Figure Of Merit Research Articles

Polymer enhanced sensitivity and figure of merit SPR optical fiber sensor for high refractive index and wide detection range

A highly sensitive sensor based on surface plasmon resonance (SPR) for high refractive index (RI) sensing is proposed, whose most unique feature lies in a high RI of polyvinylpyrrolidone (PVP) layer embedded between the optical fiber and Au film. The use of the high RI PVP layer amplifies the evanescent wave, thereby increasing sensitivity and improving figure of merit (FOM) of the SPR sensor. In addition, SPR sensor coated with a high RI PVP film breaks through the limitation that the inherent RI of optical fiber can only detect low RI, and can measure higher RI values and expand the measurement range. Experimental results demonstrate that, with a PVP layer thickness of 60 nm, showcasing superior performance compared to sensors lacking a PVP layer. Notably, this SPR sensor offers a cost-effective and straightforward fabrication process, promising broad application in environmental monitoring and biosensing.

A muon beam monitor for the CHNet-MAXI experiment at the RIKEN-RAL laboratory

The CHNet-MAXI experiment (Muonic Atom X-ray and prompt gamma spectroscopy for Isotopic analysis for cultural heritage) is an INFN Cultural Heritage program funded by Scientific Commission V, aiming at selecting the best figures of merit in the isotopic analysis of lead by means of muonic atom emission. The experiment will be deployed at RIKEN-RAL facility ISIS-STFC (UK), providing a pulsed muon beams with momenta between 15 and 90 MeV/c. The CHNet-MAXI apparatus will be mainly based on a 9 HPGe detectors array and innovative scintillator detectors read-out by SiPMs for the detection of the characteristic X and gamma rays emitted by isotopically enriched targets of Pb 204, 206, 207 and 208, after negative muon irradiation at the RIKEN-RAL beamlines. A muon beam hodoscope will be used as a beam x/y profiler and as a beam intensity monitor. This detector has been designed to provide a few mm spacial resolution, and it is based on 3 mm thick scintillating fibers, each read-out by a single SiPM at one edge. The setup is meant to be portable thanks to desktop HV and innovative open-FPGA DAQ modules. All the phases of the design, assembly, and testing of the CHNet-MAXI hodoscope are illustrated. Finally, first operation tests of this new beam monitor are shown.

Addressing the Challenge of a Simultaneous Destructive Assay of Plutonium and Uranium: Highly Precise, Robust, Universal, and Reagent-Free Differential Pulse Voltametric Method Development in Biodegradable Methanesulfonic Acid Medium.

The destructive assay of bulk uranium and plutonium, a cornerstone for chemical quality control and nuclear material accounting of fuel matrices, mandates robust and precise methodologies. Despite ongoing research, simultaneous, matrix independent determination of U and Pu has eluded solution owing to inherent limitations in aqueous acid medium, viz., coexistence of multiple oxidation states, coupled electrochemical reactions, smaller potential window, and requirement for multistep sample preconditioning and tedious electrode modification. The present study addresses this challenge wherein non-aqueous methanesulfonic acid (MSA) served the dual role of solvent and analyte media with a bare glassy carbon (GC) electrode. Fuel matrices, viz., (U, Pu)C, (U, Pu)O2, PuO2, UO3, UO2, and U3O8, were quantitatively dissolved in biodegradable MSA, without using any additives. Redox speciation of the analytes, U and Pu, in MSA was probed by ultraviolet-visible spectrophotometry and electrometry, revealing the absence of electrocatalytic regeneration and stabilization of single oxidation state, viz., U(VI) and Pu(IV), along with relevant redox-energetic (electron transfer and reversibility) and kinetic data. Bidentate coordination of MSA with the U analyte was indicated by X-ray absorption spectroscopy studies and was corroborated by density functional theory-based investigations, providing the optimized structure, viz., [UO2(MSA)2] and [Pu(MSA)4], binding modes and energy, partial charges, and molecular orbital diagrams. Based on these insights, the feasibility of differential pulse voltammetry (DPV)-based assay method development for U and Pu separately and in different U/Pu ratios, representing assorted fuel matrices, was probed. Analytical figures of merit for both U and Pu (detection limit of ∼10-5 M, precision of ∼0.2%, accuracy of ∼0.2%, high sensitivity, repeatability, and non-influence of relevant interferences) were determined, method validated employing actual fuel samples, and compared with the established, multi-step biamperometry method. Hence, a universal, simultaneous U and Pu destructive assay method in non-aqueous MSA media based on DPV with a commercial GC electrode was demonstrated.

