Compositional effects on the low-temperature transport properties of non-stoichiometric Bi2TexSey-based crystals. (1st December 2016)

• Record Type: Journal Article
• Authors: Ramachandran, B; Wu, K K; Kuo, Y K; Guo, L S; Wang, L M
• Is Part Of: Journal of physics. Volume 50:Number 2(2017)
• Publication Date: 2016-12-01
• Subjects: topological insulator -- single crystal -- induced defects -- Seebeck coefficient -- Hall coefficient -- thermal transport; Physics -- Periodicals; 530
• DOI: 10.1088/1361-6463/50/2/025302
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: We grew a series of non-stoichiometric crystals of the ternary alloy Bi2 Te x Se y via a direct solidification route. The temperature-dependent electrical and thermal transport properties, such as electrical resistivity ( ρ ), Seebeck coefficient ( S ), Hall coefficient ( R H ), and thermal conductivity ( κ ), of six selected crystals of Bi2 Te x Se y with x + y ~ 3 were studied. We found that the physical properties of the Bi2 Te x Se y -based crystals varied significantly with the Te/Se ( x / y ) content. This is essentially due to the modification of the electronic band structure of the crystals with the change in sample composition, which ultimately leads to the formation of a p -type material (Bi2 Te2.10 Se0.66 ) from an n -type Bi2 Te1.89 Se0.98 . Most importantly, the feature associated with surface-state conduction at low temperatures was also observed in some of these crystals, including Bi2 Te1.89 Se0.98, Bi2 Te2.16 Se0.71, and Bi2 Te2.10 Se0.66 . In particular, two highly resistive compounds, Bi2 Te2.16 Se0.71 and Bi2 Te2.10 Se0.66 with low carrier densities were identified as potential materials for topological applications. The observed complex transport behavior was realized in connection with the formation of impurity bands (multiband effects) in the Bi2 Te x Se y -based systems. Analysis of the lattice thermal conductivity of the Bi2 Te x Se y -based crystals indicates that the sample composition has a major effect on low-temperature heat conduction via phonon-boundary and phonon-point-defect scattering. Finally, the highest room temperature thermoelectric figure of merit, a ZT of about 0.46, was achieved for n -type Bi2 Te1.63 Se1.23 .