High Figure Of Merit Value Research Articles

First‐principles investigation of Rb2Ag(Ga/In)Br6 for thermoelectric and photovoltaic applications

AbstractIn this article, we have systematically investigated the structural, electronic, optical and thermoelectric properties of Rb2Ag(Ga/In)Br6. The resulting negative formation energy along with the absence of imaginary phonon modes confirm the thermodynamic stability of Rb2Ag(Ga/In)Br6. In addition, the derived electronic properties by using GGA‐PBE + mBJ + SOC functional show that the direct band gap values are 1.21 eV and 1.42 eV for Rb2AgGaBr6 and Rb2AgInBr6, respectively. Furthermore, the dispersed direct band nature of Rb2Ag(Ga/In)Br6 leads to their outshining optical properties such as higher order (105 cm−1) absorption coefficient, appreciable optical conductivity, and low reflectivity. Moreover, the higher figure of merit values of Rb2Ag(Ga/In)Br6 are resulted from their ultra‐low thermal conductivity and high electrical conductivity. Thus, Rb2Ag(Ga/In)Br6 are predicted to be potential photovoltaic and thermoelectric materials.

Amorphous Ge-Sb-Se-Te chalcogenide films fabrication for potential environmental sensing and nonlinear photonics

Quaternary Ge-Sb-Se-Te chalcogenide thin films were fabricated by rf magnetron sputtering from Ge19Sb17Se64−xTex (x = 5, 10, 15, 20) sputtering targets in order to select appropriate compositions for infrared sensor and optical nonlinear applications. An influence of chemical composition and deposition parameters on the optical properties, structure and wettability was thus studied. The amorphous thin films seem to be constituted by selenide entities that can include tellurium atoms in variable proportion such as [GeSe4−xTex] and [SbSe3−xTex] (x = 0, 1, 2) and Ge(Sb)-Ge(Sb) bonds according to Raman spectroscopy. Contact angle measurements of the thin films showed values of 68–71° for water and their surface energies in the range of ∼36–39 mJ·m−2 seem suitable for surface functionalization required for photonic sensor development. Furthermore, the maximum nonlinearity at the telecom wavelength with respect to the highest figure of merit value was found for the thin film with composition Ge19Sb17Se56Te8 having nonlinear refractive index of 28 × 10−18 m2·W−1. Due to their low optical bandgap energies, they may find their full interest for nonlinear optics in the mid-infrared range. Wide IR transparency in combination with high (non)linear refractive indices make these materials attractive in the field of mid-IR sensing and optical nonlinear devices.

Ultra-sensitive narrow-band plasmonic perfect absorber for sensing applications

Plasmonic nanostructure-based sensors have a broad range of applications in food assessment, hazardous gas monitoring, medical diagnosis, and vapor sensing. However, it is still challenging to establish a high performance plasmonic sensing platform that simultaneously provides high refractive index sensitivity and high figure of merit values. Based on simulations using the finite element method, we engineered an ultra-sensitive all-metal plasmonic perfect absorber (a-MPPA) for sensing applications. The proposed a-MPPA structure is based on closely spaced silver (Ag) nanocones over an Ag thin film and it exhibits ultra-sharp spectral absorption with robust hot spots of electric and magnetic fields. The high optical absorption and localized giant field enhancement depend on the structural configuration of the platform. We observed that the absorbance of the optimized structure exceeded 99%, with an ultra-narrow plasmonic peak (4.3 nm), thereby suggesting that the proposed nanostructure is a good candidate for sensing applications. The sensing performance of the a-MPPA platform was outstanding, with bulk sensitivity of 1006 nm/RIU, large figure of merit value of 233.9 RIU−1, and high quality factor of 233.4. Theoretical analyses based on Campbell’s model indicated that the a-MPPA platform is suitable for molecular detection, with a detection range extending to 50 nm. The proposed narrow-band perfect absorption plasmonic nanostructure has great potential for applications in sensing.