Investigating the optical and electrical performance of rod coated silver nanowire-based transparent conducting films

Silver nanowires (Ag NWs) are highly promising building blocks for developing transparent conducting films (TCFs) due to their high electrical conductivity and good optical transparency. The large-scale production of Ag NW-based high-quality TCFs using low-cost processing methods can replace the traditional oxide based TCFs. Therefore, developing a reliable technique for large-scale fabrication of Ag NW-based TCFs is vital. This work involves the synthesis of Ag NWs, the fabrication of large-area Ag NW-based TCFs using a simple rod coating process, its optimization, and the performance analysis of the fabricated TCFs, including their demonstration as transparent heaters. The polyol synthesis method produces Ag NWs of lengths ranging from 25-110µm and diameters from 80-180 nm. The effect of Ag NW length, the number of coating passes, and the volume of the NW dispersion used per coating pass on the electrical and optical properties of the TCFs are studied by quantifying sheet resistance(Rs)and transmittance (T) of the film. The performance of the fabricated film is evaluated by estimating the figure of merit (FoM) in both percolative and bulk regimes. The TCF made with NWs of length 25.7µm and diameter 85.1 nm had the largest value of bulk FoM (101.3), percolative FoM (43.9), and, conductivity exponent (0.6). This elucidated the superior performance of the fabricated TCFs over those fabricated by other techniques. The critical thickness of the film (tmin), at the crossover between the percolation and bulk, scales with the shortest dimension of the NW, namely its diameter. The percolative FoM showed an increase, with a decrease in both sheet resistance and diameter of the NWs, with lowern. The fabricated TCF is tested as a transparent heater and the demonstration proves that rod coated Ag NW-based TCFs can be used for transparent electrode applications.

High Performance E-mode NiO/β-Ga2O3 HJ-FET with High Conduction Band Offset and Thin Recessed Channel

—In this paper, an enhancement-mode (E-mode) NiO/β-Ga2O3 heterojunction field-effect transistor (HJ-FET) with high conduction band offset (ΔEC) and thin recessed channel is proposed and studied by Sentaurus TCAD. Different from the existing HJ-FET with low ΔEC alignment, the High ΔEC HJ-FET can achieve a much lower on-resistance (Ron) due to the strong electron confinement effect. More importantly, the disadvantage in the threshold voltage (Vth) is compensated by reducing the thickness of the recessed channel, maintaining an almost unchanged Ron with the help of the special surface conduction channel. Compared with the corresponding Low ΔEC HJ-FET, at the same Vth ( 0.82 V), the Ron is decreased from 135 Ω/mm to 90.7 Ω/mm and the maximum drain current is increased from 14.9 mA/mm to 83.1 mA/mm. By adding a top p-NiO layer for further optimization, a greatly improved power figure of merit (P-FOM) of 2.29 GW/cm2 is achieved among the E-mode HJ-FETs. These results show that the proposed High ΔEC HJ-FET with thin recessed channel is probably a better choice to achieve the high-performance E-mode lateral HJ-FET.

