Structural and optical properties of a NaCl single crystal doped with CuO nanocrystals

A cupric oxide （CuO） nanocrystal-doped NaC1 single crystal and a pure NaCl single crystal are grown by using the Czochralski （Cz） method. A number of techniques, including X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） analysis, Fourier transform infrared （FT-IR） spectroscopy, Raman spectroscopy, optical absorption in the UV-visible range, and photoluminescence （PL） spectroscopy are used to characterize the obtained NaCl and NaCI：CuO crystals. It is observed that the average radius of CuO crystallites in NaCI：CuO crystal is about 29.87 nm, as derived from the XRD data analysis. Moreover, FT-IR and Raman spectroscopy results confirm the existence of the monoclinic CuO phase in NaC1 crystal. UV-visible absorption measurements indicate that the band gap of the NaCI：CuO crystal is 434 nm （2.85 eV）, and it shows a significant amount of blue-shift （AEg = 1 eV ） in the band gap energy of CuO, which is due to the quantum confinement effect exerted by the CuO nanocrystals. The PL spectrum of the NaCI：CuO shows a broad emission band centred at around 438 rim, which is consistent with the absorption measurement.

Size and shape effects on Curie temperature of ferromagnetic nanoparticles

A simplified model was developed to describe the Curie temperature suppression of ferromagnetic nanoparticles. Based on a size and shape dependent model of cohesive energy, the critical temperature variations of ferromagnetic nanoparticles were deduced. It is predicted that the Curie temperature of nanoparticles depends on both size and shape conditions, among which the temperature suppression is strongly influenced by the particle size and the shape effect is comparably minor. The calculation values for freestanding nanoparticles are in good agreement with other theoretical model and the experimental results. The model is also potential for predictions for the nanoparticles embedded in different substrates.

Hydration and Slag-attack Resistance of Dense MgO-dolomite Refractory Grains in Relation to Their Phase Composition and Microfabric

This work aims at optimizing densification parameters as well as resistance to hydration and slag attack of MgO-Dolomite refractory grains, processed from Egyptian dolomitc-magnesite raw material up to firing for 1-4 h at 1400-1600 ℃, in relation to their phase composition and microfabric. Minor amount of natural ilmenite mineral (0-2 wt%), separated from Egyptian black sands was used in doping the dolomitc-magnesite.

Insights into the design of thermoelectric Mg_(3)Sb_(2) and its analogs by combining theory and experiment

Over the past two decades,we have witnessed a strong interest in developing Mg3Sb2 and related CaAl2Si2-type materials for lowand intermediate-temperature thermoelectric applications.In this review,we discuss how computations coupled with experiments provide insights for understanding chemical bonding,electronic transport,point defects,thermal transport,and transport anisotropy in these materials.Based on the underlying insights,we examine design strategies to guide the further optimization and development of thermoelectric Mg3Sb2-based materials and their analogs.We begin with a general introduction of the Zintl concept for understanding bonding and properties and then reveal the breakdown of this concept in AMg2X2 with a nearly isotropic three-dimensional chemical bonding network.For electronic transport,we start from a simple yet powerful atomic orbital scheme of tuning orbital degeneracy for optimizing p-type electrical properties,then discuss the complex Fermi surface aided by high valley degeneracy,carrier pocket anisotropy,and light conductivity effective mass responsible for the exceptional n-type transport properties,and finally address the defect-controlled carrier density in relation to the electronegativity and bonding character.Regarding thermal transport,we discuss the insight into the origin of the intrinsically low lattice thermal conductivity in Mg3Sb2.Furthermore,the anisotropies in electronic and thermal transport properties are discussed in relation to crystal orbitals and chemical bonding.Finally,some specific challenges and perspectives on how to make further developments are presented.

Elaboration and characterization of a KCl single crystal doped with nanocrystals of a Sb_2O_3 semiconductor

Abstract： Undoped and doped KC1 single crystals have been successfully elaborated via the Czochralski （Cz） method. The effects of dopant Sb2O3 nanocrystals on structural and optical properties were investigated by a number of techniques, including X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy disper- sive X-ray （EDAX） analysis, UV-visible and photoluminescence （PL） spectrophotometers. An XRD pattern of KCI：Sb2O3 reveals that the Sb2O3 nanocrystals are in the well-crystalline orthorhombic phase. The broadening of diffraction peaks indicated the presence of a Sb2O3 semiconductor in the nanometer size regime. The shift of ab- sorption and PL peaks is observed near 334 nm and 360 nm respectively due to the quantum confinement effect in Sb2O3 nanocrystals. Particle sizes calculated from XRD studies agree fairly well with those estimated from optical studies. An SEM image of the surface KCI：Sb2O3 single crystal shows large quasi-spherical of Sb2O3 crystallites scattered on the surface. The elemental analysis from EDAX demonstrates that the KCI：Sb2O3 single crystal is slightly rich in oxygen and a source of excessive quantities of oxygen is discussed.