Research Progress of Hyperstoichiometric UO₂Crystals

Abstract

Uranium dioxide is a potential multi-functional material as well as nuclear rod. It exhibits excellent semiconductor performance and anti-irradiation ability. It has the similar band gap (1.3 eV) of silicon crystal (1.1 eV), its Seebeck coefficient is 4 times of the commercial thermoelectric material BiTe, and it shows higher conversion efficiency of solar cells due to its nearly full absorption. These properties make it great potential applications in the fields of semiconductor, solar energy and thermoelectricity. However, the U atoms in uranium dioxide (UO 2±x ) can vary from -0.5 to 1, which is called hyperstoichiometric characteristics, resulting in some problems in crystal growth and property homogeneity. In this paper, we analyzed the structure and chemical stability of uranium oxides according to U-O phase diagrams, summarized recent research progress on crystal growth and physical properties of UO 2 crystals. UO 2 is an ideal Mott insulator with a stable electric conductivity, while the hyperstoichiometric UO 2±x crystals are semiconductors, and their physical properties, including electric conductivity, thermal conductivity and diffusion coefficient, and optical properties, are closely related to x. So far, UO 2 crystals have grown via several methods, such as chemical vapor transport (CVT), sublimation, skull melting, hydrothermal and flux. The skull melting and hydrothermal techniques are expected to improve crystal dimensions and quality in future. The growth of UO 2 crystals is ex-

Growth and Spectral Properties of Er3+ and Yb3+ Co-Doped Bismuth Silicate Single Crystal

“…Lira et al reported the photoluminescence of the Er: BSO crystal [18]. Previously, we have reported rare-earth ions and Ge 4+ -and U 4+ -doped BSO laser crystals, and laser output was realized in Ho 3+ : BSO and Tm 3+ : BSO crystals [19][20][21][22]. In the present work, the growth and spectral properties of the Er/Yb: BSO crystal are reported.…”