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Ni-doped ­Bi0.5Sb1.5Te3 single crystal: a potential functional material for thermoelectricity, topological insulator, and optoelectronics Sahiba Bano1,2 · Bal Govind1,2 · Ashish Kumar1,2 · D. K. Misra1  Received: 13 June 2020 / Accepted: 29 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract We report the growth of Ni-doped ­Bi0.5Sb1.35Ni0.15Te3 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  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 ­Bi0.5Sb1.5Te3 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 ­Bi0.5Sb1.5Te3 single crystal (6.45 × 10− 4 W/m K ­ 2). Magnetic properties of a single crystal of B ­ i0.5Sb1.35Ni0.15Te3 reveal ferromagnetic behavior at 300 K. The photoluminescence (PL) behavior of ­Bi0.5Sb1.35Ni0.15Te3 single-crystal was also scrutinized. The PL spectra of ­Bi0.5Sb1.35Ni0.15Te3 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.

1 Introduction Research on thermoelectric materials is becoming an intriguing topic since the past decades due to owing their demand for power generation and cooling applications. The performance of thermoelectric materials is elucidated by the dimensionless figure of merit, ZT = (α2σ/ κ) T where σ, α, and κ are the electrical conductivity, Seebeck coefficient, and total thermal conductivity, respectively, at the absolute temperature (T) [1]. Improving the power factor, α2σ, seems to be an excellent approach to enhance the efficiency of thermoelectric materials. There are different approaches such that multiple band convergences [2–4], tuning the bandgap [5–7], modulation of carrier scattering mechanisms [8, 9] and inducing modulated doping to enhance power factor of materials. Recently, the strategy of doping of magnetic ion has been investigated to escalate the thermopower [10–13]. * D. K. Misra [email protected] 1



CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India



Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India

2

There has also been the efficacy of magnetic doping on the thermoelectric properties of antiferromagnetic C ­ uFeS2 chalcopyrites [10, 11, and 13] and ­CuGaTe2 chalcopyrite [12]. Bi2Te3 th