Ni-doped Bi_0.5Sb_1.5Te₃ single crystal: a potential functional material for thermoelectricity, topological insulator, and optoelectronics

We report the growth of Ni-doped Bi_0.5Sb_1.35Ni_0.15Te₃ single crystal via the self-flux method. The crystalline nature of a grown single crystal was confirmed by the X-ray diffraction technique (XRD). Interestingly, the XRD pattern shows a sharp reflections of < 0 0 l > type of planes, revealing the growth of the crystal in c-direction. The grown single crystal was subjected for measurement of field dependence magnetization at 300 K and temperature-dependent magnetic moment. The electronic transport property of bulk single crystal was also carried out in a wide range of temperatures from 150 to 450 K. Reasonably large electrical conductivity σ ~ 1584 S/cm at room temperature was observed which shows  ~ 400% enhancement in σ than the electrical conductivity of bare Bi_0.5Sb_1.5Te₃ single crystal (400 S/cm at 300 K). This enhanced electrical conductivity results to significant power factor ~ 1.68 × 10^− 3 W/m K² at 300K which is 163% larger than that of bare Bi_0.5Sb_1.5Te₃ single crystal (6.45 × 10^− 4 W/m K²). Magnetic properties of a single crystal of Bi_0.5Sb_1.35Ni_0.15Te₃ reveal ferromagnetic behavior at 300 K. The photoluminescence (PL) behavior of Bi_0.5Sb_1.35Ni_0.15Te₃ single-crystal was also scrutinized. The PL spectra of Bi_0.5Sb_1.35Ni_0.15Te₃ single crystal shows the strong red emission peak in the visible region from 600 to 690 nm upon excitation at 375 nm wavelength, which corresponds to the optical bandgap of 2.1 eV.