Figure Of Merit Research Articles

Study of structural, magnetic, and physical properties in nano cobalt ferrite by computational analysis

Using the DFT+U method, we investigated the structural, magnetic, electronic, mechanical, thermal, optical, thermoelectric, and thermodynamic properties of the CoFe2O4 system. The GGA approximation was employed to calculate the exchange–correlation potential. The CoFe2O4 has a metallic bond and is ductile, as determined by Poisson’s and Pugh’s ratio mathematical calculations. Transport properties such as the figure of merit, thermal (k/τ) and electrical (σ/τ) conductivities, power factor, and Seebeck coefficient were computed to explain the thermal behavior of this spinel. Additionally, optical parameters like energy loss L(ω), absorption coefficient α(ω), dielectric constants ε(ω), optical conductivity σ(ω), reflectivity R(ω), extinction coefficient k(ω), and refractive index n(ω) are investigated. Lastly, we study how the magnetic phase transitions, magnetization, critical temperature, and specific heat capacity of this material are affected by an external magnetic field at constant pressure. Around the critical temperature, magnetic entropy and relative cooling capacity for various external magnetic fields are obtained.

Hydroelectric energy conversion of waste flows through hydroelectronic drag

Hydraulic energy is a key component of the global energy mix, yet there exists no practical way of harvesting it at small scales, from flows with low Reynolds number. This has triggered a search for alternative hydroelectric conversion methodologies, leading to unconventional proposals based on droplet triboelectricity, water evaporation, osmotic energy, or flow-induced ionic Coulomb drag. Yet, these approaches systematically rely on ions as intermediate charge carriers, limiting the achievable power density. Here, we predict that the kinetic energy of small-scale "waste" flows can be directly and efficiently converted into electricity thanks to the hydroelectronic drag effect, by which an ion-free liquid induces an electronic current in the solid wall along which it flows. This effect originates in the fluctuation-induced coupling between fluid motion and electron transport. We develop a nonequilibrium thermodynamic formalism to assess the efficiency of such hydroelectric energy conversion, dubbed hydronic energy. We find that hydronic energy conversion is analogous to thermoelectricity, with the efficiency being controlled by a dimensionless figure of merit. However, in contrast to its thermoelectric analogue, this figure of merit combines independently tunable parameters of the solid and the liquid, and can thus significantly exceed unity. Our findings suggest strategies for blue energy harvesting without electrochemistry, and for waste flow mitigation in membrane-based filtration processes.

Enhancing thermoelectric and radiation shielding performance of novel LaFe0.8Mn0.2Sb12 skutterudites for energy applications

We explore the structural, optoelectronic, and thermoelectric properties of LaFe0.8Mn0.2Sb12 skutterudites using first-principles computations and semi-classical Boltzmann Transport equations. These materials are classified as semiconductors exhibiting band gaps of 0.55 eV and 1.8 eV for spin-up and down polarizations. Valence band maxima (VBM) and conduction band minima (CBM) lie on the gamma points, indicating direct band gaps for both spin channels. The band structure, density of states, and optical characteristics reveal that the material is a semiconductor. The optical reflectivity and complex dielectric function were calculated for a wide range of photon radiation to understand these compounds' optical properties. The transport parameters were investigated using electrical conductivity, thermal conductivity, the Seebeck coefficient, the power factor, the heat capacity, and the figure of merit determined using the Boltztrap code. The LaFe0.8Mn0.2Sb12 has a Seebeck coefficient of 5.77×10−6 V/K (Up), whereas the down channel has a 4.2×10−6 V/K. The highest figure of merit is 0.99, and as a result, the theoretical findings provide a robust foundation for upcoming experimental research. In this study, utilize the Phy-X program to evaluate the radiation shielding capabilities of LaFe0.8Mn0.2Sb12, focusing on critical parameters like mass attenuation coefficients (γmac) and half-value layers (γhvl), essential for optimizing protection against hazardous ionizing radiation. Computational study of energy-renewable and thermoelectric properties enables experimenters to investigate fresh applications for predicting photovoltaic materials with atomic-level accuracy.

