Papers by Keyword: Figure of Merit

Abstract: Machine Learning (ML) approach seeks to open new frontiers in the search for novel thermoelectric materials that convert heat waste into useful electrical energy. Five regression-type ML algorithms Linear Regression, Random Forest, XGBoost, Bagging Regressor, and Gradient Boosting Regressor were employed in this study to forecast the thermoelectric figure of merit (ZT) of doped chalcogenide compounds. Gradient Boosting Regressor achieved the best baseline performance (R² = 94.5%, MAE = 0.073, RMSE = 0.128), further improved with hyperparameter tuning to R² = 95.8%, MAE = 0.065, and RMSE = 0.112. Compared to the baseline, tuning reduced RMSE by 12.6% and MAE by 10.8%. The optimized model reliably reproduced experimental ZT trends in doped Bi₂Te₂Se and Ag₂Te, validating its predictive capacity. Our findings show that hyperparameter tuning is greatly recommended for high-fidelity predictions in thermoelectrics.

Abstract: In this article, we propose a biosensor based on a hybrid photonic crystal, the studied system is a superlattice consisting of a periodic alternation of poly(methyl methacrylate) (PMMA) and silicon dioxide (SiO₂) layers. Our study demonstrates that breaking the periodicity of the superlattice enables the excitation of Bloch surface waves within the photonic bandgap. This feature, along with its experimental convenience, justifies our choice of this structure for designing a biosensor in the Kretschmann configuration. Furthermore, we also analyzed the effect of various parameters, such as the number of layer repetitions, the frequency of the light waves used, and the thickness of the defect layer, on the biosensor's performance, the optimal structure, MgF₂/(PMMA/SiO₂)₃/D, demonstrates excellent sensing performance, achieving an angular sensitivity of 74°/RIU and a high figure of merit (FOM) of 1495/RIU.

Abstract: Tin Selenide, Lead Selenide, and Lead Telluride are known best thermoelectric materials for mid and high-temperature electric generation applications. The bilayer of these materials could enhance the quality of a thermoelectric generation. The present work deals with bilayer deposition of SnSe/PbTe and SnSe/PbSe in glass substrates using physical vapor deposition followed by annealing at 323K, 423K, and 523K. The structure and morphology of the films have been investigated by XRD, SEM, and FESEM studies. The thermoelectric pursuance of both bilayer thin films was studied with the temperature as a function in the range of 300K to 623K. Both films exhibit the maximum Seebeck coefficient. The electrical Conductivity and Power factor increased gradually for SnSe/PbTe thin films and SnSe/PbSe thin films for the samples annealed up to 573K and then decreases. The electronic thermal conductivity of both films was very low compared to the total thermal conductivity. The absolute thermal conductivity at room temperature was calculated by Transient Hot Wire (THW) method. The maximum Figure of Merit (ZT) value obtained for SnSe/PbTe and SnSe/PbSe at room temperature was 0.81 and 1.3 for 573K annealed thin films respectively.

Abstract: In the last few years, materials that may have favorable thermoelectric properties have aroused great interest, because they have the ability to generate electricity through the thermoelectric effect. In this work, the temperature effect on the transport properties of a ZnSb compound having an orthorhombic structure is studied, using the local density approximation with the modified approach of Becke and Johnson (LDA + mBJ), within the framework of density functional theory (DFT). To do this, we use the BoltzTrap package implemented in the Wien2k code, with a constant relaxation time of the charge carriers. All transport properties were studied in the temperature range of 300 to 600 K. Moreover, for high temperatures, the prediction of the figure of merit of ZnSb indicates that the compound is much more suitable for thermoelectric devices. Also, the Pauli magnetic susceptibility of zinc antimonide showed that this material is non-magnetic.

Abstract: Thermoelectricity is the best technology for converting wasted heat into clean electrical energy. Calcium Bismuth cobaltites Ca_2.7Bi0_.3-xNd_xCo₄O_9+⸹ was synthesized using WOWs Sol-gel method with (x=0.0,0.05) doped with Neodymium. A structural study was carried out using the X-rays diffraction (XRD), which confirmed the Monoclinic structure of all the prepared samples. The Electrical properties were studied by using two-probe method. The thermal transport properties of the samples were measured at room temperature using the Advantageous transient plane source (ATPS) method. At room temperature thermal conductivity was measured. Seebeck coefficient as a function of temperature measurement revealed that doping Neodymium considerably increases the value of the Seebeck coefficient when compared to previously published values. At the end we measured the figure of merit (ZT).

Abstract: Thermoelectric properties of SrTiO₃ doped with 8%Pm at Sr site were investigated using density functional theory and generalized gradient approximation. The transport properties were calculated based on BoltzTraP code at temperature range 300-1200K. In electronic properties study Fermi level were shifted to conduction band region due to high contribution 4f orbital in Pm. Present study thermoelectric figure of merit ZT result was 0.395 at 300K and 0.638 at 1200K. This shows a considerably good value of ZT for SrTiO₃ as n-type oxide. Compared to previous work, ZT were at the range of 0.21 - 0.37 for temperature of 300-1000K in Pr, La, Ta and Ho.