Tuning the optoelectronic and thermoelectric characteristics of narrow bandgap Rb2AlInX6(X= Cl, Br, I) double perovskites: A DFT study

In this paper, the structural, optoelectronic, and thermoelectric characteristics of halide-based double perovskite Rb2AlInX6 (Cl, Br, I)compounds are examined by DFT. These compounds belong to the cubic family and their lattice parameter increased when halogens are replaced from Cl to I. The structural stability is confirmed by computing the enthalpy of formation, tolerance factor, and pugh's ratio. The Pugh's ratio demonstrates the ductile behavior of the compounds under consideration. A comprehensive study of the optoelectronic characteristics indicates that Rb2AlInX6 (Cl, Br, I) double perovskites are potential candidates for optoelectronic devices due to their narrow bandgap (1.05, 0.65, and 0.25 eV). The calculated power factor and thermal conductivity lead to the high figure of merit values (0.75–0.77), which show the potential of these compositions for thermoelectric devices. These investigations provide an insightful understanding of these materials for their future utilization.

Relying on Dynamically Morphing Blades to Increase the Efficiency of a Cycloidal Rotor

The configuration of the airfoil has a significant impact on its aerodynamic performance. This paper aims to improve the aerodynamic efficiency of the cycloidal rotor system by using dynamically morphing blades. Three different camber morphing concepts (leading edge deflection, trailing edge deformation and cambered NACA profile) have been applied to a baseline 2-bladed system with rotating and pitching NACA0015 aerofoils. Then, based on these camber concepts, 2D URANS numerical simulations were conducted for blades with different morphing degrees using OpenFOAM. The simulation results verified that the flow field condition could be optimized and significantly higher thrust and efficiency could be achieved by properly tuning the morphing control. Especially, in the case of 10% trailing edge camber and 16% NACA camber, compared with baseline case, 28.1% and 43.5% higher figure of merit values were obtained, respectively. The simulation files and the results for the last rotor revolution of each case presented in this paper are available in the following dataset: https://doi.org/10.18419/darus-2191.

Influence of solvent system on the optoelectrical properties of PCL/carbon black nanofibers

In this study, conductive and transparent polycaprolactone (PCL)/carbon black (CB) nanofibers are produced by electrospinning. In order to investigate the effect of solvent system on the optoelectrical properties of PCL/CB nanofibers, the fibers are produced from two different solvent systems; namely, chloroform (CHL) and dimetyl formamid (DMF). For optoelectrical characterization, nanofibers are produced with different deposition times in the range of 1–10 minutes. Surface, optical, electrical and optoelectrical properties of the PCL/CB nanofibers are evaluated. Nanofibers produced from CHL solvent system results in non-uniform nanofibers with higher diameters. They also give a larger diameter distribution. On the other hand, nanofibers with uniform and smaller diameters are obtained from DMF system. UV-spectrophotometer analysis show that nanofiber mats produced from both solvent systems have similar optical transparencies. Lower sheet resistance values are obtained with the nanofiber mats produced from DMF system according to electrical characterizations. Higher Figure of Merit values are calculated for the nanofiber mats produced in DMF solvent system. Considering all the results, it can be concluded that PCL/CB nanofibers produced from DMF solvent system are better candidates compared to the nanofibers produced from CHL solvent system for optoelectrical applications.

Optoelectronic Properties of Antimony Doped Tin Oxide Thin Films Obtained by Spray Pyrolysis

Antimony doped tin oxide (ATO) thin films are deposited on corning glass substrate using the spray pyrolysis technique. The experimental parameters such as distance between the substrate and source (10-30 cm), substrate temperature (350-450°C) and atmospheres (Nitrogen and Forming gas) are varied to study their effect on the properties of ATO thin films. The ATO thin film annealed at 425°C exhibits the lowest electrical resistivity of 2.23×10-2 Ω-cm. Besides, the film annealed in the nitrogen atmosphere showed a less resistivity value of 9.06×10-3 (Ω-cm) than the forming gas atmosphere. The film doped with 3 at% of Sb revealed the highest figure of merit value of 11.45x10-2 Ω-1. The preferential orientation is observed at the (200) diffraction plane in all the cases from the structural studies. Furthermore, the intensity of the diffraction planes decreases as the temperature increases. The average transmittance of 75% is obtained for ATO thin films.

