Merit Factor Research Articles

Polar phonons features and intrinsic dielectric properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm and Yb) double perovskites

RE-based double perovskite (DP) oxides of the RE₂TMTM'O₆ family exhibit intriguing magnetodielectric (MD) properties and magnetocaloric effects (MCEs), making them promising candidates for applications in high-performance supercapacitors, memories, spintronic devices, and cryogenic magnetic refrigeration. This paper addresses the vibrational properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm, and Yb) ceramics for the first time using infrared reflectance spectroscopy. The dielectric merit factors in the microwave (MW) range, including the quality factor (Qu) and the static dielectric constant (ɛ0), were estimated. It was observed that the intrinsic dielectric constants decrease from approximately 26.2 to 14.4 as the rare earth ionic radius decreases. The mean values of these compounds suggest their suitability for applications in MW circuitry devices.

On the skew-symmetric binary sequences and the merit factor problem

The merit factor problem is of practical importance to manifold domains, such as digital communications engineering, radars, system modulation, system testing, information theory, physics, chemistry. In this work, some useful mathematical properties related to the flip operation of the skew-symmetric binary sequences are presented. By exploiting those properties, the space complexity of state-of-the-art stochastic merit factor optimization algorithms could be reduced from O(n2) to O(n). As a proof of concept, a lightweight stochastic algorithm was constructed, which can optimize pseudo-randomly generated skew-symmetric binary sequences with long lengths (up to 105+1) to skew-symmetric binary sequences with a merit factor greater than 5. An approximation of the required time is also provided. The numerical experiments suggest that the algorithm is universal and could be applied to skew-symmetric binary sequences with arbitrary lengths.

Copper Intercalation Effect on Thermoelectric Performance of Pristine Tin Selenide

AbstractPristine tin selenide (SnSe) and copper (Cu) doped SnSe single crystals are grown by direct vapour transport technique. The energy dispersive X‐ray, X‐ray diffraction and Raman spectroscopic analysis of grown crystals show preferred stoichiometry having a single phase othorhombic SnSe. The electrical conductivity of SnSe and Cu doped SnSe are 24.24 and 106.06 S m−1 at 310 K respectively which increase as temperature increases. Carrier concentration of grown single crystals are evaluated by the Hall effect. Lattice thermal conductivity of pristine SnSe is 0.61 W mK−1, that decreased by copper doping to 0.44 W mK−1 at 310 K and for both the crystals it shows decrement as temperature increases to 483 K. Seebeck coefficient of the grown SnSe and Cu doped SnSe are positive and obtained values are 536.44 and 492.90 µV K−1 respectively at 310 K that confirm the p‐type semiconducting nature. Power factor, Figure of merit and thermoelectric compatibility factor of grown pristine SnSe is 0.25 × 108 µV mK−2, 0.005 and 0.02 Volt−1 respectively and shows improvement in Cu doped SnSe, i.e., 0.08 × 108 µV mK−2, 0.017 and 0.07 Volt−1 respectively at 310 K. This shows Cu doping in SnSe makes it an effective thermoelectric device contender.

Effect of using MgO coating with multiple coatings on the optical properties of a five-layer stack