First‐Principles Study of the Effects of High‐Order Anharmonicity on the Thermal Transport Properties and Thermoelectric Effects in the Lattice Dynamics of 12 New Full–Heusler Compounds X2YTe (X = Na, K, Rb, Cs; Y = Zn, Cd, Hg)

AbstractIn this study, advanced first‐principles calculations combined with self‐consistent phonon theory and the Boltzmann transport equation are used to assess the thermoelectric properties of novel Full–Heusler materials X2YTe (X = Na, K, Rb, Cs; Y = Zn, Cd, Hg). These materials exhibit low formation energies, facilitating synthesis under standard conditions. This analysis showed that lattice anharmonicity increases with the atomic mass of X and decreases with the atomic mass of Y due to the rattling effect of Y atoms. Significant rattling effects are identified, prompting the inclusion of higher‐order anharmonic effects. By renormalizing the phonon spectrum and accounting for three‐phonon and four‐phonon scattering, the mechanisms behind the low lattice thermal conductivity in these compounds is uncovered. The combination of low lattice thermal conductivity and high power factors resulted in remarkable thermoelectric figure of merit values at optimal doping concentrations and temperatures. Notably, except for Na2ZnTe and Na2HgTe, all other materials surpassed the long‐standing figure of merit record of less than 3, with Rb2ZnTe achieving a figure of merit of 8.11 at 700 K with an n‐type doping concentration of 2 × 1019. The inclusion of spin‐orbit coupling led to less than a 10% reduction in the thermoelectric figure of merit, underscoring the superior thermoelectric performance of these materials.

Tuning of modern speed drives using IFOC: A case study for a five-phase induction machine

Electric machines have existed since the beginning of the 19th century. Although variable-speed drive technology has evolved considerably during the last years, the indirect field-oriented control technique has been in use as a standard control method since the 1960s, using an outer speed loop and an inner current loop. This paper deals with the non-trivial problem of tuning the outer speed controller of modern variable-speed drives, where experimental results are provided to show the need for new tuning methods. The influence of non-modeled effects on the performance of the drive is illustrated considering the dynamical effect of the mechanical speed sensing procedure using optical devices. This effect has not been generally considered. However, it is shown that it has a notable effect on tuning for high performance drives. This is especially true when considering some figures of merits of relevance for drives, such as the torque ripple. A Pareto analysis is proposed to reveal trade-offs between typical figures of merit to establish new tuning methods. To focus our contribution, a five-phase induction drive is considered as the case study, using a finite-state model predictive controller for the stator current control and PI regulators for the outer speed control loop.

Unveiling the recently synthesis noncentrosymmetric layered ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te) via first principles calculations

This study explores the structural, optical, and thermoelectric properties of non-centrosymmetric layered selenite and tellurite compounds KSb3Se2O12, RbSb3Se2O12, CsSb3Se2O12, TlSb3Se2O12, KSb3Te2O12, RbSb3Te2O12, CsSb3Te2O12, TlSb3Te2O12 to assess their potential for sustainable and renewable energy technologies. The selenite and tellurite compounds feature distinct non-centrosymmetric layered crystal structures, which are key to their unique optical and electronic properties. The materials display a layered structure without a center of symmetry, characterized by distinct atomic arrangements, and their band gaps vary depending on the constituent elements. For selenites, band gaps range from 2.97 eV to 3.19 eV, while for tellurites, they range from 2.75 eV to 3.02 eV, indicate their suitability for indirect semiconducting applications. The investigated materials exhibit high absorbance in the ultraviolet region, suggesting they are promising for solar cell applications. The energy loss function peaks at 14 eV, indicating minimal optical loss in the infrared and visible spectra. The static dielectric constants ε1(0) were calculated, showing variations based on the elemental composition. The response of ε2(ω) demonstrates strong interactions in the ultraviolet region, corresponding to electronic transitions from the valence to the conduction bands. Thermoelectric properties, evaluated with the BoltzTrap code using transport theory. The Seebeck coefficient of p-type semiconductors typically increases with temperature, but TlSb3Se2O12 shows an even greater increase, suggesting enhanced thermoelectric properties. Both selenites and tellurites have rising electrical conductivities, with ASb3Se2O12 peaking at 800 K. The Power Factor improves with temperature, reaching a peak for TlSb3Se2O12. These compounds exhibit favorable electrical conductivity and power factor, suggesting potential applications in thermoelectric systems. The figure of merit (ZT) values spanning from 0.90 to 1.51, with a maximum ZT value of 1.41 at 800 K, TlSb3Se2O12 shows great potential for high-temperature thermoelectric applications. These findings advance the understanding of non-centrosymmetric oxide materials and provide valuable insights for developing advanced materials for energy technologies.

