Excellent Conversion Performance Research Articles

Two-Dimensional β-PdX2 (X=S, Se, and Te) Monolayers with Promising Potential for Thermoelectric Applications

Transition metal dichalcogenides have attracted extensive research attention due to their unique electronic, topological, and optical properties. Based on first-principles methods and Boltzmann transport theory, the thermoelectric performance of β-PdX2 (X = S, Se, and Te) monolayers was comprehensively studied in this work. It is worth noting that the structural anisotropy of β-PdX2 monolayers leads to obvious anisotropy of thermoelectric coefficients along the x and y directions. By investigating the thermal transport up to four-phonon scattering, it was found that the strong higher-order phonon scattering plays a decisive role in ultra-low lattice thermal conductivity of β-PdX2 monolayers. A low lattice thermal conductivity of 3.4 (1.0) W m–1 K–1 is predicted for β-PdTe2 at 300 K along the x (y) direction. In addition, due to the suitable band gap and high carrier mobility, the highest power factor of 25.7 mW m–1 K–2 is obtained in n-type β-PdX2 monolayers, which is superior to many other two-dimensional thermoelectric materials. Finally, a maximum ZT of 5.2 is achieved for the n-type β-PdS2 monolayer along the y direction at 600 K. Meanwhile, the maximum p-type ZT also reaches 3.3 along the y direction at 600 K in the β-PdSe2 monolayer. Our results demonstrate that β-PdX2 monolayers are promising candidates for two-dimensional thermoelectric materials with excellent conversion performance.

First-principle investigation on the thermoelectric properties of XCoGe (X = V, Nb, and Ta) half-Heusler compounds

Half-Heusler compound is a promising thermoelectric material due to its excellent conversion performance. In this study, we investigate the electronic structure, and thermoelectric properties of XCoGe (X = V, Nb, and Ta) compounds based on density functional theory. Combining the semi-classical Boltzmann transport equation and the deformation potential theory, the thermoelectric properties such as Seebeck coefficient, relaxation time, electrical conductivity, power factor, electronic thermal conductivity, and lattice thermal conductivity are analyzed. The NbCoGe compound possesses a large dimensionless figure of merit, which is related to the large electrical conductivity, small effective mass, and large relaxation time. The ZT values of n- and p-type NbCoGe compounds reach 1.6 and 1.3 at T = 1200 K, respectively. These findings will provide valuable guidance for exploring half-Heusler compounds with high thermoelectric performance.

Color characteristic design for color scanners

We propose a method of quantitative color characteristic design for color scanners. We used calorimetric simulation with an optical model and a color conversion circuit to match the scanner color characteristic to an objective color standard. A compensation matrix is defined using the least-squares method to minimize the average error for many colors. To determine the matrix, a color space must be selected. We compared the results of conversion using matrices obtained in the CIELAB color space and in the RGB color space. The comparison shows that both conversions are nearly the same. Using computer simulation, we designed a color scanner with excellent conversion performance. The average color difference for 440 colors was ~1.3.