Microstructure-electrical conductivity relationship in various amounts of Al203 doped 8 mol % ytria stabilized cubic zirconia

MICROSTRUCTURE-ELECTRICAL CONDUCTIVITY RELATIONSHIP INVARIOUS AMOUNTS OF Al2O3 DOPED 8 MOL % YTRIA STABILIZEDCUBIC ZIRCONIA(M.Sc. Thesis)Ahmet KAYIŞGAZ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYSeptember 2006ABSTRACTIn order to determine the influence of Al2O3 content on phase stability,microstructure and electrical conductivity of cubic zirconia, high puritycommercial powders of 8 mol% yttria-stabilized cubic zirconia (c-ZrO2)doped with up to 10 wt% Al2O3 were used. Colloidal processing wasused for the mixing of powders in order to achieve a uniformdistribution and homogeneous microstructure. X-ray diffraction resultsshowed that the average lattice parameter of c-ZrO2 linearly decreasedfrom 5.139 Å to 5.134 Å, as the Al2O3 content increased up to 0.3 wt%and the parameter did not vary with further increase in the Al2O3content. This linearity shows that solid solubility limit of Al2O3 in c-ZrO2is about 0.3 wt%. The lower values of the lattice parameter found forAl2O3-doped c-ZrO2 could be due to the dissolution in the cubic phaseof some Al2O3 which has a smaller ionic radius than Zr+4 and Y+3 andthus replacing the smaller Al+3 ions with Zr+4 and Y+3 in the cubiclattice. It was also seen that the grain growth in Al2O3 doped c-ZrO2occured slowly and more sluggish than that in undoped c-ZrO2 and thegrain growth decreased with increasing Al2O3 content.The electrical conductivity of the specimens was measured using afrequency response analyzer in the frequency range of 5 Hz-13 MHz inair and in the temperature range of 300-800 oC. The experimental resultsshowed that the conductivity increased with increasing temperature atconstant Al2O3 amount. This increase was mainly a result of theincreased grain size and the consequent reduction in the total grainboundary area. The bulk conductivity of Al2O3 doped c-ZrO2 increasedwith increasing Al2O3 content up to 1 wt% and and the parameterdecreased with further increase in the Al2O3 content. The grainboundary and total conductivity both decreased with increasing Al2O3content.Science Code : 703-710.1.092: Cubic Zirconia, Microstructure, Al2O3, grainKey Wordsgrowth, electrical conductivityPage Number : 108Advisers : Assoc. Prof. Dr. Osman GÜRDALProf. Dr. Süleyman TEKEL