Excess Conductivity Research Articles

Geophysical survey at the southern end of the Degtyarsky pyrite deposit

Research aim is to study features peculiar to geophysical fields over the main geological features of the southern part of the Degtyarsky pyrite deposit at the Middle Urals. Methodology. Electromagnetic survey included symmetrical electric profiling (SEP) with ERA-MAX equipment (ERA Research and Production Enterprise, St. Petersburg) and rapid audio-magnetotelluric sounding (ATMS) with OMAR-2m wideband receiver (Institute of Geophysics UB RAS, Ekaterinburg). Magnetic survey was carried out with the help of the proton procession magnetometer GSM-19T (GEM Systems, Canada), gamma field survey was carried out with a survey meter SRP-68-01 (Electron, Zhovti Vody). Results. According to the results of observational analysis, high-quality sections of electrophysical parameters of the environment were constructed at the parametric profile together with the charts of other geophysical fields. The studies have shown significant changes of resistivity and potential fields anomalies over various geological features of the ore field. Summary. Geophysical indications of border line of the main geologic features have been determined. Excessive electrical conductivity of ore control tectonic structures and radiation anomaly have been revealed in the promises of the ore body, which can serve a prospecting criterion for a similar ore body. Geophysical results are well within the existing geological data on the Degtyarsky mine.

Magnetized MXene Microspheres with Multiscale Magnetic Coupling and Enhanced Polarized Interfaces for Distinct Microwave Absorption via a Spray-Drying Method.

As a typical 2D (two dimensional) material, Ti3C2Tx, has been used as a promising microwave absorber (MA) because of its massive interface architecture, abundant natural defects, and chemical surface functional groups. However, its single dielectric-type loss and excessive high conductivity seriously restrict the further enhancement of MA performance. Herein, we first describe a simple spray-drying routine to reshape the 2D MXene into a confined and magnetized microsphere with tightly embedded Fe3O4 nanospheres (designated as M/F), contributing to the enhanced specific interfaces and strong dielectric polarization. These Fe3O4 magnetic units are highly dispersed into the dielectric Mxene framework, leading to the optimized impedance balance and electromagnetic coordination capability. This composite way effectively exceeds the conventionally physical mixing, simple loading, and local phase separation method. Meanwhile, strong magnetic loss capability with significantly improved magnetic flux line density is achieved from microscale MXene and nanoscale Fe3O4, confirming our 3D multiscale magnetic coupling network. Accordingly, the M/F composites hold distinct microwave absorption property with the strong reflection loss (-50.6 dB) and effective absorption bandwidth (4.67 GHz) at the thickness as thin as only 2 mm. Our encouraging strategy provides important designable implications for MXene-based functional materials and high-performance absorbers.

Electron irradiation and annealing effects on the pseudogap in optimally doped YBCO single crystals

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity [Formula: see text] of the samples obeys an exponential temperature dependence in a broad temperature range [Formula: see text]. Here, [Formula: see text] is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression [Formula: see text] can be interpreted in terms of the mean-field theory where [Formula: see text] corresponds to the mean-field transition temperature to the pseudogap state and the dependence [Formula: see text] is described within the framework of the BCS-BEC crossover theory.

