6 06 and 5 96 respectively all compositions appeared fully dense from microstructures phase content analysis using x ray diffraction revealed that all 3 mol yttria doped zirconia hsy 3 0 4 5 mol yttria doped zirconia hsy 4 5 and 8 mol yttria doped zirconia hsy 8 0 as sintered materials contained no monoclinic phase with the exception of 8 mol yttria doped samples all other samples contained both cubic and tetragonal phases the 8 mol yttria doped material contained only the cubic phase while 12 mol ceo 2 doped zirconia was fully tetragonal these results are consistent with the existing phase diagrams fig4 shows a scanning electron microscope sem micrograph of an as sintered 3 mol yttria doped zirconia sample sintered at 1450 u00b0 c the microstructure is seen to be duplex with relatively coarse grains 3 to 4 u03bcm in a fine grained lt 0 5 u03bcm matrix the larger grains were identified to be of the cubic phase while the smaller grains are of the tetragonal polymorph t phase the volume fraction of the coarse grains is about 15 it is also seen that in the 4 5 mol yttria doped samples the amount of the cubic phase is greater as expected that is the amount of the cubic phase increases with the yttria content samples with 8 mol yttria content are fully cubic with a grain size on the order of about 5 u03bcm after sintering at 1450 u00b0 c xrd traces of samples after 2000 u00b0 c heat treatment t u2032 phase revealed no monoclinic.