NiTiHf shape memory alloys as phase change thermal storage materials

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Computational Search for Better Thermoelectric Performance in Nickel-Based Half-Heusler Compounds.

Half-Heusler alloys have recently received extensive attention because of their promising thermoelectric (TE) properties and great potential for applications requiring efficient thermoelectricity. Although the conversion efficiency of these materials can be greatly improved by doping, it is still far away from the real-life applications. Therefore, search for better parent TE compounds is deemed urgent. Using a high-throughput search method based on first-principles calculations in newly proposed 378 half-Heusler alloys, we identify nine nickel-based half-Heusler semiconductors as candidates and systematically study their mechanical, electronic, and transport properties. Their mechanical and dynamical stabilities are verified based on the calculated elastic constants and phonon spectra. The electronic structure calculations indicate the existence of direct energy gaps in the NiVZ (Z = Al, Ga, and In) and indirect energy gaps in the NiTiZ (Z = Si, Ge, and Sn) and NiScZ (Z = P, As, and Sb) compounds. Among them, NiVAl, NiVGa, and NiVIn exhibit a sharp slope of density of states near the Fermi level, which is predicted to be essential for a high TE performance. Further investigation on carrier concentration and temperature dependence of TE properties shows the high power factors of NiVAl, NiVGa, and NiVIn, which are responsible for their high figure of merit values. The highest maximum power factor of 5.152 mW m–1 K–2 and figure of merit of 0.309 are predicted for pristine half-Heusler NiVIn, which are larger than the values of some known pristine and doped half-Heusler TE materials. Our work opens up new avenues for rationally searching better TE materials among half-Heusler alloys for applications in fields requiring efficient thermoelectricity.

New p-type sp-based half-Heusler compounds LiBaX(X = Si, Ge) for spintronics and thermoelectricity via ab-initio calculations

We have investigated the structural, electronic, magnetic, elastic and thermoelectric properties of the sp-based half-Heusler LiBaX (X = Si and Ge) alloys using the full-potential linearized augmented plane wave method of density functional theory. Two approaches are employed to approximate the correlation-exchange potential, namely the generalized-gradient approximation and the modified Becke–Johnson. Both compounds free of transition metals are ferromagnetic, half metallic with a large spin-flip gaps which are appropriate for Spintronic applications. Their half-metallicity is preserved under large lattice constant and pressure change which make them promising candidates for spintronic devices. The transport properties reveal high figure of merit values making these compounds great thermoelectric candidates. Moreover, the studied half-Heuslers are mechanically stable and both of them exhibit negative formation energy and cohesion which indicate the possibility of synthesizing and stabilizing these cheap and available materials. Up to date, no experimental or theoretical studies have been carried out regarding LiBaSi, while for LiBaGe, thermoelectric properties have not been investigated yet.

Thermoelectric properties of Pr-substituted YBCO ceramics

The thermoelectric properties of Pr-substituted YBCO ceramics were investigated from room temperature to 773 K. The ceramics of (PrxY1−x)1.06Ba1.94Cu3O7−y ((PrxY1−x)BCO) where x = 0–1 were successfully prepared by a conventional sintering method at 920 °C for 12 h in normal air atmosphere. Phase identification was carried out by X-ray diffraction (XRD) technique. The microstructure of samples was studied using scanning electron microscopy (SEM). The thermogravimetric and differential thermal analyses (TG/DTA) were used to examine the thermal properties of samples. In addition, electrical resistivity, Seebeck coefficient, and thermal conductivity were investigated and discussed. The average phonon velocity was measured using the Pulse-echo technique at room temperature to discuss the substitution effect on the lattice thermal conductivity. It was observed that the substitution of Pr in YBa2Cu3O7−y improved the Seebeck coefficient (α) and showed higher figure of merit values at a wide temperature range from 298 to 773 K compared to those of pure YBCO. These results suggested that Pr substitution was a promising approach for improving thermoelectric properties of YBCO-based compounds. This suggests that, when optimized, the YBCO-based materials could show high potential for intermediate and high-temperature thermoelectric applications.

