Electrical conductivity, Seebeck coefficient, and crystal growth of p-type tellurium films through temperature dependent RF sputtering.

Te thin films have recently received considerable attention owing to its superior electrical and thermoelectric properties. During the deposition process, if the temperature of the substrate is raised, high crystallinity and improved electrical properties can be expected. In this study, we used radio frequency sputtering for Te deposition to study the relationship between the deposition temperature, crystal size, and electrical performance. As the deposition temperature is increased from room temperature to 100 °C, we observed an increase in crystal size from the x-ray diffraction patterns and full-width half maximum calculations. With this grain size increment, the Hall mobility and Seebeck coefficient of the Te thin film increased significantly from 16 to 33 cm2V-1s-1and 50 to 138µV K-1, respectively. This study reveals the potential of a facile fabrication method for enhanced Te thin films using temperature control and highlights the importance of the Te crystal structure in determining the electrical/thermoelectrical properties. These findings are particularly significant for the development of semiconductor material systems for various applications, including thermoelectric devices, CMOS, FET, and solar devices.

Room-Temperature Fast H- Conduction in Oxygen-Substituted Lanthanum Hydride.

The hydride ion (H-) is a unique anionic species that exhibits high reactivity and chemical energy. H- conductors are key materials to utilize advantages of H- for applications, such as chemical reactors and energy storage systems. However, low H- conductivity at room temperature (RT) in current H- conductors limit their applications. In this study, we report a H- conductivity of ∼1 mS cm-1 at RT, which is higher by 3 orders of magnitude than that of the best conductor, in lightly oxygen-doped lanthanum hydride, LaH3-2xOx with x < 0.25. The oxygen concentration (x) is crucial in achieving fast H- conduction near RT; the low activation barrier of 0.3-0.4 eV is attained for x < 0.25, above which it increases to 1.2-1.3 eV. Molecular dynamics simulations using neural-network potential successfully reproduced the observed activation energy, revealing the presence of mobile and immobile H-.

Characteristic fast H- ion conduction in oxygen-substituted lanthanum hydride.

Fast ionic conductors have considerable potential to enable technological development for energy storage and conversion. Hydride (H-) ions are a unique species because of their natural abundance, light mass, and large polarizability. Herein, we investigate characteristic H- conduction, i.e., fast ionic conduction controlled by a pre-exponential factor. Oxygen-doped LaH3 (LaH3-2xOx) has an optimum ionic conductivity of 2.6 × 10-2 S cm-1, which to the best of our knowledge is the highest H- conductivity reported to date at intermediate temperatures. With increasing oxygen content, the relatively high activation energy remains unchanged, whereas the pre-exponential factor decreases dramatically. This extraordinarily large pre-exponential factor is explained by introducing temperature-dependent enthalpy, derived from H- trapped by lanthanum ions bonded to oxygen ions. Consequently, light mass and large polarizability of H-, and the framework comprising densely packed H- in LaH3-2xOx are crucial factors that impose significant temperature dependence on the potential energy and implement characteristic fast H- conduction.