Fertilization Methods for Organic and Conventional Potted Blueberry Plants

This study determined optimal fertilization for each of three production methods (i.e., two organic and one conventional) of potted Vaccinium corymbosum ‘Duke’ northern highbush blueberry plants. The three production methods were as follows: 1) organic granular [(OG) organic coir substrate fertilized with Bio-Fert General Purpose + bloodmeal applied at 4.4, 7.3, 10.2, 13.1, and 16.0 g/pot nitrogen (N)], 2) organic liquid [(OL) organic coir substrate fertilized with Bio-Fert General-Purpose Liquid + calcium oxide (CaO) applied at 12.2, 14.7, 18.6, 25.3, and 39.5 mmol·L–1 N), and 3) conventional (C; pine bark, coir, and peat substrate fertilized with Osmocote Plus 15N–3.9P–9.9K, 5- to 6-month-duration controlled-release fertilizer applied at 4.4, 7.3, 10.2, 13.1, and 16.0 g/pot N). Blueberry plants were grown in #5 black, squat nursery containers outdoors in the Niagara peninsula, ON, Canada for two (2015–16) growing seasons. Both of the organic and the conventional production systems produced healthy blueberry plants when fertilizer was applied appropriately. With fertilizer application at 4.4 and 7.3 g/pot N for C, 12.2 and 14.7 mmol·L–1 N for the OL, and 8.50 to 13.95 g/pot N for the OG treatments, healthy plant growth was observed in combination with low nutrient leaching. High fertilizer rates resulted in excessive root zone electrical conductivity (EC), poor plant growth, and interveinal chlorosis, which affected fruit production negatively. For C and OL treatments, fertilization at rates of 4.4, 7.3 and 10.2 g/pot N, and 12.2, 14.7, and 18.6 mmol·L–1 N, respectively, produced the greatest total fresh weight of fruit. For OG, a large total fruit fresh weight was produced by all plants with no difference among fertilizer rates. This study suggests optimal fertilizer rates from 4.4 to 7.3 g/pot N for C, 12.2 to 14.7 mmol·L–1 N for the OL treatment, and from 8.50 to 13.95 g/pot N for the OG treatment can be applied based on the methods described in this study during potted blueberry production in nurseries and home gardens.

Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields

We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T*(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest the presence of a highly conducting region that is dominating the electric transport in narrow bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.

Temperature effect on dynamic properties of the 1D CDW system in the presence of the uncondensed-carriers: A numerical study

We report results regarding the temperature effect on dynamic properties of a 1D CDW system in the presence of normal carriers. It was showed that, for a given normal carriers concentration, the CDW phase profile fluctuations are attenuated by thermal fluctuations for the reason that the free-carrier relaxation process leads to a screening of the applied electrical field to depin the CDW. Further, the behavior of both the threshold field and nonlinear excess conductivity with respect to temperature were found to be non-monotonous. These findings are explained by the damping process and by generating CDW dislocation.

Direct-patterned copper/poly(ethylene oxide) composite electrodes for organic thin-film transistors through cone-jet mode by electrohydrodynamic jet printing

Direct-patterned Cu-based conductive electrodes were printed through electrohydodynamic (EHD) jet printing via cone-jet mode. The introduction of a capping agent in the synthesis of the Cu ink limited excessive conductivity, which enabled the pristine Cu ink to achieve the various printing modes of EHD jet printing: dripping, micro-dripping, cone-jet, and multi-jet. We also obtained optimal printing conditions by adjusting the viscosity by adding poly(ethylene oxide) (PEO) to the pristine Cu inks, resulting in well-defined printing patterns. The optimized PEO content in the ink was determined to be ∼10 wt%, which gave us a stable cone-jet mode and well-defined Cu/PEO composite electrode lines with sharp edges. We utilized the Cu/PEO composite electrode lines as source and drain and a triisopropylsilylethynyl (TIPS)–pentacene/PS blend as the active layer for bottom-gate bottom-contact organic field-effect transistors (OFETs). The resulting devices exhibited an average field-effect mobility (μFET), threshold voltage (Vth), and on/off current ratio (Ion/Ioff) of 0.253 cm2/V, 0.253 V, and ∼106, respectively.

Enhanced surface superconductivity in Ba(Fe0.95Co0.05)2As2

We present direct evidence for an enhanced superconducting Tc on the surface of cleaved single crystals of Ba(Fe0.95Co0.05)2As2. Transport measurements performed on samples cleaved in ultra-high vacuum show a significantly enhanced superconducting transition when compared to equivalent measurements performed in air. Deviations from the bulk resistivity appear at 21 K, well above the 10 K bulk Tc of the underdoped compound. We demonstrate that the excess conductivity above the bulk Tc can be controllably suppressed by application of potassium ions on the cleaved surface, indicating that the enhanced superconductivity is strongly localized to the sample surface. Additionally, we find that the effects of the potassium surface dosing are strongly influenced by the presence of residual gas absorbates on the sample surface, which may prevent effective charge transfer from the potassium atoms to the FeAs plane. This further supports the conclusion that the effects of the dosing (and enhanced superconductivity) are localized within a few layers of the surface.