Electrical and thermal transport properties of Cr2Se3-Cr2Te3 solid-solution alloy system and estimation of optimal thermoelectric properties

Cr2Se3 is a layered narrow-bandgap semiconductor with a low lattice thermal conductivity of ∼1 W/mK, which can be considered as a potential thermoelectric material. A solid-solution alloy system with Cr2Te3 can be designed to manipulate the electrical and thermal transport properties. In this study, a series of Cr2Se3-Cr2Te3 solid-solution alloys (Cr2(Se1-xTex)3, x = 0, 0.33, 0.5, 0.67, 0.83, and 1) were synthesized, and their electrical and thermal transport properties were investigated. Regarding the electrical transport properties, the power factor (∼0.35 mW/mK2) of Cr2Se3 gradually and significantly decreased as the Te content (x) increased owing to the significant decrease in the Seebeck coefficient that resulted from the large increase in the carrier concentration. Regarding the thermal transport properties, the total thermal conductivity increased with x as a result of the large increase in the electrical conductivity, despite the continuous decrease in the lattice thermal conductivity. Consequently, the thermoelectric figure of merit (zT ∼ 0.20) of Cr2Se3 gradually and significantly decreased to 0.009 for Cr2Te3 at 700 K; thus, no enhancement of zT was observed from the experimental results of simple solid-solution alloying. On the other hand, the thermoelectric quality factors of the solid-solution compositions for x = 0.33–0.83 were found to be enhanced compared to that of the Cr2Se3 sample, implying that zT could be further enhanced by optimizing the carrier concentration. Indeed, enhanced zT values were estimated based on a single parabolic band model for the solid-solution compositions with x = 0.33–0.83 if the carrier concentration was optimized to ∼1019 cm−3, which was found to be owing to the increased nondegenerate and weighted mobility (inferring weaker carrier–phonon interaction). Therefore, it is suggested that the solid-solution alloying approach could provide a feasible strategy to enhance the thermoelectric performance by reducing carrier-phonon interaction when further combined with carrier concentration optimization.

Computational investigation of electronic, thermoelectric, and optical properties in Cs2Li[formula omitted](X = Br, I) for energy harvesting applications

The remarkable potential of double perovskite materials, characterized by lead-free, non-toxic attributes and robust dynamical stability, positions them as highly promising candidates for both thermoelectric and optoelectronic applications. In light of this, a comprehensive investigation is undertaken through density functional theory to thoroughly explore the optoelectronic and transport characteristics of Cs2LiBiX6 (X = Br, I) double perovskite materials. To ascertain dynamic stability, phonon dispersion band structures are computed, and the structural stability is evaluated through the tolerance factor. The resulting band structures reveal narrow band gaps of 3.45 eV and 1.79 eV for the Br and Indium-based DPs, respectively. These narrow band gaps hold significant importance for applications such as ultraviolet detectors and other optoelectronic devices that function in the visible and UV-light spectrum. Notably, absorption peaks of maximal intensity emerge at 5.1 eV (76 nm) and 4.0 eV (67 nm) for the Br and Indium-based double perovskites, respectively. Furthermore, a comprehensive analysis of thermoelectric behavior is conducted, encompassing the figure of merit, power factor, Seebeck coefficient, and the ratio of electrical to thermal conductivity across a temperature range of 50–800 K. The exceptionally low lattice vibration values, coupled with a substantial enhancement in the thermoelectric figure of merit (ZT), notably underscore their significance for advanced thermoelectric generator applications.