Ultralow lattice thermal conductivity in K2AuBi and its thermoelectric properties

Thermoelectric materials are best known for their prowess to transform the environment’s waste heat into electricity. In an endeavor to explore new thermoelectric prospects, in the present study, we investigate K2AuBi using density functional theory-based first-principles simulations. From our simulations, we find an intrinsically low lattice thermal conductivity of 0.43 W m−1 K−1 at 300 K in K2AuBi. Based on our detailed analysis, we find the reasons for such a low value of lattice thermal conductivity as, low phonon group velocities, short phonon lifetimes, anharmonicity in the lattice vibrations, and significant mean square displacements of K and Au atoms. The large mean square displacements hint at weak bonding and anharmonicity in the lattice vibrations, favoring more phonons scattering. We also find that the vibrations of K-atoms can be related to rattlers, conducive to low lattice thermal conductivity. Our simulations predict a high value, ∼784 μV K−1, of Seebeck coefficient at 700 K on account of the large density of states in the vicinity of Fermi level. Combining our computed lattice thermal conductivity with electrical transport properties, we obtain a high figure of merit, ZT∼ 1.04, at 700 K in K2AuBi.

Structural, Magnetic, and Transport Properties of Ti(Fe,Re)2Sn Heusler Alloys

This study investigates polycrystalline samples of TiFe2−xRexSn (with x = {0, 0.02, 0.04, 0.06, 0.2}) synthesized using conventional arc-melting and spark plasma sintering. Structural and morphological analysis shows that low Re substitutions result in good phase purity with minor traces of secondary phases, while higher Re content leads to the segregation of additional phases. The magnetism and electrical resistivity of the samples are affected by inherent Fe–Ti atomic disorder, with the effects of secondary phases becoming more prominent in the samples with higher Re content. The Seebeck coefficient values increase only for TiFe1.98Re0.02Sn, while the power factor increases for x = {0, 0.02, 0.04}, reaching maximal values for x = 0.02 at ~ 300 K and x = 0.04 at ~ 325 K, i.e., (2.22 ± 0.2) × 10−4 Wm−1 K−2. The thermal conductivity of the samples increases with x, resulting in modest values of the figure of merit, with the maximum achieved for x = 0.02 at 325 K, i.e., 0.015 ± 0.002.

Cr2O3–NiO mixed oxides thin films for p-type transparent conductive electrodes

The Cr2O3–NiO mixed oxides’ thin films were formed by means of the layer-by-layer magnetron sputtering deposition of Cr2O3, NiO, and Cr2O3 layers on c-plane sapphire substrates. These thin-film structures, subjected to subsequent annealing, constituted a combination of the monocrystalline (0001) Cr2O3 and nonordered nickel oxide phase, which was a mixture of NiO and Ni2O3. The annealing at 900 and 1000 °С in air facilitated the diffusion of Ni and Cr atoms into the layers. Varying the annealing time allowed us to control the uniformity of the Ni and Cr distribution, the microrelief of the film surface, the transmittance in the visible region, and the sheet resistance of the Cr2O3–NiO thin-film structures. Thus, the films annealed at 900 °C during 30 min were characterized by a uniform distribution, a relatively weakly developed surface, a low sheet resistance, and the highest Haacke's Figure of Merit of 1.49 × 10–9 Ω–1. The formation of mixed Cr2O3–NiO oxides by the proposed approach was found to be an effective way to improve the performances of Cr2O3 based p-type transparent conductive electrodes.