Numerical experiments on the dynamics of two-dimension charge-density-waves (CDW’s) system in the presence of the weak interchain interaction effect

Layered charge-density-wave (CDW) materials exhibit a lot of interesting aspects for their potential in a variety of device applications. So, a good understanding of their properties may enable the better development of new devices based on them. We address in this paper a study of the dynamic properties of CDW two-dimension electronic crystal in the presence of weak interchain interaction. This study was done through numerical experiments based on the generalized Fukuyama–Lee–Rice (FLR) model. One of the results of this Letter showed that the time-dependent spatially averaged velocity exhibits the steady-state regime characterized by a series of quasi-periodic fluctuations. Moreover, it was found that the increase in the weak interchain interaction effect reduces the NBN amplitude and normalized excess conductivity. All findings accessed here were discussed in the context of the inhomogeneous nature of CDW’s dynamics, damping mechanism as well as the attenuation of phase solitons which are nucleated when the CDW’s slide.

Dimensionality and superconducting parameters of YBa2Cu3O7−d/(WO3 NPs)x composites deduced from excess conductivity analysis

Superconducting composite products of type YBa2Cu3O7−d (noted Y-123) added with different contents (x wt.%) of tungsten oxide nanoparticles (WO3 NPs), x = 0.0–1.0 wt%, were produced via the standard solid-state reaction technique. Samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical resistivity measurements. XRD examination showed that the Y-123 orthorhombic structure is not altered by WO3 NPs additions. SEM observations indicated a reduction in the grains size with the increase of nanoparticles content. The investigation of the excess conductivity of different prepared composites was analyzed using Aslamazov-Larkin (AL) model. The investigated samples comprised of five distinct fluctuation regimes, namely short-wave (SWF), one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and critical (CR) fluctuations regimes. The coherence length along c-axis at zero-temperature (ξc(0)), lower and upper critical magnetic fields (Bc1 and Bc2), critical current density (Jc) and numerous other superconducting parameters were estimated with respect to WO3 NPs content. Compared to undoped Y-123 sample, it was found that an amount of x = 0.05 wt% of WO3 NPs is appropriate to improve the physical performances of Y-123, whereas with further increasing x, these performances were weakened.

Enhanced Anharmonic Oscillations in Cu0.5Tl0.5Ba2(Ca2−yMgy)Cu3−xCdxO10−δ (y = 0, 1; x = 0, 1.5) Superconductors

Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (undoped), Cu0.5Tl0.5Ba2(CaMg)Cu3O10−δ (Mg-doped), Cu0.5Tl0.5Ba2Ca2Cu1.5Cd1.5O10−δ (Cd-doped), and Cu0.5Tl0.5Ba2(CaMg)Cu1.5Cd1.5O10−δ (Cd/Mg-codoped) samples were synthesized by two-step solid-state reaction at 860°C to investigate the possible role of anharmonic oscillations of atoms in the mechanism of high critical temperature (Tc) superconductivity. The samples showed orthorhombic crystal structure with smaller and larger unit cell volume for the Mg- and Cd/Mg-codoped samples, respectively, compared with the undoped sample. Tc observed by resistivity measurements decreased in the Cd-doped samples, but the maximum suppression was observed in the Cd/Mg-codoped sample showing semiconductor behavior. Fourier-transform infrared (FTIR) absorption spectroscopy revealed hardening of apical oxygen modes on the incorporation of Mg atoms as compared with the undoped sample and similarly with the doping of Mg atoms in the Cd-doped sample, confirming the intrinsic inclusion of these elements in the final compound. Excess conductivity analysis revealed suppression in the coherence length (ξc(0)), interlayer coupling (J), phase relaxation time (τφ) of carriers, Fermi velocity (VF) of carriers, Ginzburg–Landau (GL) parameter κ, breaking energy (Ebreak), and magnetic field penetration depth (λp.d) in Cd-doped samples. The values of Bc0(T), Bc1(T), and Jc(0) increased in the Cd-doped samples, showing enhancement of flux-pinning characteristics. It is proposed that Cd doping at CuO2-planar site induces anharmonic oscillation in the solid-state medium, which suppresses the density of phonons and thereby the density of Cooper pairs and hence superconductivity. These studies emphasize the essential role of electron–phonon interactions in the mechanism of high-Tc superconductivity.