تم استخدام المادة العازلة MgO ذات معامل الانكسار العالي (H) 1.737 مع أربعة مواد عازلة BaF2 (فلوريد الباريوم) و Al2O3 (الألومينا) و GdF3 (فلوريد الجادولينيوم) و LaF3 اللانثانوم فلورايد ذوات معامل انكسار واطيء (L) 1.4825 و 1.5322 و 1.59 و 1.6056 على التوالي كطلاءات بصرية لخمس طبقات وللتصميمين الأول هو ((Glass/H/L/H/L/H والثاني (Glass/L/H/L/H/L) ، باستخدام برنامج MATLAB. تم حساب الخصائص البصرية (M، Rvis.، Rsol.، Tsol.) للطلاءات البصرية الأربعة المتكونة ، وذلك لمعرفة أي طلاء منها كفوء لتلوين زجاج الأنظمة الشمسية المستخدمة كواجهات للأبنية وأيها غير كفوء. تظهر النتائج أنه في التصميم الأول (Glass/H/L/H/L/H) للطبقات الخمس ، يوجد طلاءان فقط لهما كفاءة للتلوين ، وهما الطلاءان (MgO + BaF2) و (MgO + Al2O3) ، لأنهما يحققان القيم المطلوبة من عامل الجدارة (M) والانعكاسية المرئية Rvis. حيث ان القيم المطلوبة لقيم عامل الجدارة (M) و.Rvis والتي تجعل الطلاء كفوءاً للتلوين هي 6% و12% على التوالي ، ولهما قمة انعكاس منتظمة وحادة للتلوين في المنطقة المرئية. في التصميم الأول ، يتناسب معامل الانكسار عكسياً مع الخصائص البصرية للطلاء وبالتالي كفاءة تلوين الطلاء ، مما يعني أن طلاء (MgO + BaF2) أكثر كفاءة من طلاء (MgO + Al2O3) للتلوين. يعتبر التصميم الثاني (Glass/L/H/L/H/L) للطبقات الخمس غير كفوء للتلوين للطلاءات الأربعة ( (MgO + BaF2 ، (MgO+ Al2O3) ، (MgO + GdF3) ، MgO + LaF3)) لأنها لا تمتلك القيم المطلوبة من (M) و . Rvis

Thermoelectric properties of monolayered MnBi2Te4

AbstractThe thermoelectric properties of monolayered MnBi2Te4 are investigated using first‐principles calculations based on density functional theory (DFT) and Boltzmann transport theory. Our research indicates significant thermoelectric performance in monolayered MnBi2Te4, with a maximum figure of merit () and power factor () ranging from approximately 3.58 to 9.267 and 0.012 to 0.021 across a temperature range of 300–700 K. The exceptional thermoelectric performance of monolayered MnBi2Te4 can be attributed to its unique structural and electronic properties, which lead to ultralow lattice thermal conductivity and high electrical transport properties. Ultralow lattice thermal conductivity as low as at 300 K is found in the monolayered MnBi2Te4, which is mainly contributed from the anharmonic scatterings of low‐frequency phonons. And high electronic conductivity and a notable Seebeck coefficient are also observed in our system, which has close relationship with its distinctive electronic band structure. Besides, the two‐dimensional structure makes it a great candidate to holding greater PF by enhancing the quantum confinement. Our findings may lay a strong theoretical groundwork for future experimental inquiries. Subsequent experimental investigations will be crucial to confirm these findings, refine synthesis methods, and explore the practical applications of monolayered MnBi2Te4 in thermoelectric devices.

In Memoriam: Peter Benjamin Borwein (1953–2020)

Peter Borwein had wide-ranging mathematical interests, and was a pioneer in computational and experimental investigations in many areas. We fondly recall some of his interests and contributions in a number of topics in analysis, number theory, and other areas, especially work where computation and experimentation played an important role. This includes his work on a number of extremal problems regarding Littlewood polynomials and other families of integer polynomials with restricted coefficients, questions regarding the Mahler measure of an integer polynomial, problems on merit factors and Barker sequences, the Prouhet–Tarry–Escott problem, problems of Pólya and Turán regarding sums of the Liouville function, and questions in combinatorial geometry regarding arrangements of points and lines.

