

A diode requires the combination of p- and n-type semiconductors or at least the defined formation of such areas within a given compound. This is a prerequisite for any IT application, energy conversion technology, and electronic semiconductor devices. Since the discovery of the pnp-switchable compound Ag10 Te4 Br3 in 2009, it is in principle possible to fabricate a diode from a single material without adjusting the semiconduction type by a defined doping level. Often a structural phase transition accompanied by a dynamic change of charge carriers or a charge density wave within certain substructures are responsible for this effect. Unfortunately, the high pnp-switching temperature between 364 and 580 K hinders the application of this phenomenon in convenient devices. This effect is far removed from a suitable operation temperature at ambient conditions. Ag18 Cu3 Te11 Cl3  is a room temperature pnp-switching material and the first single-material position-independent diode. It shows the highest ever reported Seebeck coefficient drop that takes place within a few Kelvin. Combined with its low thermal conductivity, it offers great application potential within an accessible and applicable temperature window. Ag18 Cu3 Te11 Cl3 and pnp-switching materials have the potential for applications and processes where diodes, transistors, or any defined charge separation with junction formation are utilized.

Novel core-shell nanocomposites based on TiO2 -covered magnetic Co3 O4 for biomedical applications.

Magnetic Co3 O4 nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co3 O4 NPs were prepared via sol-gel method and encapsulated with a layer of TiO2 , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co3 O4 spinel with TiO2 . The Co3 O4 cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO2 . According to the neutral red uptake assay, the coating of the cores with TiO2 significantly decreases the cytotoxic character of the Co3 O4 particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co3 O4 @TiO2 core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.

The mechanism of dephosphorylation of bis(2,4-dinitrophenyl) phosphate in mixed micelles of cationic surfactants and lauryl hydroxamic acid.

Mixed micelles of cetyltrimethylammonium bromide (CTABr) or dodecyltrimethylammonium bromide (DTABr) and the alpha-nucleophile, lauryl hydroxamic acid (LHA) accelerate dephosphorylation of bis(2,4-dinitrophenyl)phosphate (BDNPP) over the pH range 4-10. With a 0.1 mole fraction of LHA in DTABr or CTABr, dephosphorylation of BDNPP is approximately 10(4)-fold faster than its spontaneous hydrolysis, and monoanionic LHA(-) is the reactive species. The results are consistent with a mechanism involving concurrent nucleophilic attack by hydroxamate ion (i) on the aromatic carbon, giving an intermediate that decomposes to undecylamine and 2,4-dinitrophenol, and (ii) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement yielding a series of derivatives including N,N-dialkylurea, undecylamine, undecyl isocyanate, and carbamyl hydroxamate.