Dramatically Improved Thermoelectric Properties by Defect Engineering in Cement-Based Composites.

In recent years, the problem of overheating in summer has been of great concern. Pavements are continuously exposed to solar radiation, and because of high temperatures, pavement temperatures reach 60 to 70 °C. This potential low-grade heat has been unused. Cement-based composites with thermoelectric properties can convert this low-grade heat to useful electrical energy. The importance of this green technology for generating renewable energy and sustainable development has been widely accepted and noticed. However, the power factor of current cement-based composites is too low, and harvesting low-grade heat on a large scale and at low cost requires improving the thermoelectric properties of cement-based composites. In this paper, we present a method to increase the electrical conductivity of ZnO and thus improve the thermoelectric properties of cement-based composites by defect engineering, obtaining a high power factor of 224 μWm-1 K-2 at 70 °C, a record value recently reported for thermoelectric cement-based composites. Zinc oxide powder was treated with a reducing atmosphere to increase the content of oxygen defects and thus improve the electrical conductivity. Pretreated ZnO powder of 5.0 and 10.0 wt % expanded graphite were added to the cement matrix. The ZnO/expanded graphite cement-based composites were made and tested for their thermoelectric properties using a dry pressing process, which exhibited excellent thermoelectric properties. The result showed high conductivity (12.78 S·cm-1), a high Seebeck coefficient (-419 μV/°C), a high power factor (224 μWm-1 K-2), and a high figure of merit value (8.7 × 10-3), which facilitate future large-scale applications. Using the cement-based composites to lay a road of 1 km in length and 10 m in width, 35.2 kW·h of electricity can be collected in 8 h. This study will inspire how to improve thermoelectric performance of cement-based composites.

Large-area spray deposited Ta-doped SnO2 thin film electrode for DSSC application

Large-area (10 × 10 cm2) Ta-doped SnO2 (TTO) thin film was deposited by a facile spray pyrolysis method. The crystallinity, phase purity, and texture properties of the film are studied using XRD analysis. The XPS study confirmed the charge state of Sn to be in 4+, O1s in 2−, and Ta to be in 5+ state. A homogeneous polyhedron morphology was witnessed owing to the Ta dopant effect. The TTO film was highly transparent in the visible to near infrared region (NIR) with an average transmittance value of 81% at 550 nm. The TTO film was having a free carrier concentration of 5.42 × 1021 cm−3 and mobility of 41.7 cm2/Vs. The 4 wt% Ta doped SnO2 electrode exhibits a low sheet resistance of 26 Ω/□ and a high figure of merit value of 6.15 × 10−3 Ω−1. The resistance stability of sheet resistance was fairly good up to 400 °C indicating suitability of the TTO electrode to serve as conducting photoanode/counter electrode in dye-sensitized solar cell (DSSC) device. The DSSC device fabricated with the TTO electrode exhibited appreciable efficiency of 3.26% which is attributed to the enhanced electrical and optical properties by way of doping with Ta element.

Transparent conducting SnO2 thin films synthesized by nebulized spray pyrolysis technique: Impact of Sb doping on the different physical properties

