THE ELECTRICAL CHARACTERIZATION OF GRAIN-BOUNDARIES IN ULTRA-FINE GRAINED Y-TZP

Starting from a sinter reactive powder prepared by a gel precipitation technique, dense, ultra-fine grained (100-200 nm) yttria stabilized t etragonal zirconia ceramics were obtained by sinter forging at a tempe rature of 1100-degrees-C or by pressureless sintering at 1150-degrees- C. The pressureless sintered compacts were subjected to further heat t reatments at temperatures of 1250-1450-degrees-C or compressive deform ation at 1250-degrees-C under uniaxial stresses of 20-100 MPa. The obt ained samples were characterized mainly by impedance spectroscopy. Aft er compressive deformation a decrease in grain boundary resistivity wa s found which increased with applied stress. This can be interpreted i n terms of a decrease in impurity segregation and a partial removal by compressive deformation of a poorly conducting amorphous film around the grains. It was also found that the grain boundary resistivity of s amples sintered at 1150-degrees-C could be considerably reduced by fur ther pressureless heat treatments at temperatures above 1250-degrees-C . This effect is probably owing to dewetting of the grain boundary and dissolution of grain boundary impurities into the bulk of the grains.