Significantly Enhanced Thermoelectric Performance of p-Type Mg3Sb2 via Zn Substitution on Mg(2) Site: Optimization of Hole Concentration Through Ag Doping.

n-Type Mg3Sb2-based thermoelectric materials have recently garnered significant interest due to their superior thermoelectric efficiency. Yet, the advancement of p-type Mg3Sb2 for thermoelectric applications is impeded by its lower dimensionless figure of merit (zT). In this study, we demonstrate the improved thermoelectric performance of p-type Mg3Sb2 through the strategic optimization of Zn content and Ag doping on the Mg/Zn(2) site. Initially, samples of Mg3-xZnxSb2 (x = 0, 0.5, 1.0, and 1.5) were synthesized via elemental reactions within a Pyrex tube, followed by densification through hot pressing. X-ray diffraction analysis confirmed that the Mg3-xZnxSb2 phases retain the same Pm1 space group as the pristine Mg3Sb2 phase. The strategic substitution of Zn improved the power factor via band convergence and reduced lattice thermal conductivity by introducing point defect phonon scattering. This led to a peak zT of 0.5 at 725 K, with an average zT of 0.25 across the 325-725 K range. Enhancement in carrier concentration was achieved by doping Ag onto the Zn site, culminating in a peak zT of 0.95 at 725 K and an average zT of 0.46 between 325 and 725 K for the Mg2Zn0.97Ag0.03Sb2 sample. This performance surpasses that of most p-type Mg3Sb2-based materials, markedly advancing the potential for Mg3Sb2-based materials in midtemperature heat recovery thermoelectric generators.

A semi-transparent thermoelectric glazing nanogenerator with aluminium doped zinc oxide and copper iodide thin films

To address the pressing need for reducing building energy consumption and combating climate change, thermoelectric glazing (TEGZ) presents a promising solution. This technology harnesses waste heat from buildings and converts it into electricity, while maintaining comfortable indoor temperatures. Here, we developed a TEGZ using cost-effective materials, specifically aluminium-doped zinc oxide (AZO) and copper iodide (CuI). Both AZO and CuI exhibit a high figure of merit (ZT), a key indicator of thermoelectric efficiency, with values of 1.37 and 0.72, respectively, at 340 K, demonstrating their strong potential for efficient heat-to-electricity conversion. Additionally, we fabricated an AZO-CuI based TEGZ prototype (5 × 5 cm²), incorporating eight nanogenerators, each producing 32 nW at 340 K. Early testing of the prototype showed a notable temperature differential of 22.5 °C between the outer and inner surfaces of the window glazing. These results suggest TEGZ could advance building energy efficiency, offering a futuristic approach to sustainable build environment.

Optical nonlinear properties of a new polyamide from crystal violet terephthalate

In this study, the nonlinear optical properties of a new polymer poly crystal violet terephthalate (PCVT) as a solution and a thin film with different concentrations of 0.2, 0.6, and 1 mM and input power were investigated by using Z-scan technique at 532 nm CW laser beam wavelength. The negative nonlinear refractive index n 2 as well as reverse saturable and saturable absorption β of the solution and film PCVT samples were determined. Figures of merit were also determined. In comparison with the Z-scan results, a self-diffraction pattern setup was used to measure nonlinear refractive index. Results showed a significant laser power dependence of the number of far-field diffraction rings with power and concentration, consistent with the Z-scan data. The PCVT sample exhibited good optical limiting behavior. Hence, PCVT has important nonlinear properties, and its figures of merit can be optimized by adjusting the PCVT concentration and input power. PCVT is a promising candidate for the design of optical photonic switching and optical limiter devices.

Self-referencing refractive index sensor based on graphene-assisted TAMM plasmon cavity resonance.

In this Letter, we report TAMM plasmonic polaritons (TPPs) generated by few-layer MoS2 with a distributed Bragg reflector (DBR) structure in the terahertz frequency region by utilizing the transfer matrix method (TMM) and finite element method (FEM). By inserting a mono-graphene embedded cavity layer, we realize the graphene-induced mode strong coupling (GCM), which is a strategy of a refractive index sensor by optimizing the cavity layer spacing. By adjusting the chemical potential of graphene, GCM is modulated. μc = 0.1 eV and μc = 0.9 eV are selected as the on-off-state parameters, respectively. The difference in reflectance spectra presents a differential signal and a self-reference operation. The sensitivity of the designed refractive index sensor is 7.8 THz/RIU and a figure of merit (FOM) of 882 RUI-1 can be obtained. The proposed structure in our Letter demonstrates its potential application in high-performance self-reference refractive index sensors.