Exploring the Mn doped BaTe alloy for spintronics and energy harvesting applications

In the present study, the ferromagnetic semiconductor behavior of Mn doped BaTe is reported along with their physical properties. The calculations are done by full potential linearized augmented plane wave (FP-LAPW) approach within spin-polarized density functional theory (SP-DFT). Formation energies were computed to satisfy the stability of reported alloys. The spin-polarization is included in the calculations to study the electronic (band structure (BS), density of states (DOS)) and magnetic characteristics. Ba1−xMnxTe elucidates the magnetic semiconductor nature with direct band gap (Eg) in both spin channels while indirect Eg (1.66 eV) is observed for pure BaTe compound. Stable ferromagnetic (FM) states are vindicated owing to the p-d hybridization which are contributors in inducing magnetic moments (μ B) at interstitial and non-magnetic sites. The optical parameters (reflectivity, absorption coefficient, refraction, optical conductivity and dielectric function) were computed within an energy range of 0–10 eV. Thermoelectric (TE) features are also figured using Boltaz-Trap code in terms of thermal and electrical conductivity, figure of merit, Seebeck coefficient and power factor. The analysis of optical parameters suggests that the considered alloys is active within visible to UV-range, having potential applications in optoelectronic, photovoltaic and thermoelectric applications.

Optoelectronic and transport properties of Lead-Free halide based Na2AgTlZ6 (Z = Cl, Br, I) double perovskites for energy harvesting applications

The bandgap engineering and deliberate band edge manipulation of perovskites make them potential candidates for the photovoltaic industry. Here we theoretically investigate the structure, density of states, and photovoltaic and thermoelectric characteristics of Na2AgTlZ6 (Z = Cl, Br, I) using WIEN2k code. The incorporation of Br and I at the Cl site caused the increase in lattice constant which leads to the decrease in bulk modulus and Debye temperature. The computed values of Poisson (<0.26) and Pugh (<1.75) ratio verified their brittle nature. The bandgap analysis reveals direct bandgap nature and bandgap value lie in the visible region for parent composition and infrared and far infrared when Cl is replaced with Br and I. The density of state plots uncovers the shifting of energy states in valence and conduction bands towards the Fermi level with the increasing number of electrons in the halogens. The increase in the value of dielectric constant, refractive index, and shifting of peaks towards lower energy value is witnessed with atomic number of halogen atoms. The viability of these compositions for thermoelectric devices is further confirmed when electrical conductivity and Seebeck coefficient dependent Figure of merit and power factor are evaluated in the temperature range of 200–800 K. In addition, the anisotropic nature of studied compositions is explored through the computation of the modulus of elasticity including Young’s modulus, Shear modulus in addition to compressibility, and Poisson’s ratio.

Thermoelectric Properties of Layered CuCr0.99Ln0.01S2 (Ln = La…Lu) Disulfides: Effects of Lanthanide Doping

A comprehensive study of the thermoelectric properties of CuCr0.99Ln0.01S2 (Ln = La…Lu) disulfides was carried out in a temperature range of 300 to 740 K. The temperature dependencies of the Seebeck coefficient, electrical resistivity, and thermal conductivity were analyzed. It was found that the cationic substitution of chromium with lanthanides in the crystal structure of layered copper–chromium disulfide, CuCrS2 resulted in notable changes in the thermoelectric performance of CuCr0.99Ln0.01S2. The cationic substitution led to an increase in the Seebeck coefficient and electrical resistivity and a thermal conductivity decrease. The highest values of the thermoelectric figure of merit and power factor corresponded to the praseodymium-doped sample and an initial CuCrS2-matrix at 700–740 K. The cationic substitution with lanthanum, cerium, praseodymium, samarium, and terbium allowed for an enhancement of the thermoelectric performance of the initial matrix at a temperature range below 600 K. The cationic substitution of CuCrS2 with lanthanum and praseodymium ions appeared to be the most promising approach for increasing the thermoelectric performance of the initial matrix.