Performance analysis of quantum harmonic Otto engine and refrigerator under a trade-off figure of merit

Abstract We investigate the optimal performance of the quantum Otto engine and refrigeration cycles of a time-dependent harmonic oscillator under a trade-off figure of merit for both adiabatic and nonadiabatic (sudden-switch) frequency modulations. For heat engines (refrigerators), the chosen trade-off figure of merit is an objective function defined by the product of efficiency (coefficient of performance) and work output (cooling load), thus representing a compromise between them. We obtain analytical expressions for the efficiency and coefficient of performance of the harmonic Otto cycle for the optimal performance of the thermal machine in various operational regimes. Particularly, in the sudden-switch regime, we discuss the implications of the nonadiabatic driving on the performance of the thermal machine under consideration and obtain analytic expressions for the maximum achievable efficiency and coefficient of performance of the harmonic Otto thermal machine. Particularly, we show that the quantum harmonic Otto cycle driven by sudden-switch protocol cannot work as a heat engine or refrigerator in the low-temperature limit. Finally, we show that in the high-temperature limit, the frictional effects give rise to a richer structure of the phase diagram of the harmonic Otto cycle. We identify the parametric regime for the operation of the Otto cycle as a heat engine, refrigerator, accelerator, and heater.

Porous Structure Enhances the Longitudinal Piezoelectric Coefficient and Electromechanical Coupling Coefficient of Lead-Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3.

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d33) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, this paper demonstrates an unusual 22-41% enhancement in the d33 compared to its dense counterpart. This unique combination of high d33 and a low permittivity leads to a significantly improved voltage coefficient (g33), energy harvesting figure of merit (FoM33) and electromechanical coupling coefficient ( ). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators.

Gate mesa terminal with drain-field-plated β-Ga2O3 MOSFET with ultra-high power figure of merit

In this article, a novel gate mesa terminal (GMT) device structure incorporating a drain field plate is proposed. This design features mesa terminals with varying bevel angles positioned atop the gate. The objective is to enhance the breakdown voltage (Vbr) and reduce the on-resistance (Ron) of the lateral β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET). Through the implementation of the GMT structure, the peak electric field within the β-Ga2O3 MOSFET is redirected towards the passivation layer. This effectively mitigates the electric field in the epitaxial layer, thereby increasing Vbr. The optimal values for Vbr, specific on-resistance (Ron,sp) and maximum transconductance (gm) across various GMT structures are 4827 V, 9.9 mΩ·cm2 and 15.32 mS/mm, respectively. These metrics represent a 2.63-fold, 0.88-fold, and 1.25-fold improvement compared to the non-GMT structure. Additionally, when the doping concentration of epitaxial layer is 1 × 1016 cm−3, the GMT achieves an enhanced threshold voltage of +0.26 V. By simulating different bevel angles, field plate parameters, epitaxial layer doping concentrations, and mesa thicknesses, an optimal power figure of merit (PFOM) of 1.914 GW cm−2 is attained. This innovative design introduces a fresh concept for the development of the next generation of high voltage and high-power devices rated above 4 KV.

Flexible Perovskite Solar Cells: A Futuristic IoTs Powering Solar Cell Technology, Short Review.

The perovskite solar cells (PSCs) technology translated on flexible substrates is in high demand as an alternative powering solution to the Internet of Things (IOTs). An efficiency of ∼26.1% on rigid and ∼25.09% on flexible substrates has been achieved for the PSCs. Further, it is also reported that F-PSC modules have a surface area of ∼900 cm2, with a PCE of ∼16.43%. This performance is a world record for an F-PSC device more significant than ∼100 cm2. The process optimization, and use of new transport materials, interface, and compositional engineering, as well as passivation, have helped in achieving such kind of performance of F-PSCs. Hence, the review focuses mainly on the progress of F-PSCs and the low-temperature fabrication methods for perovskite films concerning their full coverage, morphological uniformity, and better crystallinity. The transmittance, band gap matching, carrier mobility, and ease of low-temperature processing are the key figures of merit of interface layers. Electrode material's flexible and transparent nature has enhanced the device's mechanical stability. Stability, flexibility, and scalable F-PSC fabrication challenges are also addressed. Finally, an outlook on F-PSC applications for their commercialization based on cost will also be discussed in detail.

