Recently SnSe, a layered chalcogenide material, has attracted a great deal of attention for its excellent p-type thermoelectric property showing a remarkable ZT value of 2.6 at 923 K. For ...thermoelectric device applications, it is necessary to have n-type materials with comparable ZT value. Here, we report that n-type SnSe single crystals were successfully synthesized by substituting Bi at Sn sites. In addition, it was found that the carrier concentration increases with Bi content, which has a great influence on the thermoelectric properties of n-type SnSe single crystals. Indeed, we achieved the maximum ZT value of 2.2 along b axis at 733 K in the most highly doped n-type SnSe with a carrier density of -2.1 × 10
cm
at 773 K.
Biocompatible microlasers, generally made of bio-derived materials, are promising for biosensing and cell-tracking. These kinds of lasers offer favourable opportunities like biocompatibility and ...biodegradability but the materials used often require complicated synthesis and high cost. In this work, we demonstrate that polyvinyl alcohol (PVA), a synthetic water-soluble low-cost polymer, with fascinating properties such as good transparency, biocompatibility, biodegradability is an excellent candidate for making laser cavity. Using a simple and effective technique, dye-doped PVA microspheres can be fabricated with various sizes from 10 to 200 μm. These microspheres can act as excellent lasers under optical excitation with a lasing threshold of ∼2 μJ/mm2 and Q factor of lasing modes of ∼3000. The lasing mechanism is studied and it is ascribed to whispering gallery mode (WGM). Size-dependent lasing characteristics including lasing spectrum, quality (Q) factor and lasing threshold are investigated. Owing to the ease of fabrication, the cost-effectiveness, the biocompatibility of the PVA material, our biocompatible microlasers are promising for future biosensing applications.
We reported the room-temperature ferromagnetism in iron doped Bi0.5K0.5TiO3 nanocrystals. The reduction of band gap from 3.31eV to 2.27eV was obtained after introduction of iron to Bi0.5K0.5TiO3 with ...concentration up to 7mol%. The first-principles density function theory (DFT) calculations indicate that the reduction of band gap is due to the presence of conduction bands of iron, and the ferromagnetism in iron-doped Bi0.5K0.5TiO3 samples was explained by the exchange splitting between spin subbands through crystal field theory. This method may provide an available way to get single-phase multiferroics and resolve the problem of the scarcity of single-phase multiferroics in nature.
Display omitted
•The un-doped and Fe-doped Bi0.5K0.5TiO3 were synthesized by using sol–gel technique.•The reduction of band gap was obtained after introduction of iron to Bi0.5K0.5TiO3.•The un-doped and Fe-doped Bi0.5K0.5TiO3 exhibited room temperature ferromagnetism.•This can be explained by the first-principles density function theory calculations.
We report on the effects of Se/Sn flux ratio to the growth and thermoelectric properties of SnSe thin films on MgO (100) substrate. All films were epitaxially grown at 300 °C with various Se/Sn flux ...ratios of 0.8, 0.9, 1, 3, 5, and 7. The crystal structure of the obtained SnSe thin films was orthorhombic (Pnma space group) with a-axis (h00) orientation. XRD Φ-scan studies showed an existence of orthorhombic domains, whose rotation can be modulated by the Se/Sn flux ratio. A structure consisting of 0° and 90° rotated domains was observed in all samples, while additional 45° rotated domains were simultaneously observed in the samples with higher Se/Sn ratio of 5 and 7. Especially, 135° rotated domains were observed in sample Se/Sn = 7. Interestingly, the best crystalline film was obtained at the Se/Sn = 1. We found that Seebeck coefficients were positive at room temperature, decreased with temperature and became negative for the sample Se/Sn = 1, indicating bipolar transport in the samples. A maximum PF value of 3.74 μWcm−1K−2 was obtained at 550 K for sample Se/Sn = 0.8.
•We have successfully grown SnSe epitaxial thin films on MgO (100) at 300 oC with various Se/Sn flux ratio.•The films exhibit orthorhombic domains, whose rotation can be effectively modulated by the Se/Sn flux ratio.•The highest crystallinity film is obtained at Se/Sn flux ratio of 1.