Abstract: Type-I clathrates have been considered as very promising thermoelectric (TE) materials thus attracting attention widely. Here we report new clathrates Ba₈Cu_xSi_yGe_46-x-y (4≤ x ≤ 6.5, y = 0 and 5.15 ≤ x ≤ 6.425, 2.05≤ y ≤ 36.9), focusing on their phase purity and TE properties. Our results show that samples prepared by arc melting followed by annealing are multi-phases alloys. The composition of the clathrate phase is also inhomogeneous. This indicates that the kinetic factor dominates the reaction of forming the clathrate phase during element-melting and sample-annealing. We select three compositions in these two series of samples, which have less impurity and better composition homogeneity for the clathrate phase, and the annealed alloys are furthered processed by ball milling (BM) and powder-solidification (either by hot pressing (HP) or by spark plasma sintering (SPS)) for TE properties investigations. The BM and HP/SPS processes can improve the phase purity and homogeneity. The TE measurements show that the Si-substituted samples have better performance than the Ge-based sample, mainly by decreasing the electrical resistivity. This indicates that the elemental substitution may be still an effective way to improve the TE performance of clathrates.

Abstract: Multilayer structure with SnO₂/Ag//SnO₂ was prepared on glass substrates by sequential using RF/DC magnetron sputtering at room temperature. In order to estimate and compare with the experimental results in advance, EMP (Essential Macleod Program) simulation program was adopted. EMP simulation results suggested that the multilayered thin film of SnO₂ (30 nm)/Ag (10 nm)/SnO₂ (30 nm) exhibited the highest visible transmittance of 88.8 % at 550 nm, whereas experimentally measured transmittance showed 85.5 %, somewhat lower than simulation data. Even though most of films exhibit transmittance of about 88 % at 550 nm wavelength, there are some distinct differences between the experimental and simulated results. Sheet resistance (Rs) were almost constant and the lowest Rs value about 9.51 Ω/sq was acquired at the multi layers with the structure of SnO₂ (30nm)/Ag (10nm)/SnO₂ (30nm). However, the resistivity of the SnO₂/Ag/SnO₂ multi layer film increased systematically with increasing thickness of SnO₂ layer from 30 to 50 nm. SnO₂/Ag/SnO₂ multilayer with 50 nm of SnO₂ thickness resulted in a decrease of Φ_TC due to decrease of transmittance. The highest Φ_TC value of SnO₂/Ag/SnO₂ film was obtained at a SnO₂ thickness of 35 nm.

Abstract: Nowadays, the concept of harvesting energy from the environment, for example, thermal, wind, sun, vibration and human activities is much of interest. PZT is one of the materials which show an ability to harness vibration energy and then change to electrical energy. Therefore, the PZT (Pb(Zr_0.53Ti_0.47)O₃) doped with 0.02 mol% BYF (Bi(Y_0.7Fe_0.3)O₃) piezoelectric ceramics has been studied to improve the figure of merit (d₃₃*g₃₃). The PZT and BYF powder systems were prepared by solid state reaction with calcination temperature of 800 and 850 °C for 2 h, respectively. XRD results showed that both powders exhibited pure perovskite phase for PZT and single phase of BYF without pyrochlore phase. Then, the two calcined powders (PZT and BYF) were mixed according to the composition of 0.02 mol% BYF doped PZT by two different milling techniques called conventional ball-milling (CBM) and high energy ball-milling (HBM) for 10 h. The result showed that average particle size obtain from HBM was 1 µm which was smaller than from CBM shown up to a few microns in bimodal mode. The PZT-BYF-HBM ceramics showed higher physical and electrical properties but lower K value. Thus promoting to higher g₃₃ which was equal to 36.89 * 10^-3(Vm/N) and FOM was 11,632*10^-15(m²/N), while PZT-BYF-CBM had g₃₃ of 26.86* 10^-3(Vm/N) and FOM at 8,016*10^-15(m²/N), respectively.

Abstract: Recently, Lead Zirconate Titanate (PZT) has been attracted for energy harvesting (EH) devices because of their excellent piezoelectric properties at the morphotropic phase boundary (MPB). The EH devices require high energy density related to high figure of merit (FOM: g₃₃ x d₃₃). As a result, the improvement of piezoelectric voltage coefficient (g₃₃) and piezoelectric charge coefficient (d₃₃) to better energy density property obtained should be searching for. Therefore, PZT-BYF system was chosen for piezoelectric energy harvester by focusing to study on the composition of 0.99PZT-0.01BYF (0.99Pb(Zr_0.53Ti_0.47)O₃-0.01Bi(Y_0.7Fe_0.3)O₃). In this study, PZT and BYF systems were calcined separately and then 0.99PZT-0.01BYF powders were prepared by solid state method and mixed via high-energy ball milling in various milling time (2, 4, 10 and 16 hrs). The effect of milling time on the physical and electrical properties, figure of merit and microstructure were investigated.