KNN composite ceramics with superior pyroelectric performance for self-powered thermal detector

The thermal detector based on pyroelectric effect has attracted widespread attention due to its self-powering and rapid response. Although phase boundary engineered lead-free potassium sodium niobate [K0.5Na0.5NbO3, KNN] based ferroelectrics exhibit promising for pyroelectric sensor application, the high dielectric constants (εr) of these materials significantly constrain their pyroelectric figures of merit (FOMs), owing to the inverse correlation between FOMs and εr. To address this problem, we innovatively introduce perovskite bismuth sodium titanate [Bi0.5Na0.5TiO3, BNT] with low εr and high pyroelectric coefficient as the second phase to construct a KNN/BNT composite. The introduction of BNT can not only remain the high pyroelectric coefficient (p=7.12 × 10−4 C m−2 K−1) of KNN matrix, but also result in superior FOMs (Fv increased by 74 %), outperforming previous KNN-based pyroelectric ceramics. The excellent pyroelectric performance originates from the unique composite microstructure with compositional heterogeneity. That is, both the low εr BNT enriched phase and refined grain size as well as the promoted vibration of Nb–O octahedron contribute to the superior pyroelectric performance. A self-powered thermal detector with great thermal response has been developed, which also exhibits potential for detecting ultraviolet energy and infrared radiation.

A near-infrared metastructure to realizing polarization conversion and sensing based on the electromagnetic induced reflection

A multifunctional metastructure (MS) working in the near-infrared band is proposed that achieves linear to circular polarization conversion (LTCPC) and electromagnetically induced reflection (EIR). In addition, due to the use of reflected electric fields to overcome the influences of near-infrared band thermal radiation, MS has a good multifunctional sensing detection. The given MS is composed of a four-layer stacked structure. From the substrate to the top layer (along the +z-direction), it consists of silver, a silicon dioxide layer, and two layers of silicon (Si) resonators. Each layer of the Si resonator has four holes created by rotation. By breaking the symmetry of the upper and lower Si layers of MS, the deviation of the rotation angle of the upper and lower holes is introduced, so the MS achieved a near-infrared EIR with an ultrahigh quality factor (Q-factor). Under electromagnetic wave incidence, at 187.89 THz, the Q-factor of MS's reflection peak reaches 2441.25. Due to the unique shapes of the two resonator layers' holes, the axial ratio (AR) is less than 3 dB between 187.844 THz and 187.871 THz, realizing LTCPC. Utilizing the relationship between the optimal polarization conversion frequency point (the frequency corresponding to the lowest AR) and the environmental refractive index, the MS can be used for detecting cancer cells with a sensing sensitivity (S) of 37.24 THz/RIU (36.06 THz/RIU). By introducing the alcohol into the MS, the refractive index of the alcohol to be measured. MS achieved the detection function of the alcohol solution volume fraction, with an S reaching 33.32 THz/RIU, and a figure of merit as high as 154.202. Finally, the related parameters and polarization angle are discussed. The effects of different parameters on EIR and AR also are analyzed. The innovation of this paper lies in the realization of EIR, and a method to improve the Q-factor of near-infrared EIR by rotating the structure is proposed. The combination of a high Q-factor and polarization conversion overcomes the disadvantage that both are difficult to achieve together, and the EIR is easier to detect than the electromagnetically induced transparency. The design also has potential applications in biomedical sensors and industrial production.

Insights into Ag2Mo3SeO12 for photovoltaic and optoelectronic applications: A theoretical exploration of its structural, electronic, and thermoelectric behavior

