Size-selective and High-yield Nanocrystal Growth of PbTe Compounds Using a Chemical Vapor Deposition Technique
- PDF / 239,025 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 117 Downloads / 179 Views
0886-F05-01.1
Size-selective and High-yield Nanocrystal Growth of PbTe Compounds Using a Chemical Vapor Deposition Technique B. Zhang, N. Gothard, J. He, D. Thompson and Terry M. Tritt. ABSTRACT: The nanocrystals of PbTe and related compounds (Pb1-xSnxTe, PbTe1-xSex), differing by size and composition, have been synthesized using a chemical vapor transport (CVD) technique. The size–selective precipitation mechanism relying on the variation of heating temperatures, Ar flow rates and admixture with Au particles, enables a relatively good control of particle size distribution. In addition, the doping ratios of those nanocrystals are readily modified by changing the atomic ratio in the raw starting materials. Subsequently, a yield of hundreds of milligrams of nanocrystals which exhibit narrow size distributions at 100 nm, 300 nm and 600 nm and controllable composition have been obtained. XRD patterns taken on the PbTe samples show sharp, which indicate good crystallinity of samples. According to the shift of the Bragg reflections, the lattice constants of (Sn / Se) doped PbTe change with the variation of the doping ratios. INTRODUCTION: Bulk PbTe and related compounds are well established and the most commonly used high temperature thermoelectric (TE) materials, which reach their best efficiencies in intermediate temperature range, 450–800 K. Since most Carnot heat engines are working in the same temperature region, PbTe compounds have a potential application in the conversion of waste heat into electricity. PbTe has a cubic (rock salt) crystal structure (space group F m -3 m, and a lattice parameter, a = 6.459Å at room temperature and under ambient pressure) and behaves as a typical semiconductor with a narrow band gap (EG ≈ 0.34eV at 300K). Due to its high atomic mass, good electrical properties, and low thermal conductivity, it was one of the first studied TE materials when Iofee and his colleagues led the revival of interests in thermoelectricity in the middle of the twentieth century. [1] In previous studies, doping elements and decreasing grain size were the main research directions to enhance the figure of merit, ZT, of PbTe. Several elements with different doping ratio: Na, Au, Ti, O as accepters; Zn, Cd, In, Bi, Cl as donors, have been employed to be the dopants in order to optimize the ZT. As recommended by Rosi et al., the best composition is a Sn doped system: Pb0.75Sn0.25Te.[2] It was also known back in 1980s that the ZT for highly disordered alloys of PbTe with a mean grain size of 1 µm could be ~10% higher than the equivalent single-crystal value. Recently significant enhancement of ZT (ZT > 2,) has been reported on the nanoscaled systems based on those commonly used bulk TE materials (e.g., Bi2Te3, PeTe/PbTeSe).[3,4] These were thin film superlattice and quantum dot materials and the results were theoretically interpreted in terms of the quantum confinement effects on the electrical properties and interface scattering effects (or Kapitza resistance) on the thermal conductivity. Considering the extremely
Data Loading...