Effect of mechanical vibration and its influence on thermal performance of a nanofluid heat exchanger

Many situations involve flowing fluids on nonstationary platforms. For example, moving vehicles undergo vibrations in their transit. The effect of vibration on heat exchangers with nanofluids as working fluids has not been explored systematically, and this study examines the impact of vibrations in these situations. Vibrations having amplitudes in the range of 1–5 mm, and frequencies from 6 to 25 Hz are investigated. A 2% volume fraction Al2O3 solution with water as the base fluid has been utilized as the fluid; Reynolds numbers ranging from 10,000 to 25,000 were considered. The Nusselt number, friction factor, factor of merit, and effective thermal performance have been used to assess the heat transfer augmentation caused by vibration. It is found that the heat transfer characteristics are significantly enhanced by the active vibration provided in the form of a time-dependent sinusoidal velocity perpendicular to the axis of the heat exchanger tube. An increase of up to 70% in the Nusselt number was observed compared to the case without vibration. But, the friction factor was also enhanced; hence, a factor of merit and thermal performance factor was used as a comprehensive measure for changes to the performance. It was found that for a 5 mm amplitude and a 25 Hz frequency, a 30.7% rise in the factor of merit was observed with respect to the case where the tube is static. In addition, the thermal performance factor increased by 1.3.

Analyzing the physical properties of perovskite oxides CeBO3 (B=Be, Mg) for optoelectronic and thermoelectric applications

The structural, electronic, elastic, thermoelectric and optical properties of CeBO3 (B = Be, Mg) oxide perovskites were investigated using density functional theory. Exchange and correlation effects were addressed through the GGA approximation and the TB-mBJ potential. Thermodynamic stability was confirmed by assessing cohesive energy and formation enthalpy. The band structures reveal a semiconductor nature with a moderate indirect band gap of 0.73 (CeBeO3) and 0.51 (CeMgO3). The TB-mBJ approximation has enhanced the gap value with a 55% approaching rate. These compounds exhibited a rigid and elastically anisotropic behavior with chemical bonds manifesting as a mixture of metallic and covalent types. The CeBeO3 displayed ductility while CeMgO3 exhibited brittleness. The optical examination suggests that these oxides exhibit activity across a broad range of the electromagnetic spectrum. Their strong reflectivity in the near-infrared region was particularly noteworthy suggesting potential use as effective shields in this domain. The replacement of beryllium with a magnesium atom enhanced thermoelectric performance by reducing thermal conductivity and increasing the merit factor. Based on the obtained results, the semiconductor perovskites CeBeO3 and CeMgO3 hold promise for efficient applications in optical and thermoelectric devices.

Parallel self-avoiding walks for a low-autocorrelation binary sequences problem

A low-autocorrelation binary sequences problem with a high figure of merit factor represents a formidable computational challenge. An efficient parallel computing algorithm is required to reach the new best-known solutions for this problem. Therefore, we developed the sokolskew solver for the skew-symmetric search space. The developed solver takes the advantage of parallel computing on graphics processing units. The solver organized the search process as a sequence of parallel and contiguous self-avoiding walks and achieved a speedup factor of 387 compared with lssOrel, its predecessor. The sokolskew solver belongs to stochastic solvers and cannot guarantee the optimality of solutions. To mitigate this problem, we established the predictive model of stopping conditions according to the small instances for which the optimal skew-symmetric solutions are known. With its help and 99% probability, the sokolskew solver found all the known and seven new best-known skew-symmetric sequences for odd instances from L=121 to L=223. For larger instances, the solver cannot reach 99% probability within our limitations, but it still found several new best-known binary sequences. We also analyzed the trend of the best merit factor values, and it shows that as sequence size increases, the value of the merit factor also increases, and this trend is flatter for larger instances.

First‐principles studies on physical properties for new half‐metallic perovskites AFeO3 (A = Ca, Sr, Ba): Spintronics and energy harvesting applications