Excess conductivity investigations of WO3 nanowires added to YBa2Cu3O7-d superconductor

Series of YBa2Cu3O7-d + x wt% WO3 nanowire mixtures where x = 0.0–2.0 wt% were prepared via solid-state reaction method. X-ray diffraction (XRD) patterns show the unaffected orthorhombic structure in various composites. Scanning electron microscopy (SEM) micrographs show the increase in grains size and the filling of voids between grains by WO3 nanowires. The superconducting transition temperatures deduced from electrical resistivity versus temperature (ρ(T)) measurements are almost unchanged by lower WO3 nanowires addition (i.e., x 0.5 wt%). The analysis of excess conductivity fluctuation (∆σ) by means of Aslamazov–Larkin (AL) and Lawrence–Doniach (LD) approaches was investigated. Dimensional fluctuations, coherence lengths, effective layer thickness, zero temperature lower and upper critical magnetic fields (Bc1 (0) and Bc2 (0)), and critical current density at temperature T = 0 K (Jc(0)) were extracted and discussed in relation with the structure and morphology. Improvements in Bc1 (0), Bc2 (0), and Jc(0)) were noticed for samples added with lower WO3 nanowires content, particularly for x = 0.1 wt% composite sample.

Fluctuation Conductivity and Its Scaling Behavior in BaFe1.9Co0.1As2 Superconductor

Excess fluctuation conductivity of BaFe1.9Co0.1As2 single crystal was studied by measurements of temperature and magnetic field dependence of resistance. The mean field critical temperature Tc (H) is determined by using the criterion of the dR/dT as a function of temperature, where a unique sharp peak appears in the dR/dT curves. By analyzing the excess fluctuation conductivity and the resistance experimental data in the framework of Aslamazov and Larkin theory, different fluctuation regimes such as the three-dimensional (3D), the two-dimensional (2D), the one-dimensional (1D), and short-wave fluctuation (SWF) were identified. In the mean field region, it was also found that the analyses of the resistance experimental data based on the Aslamazov-Larkin theory describes the real measured resistance data very well down to about 0.5 Rn at different regions, which supported the excess fluctuation conductivity results. Based on the lowest Landau level method, both the three-dimensional (3D) and two-dimensional (2D) scaling behaviors were observed in the fluctuation conductivity at magnetic field larger than 5 T and different temperature interval around the mean-field critical temperature Tc.

The effect of high-temperature annealing on the temperature dependence of the pseudogap of YBa2Cu3O7–δ single crystals irradiated with high-energy electrons

The effect of high-temperature annealing on the basal-plane conductivity of HTSC YBa2Cu3O7–δ single crystals irradiated with high-energy electrons is investigated. It is found that the excess conductivity Δσ(Т) of YBa2Cu3O7–δ single crystals in a broad temperature range Tf<T<T∗ is described by an exponential temperature dependence. Moreover, the description of excess conductivity using the Δσ∼exp(Δab∗/T) relation can be interpreted in terms of the mean-field theory, where T∗ is presented as the average field temperature of the transition to the pseudogap (PG) state, and the temperature dependence of that pseudogap is adequately described in terms of the BCS-BEC crossover theory. The high-temperature annealing results in an unexpected phenomenon: the absolute value of the pseudogap is increased, and the excess conductivity is generally decreased with respect to the initial unirradiated sample.

Features of Excess Conductivity Behavior in a Magnetic Superconductor Dy0.6Y0.4Rh3.85Ru0.15B4

The temperature dependencies of the excess conductivity σ′(T) and possible pseudogap (PG), Δ*(T), in a Dy0.6Y0.4Rh3.85Ru0.15B4 polycrystal were studied for the first time. It was shown that σ′(T) near Tc is well described by the Aslamazov–Larkin (AL) fluctuation theory, demonstrating a 3D–2D crossover with increasing temperature. Using the crossover temperature T0, the coherence length along the c axis, ξc(0), was determined. Above the level of T2D > T0, an unusual dependence σ′(T) was found, which is not described by the fluctuation theories in the range from T0 to TFM, at which a ferromagnetic transition occurs. The range in which superconducting fluctuations exist is apparently quite narrow and amounts to ΔTfl ≈ 2.8 K. The resulting temperature dependence of the PG parameter Δ*(T) has the form typical of magnetic superconductors with features at Tmax ≈ 154 K and the temperature of a possible structural transition at Ts ∼ 95 K. Below Ts, dependence Δ*(T) has a shape typical for PG in cuprates, which suggests that the PG state can be realized in Dy0.6Y0.4Rh3.85Ru0.15B4 in this temperature range. Comparison of Δ*(T) with the Peters–Bauer theory made it possible to determine the density of local pairs near Tc, 〈n↑n↓〉(TG) ≈ 0.35, which is 1.17 times greater than in optimally doped YBa2Cu3O7–δ single crystals.

