High-pressure synthesis, crystal structure, and physical properties of NaAlB14 single crystals

Pure NaAlB14 single crystals were successfully synthesized directly from Na, Al, and B at high pressure and high temperature, different from the previously reported method, that is, synthesized from Na2B4O7, Al, and B. The growth of NaAlB14 single crystals was promoted by increasing the reaction temperature. The atomic structures of NaAlB14 single crystal along the [100], [010], [001], and [021] axes were characterized by using a scanning transmission electron microscope. The Raman spectra of NaAlB14 were investigated theoretically and experimentally, and they showed the expected oscillations of the covalent framework. In addition, photoluminescence spectra indicated that NaAlB14 is a semiconductor luminescence material with red (1.68 eV) and near-infrared (1.50 and 1.36 eV) emission characteristics. The band structure revealed that NaAlB14 is an indirect band gap semiconductor with a wide band gap of 2.22 eV.