The theoretical investigation of the newly discovered quadruple perovskite Ag₂Mo₃SeO₁₂ was conducted using density functional theory (DFT) with the generalized gradient approximation (GGA-PBE) for the structural properties. This study examined the compound's structural, electronic, optical, and thermoelectric properties, utilizing the Tran Blaha modified Becke-Johnson exchange potential (mBJ) for accurate band gap measurement to overcome the bandgap underestimation by GGA-PBE. The stable structure was confirmed through energy-volume optimization and fitted with the Birch-Murnaghan equation of state, using PBE-GGA exchange correlation functional. The findings revealed a band structure with direct transition under the TB-mBJ approach with an energy gap of 1.45 eV. Detailed analyses were conducted, including the density of states and charge density distribution maps. Various optical parameters such as the dielectric function, absorption coefficient, refractive index, and reflectivity were computed, with the static dielectric constant measured at 6.3. Notably, a significant evolution of the absorption coefficient in the visible region highlights the potential of Ag₂Mo₃SeO₁₂ for solar cell and optoelectronic applications. These results pave the way for new photovoltaic material designs. Furthermore, the material demonstrates promising thermoelectric properties with an appropriate figure of merit, Seebeck coefficient, and electrical and thermal conductivity evolution under different temperature conditions, indicating its potential for photovoltaic and optoelectronic applications.

Design of optical Kerr effect in multilayer hyperbolic metamaterials

Abstract The design of optical materials in nonlinear devices represents a fundamental step for their optimization and miniaturization, that would significantly contribute to the progress of advanced nanophotonics and quantum technologies. In this work, the effect of geometry and composition of multilayer hyperbolic metamaterials on their third-order nonlinear optical properties, i.e. the optical Kerr effect, is investigated. One figure of merit is provided to be used as a predictive tool to design and best exploit the local intensity enhancement in low-loss metamaterials to be used for various applications in nonlinear nanophotonics.

Colloidal synthetic environmental design towards high-density twin boundaries and boosted thermoelectric performance in Cu5FeS4 icosahedrons

High-density twin boundaries can significantly influence materials’ functional and mechanical properties. In thermoelectrics, twin engineering is able to manipulate the carrier and phonon transport in semiconductors, leading to improved dimensionless figure of merit (zT). However, obtaining twin boundaries with tunable density and uniform distribution in thermoelectric semiconductors is rather challenging. Here, by precisely controlling the temperature of sulfur precursor, the particle size of synthesized Cu5FeS4 icosahedrons can be decreased to produce higher-density twin boundaries. Accordingly, the optimized average distance between two adjacent twin boundaries matches the mean free path of phonons but is much larger than that of carriers, thereby efficiently lowering the lattice thermal conductivity without affecting the carrier mobility significantly. In combination with the enhanced power factor caused by increased carrier concentration, a maximal zT of 0.95 is achieved at 773 K in a p-type Cu5FeS4 derivative material, which is one of the highest values among those in Earth-abundant, environmentally-friendly thermoelectric sulfides. This work uncovers the crucial role of high-density twin boundaries in decoupling the carrier and phonon transport for improved thermoelectric performance in Cu5FeS4-based materials.

Halide perovskite and few-layer silicon-based surface plasmon resonance sensor for the detection of chemical and biochemical sensing

This paper examines the combined effect of perovskite/silicon (Si) material on the performance of a surface plasmon resonance (SPR) sensor using the Kretschmann structure. The proposed sensor incorporates the BAF10/Cu/perovskite materials/Si/sensing medium (SM) layers. This paper incorporates the optimized parameters into the proposed sensor by comparing the results without perovskite material and existing work. The proposed modified Kretschmann structure consists of perovskite material such as CsPbI3, FASnI3, KSnI3, and CsSnI3, with few Si layers. All the performance parameters are calculated at 633 nm wavelength. The sensitivity (S), full width at half maximum (FWHM), detection accuracy (DA), and figure of merit (FoM) of 348.75°/RIU, 3.22°, 0.31/° and 108.11/RIU using perovskite material of KSnI3, are measured, respectively by the proposed sensor. The perovskite material of KSnI3 shows the best performance parameter among CsPbF3, FASnF3, and CSSnF3. These results should greatly impact the biosensing application, especially for chemical and biochemical.