The impact of antimony (Sb) doping concentration on the different physical properties of transparent conducting tin oxide (SnO2) thin films synthesized through nebulized spray pyrolysis (NSP) method have been explored systematically. X-ray diffraction (XRD) results reveal the tetragonal cassiterite structure of single phase SnO2 and the decrement of crystallite size with rising Sb doping concentration. Uniform and compact surface morphology with continuous distribution of grains and reduction of grain size with increasing dopant amount are illustrated by scanning electron microscopy (SEM). The stoichiometry of SnO2 film with 2% Sb doping is confirmed by energy dispersive X-ray spectroscopy (EDS) study. The optical transmittance is more than 85% in the visible region for undoped film and enhanced in the near infrared (NIR) spectral region for all the films. The transparency is reduced and the optical band gap is found to increase from 3.69 eV to 3.90 eV upon Sb inclusion. The extinction coefficient, refractive index, dielectric constant, dissipation factor, volume energy loss function, surface energy loss function, optical conductivity and optical density of the films are determined and interpreted for different dopant concentrations. The photoluminescence (PL) spectrum demonstrates the enhancement of emission intensity with increasing Sb incorporation representing its suitability in the application of solid state lighting. The lowest resistivity of 6.435 × 10−4 Ω cm and the highest carrier concentration of 1.316 × 1021 cm−3 are achieved for the film with 8% Sb doping concentration. The mobility of the studied degenerated films is varied from 54.743 cm2/Vs for undoped films to 7.378 cm2/Vs for 8% Sb doped film and limited by ionized impurity scattering. The film deposited with 2% Sb doping level exhibits the highest figure of merit values in both visible and NIR wavelength region indicating its better role in optoelectronic applications.

Highly conducting and transparent low-E window films with high figure of merit values based on RF sputtered Al and In co-doped ZnO

In this work, we have studied the correlation between the electrical, optical and plasma properties of RF sputtered 1 at.% Al and In co-doped ZnO (AIZO) thin films with thickness 210–1590 nm in a comprehensive manner. The lattice strain of the hexagonal wurtzite ZnO structure decreases as the film thickness increases. The lowest resistivity of 8.9 × 10−4 Ω-cm is obtained for the 930 nm thick film with an electron concentration and mobility values of 3.96 × 1020 cm−3 and 17.7 cm2/Vs respectively. Optical transmission value is ~85%–90% in the range 400–700 nm for all the films. Most notably the figure of merit value of 2.65 × 10−2 Ω−1 for the 930 nm thick film is the highest among all the reports on AIZO films till date. High transparency in the visible region as well as higher reflectivity in the NIR region (with a plasma frequency of 8.2 × 1014 Hz) indicates its promising application in the low-E window.

Improvement of transparent conductive properties of Cu films by introducing H2 into deposition atmosphere during RF magnetron sputtering

Abstract Different thicknesses (2–250 nm) of Cu films were deposited on glass substrate by RF magnetron sputtering in Ar and Ar + H2 atmospheres at room temperature. It is found that crystallinity and conductive properties of the films enhance but visible light transmittance (TVis) decreases with increase of film thickness. Compared with the Cu films deposited in Ar, those deposited in Ar + H2 have higher crystallinity and surface roughness, and they have better conductive properties and higher TVis at film thickness above 5 nm. Overall, the Cu films deposited in Ar and Ar + H2 can be achieved higher figure of merit (FOM) in a thickness range of 3~5 and 5~8.5 nm, respectively. Furthermore, the higher FOM values of Cu film deposited in Ar + H2 atmosphere are higher than those of Cu film deposited in Ar atmosphere. The correlation between the improvement of transparent conductive properties of Cu films and modification of film microstructure due to introduction of H2 into deposition atmosphere is discussed.

Cold sintering and thermoelectric properties of Ca3Co4O9 ceramics

In this study, Ca3Co4O9 ceramics were successfully prepared using a cold sintering process at significantly low temperatures of approximately 150 °C. This new procedure was used to produce Ca3Co4O9 ceramics, in particular, as this material is extremely sensitive to the synthesis and processing owing to its partial decomposition into Co3O4 or Ca2Co2O5 as a secondary phase. Ca₃Co₄O₉ powder was prepared through a solid-state reaction and calcined at 900 °C. For the cold sintering process, the prepared powders were uniaxially pressed into 12 mm diameter discs of approximately 1 mm thickness, at 350 MPa, while the temperature was isothermally maintained at 150 °C for 1 h. Subsequently, selected “as prepared” ceramics were re-sintered at 900 °C for 6 h or 24 h. The results indicated that bulk densities greater than 74% of the theoretical density were obtained for the cold sintered ceramics. Compared to conventionally sintered ceramics, the cold sintered ceramics exhibited greater electrical conductivity (6459 S/m) and reduced thermal conductivity (0.672 W/m K) at 600 °C. The highest Figure of Merit value obtained was 0.12 for the cold sintered ceramics, which is thrice that of conventionally sintered ceramics. The cold sintering process was observed to be efficient in increasing bulk densification and improving the thermoelectric properties of Ca₃Co₄O₉ ceramics compared to the conventional sintering method.

