Superior intrinsic thermoelectric performance with zT of 1.8 in single-crystal and melt-quenched highly dense Cu2-xSe bulks

Practical applications of the high temperature thermoelectric materials developed so far are partially obstructed by the costly and complicated fabrication process. In this work, we put forward two additional important properties for thermoelectric materials, high crystal symmetry and congruent melting. We propose that the recently discovered thermoelectric material Cu2-xSe, with figure of merit, zT, over 1.5 at T of ~ 1000 K, should meet these requirements, based on our analysis of its crystal structure and the Cu-Se binary phase diagram. We found that its excellent thermoelectric performance is intrinsic, and less dependent on grain size, while highly dense samples can be easily fabricated by a melt-quenching approach. Our results reveal that the melt-quenched samples and single crystals exhibit almost the same superior thermoelectric performance, with zT as high as 1.7-1.8 at T of ~973 K. Our findings not only provide a cheap and fast fabrication method for highly dense Cu2-xSe bulks with superior thermoelectric performance, paving the way for possible commercialization of Cu2-xSe as an outstanding component in practical thermoelectric modules, but also provide guidance in searching for new classes of thermoelectric systems with high crystal symmetry or further improving the cost performance of other existing congruent-melting thermoelectric materials

Correlation between crystal structures, Raman scattering and piezoelectric properties of lead-free Na0.5K0.5NbO3

Relationships between crystal structures, lattice parameters, bond lengths and angles, vibration modes, and dielectric and piezoelectric properties of LiNbO3, LiTaO3, and LiSbO3 substituted lead-free Na0.5K0.5NbO3 (NKN) ceramics were investigated. Their crystal structures have been characterized using X-ray diffraction and analysed with the Rietveld method. The refinement results revealed that substitution with small cations to replace host ions in the NKN unit cell reduced the bond distances between B+ ions (Nb5+, Ta5+, and Sb5+) and their coordinated oxygens in the BO6 octahedron. Shortening of the bond distances led to noticeable shifts toward higher frequencies in the bending vibration ν5 and stretching vibration ν1 modes. The unit cell shrinkage and distortion, in addition to the incorporation of doped ions with higher charge density in the A and B sites, remarkably enhanced the piezoelectric and electrical properties of the doped NKN ceramics

Correlation between crystal structures, Raman scattering and piezoelectric properties of lead-free Na0.5K0.5NbO3

Relationships between crystal structures, lattice parameters, bond lengths and angles, vibration modes, and dielectric and piezoelectric properties of LiNbO3, LiTaO3, and LiSbO3 substituted lead-free Na0.5K0.5NbO3 (NKN) ceramics were investigated. Their crystal structures have been characterized using X-ray diffraction and analysed with the Rietveld method. The refinement results revealed that substitution with small cations to replace host ions in the NKN unit cell reduced the bond distances between B+ ions (Nb5+, Ta5+, and Sb5+) and their coordinated oxygens in the BO6 octahedron. Shortening of the bond distances led to noticeable shifts toward higher frequencies in the bending vibration ν5 and stretching vibration ν1 modes. The unit cell shrinkage and distortion, in addition to the incorporation of doped ions with higher charge density in the A and B sites, remarkably enhanced the piezoelectric and electrical properties of the doped NKN ceramics

Improvement of thermoelectric properties and their correlations with electron effective mass in Cu1.98SxSe1−x

Sulphur doping effects on the crystal structures, thermoelectric properties, density-of-states, and effective mass in Cu1.98SxSe1−x were studied based on the electrical and thermal transport property measurements, and first-principles calculations. The X-ray diffraction patterns and Rietveld refinements indicate that room temperature Cu1.98SxSe1−x (x=0, 0.02, 0.08, 0.16) and Cu1.98SxSe1−x (x=0.8, 0.9, 1.0) have the same crystal structure as monoclinic-Cu2Se and orthorhombic-Cu2S, respectively. Sulphur doping can greatly enhance zT values when x is in the range of 0.8≤x≤1.0. Furthermore, all doped samples show stable thermoelectric compatibility factors over a broad temperature range from 700 to 1000K, which could greatly benefit their practical applications. First-principles calculations indicate that both the electron density-of-sates and the effective mass for all the compounds exhibit nonmonotonic sulphur doping dependence. It is concluded that the overall thermoelectric performance of the Cu1.98SxSe1−x system is mainly correlated with the electron effective mass and the density-of-states

Cobalt doping effects on photoluminescence, Raman scattering, crystal structure, and magnetic and piezoelectric properties in ZnO single crystals grown from molten hydrous LiOH and NaOH solutions

Transparent, olive-green single-crystal Zn1- xCoxO in the form of hexagonal lamellae grown from molten hydrous LiOH and NaOH solutions have been studied in terms of crystal structure, optical properties, Raman scattering, and magnetic and piezoelectric properties. Rietveld refinement shows that the lattice parameters and bond lengths decrease with increasing cobalt concentration. Cobalt doping results in slight changes to the piezoelectricity of ZnO, but leads to two new photoluminescence emission peaks at wavelengths of 443 and approx. 510 nm, along with the disappearance of certain Raman active modes. Furthermore, the ferromagnetic state is absent in all Zn1- xCoxO crystals, and they are all typically paramagnetic instead

High thermoelectric and mechanical performance in highly dense Cu2−xS bulks prepared by a melt-solidification technique

Highly dense Cu2−xS bulks, fabricated by a melt-solidification technique, show high thermoelectric performance with zT of approx. 1.9 at 970 K. The Cu2−xS bulks show good thermal heat flow and diffusivity stability, and they exhibit excellent mechanical properties, with hardness of approx. 1 GPa. Density functional theory calculations indicate that Cu2−xS is an intrinsic p-type conductor

