Search Results (4)

Nowadays, the search for the coupled polymer nanocomposite thermoelectrics that exhibit a high value of thermoelectric figure of merit (ZT) and similar behaviour of physical properties for the use as legs of thermoelectric cells is a current challenge. The direct current (DC) conductivity is one of the three important components of thermoelectric figure of merit. The aim of this study was to obtain PANI-based nanothermoelectrics with Te⁰ and Bi₂Te₃ nanoparticles and MWCNT by mechanochemical methodology and to investigate the dependency of their DC electrical conductivity on temperature in the 298–353 K range using the Arrhenius and Mott’s variable range hopping (VRH) models. Inorganic Te⁰ and Bi₂Te₃ nanoparticles were pre-synthesized by the available and environmentally friendly method using a commercial tellurium powder. The samples obtained were characterized by X-ray diffractometry (XRD), IR and UV-Vis spectroscopy. The XRD study of ES-PANI/Te⁰ (4.4 wt% Te⁰) and ES-PANI/Bi₂Te₃ (2.9 wt% Bi₂Te₃) nanocomposites found that the nanoparticle average size was 32 nm and 17 nm, respectively. The DC conductivity study of the samples with different nanophase content (2.1, 4.4, 10.2 wt% Te⁰, 1.5, 2.9, 7.3 wt% Bi₂Te₃, 1.5 wt% MWCNT) by the two points measurement method reveals the following: (a) the presence of inorganic nanophase reduces the conductivity compared to the matrix, (b) the addition of MWCNT in ES-PANI increases its electrical conductivity, (c) the conductivity of ES-PANI/Te⁰ as well as ES-PANI/Bi₂Te₃ nanocomposite rises with the increasing inorganic nanophase content, (d) the observed increase in the electrical conductivity of MWCNT-based nanocomposites with increasing inorganic nanophase content is interrupted by a characteristic area of decrease in its value at average values of inorganic nanoparticles content (at Te⁰ content of 4.4 wt%, at Bi₂Te₃ content of 2.9 wt%), (e) a similar DC conductivity behaviour in ES-PANI/Te⁰—ES-PANI/Bi₂Te₃ and ES-PANI/Te⁰-MWCNT—ES-PANI/Bi₂Te₃-MWCNT nanocomposite pairs is observed. Full article

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba${}_2$ScRuO${}_6$ synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P$\overline{3}$m1. The Rietveld refinement using the room-temperature powder XRD pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the DC electrical resistivity highlights a semiconducting behavior with the electron conduction corresponding to Mott’s 3D variable range hopping (VRH) model. The detailed magnetization measurements show that Ba${}_2$ScRuO${}_6$ develops antiferromagnetic ordering at $T_N$≈ 9 K. Interestingly, below 9 K (T${}_N$), the field-cooled magnetic field variation (FC) of the magnetization curves highlights an exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to the inhomogeneous magnetic correlations due to the disorder in the structure. Remarkably, the appearance of a large exchange bias field in Ba${}_2$ScRuO${}_6$ indicates that inhomogeneous hexagonal double perovskites are a promising class to explore new materials having potential applications in spintronics. Full article

Graphene oxides with different degrees of oxidation are prepared by controlling UV irradiation on graphene, and the charge transport and the evolution of the transport gap are investigated according to the extent of oxidation. With increasing oxygenous defect density $n_{\mathrm{D}}$, a transition from ballistic to diffusive conduction occurs at $n_{\mathrm{D}}\simeq {10}^{12}$ cm${}^{-2}$ and the transport gap grows in proportion to $\sqrt{n_{\mathrm{D}}}$. Considering the potential fluctuation related to the $e-h$ puddle, the bandgap of graphene oxide is deduced to be $E_{\mathrm{g}}\simeq 30\sqrt{n_{\mathrm{D}}\left({10}^{12}{\mathrm{cm}}^{-2}\right)}$ meV. The temperature dependence of conductivity showed metal–insulator transitions at $n_{\mathrm{D}}\simeq 0.3\times {10}^{12}$ cm${}^{-2}$, consistent with Ioffe–Regel criterion. For graphene oxides at $n_{\mathrm{D}}\ge 4.9\times {10}^{12}$ cm${}^{-2}$, analysis indicated charge transport occurred via 2D variable range hopping conduction between localized $s{p}^2$ domain. Our work elucidates the transport mechanism at different extents of oxidation and supports the possibility of adjusting the bandgap with oxygen content. Full article

As an emerging research field, two-dimensional (2D) metals have been the subject of increasing research efforts in recent years due to their potential applications. However, unlike typical 2D layered materials, such as graphene, which can be exfoliated from their bulk parent compounds, it is hardly possible to produce 2D metals through exfoliation techniques due to the absence of Van der Waals gaps. Indeed, the lack of effective material preparation methods severely limits the development of this research field. Here, we report a PDMS-assisted hot-pressing method in glovebox to obtain ultraflat nanometer-thick 2D metals/metal oxide amorphous films of various low-melting-point metals and alloys, e.g., gallium (Ga), indium (In), tin (Sn), and Ga_0.87Ag_0.13 alloy. The valence states extracted from X-ray photoelectron spectroscopy (XPS) indicate that the ratios of oxidation to metal in our 2D films vary among metals. The temperature-dependent electronic measurements show that the transport behavior of 2D metal/metal oxide films conform with the 2D Mott’s variable range hopping (VRH) model. Our experiments provide a feasible and effective approach to obtain various 2D metals. Full article