Transmission enhancement mechanism of PT symmetric photonic crystal coupled with grooved sub-wavelength grating

In order to enhance the sensing characteristics of the sensor, based on the periodic sub-wavelength grating(SWG), a groove structure is introduced to make the Fano resonance waveform sharper. At the same time, based on the Parity-Time(PT) symmetry principle, by making the periodic photonic crystal meet the PT symmetry condition, the structure can absorb the energy of the emitted light on the original basis, produce the transmission enhancement effect, and make the transmission peak of the structure exceed 1. The sensing is realized by using the property that the different refractive indices of the detected medium corresponds to different transmission. When the incident light is 1550 nm, the sensitivity and FOM (Figure of Merit) value of the proposed structure reach 5.702 × 105RIU−1and 1.9 × 107 respectively, which greatly improves the performance of the sensor.

Enhancing low-level tritium detection in environmental waters: assessing the Hidex ULLA liquid scintillation counter

Tritium (³H) is a vital tracer in isotope hydrology and environmental studies, necessitating accurate and precise low-level detection methods. This study evaluated the performance of the new Hidex ULLA Liquid Scintillation Counter for ultra-low-level tritium assays in environmental water samples. The optimization of instrumental parameters enabled accurate and reproducible 3H measurements. Test samples (10–132 TU) were analyzed in triplicate, including 3H-free water and NIST traceable standards. The results demonstrated excellent accuracy and reproducibility, as evidenced by Zeta scores and linearity across these tritium concentrations. The system's stability over extended measurement time periods ensured reliable performance for routine ultra-low level 3H analysis. The optimization of key parameters such as coincidence time and region of interest (ROI) achieved the highest figure of merit (FoM) by using a 25 ns coincidence time and the DigPb open mode for optimal spectral fittings. Detection limits (DL) based on ISO11929 recommendations were significantly improved but highlighted the need for sample enrichment for most low-level environmental applications, with LSC counting times preferably exceeding 1000 min. Overall, the Hidex ULLA Liquid Scintillation Counter proved to be a robust and reliable instrument suitable for ultra-low-level tritium detection in environmental water samples.

Aspect ratio optimization of piezoelectric extensional mode resonators for quality factor and phase noise performance enhancement

Abstract This study focuses on optimizing the resonator geometry via the aspect ratio design of a width-extensional mode resonator to improve its quality factor (Q), which is one of the critical performance parameters for resonators in either sensing (Allan deviation) or frequency reference (phase noise) applications. The proposed approach uses finite element analysis to reduce the strain energy at anchor supports by altering the resonator geometric structure, thereby reducing energy loss through anchors. Moreover, process limitations on feature sizes are used as constraints to find aspect ratios that can not only increase the Q but also reduce spurious modes near the targeted frequency. The devices were fabricated using AlN thin film piezoelectric on a substrate (TPoS) process. The simulated energy dissipation trends for specific length-to-width (L/W) ratios closely match the measured changes in the resonator Q values in vacuum. In vacuum, the highest Q-factor achieved by the device is close to 8816, with a motional resistance of a few tens of ohms. Additionally, a board-level oscillator realized using a commercial low-noise amplifier exhibits phase noise performance of −141.21 dBc Hz−1 and −164.25 dBc Hz−1 at 1 kHz and 1 MHz frequency offsets, respectively. The calculated figures of merit for these offsets are 204 and 168, respectively.

Effect of AFM ordering on thermoelectric responses of Mg3X2 (X: C, Si, Ge) monolayers : a DFT insight

Two-dimensional materials have gained a lot of attention in the last few decades due to their potential applications in thermoelectric and nano-electronic devices. This study systematically presents the mechanical, electronic and thermoelectric characteristics of two-dimensional honeycomb-kagomeMg3X2(X:C,Si,Ge) structures in the framework of density functional theory computations and by solving semiclassical Boltzmann transport equation. The geometrical stability of these structures is validated by phonon spectrum and molecular dynamics simulations. Following the elastic constants, we have inferred that all the systems are mechanically stable and brittle in nature. Lower values of Debye temperature of all structures suggest thatMg3X2monolayers should have lower values of lattice thermal conductivity compared to graphene. Electronic structure calculations indicate that these materials are semimetallic in their nonmagnetic phase. All the structures display remarkably low lattice thermal conductivity (0.9-1.5 W (mK)-1) due to a large scattering factor and higher anharmonicity. The presence of sharp density of states peaks close to the Fermi level, arising from nearly flat and dispersionless band in the antiferromagnetic (AFM) arrangement, is poised to enhance the Seebeck coefficient, thereby potentially boosting the thermoelectric performance. The estimated values of thermoelectric figure of merit (ZT) are around 0.78 and 0.67 forMg3Si2andMg3Ge2structure respectively in AFM phase atT= 700 K. These outcomes of our findings suggest thatMg3X2monolayers exhibit substantial promise for thermoelectric device application.