AbstractIn this manuscript, structural, electronic, magnetic, and thermoelectric aspects of AFeO3 (A = Ca, Sr, Ba) have been calculated by means of the Full‐Potential Linearized Augmented Plane Wave Method (FP‐LAPW) using spin‐polarized Density Functional Theory (DFT). The calculated structural parameters have been found to be in good resemblance with previously available work. Enthalpy of formation and cohesive energy along with tolerance factor confirms structural stability. Electronic properties by Trans Blaha modified Becke–Johnson potential (TB‐mBJ) suggest metallic behavior in the spin‐up channel and semi‐conducting behavior in the spin‐down channel that supports half‐metallic behavior with mixed covalent and ionic bonding. Density of States (DOS) analysis confirms the major contribution of Fe‐3d‐states in the conduction band and O‐2p states in the valence band. The half‐metallic nature is further confirmed by the integer value of the total magnetic moment. The real and imaginary parts of dielectric functions, optical conductivities, absorption coefficients, reflectivity, and energy loss function have been calculated to evaluate suitability for optical applications. Thermoelectric properties with temperature range 300–900 K against chemical potential including figure of merit, Seebeck coefficient, thermal conductivities, and power factor, were examined using BoltzTraP code. Findings suggest that AFeO3 (A = Ca, Sr, Ba) compounds suitable for spintronic, thermoelectric as well as energy harvesting applications.

Ramifications of chromium-to-bismuth ions substitution on the structural and optical characteristics of bismuth borate glasses for optoelectronic applications

The exploration of optoelectronic materials with distinctive properties is still ongoing. To this end, a series of quaternary glassy materials of the composition 15Na2O–65B2O3–(20–x)Bi2O3–xCr2O3, denoted as NBBC, is synthesized using the melt quenching method, where x = 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mol%. X-ray diffraction (XRD) confirms that the glasses under investigation are amorphous, except for the sample with a molar ratio of 10% Cr2O3, which showed a polycrystalline structure. FTIR analysis of the NBBC glasses reveals structural changes affecting Bi-O and B-O vibrations, suggesting a correlation between composition and optical properties. Interestingly, the bandgap energy of the NBBC glasses, determined optically, demonstrates a reduction from 2.881 eV to 1.941 eV with increasing Cr2O3 content. Conversely, the tail energy exhibits an opposite trend. The observed reduction in the bandgap with increasing Cr-ions is attributed to the introduction of chromium in the glassy matrix, which changes the electronic structure and enhances the light absorption efficiency. Furthermore, various optical parameters are calculated, such as the optical constants, dielectric constants, loss energy, the density of coverage, sheet resistance, the figure of merit factor, and dispersion parameters. Notably, all of these parameters demonstrate a remarkable sensitivity to the gradual increment of chromium ions. These findings imply that the NBBC glasses could be appropriate for optoelectronic purposes.

A computational study of the structural and thermal conduct of MgCrH3 and MgFeH3 perovskite-type hydrides: FP-LAPW and BoltzTraP insight

The structural and thermal conduct of MgCrH3 and MgFeH3 perovskite have been investigated using the full-potential linearized augmented plane wave (FPLAPW) method and the BoltzTraP package, implemented in the Wien2k code. The calculations involved fitting the Murnaghan equation of state to the calculated total energy and atomic volume. The present analysis includes key groundstate parameters, such as the lattice parameter and its pressure derivative. Where the electrical conductivity of MgTMH3 (TM=Cr and Fe), the thermal conductivity, merit factor, and power factor were discussed in the range of 300-900 K. The obtained outcomes exhibit interesting results to make these compounds as promising materials for thermoelectrical applications.

The Mean and Variance of the Reciprocal Merit Factor of Four Classes of Binary Sequences

The Mean and Variance of the Reciprocal Merit Factor of Four Classes of Binary Sequences

Theoretical Investigations of Lead-Free Halide Perovskites Na2AgInY6 (Y = Cl, Br, I) for Transport and Optoelectronic Devices

Lead-free double perovskites are stable, non-toxic, and have high conversion efficiency, better oxidation resistance, and high-temperature stability, making them promising for optoelectronic and thermoelectric materials. In the current report, we have examined structural, electronic, optical, and transport characteristics of Na2AgInY6 (Y = Cl, Br, I) utilizing DFT-based Wien2k code. Thermodynamic stability is verified by calculating the enthalpy of formation. TB-mBJ measures the bandgap computations, and the investigated compositions have indirect bandgaps. The bandgap values are decreased from 3.1 eV to 1.2 eV as the halide ion is replaced from Cl - I. This substitution-dependent tuning of band edge across the visible-infrared boundary makes them favorable for solar cell applications. The optical response is evaluated by measuring the refractive index, dielectric constant, absorption coefficient, and reflectivity. The thermoelectric efficiency of Na2AgInY6 (Y = Cl, Br, I) is calculated by figure of merit and power factor. The findings of this study unveil the potential of these novel compositions for next-generation energy harvesting devices, including solar cells and thermoelectric devices.