Effect of Cd intercalation on the superconducting properties of (Cu0.5-yKyTl0.5)Ba2Ca2Cu3-xCdxO10-δ (y = 0, 0.25; x = 0, 0.5, 1.0, 1.5, 2.0) superconductors

(Cu0.5Tl0.5)Ba2Ca2 Cu3-xCdxO10-δ (x = 0, 0.5, 1.0, 1.5, 2.0) samples are synthesized for the investigation of role of an-harmonic oscillations in the mechanism of high Tc superconductivity. The density of carriers in the conducting planes is enhanced with the doping of K at the (Cu0.5Tl0.5)Ba2O4-δ by synthesizing (Cu0.25K0.25Tl0.5)Ba2Ca2Cu3-xCdxO10-δ (x = 0, 0.5, 1.0, 1.5, 2.0) samples. These samples were synthesized by two step solid state reaction method accomplished at 860 °C and studied their superconducting properties by resistivity measurements, X-ray diffraction analysis and FTIR absorption measurements. The planar reflections observed in the XRD analysis of the samples are best fitted to the orthorhombic crystal structure. The c-axis length and the volume of the unit cell increases with the enhanced doping of Cd in the final compound. The onset temperature of superconductivity Tc (onset) and the zero-resistivity critical temperature Tc (R = 0) suppresses with the increased doping of Cd in the final compound. An improvement in the Tc (onset) and Tc (R = 0) is observed in K-doped samples that arises due to increase in the density of free carriers supplied by alkali atoms. A softening of apical oxygen mode of type Cu(1)‒OA‒Cu(2)/Cd is observed with the increased doping of Cd at the CuO2 planar sites. The apical oxygen mode of type Tl‒OA‒Cu(2)/Cd is, however, did not change with the doping of Cd in the final compound. The planar oxygen mode (545 ‒ 570 cm−1) is hardened with the enhanced doping of Cd in the final compound. The excess conductivity analyses of conductivity data have shown a shift in the various cross-over temperatures, Tcmf and T* towards lower temperatures with the enhanced doping of Cd in the final compound. The value of α determining the defect density also increases with the increased doping of Cd in the final compound. The coherence length along the c-axis ξc(0), interlayer coupling J, magnetic field penetration depth λp.d and Ginzburg Landau (GL) parameter κ decreased with the increase doping of Cd. The phase relaxation time of the carriers Ꞇϕ, the Fermi velocity VF of the carriers decreased while Bc0(T), Bc1(T) and Jc (0) are enhanced with increase doing of Cd in the final compound.

Characterization of a microwave plasma jet (TIAGO) in‐contact with water: Application in degradation of methylene blue dye

AbstractPlasma in or in‐contact with liquids is a research field that has great potential in the treatment of wastewater. Today, efforts are focused on finding a plasma source that can efficiently remove persistent pollutants from water. In this study, we evaluate the effectiveness of a microwave plasma jet, in TIAGO (Torche à Injection Axiale sur Guide d'Ondes) configuration, using methylene blue (MB) as a model organic contaminant. The assessments conducted herein show that MB degradation is promoted at short nozzle–water distance, high gas flow rate, elevated microwave power, and excessive initial water conductivity (up to 10,000 µS/cm). The plasma characteristics, namely composition, electron density, and OH rotational temperature, as well as water acidity and conductivity are also evaluated.

Conductivity Fluctuation and Some Parameters of High temperature Superconductor Polycrystalline Y1Ba2Cu3O7−δ doped with Silver Nanoparticles