Copper chalcogenide Cu2(Se,Te) compounds are well known as typical p-type thermoelectric materials with a figure of merit (ZT) that can be optimized by the ratio of Se : Te. Here, by using the ...mechanical alloying and solid-state reaction methods, Te was substituted into Se sites within Cu2Se as the formula Cu2Se1−xTex (x = 0.1, 0.2, 0.25, and 0.3). The observed changes in structural phase, grain morphologies, and grain size were recorded by XRD and FE-SEM imaging with the appearance of the secondary phase of Cu2Te, with a Te content of x = 0.25. The layered structure morphology was observed more clearly at the high Te content. The electrical conductivity was greatly increased with enriched Te content while the maximum Seebeck coefficient was obtained in the Cu2Se0.75Te0.25 sample. Accordingly, a power factor value of up to 9.84 μW cm−1 K−2 at 773 K was achieved. The appearance of a Cu2Te phase with a Te content of 0.25 created a structural phase transition which results in a ZT value of 1.35 at 773 K in the Cu2Se0.75Te0.25 sample.
In our work, SnSe nanosheets and nanostructured thin films were successfully synthesized via sonication-assisted exfoliation and coating process. The SnSe nanosheets respond to a uniform lateral ...size, with two to three single layers by 2.82 nm and 280 nm
2
of average thickness and average area, respectively. The results were confirmed by Scanning Electron Microscope, Transmission Electron Microscope, and Atomic Force Microscope. X-ray diffraction and Raman spectra indicate that the SnSe nanosheets have high crystalline quality along
a
-axis. The SnSe nanostructured thin films were prepared in various thicknesses from 350 to 650 nm. The highest power factor value is achieved at 450 nm in 375–600 K temperature range. A simple method of fabrication and controllable thermoelectric properties of SnSe nanostructured thin films as well as other two-dimensional (2D) materials are introduced.
The lead-free piezoelectric ceramics display good piezoelectric properties which are comparable with Pb(Zr,Ti)O3 (PZT) and these materials overcome the hazard to the environment and human health. The ...Bi0.5(Na,K)0.5TiO3 (BNKT) is rapidly developed because of good piezoelectric, ferroelectric, and dielectric properties compared to PZT. The origin of giant strain of BNKT piezoelectric materials was found at morphotropic phase boundary due to crystal change from tetragonal to orthorhombic and/or precipitation of cubic phases, in addition to domain switching mechanism. The dopants or secondary phases with ABO3 structure as solid solution are expected to change the crystal structure and create the vacancies which results in enhancement of the piezoelectric properties. In this work, we reviewed the current development of BNKT by dopants and secondary phase as solid solution. Our discussion will focus on role of dopants and secondary phase to piezoelectric properties of BNKT. This result will open the direction to control the properties of lead-free piezoelectric materials.
Abstract
Tin selenide (SnSe) is considered a robust candidate for thermoelectric applications due to its very high thermoelectric figure of merit, ZT, with values of 2.6 in p-type and 2.8 in n-type ...single crystals. Sn has been replaced with various lower group dopants to achieve successful p-type doping in SnSe with high ZT values. A known, facile, and powerful alternative way to introduce a hole carrier is to use a natural single Sn vacancy,
V
Sn
. Through transport and scanning tunneling microscopy studies, we discovered that
V
Sn
are dominant in high-quality (slow cooling rate) SnSe single crystals, while multiple vacancies,
V
multi,
are dominant in low-quality (high cooling rate) single crystals. Surprisingly, both
V
Sn
and
V
multi
help to increase the power factors of SnSe, whereas samples with dominant
V
Sn
have superior thermoelectric properties in SnSe single crystals. Additionally, the observation that
V
multi
are good p-type sources observed in relatively low-quality single crystals is useful in thermoelectric applications because polycrystalline SnSe can be used due to its mechanical strength; this substance is usually fabricated at very high cooling speeds.
Sn-doped n-type and Cu-doped p-type ZnO films were fabricated by depositing solutions derrived by sol–gel route on glass substrates through dip-coating cycles. The X-ray diffractometry demonstrates ...the typical crystalline structure of hexagonal wurzite of ZnO. The surface morphology was made through scanning electronmicroscopy showing the density and shape of films’ grains of which size was determined between 40 and 55 µm. The results of Hall measurement indicate clearly the material nature of fabricated films at room temperature. The best electrical property of Sn-doped n-type ZnO films is corresponding to Sn content of 2 at.% with carrier concentration of 3.0 × 10
18
cm
−3
. The formation of p-type ZnO thin films was elucidated by the manner of solution synthesis that glucose was added into the solube mixer of zinc acetate and copper(II) nitrate trihydrate and the way of thermal treatment for films in vacuum with pretty good hole concentration of about 10
15
cm
−3
. The electrical transport properties characterizing thermoelectric (TE) behavior of all films were investigated between room temperature to 400 °C (or from 300 to 673 K). The obtained results of electrical conductivity, Seebeck coefficient and power factor revealed that Sn-doped n-type ZnO films have the quality and properties similar to Al-doped ones and Cu-doped ZnO films can be promising p-type materials for TE applications.
PDF