A colossal dielectric constant of an amorphous TiO2:(Nb, In) film with low loss fabrication at room temperature

High-performance dielectric materials continue to arouse considerable interest due to their application in the field of solid state capacitors. In, Nb co-doped TiO2 thin films with the composition of (In 0.5Nb0.5)xTi1-xO2 (x = 0.10) were fabricated on a Pt substrate by pulsed laser ablation at room temperature. In addition to their colossal permittivity (εr \u3e 4000), they exhibit correspondingly a low dielectric loss (about 5.5%) and high frequency-stability (up to 10 MHz), making the film suitable for myriad device miniaturization and high-energy-density storage applications. The preparation of this amorphous CP TiO2 film at room temperature possesses great significance in microelectronic packaging not only because the CP film can be prepared on any kind of substrate including plastic or paper but also because the low temperature can protect the preparation of microelectronic devices. The procedure without annealing is simple and easy to operate, which will raise the efficiency and reduce the production cost in the semiconductor industry. As remarked above, In, Nb co-doped amorphous TiO2 films with colossal permittivity would be a highly attractive proposition

Modulation of ovine SBD-1 expression by 17beta-estradiol in ovine oviduct epithelial cells

Abstract Background Mucosal epithelia, including those of the oviduct, secrete antimicrobial innate immune molecules (AIIMS). These have bactericidal/bacteriostatic functions against a variety of pathogens. Among the AIIMs, sheep β-defensin-1 (SBD-1) is one of the most potent. Even though the SBD-1 is an important AIIM and it is regulated closely by estrogenic hormone, the regulation mechanism of 17β-estradiol has not been clearly established. We investigated the effects of E2 and agonist or inhibitor on ovine oviduct epithelial cells in regard to SBD-1 expression using reverse transcription quantitative PCR (RT-qPCR). In addition, three different pathways were inhibited separately or simultaneously to confirm the effect of different inhibitors in the regulation mechanism. Results 17beta-estradiol (E2) induced release of SBD-1 in ovine oviduct epithelial cells. SBD-1 expression was mediated through G-protein-coupled receptor 30 (GPR30) and Estrogen Receptors (ERs) activation in ovine oviduct epithelial cell. Inhibition of gene expression of protein kinase A (PKA), protein kinase C (PKC), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) led to a decreased SBD-1 expression. Conclusions Taken together, E2-induced up-regulation of SBD-1 expressions were GPR30-dependent during prophase and ERs-dependent during later-stage in ovine oviduct epithelial cells, and we assume that the effect was completed by the PKA, PKC, and NF-κB pathways simultaneous.</p

ORF7 of Varicella-Zoster Virus Is a Neurotropic Factor

Research Center for Minority Institutes (RCMI) Program [2G12RR003050-24]; American Cancer Society grant [RSG-090289-01-MPC]; NIH/NCRR [U54RR022762]Varicella-zoster virus (VZV) is the causative agent of chickenpox and herpes zoster (shingles). After the primary infection, the virus remains latent in sensory ganglia and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine is highly attenuated in the skin and yet retains its neurovirulence and may reactivate and damage sensory neurons. The factors involved in neuronal invasion and establishment of latency are still elusive. Previously, we constructed a library of whole-gene deletion mutants carrying a bacterial artificial chromosome sequence and a luciferase marker in order to perform a comprehensive VZV genome functional analysis. Here, screening of dispensable gene deletion mutants in differentiated neuronal cells led to the identification of ORF7 as the first known, likely a main, VZV neurotropic factor. ORF7 is a virion component localized to the Golgi compartment in infected cells, whose deletion causes loss of polykaryon formation in epithelial cell culture. Interestingly, ORF7 deletion completely abolishes viral spread in human nervous tissue ex vivo and in an in vivo mouse model. This finding adds to our previous report that ORF7 is also a skin-tropic factor. The results of our investigation will not only lead to a better understanding of VZV neurotropism but could also contribute to the development of a neuroattenuated vaccine candidate against shingles or a vector for delivery of other antigens

Significant enhancement of figure-of-merit in carbon-reinforced Cu2Se nanocrystalline solids

Liquid-like ionic conductors in the copper selenide family represent a promising class of thermoelectric materials capable of recycling waste heat into electrical energy with an exemplary figure-of-merit (zT \u3e 1.4) above 800 K. Ion diffusion, however, is enhanced at such high temperatures and drives a non-reversible phase segregation that inhibits practical applications. In tandem, the thermoelectric performance at moderate temperatures (500-750 K) where ion diffusion is less problematic, is not optimal for real-world applications (zT \u3c 1). In this work, we demonstrate that incorporating a small weight fraction of carbon using various carbon sources can significantly enhance the zT of Cu 2 Se at both middle and high temperatures. All the carbon-doped Cu 2 Se samples exhibit weak temperature dependent zT higher than 1.0 over a broad temperature range from 600 to 900 K, with the 0.6 wt% Super P doped Cu 2 Se sample achieving a zT of 1.85 at 900 K. Furthermore, the 0.3 wt% carbon fiber doped Cu 2 Se shows zT \u3e 1 for T \u3e 520 K and reaches a record level of zT of ~ 2.4 at 850 K. These values for the carbon doped Cu 2 Se are comparable or superior to those for the current state-of-the-art thermoelectric materials. Microstructure studies on graphite incorporated Cu 2 Se revealed that graphite nanostructures interspace between Cu 2 Se nanoscale grains being responsible for the significantly enhanced zT. The low thermal conductivity in the nanostructured composite is attributed to the high density of interfaces caused by the small grain diameters (30-60 nm), along with the strong acoustic mismatch between Cu 2 Se and carbon phonon states which enhances the thermal boundary resistance. This discovery indicates strong prospects for engineering carbon thermoelectric nanocomposites for a range of energy applications