Preparation by solar physical vapor deposition (SPVD) and nanostructural study of pure and Bi doped ZnO nanopowders

Pure and Bi doped ZnO nanopowders have been prepared by a physical vapor deposition process in a solar reactor (SPVD). From X-ray diffraction (XRD) spectra performed on initial targets and on the nanopowders obtained, the lattice parameters and the phase changes as well as the average grain sizes and the grain shape anisotropies have been determined. High Resolution Transmission Electron Microscopy (HRTEM) observations support the results. The pure ZnO nanopowders "grain size" and "grain shape anisotropy" (whiskers with an average diameter of 20-40 nm) is a function of the air pressure during the vaporisation-condensation process: the higher the pressure, the longer the whiskers. The bismuth doped ZnO nanopowders are polyphased but the ZnO based majority phases behave similarly to pure ZnO with a tendency to form whiskers but with a grain size and grain shape anisotropy decreasing when the Bi content increases. Preliminary electrical measurements at temperatures below 300 degrees C have shown that the ionic conductivity of the nanocomposites obtained starting from ZnO + 23 wt% Bi2O3 targets is high and promising for applications. (c) 2007 Elsevier Ltd. All rights reserved.