Influence of Ti doping on SnO2 thin films properties prepared by ultrasonic spray technique

Titanium doped tin dioxide (Ti-SnO2) thin films have been deposited using ultrasonic spray technique to minimize the poor properties of the pure SnO2. The process has been carried out by doping SnO2 films with the appropriate percentage of titanium. X Ray Diffraction shows that the rutile structure remains the same of pure tin dioxide but with better crystallization. The titanium doping enhances the transmittance up to 83% and the conductivity about 1.4×102(Ω.cm)−1 approximately, with high figure of merit values about 7.64×10−3 Ω−1.these results are required specially for bio-sensors and optoelectronics

Using aluminum for scatter control in mammography: preliminary work using measurements of CNR and FOM.

Full-field digital mammography (FFDM) systems provide the current gold standard in mammographic examinations. Although FFDM provides the lowest mammographic doses, the radiation dose to the breast during mammographic examinations is still a concern. Thus, image quality optimization at the lowest dose is a major goal. In planar X-ray imaging, thin sheets of aluminum (Al) are used as filtration to reduce the number of low-energy X-ray photons reaching the patient. The goal of this work was to evaluate whether Al can be used in FFDM to remove scatter radiation from reaching the image detector, hence improving image quality. Doses were compared with the use of a grid. A Hologic Selenia mammographic unit was used to acquire images of two phantoms, namely, the ACR phantom and a Perspex phantom of 5cm. Images were acquired using two tube voltages (kVp) and filter combinations under two exposure/dose conditions. Al sheets of various thicknesses were placed between the phantom and the image detector. Contrast-to-noise ratio (CNR) and figure of merit (FOM) values were measured and compared with images acquired using a grid. When a constant dose was delivered to the image detector, the highest CNR was achieved using a grid; however, the highest FOM values were achieved when using 0.05mm thick Al sheets. This study successfully demonstrates that thin sheets of Al can be used in mammography examinations to reduce scattered radiation and improve image quality, as indicated by the measured CNR values. Given the limitations of this work, further kVp and target/filter combinations and various methods of image quality measurement need to be studied.

Highly transparent low resistance ATO/AgNWs/ATO flexible transparent conductive thin films

Indium-free flexible transparent conductive thin films (TCFs) composed of silver nanowire (AgNW) networks and Sb doped SnO2 (ATO) layers were prepared on polyethylene terephthalate (PET) substrates. The ATO layers were deposited via radio frequency (RF) magnetron sputtering at room temperature. The AgNWs were achieved via a modified polyol reduction method and embedded between the ATO layers. The effects of AgNW networks and ATO layers on electrical and optical properties of the ATO/AgNWs/ATO flexible tri-layer thin films are investigated. The ATO layers can improve the optical transmittance and reduce the resistivity of tri-layers, and the corresponding mechanisms are proposed. Typically, an ATO/AgNWs/ATO flexible tri-layers show a high figure of merit value (30.06 × 10-3 Ω-1) with a low sheet resistance of 7.1 Ω/sq. and a high transmittance of 85.7%. Meanwhile, the tri-layers present excellent mechanical flexibility, and the ATO layers acted as the protecting layers improve the adhesive and environmental stability at high temperature and humidity for the ATO/AgNWs/ATO flexible tri-layers. These results indicate that ATO/AgNWs/ATO flexible tri-layer thin films can be useful for the fabrication of wearable electronic devices.