Orientation effects, hydrostatic response, and figures of merit in 2–2-type composites based on relaxor-ferroelectric single crystals

The article reports new results on the hydrostatic performance of laminar piezo-active composites based on domain-engineered relaxor-ferroelectric single crystals (SCs) with the perovskite-type structure. Layers of the composites are either single-crystal poled along [011] (where rotations of the main crystallographic axes around two co-ordinate axes are considered) or porous polymer, with aligned spheroidal pores. These composites are described by 2–2–0 connectivity. An influence of the rotation of the main crystallographic axes and porosity is analyzed, and maxima of the hydrostatic piezoelectric coefficient figure of merit and electromechanical coupling factor of the composites are found as functions of a few parameters. New diagrams are built to show regions of the large (over 1000 pC/N) at variations of two rotation angles in the single-crystal layers. Large values of the hydrostatic figure of merit ∼ (10−10 – 10−9) Pa−1 and electromechanical coupling factor are achieved in specific volume-fraction and rotation-angle ranges. These and other large values of the hydrostatic parameters of the studied 2–2-type composites are important for effective hydroacoustic applications.

Study of physical properties of the new inorganic perovskites LiSnX3 (X=Br or I): A DFT approach

This work aims to study the optoelectronic and thermoelectric properties of the new perovskites LiSnX3 (X[Formula: see text]Br or I). This study is carried out by using the density functional theory (DFT) combined with the Boltzmann transport theory. First, the investigation of the structural, electronic and optical properties of such materials, using the Generalized Gradient Approximation (GGA), has been performed. This latter method has been performed under the Perdew–Burke–Ernzerhof (GGA–PBE) approximation applying the exchange correlation potential. It is found that the two compounds exhibit a p-type semiconductor characteristic and interesting optical properties. Moreover, the thermoelectric properties of the studied materials, such as the Seebeck coefficient, electrical conductivity, thermal conductivity, figure of merit and power factor, have been examined. It is found that the Seebeck coefficient takes positive values. This finding reveals and confirms the p-type semiconductor characteristic for two studied compounds. On the other hand, such materials display large values of the figure of merit (ZT) in comparison with the existing thermoelectric materials. Such large values of ZT are found for both small or large temperature values. The obtained results of the optoelectronic and thermoelectric properties show that these materials could be useful both for photovoltaic and thermoelectric applications.

3D printing of lead zirconate titanate piezoelectric ceramics via digital light processing (DLP)

Research of piezoelectric ceramics via DLP technology has drawn considerable interest due to its high geometrical flexibility. However, the poor curing properties limit the use of DLP technology to fabricate piezoelectric ceramics. Herein, we overcome this challenge in prepared lead zirconate titanate (PZT) piezoelectric ceramics via DLP technology by incorporating ultralow refractive index and ultraviolet light absorptivity of soluble starch in PZT ceramic slurry. After the post-process, the relative density of printed PZT ceramic with 20 vol% soluble starch could reach about 89.51% of theoretical density. The printed PZT ceramic exhibits remarkable dielectric permittivity, remnant polarization, piezoelectric strain constant, piezoelectric voltage constant, figure of merit and electromechanical coupling factor of 2196, 35.56 μC/cm2, 373 pC/N, 1.92 × 10−2 Vm/N, 7.16 × 10−12 m2/N and 42.28%, respectively. The results achieved in this research indicate that our work provides a promising route for fabrication of advanced ceramics with high performance and designed complex structures by digital light processing.