Title: Solution processing of conducting dense and porous films; doped ZnO and TiO₂, and perovskites

Authors: Gunnar Westin, Michael Leideborg, Koroush Lashgari, Victoria A. Coleman, Kjell Jansson, Annika Pohl

Addresses: Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden. ' Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden. ' Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden. ' Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden. ' Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden. ' Department of Materials Chemistry, Angstrom Laboratory, Uppsala University, 75121 Uppsala, Sweden

Abstract: Solution based processing of porous and dense films by all-alkoxide based precursor systems have been investigated and compared, with a focus on the connection between the precursors and heat-treatment, and the product oxide quality and structure. Three systems were investigated typically with TGA, DSC, XPS, IR spectroscopy, X-ray diffraction, TEM-EDS and SEM-EDS, but also with other advanced characterisation techniques: (i) manganate and cobaltate perovskites of the LCMO (La_0.67Ca_0.33MnO₃), LSMO (La_0.75Sr_0.25MnO₃), LNCMO (La_0.33Nd_0.33Ca_0.33MnO₃), LBSM (La_0.75Ba_0.125Sr_0.125MnO₃) and LSCO (La_0.50Sr_0.50CoO₃) compositions were investigated. Highly epitaxial films of LCMO and LSCO were prepared, and the CMR properties of the LCMO were comparable to those of PVD derived films. Polycrystalline films were prepared for all perovskites. (ii) Three routes to ZnO : Co/Al were investigated and compared; an acetate based route and two alkoxide based routes with different heat-treatments. With the acetate based and the alkoxide based route using hydrolysis in air, a maximum Co doping of 6% was obtained, while in absence of CO₂ and O₂, the doping range could be extended to 20%Co. Both dense films and porous nano-structured films were prepared. The magnetic properties of the Co-doped films did not show any room-temperature ferro-magnetism. (iii) ZrO₂ and NbO_2.5 doped anatase TiO₂ were prepared by heat-treatment or hydrothermal routes. Alio-valent doping of up to more than 35% of NbO_2.5 could be achieved in the anatase. It is believed that the pentavalent metal doping is compensated by metal vacancies, and as expected from this assumption, the materials have a low density. ZrO₂ doping in titania led to an increase in the dye-sensitised solar cell efficiency and highly active and stable photo-catalysts.

Keywords: perovskites; titania; doped ZnO; sol-gel; thin films; nanoparticles; alkoxide; zinc oxide; tin oxide; porous films; porous films; heat treatment; nanotechnology; solar cells.

DOI: 10.1504/IJNT.2009.026743

International Journal of Nanotechnology, 2009 Vol.6 No.9, pp.828 - 849

Published online: 24 Jun 2009 *

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