In this study, we report the effect of Ag nanoparticles doping on the dimensional fluctuations of superconducting order parameters, crystal structure, and some parameters of Y1Ba2Cu3O7−δ + × Ag (x = 0.0, 0.06, 0.1, 0.3, and 0.6 wt%) polycrystalline ceramics. By increasing the content of Ag in YBCO matrix, X-ray diffraction (XRD) with the Rietveld refinement technique revealed that the crystal lattice parameters changed and the orthorhombicity decreased slightly. Also, the increase of Ag wt% caused a decrease of superconducting transition temperatures (Tc) which are determined from the standard four-probe method and dropped abruptly. Aslamazov–Larkin (AL) model was used to analyze excess conductivity fluctuation. Lawerence–Doniach (LD) temperature named TLD which is responsible for the dimensional nature of fluctuation inside the grains is influenced by nano-silver combination in the compound. Crossover temperature from 2D to 3D (TLD) decreased in the mean-field region as a resultant dominance of 3D region by increasing of Ag in YBCO matrix. The decrease in zero-resistance critical temperature (Tc zero), zero-temperature coherence length along the c-axis ξc(0), and super layer length d values implies the degradation of inter-grain weak links, more disorder state of samples and unsettling of the mean free path for the charge carriers respectively with addition of silver nanoparticles. The calculations based on AL and LD model showed the highest anisotropy (γ = 1.34681) for the x = 0.6 sample. The size of the Ag ions, being larger compared to Cu ions, and the number of substitution sites affects the coupling between the CuO2 planes and that results in higher anisotropy. Critical magnetic fields Bc1(0), Bc2(0), and critical current density Jc(0) were indirectly calculated from the Ginzburg–Landau (GL) number and GL equations. By increasing the doping level of silver nanoparticle, these parameters were found to be higher in Ag-added YBCO samples compared to the pure Y123, meaning better intrinsic flux pinning properties of doped Y123. The silver nanoparticle inclusion reduces the grain size and increases the strength and hardness of the parent compound.

Argon Annealing and Oxygen Purity Affect Structural and Critical Parameters of YBCO Copper Oxide System

We report here the effects of argon annealing on the structural and critical parameters of oxygenated copper oxide system with different oxygen purities (Hp 99.99% and Lp 93%). It is found that the structure of the samples maintains orthorhombic single phase independent of both oxygen purity and annealing. The mean field temperature Tcmf is increased by annealing from 92 to 94 K for Lp sample, but it is decreased from 93 to 90 K for Hp sample. Similar behavior is obtained for crossover temperatures To. Further, the coherence length and interlayer coupling are decreased by annealing for both samples, and their values are higher for Lp samples than those for Hp samples. The excess conductivity analysis reveals two different exponents corresponding to crossover temperature for each plot: The first exponent is obtained in the normal field region at a temperature range of ln e (0 ≥ ln e ≥ − 2), and their values are 1.50, 1.53, 1.62 and 1.47 for both samples, in which the order parameter dimensionality (OPD) is one dimension, while the second exponent is obtained in the mean field region at a temperature range of ln e (− 2 ≥ ln e ≥ − 4), and their values are 0.39, 0.59, 0.56 and 0.41 for both samples, in which the OPD is 3D. Although the critical temperatures are decreased by annealing for both samples, the critical fields and critical currents are increased by annealing for both samples and their values are higher for Hp sample than those for Lp sample. Our results are discussed in terms of oxygen vacancies and concentration of carriers which are produced by annealing and oxygen purity for the considered samples.

Effect of In and Cd co-doping on the thermoelectric properties of Sn1−xPbxTe

Pristine tin telluride (SnTe) with a similar electronic structure to PbTe shows inferior thermoelectric performance owing to high p-type hole concentration (1021 cm−3), high lattice thermal conductivity, κlatt (∼2.8 W mK−1 at room temperature) and large energy gap between light and heavy hole valence bands. Interestingly, 30 mol% substitution of lead in SnTe decreases the excess hole carrier concentration and lattice thermal conductivity (∼0.67 W m−1K−1 at 300 K) significantly. Here, we report the promising thermoelectric performance in Sn0.70Pb0.30Te by enhancing the Seebeck coefficient via the co-adjuvant effect of resonant level formation and valence band convergence. We obtain a Seebeck coefficient value of ∼141 μV K−1 at 300 K, which further increases to ∼260 μV K−1 at 708 K for Sn0.70Pb0.30Te—3% Cd and 0.50% In sample. This is one of the highest S values for SnTe based system, to the best of our knowledge. In and Cd have discrete but complementary roles to augment the Seebeck coefficient value of Sn0.70Pb0.30Te where In acts as a resonant dopant and Cd serves as valence band convergent, respectively, as demonstrated by the well-known Pisarenko plot of SnTe. Finally, we have achieved a maximum thermoelectric figure of merit, zT, of ∼0.82 at 654 K for Sn0.70Pb0.30Te—3% Cd and 0.25% In sample.