Production of Lead-free Electroceramics: K0.5Na0.5NbO3 substituted with Li & Ta
K0:485Na0:485Li0:03Nb0:8Ta0:2O3 powder has been prepared by spray pyrolysis of
aqueous solutions of K/Na/Li nitrates mixed with water soluble Nb and Ta precursors.
The as-prepared ceramic powder was calcined at 600 °C to remove any organic residues
after the spray pyrolysis process. Different milling methods for the calcined powders
were attempted, revealing dry planetary milling to be the most suitable milling method.
The powders were characterised using scanning electron microscopy. A complete milling
process was developed based on sufficient destruction of the egg-shell like agglomerates from the spray pyrolysis process, avoidance of flake formation and reproducibility.
Sintering was attempted using three different sintering methods, all using the reverse crucible method to limit the amount of alkali evaporation. An optimal temperature range was found for each of the three, achieving densities in the range of 94-97%. The microstructure of the different samples was explored by polishing the samples and investigating the surfaces by scanning electron microscopy. It was found that the average grain sizes were in the range of a few microns, with large variations in the broadness of the grain size distribution when comparing different sintering methods. For two of the three sintering methods a standard deviation of less than 0.3 micron is reported. An EDS analysis was performed, and it was found that all the samples demonstrate
Dielectric testing was performed on the samples sintered using the three different
sintering methods. Polishing of the sample surfaces and storage in dessicators had to
be performed in order to avoid moisture influence and achieve reproducibility. The
piezo- and ferroelectric effect was observed for all the different sintering methods, along with coercive fields in the range of 669 - 889 V
mm and remnant polarizations in the range of 16 - 29 C/cm2 , depending on the sintering method used. A strictly monotonic relationship between average grain size and the coercive field was identified. The normalized strain d*33 was found to be in the range of 230 - 330 pm/V , after poling using an electric field of 4 kV
mm at 100 °C. It is argued that on the basis of the present results,
K0:485Na0:485Li0:03Nb0:8Ta0:2O3 has potential as a leading candidate for environmentally friendly ferroelectric materials, and spray pyrolysis seems an excellent choice of synthesis method.
Place, publisher, year, edition, pages
Institutt for materialteknologi , 2011. , 99 p.
ntnudaim:6449, MTNANO Nanoteknologi, Nanoteknologi for materialer, energi og miljø
IdentifiersURN: urn:nbn:no:ntnu:diva-16305Local ID: ntnudaim:6449OAI: oai:DiVA.org:ntnu-16305DiVA: diva2:517067
Wiik, Kjell, ProfessorGrande, TorEinarsrud, Mari-AnnHaugen, Astri