CuAgSe is a promising thermoelectric material due to its superionicity. In this work, β-Cu1−xAg1−ySe (x = 0, 0.02, and 0.04; y = 0, 0.02, and 0.04) samples are synthesized by solid-state reaction method. The vacancies in samples are characterized by positron annihilation spectroscopy. Thereafter, the effects of vacancies on thermoelectric properties are investigated. The positron annihilation results reveal that Ag vacancies exist in the Ag-deficient samples (β-CuAg0.98Se and β-Cu0.98Ag0.98Se) but also in the Cu-deficient samples (β-Cu0.96AgSe and β-Cu0.98AgSe). For the Cu-deficient samples, the existence of Ag vacancies is attributed to the formation of impurity phases. For the nonstoichiometric samples, the vacancies are responsible for the decrease in the Seebeck coefficient in the temperature range from 300 to 400 K. However, for β-CuAgSe, no decrease in the Seebeck coefficient is observed due to the lack of extra holes, and electrons are still the majority carriers. For CuAgSe, the ZT value is mainly determined by the Seebeck coefficient. Therefore, for the nonstoichiometric samples, the ZT value reduces drastically with increasing temperature and drops to nearly zero at 400 K. In contrast, with the temperature increasing from 300 to 450 K, the ZT value of β-CuAgSe goes up from 0.4 to 0.5.
200 keV Cu þ ions were implanted into 6H-SiC single crystal at room temperature with fluence of 8 Â 10 15 cm À2. No ferromagnetism (FM)-related secondary phase was found by the results of high-resolution x-ray diffraction and x-ray photoelectron spectroscopy. Positron annihilation lifetime spectroscopy results indicated that the main defect type was silicon vacancy and the concentration of it increased after Cu implantation. The room-temperature ferromagnetism was detected by superconducting quantum interference device. First-principles calculations revealed that the magnetic moments mainly come from the 2p orbitals of C atoms and 3d orbitals of Cu dopant. The origin of the FM has been discussed in detail. V
Diluted magnetic semiconductors (DMSs) have numerous potential applications, particularly in spintronics. Therefore, the search for advanced DMSs has been a critical task for a long time. In this work, room-temperature ferromagnetism is observed in the C+-implanted AlN films with C+ doses of 5×1016 (AlN:C5×1016) and 2×1017 cm−2 (AlN:C2×1017). AlN:C2×1017 exhibits a saturation magnetization of ∼0.104 emu/g, nearly 1.5 times that of AlN:C5×1016. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) measurements reveal that the implanted C+ ions occupy the interstitial lattice sites and substitute at the sites of Al atoms. XPS and Doppler broadening of positron annihilation radiation measurements demonstrate the existence of the Al-vacancy related defects in the C+-implanted AlN films. First-principles calculations indicate that the ferromagnetism in AlN:C5×1016 and AlN:C2×1017 is mainly originated from defect complexes involving interstitial C atoms and Al vacancies, which have the lowest formation energy among AlN:C defects containing C atoms and Al vacancies. This work provides a feasible route to develop advanced DMSs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.