High-performance InGaZnO power transistors: Effect of device structural parameters

In this work, the effect of offset channel length (Loffset) and the dielectric layer thickness (d) on the InSnO/InGaZnO (ITO/IGZO) dual-active-layer (DAL) high-voltage thin-film transistors (HV-TFTs) is systematically investigated. The characteristics of the DAL HV-TFTs resemble that of GaN high electron mobility transistors, wherein the breakdown voltages (VBD) reach saturation at a certain Loffset, and the on-resistance (Ron) linearly increases with Loffset. The linear fitting of Ron vs Loffset indicates that d has a multifaceted impact on the performance of HV-TFTs. In addition to its theoretical role in transistor models, d also influences the channel doping concentration and sidewall deposition issues in practical devices. The DAL HV-TFT with a 30-nm Al2O3 gate dielectric achieves a remarkable VBD of 450 V, the highest figure of merit of 118.2 kW/cm2, and a positive threshold voltage of 3.65 V. Both experiments and simulations indicate that the breakdown occurs within the semiconductor channel, paving the way for further improvement of the performance.

Exploring energy harvesting potential of lithium-based halide perovskites Li2CuSbZ6 (Z=Cl, Br): First principles approach

Recent research has focused on investigating the physical characteristics of the halide perovskite combinations, Li2CuSbZ6 (Z = Cl, Br) within the context of Density Functional Theory (DFT). The optimized FCC cubic structure lattice parameters for Li2CuSbCl6 and Li2CuSbBr6 are 10.57 and 11.10 Å, respectively. We have examined the stability by evaluating the tolerance factor, formation energy, and the Born Criteria. The analysis conducted on the elastic constants identifies the ductility, anisotropy, melting, and Debye temperatures. First-principles calculations reveal that computed electronic features using the TB-mBJ approximation unveiled an indirect band gap of 1.33 and 1.04 eV, respectively. Optical analyses indicate that the studied halide perovskites exhibits significant absorption in the visible and ultraviolet regions. Boltzmann's classical theory explains the transport features and attained higher figure of merit (ZT) values for both perovskites. These research findings provide a significant potential for these materials in the absorber layer of perovskite-based solar cells as well as thermoelectric devices.

High thermoelectric performance in Ag-doped Bi0.5Sb1.5Te3 nanocomposites synthesized via low-temperature liquid phase sintering

In recent years, low-temperature liquid phase sintering (LPS) has emerged as a cost-effectiveness method for designing thermoelectric nanocomposites with reduced lattice thermal conductivity. However, their electrical conductivity often remains suboptimal, limiting the overall figure of merit (ZT). In this study, xwt% Ag/Bi0.5Sb1.5Te3 (x = 0,0.1,0.2,0.3,0.4) nanocomposites are prepared through low-temperature LPS method followed by subsequent annealing. Remarkably, a small amount of silver atoms was doped into the Bi0.5Sb1.5Te3 matrix post-annealing, significantly increasing carrier concentration and improving electrical conductivity. Additionally, residual Ag atoms formed Ag₂Te nanoprecipitates, and lattice defects (including grain boundaries, twin boundaries, dislocations, and lattice distortions) effectively reduced lattice thermal conductivity. The 0.3 wt% Ag/Bi0.5Sb1.5Te3 sample achieved a maximum ZT value of 1.36 at 400 K, double that of the pure Bi0.5Sb1.5Te3 sample, with an average ZT value of 1.17, among the highest reported. This work demonstrates significant potential for synthesizing high-performance thermoelectric materials via low-temperature LPS methods.