Transverse magneto-optical Kerr effect enhanced by surface plasmon resonances at the critical coupling condition

Nanostructures possessing plasmonic and magnetic properties can enhance the transverse magneto-optical Kerr effect (TMOKE) by exciting surface plasmon resonances (SPRs). This provides a promising platform for magneto-optical SPR sensors with significantly improved sensing performance. Here, we propose a high-performance magneto-optical SPR sensor, which consists of a bilayer Au/Co grating placed on a gold film. By tuning the structural parameters, a Fano-like TMOKE spectrum with a linewidth of only 0.0135 nm and an amplitude approaching the theoretical maximum is obtained. We attribute the optimal TMOKE signal achieved by the sensor to the critical coupling concept which is associated with the trade-off between scattering and intrinsic decay rates of the system. The optimized nanostructure sensor demonstrates a sensitivity of 1432 nm/RIU to refractive index fluctuations as small as 0.0001 in air, and all figures of merit (FOM) up to 105 RIU−1, making it suitable for gas sensor fabrication.

An ab initio analysis of the electronic, optical, and thermoelectric characteristics of the Zintl phase CsGaSb2

We present and analyze the findings of a comprehensive ab initio computation that examines the electronic, optical, and thermoelectric characteristics of a recently synthesized Zintl compound known as CsGaSb2. The electronic and optical characteristics were examined using the DFT-based FP-L/APW+loapproach. Toaddress the exchange–correlation effects, we employed the GGA-PBEsol and TB-mBJ approaches.The CsGaSb2 semiconductor exhibits an indirect bandgap of 0.695 eV when analyzed with the GGA-PBEsol approach, and a bandgap of 1.254 eV when analyzed with the TB-mBJ approach.The PDOS diagrams were used to discover the origins of the electronic states that make up the energy bands. The charge density study reveals that the Ga-Sb link within the [GaSb2] block is mostly governed by a covalent character, whereas the cation Cs+ and polyanion [MSb2]−bonding is predominantly ionic. The frequency dependence of macroscopic linear optical coefficients was evaluated over a broad range of photon energies from 0 to 25 eV. The thermoelectric characteristics were investigated via the Boltzmann kinetic transport theoryassuming a constant relaxation time.The compound’s figure of merit at a temperature of 900 K is roughly 0.8.

Enhancement of Thermoelectric Performance through Transport Properties Decorrelation in the Quaternary Pseudo-Hollandite Chalcogenide Rb0.2Ba0.4Cr5Se8.

The novel quaternary compound Rb0.2Ba0.4Cr5Se8 was synthesized and characterized in both single crystal and polycrystalline forms. Crystallizing in the monoclinic crystal system (space group C2/m, cell parameters a = 18.7071(4) Å, b = 3.6030(1) Å, c = 8.9637(3) Å, β = 104.494(2)°) and isostructural to pseudo-hollandite compounds, it features mixed Rb and Ba occupancy within its one-dimensional channels. High-temperature X-ray diffraction revealed no decomposition up to 973 K, and the thermal expansion coefficient at 300 K was determined to be 2.6(1)·10-5 K-1. Spin-polarized density functional theory (DFT) calculations showed that the density of states for Rb0.2Ba0.4Cr5Se8 is more polarized than that of Ba0.5Cr5Se8, resulting in a higher Seebeck coefficient, which was experimentally confirmed to reach a peak value of 400 μV·K-1 at 620 K. Resistivity measurements indicated a degenerate semiconducting behavior below 550 K, with a resistivity peak of 100 mΩ·cm at that temperature, leading to a maximum power factor of 0.21 mW·m-1·K-2. Thermal conductivity measurements indicated low values around 0.8 W·m-1·K-1 in the 300-900 K range, resulting in a thermoelectric figure of merit of 0.22 at 873 K. Decorrelated transport properties observed in this double-inserted pseudo-hollandite compound make Rb0.2Ba0.4Cr5Se8 a good example of beneficial synergistic effects for higher thermoelectric performance.