Fig. 1 shows the SEM micrographs of the samples for
different amount of Y2O3. On the whole, the grains of the
samples were uniformly distributed and one of the features of
surface morphology is some little porosity. It was obvious that
the porosity decreased with an increase in the amount of Y2O3.
All the samples revealed the presence of Pr-rich (Pr6O11 and
Pr2O3) and Y-rich intergranular layer (whitish bulk) as minor
secondary phases, in addition to major phase of ZnO (blackish)
by the XRD patterns as indicated in Fig. 2, whereas no La-rich
phase was detected within detection limit of XRD. As a result,
this system shows simple microstructure consisted of only
major phase and intergranular layer [4,6–8], unlike multiphases in ZnO–Bi2O3-based varistor ceramics. As the amount
of Y2O3 increased, the densities (ρ) sintered pellets noticeably
increased from 4.97, 5.18, and 5.20 g/cm3 (5.78 g/cm3 in pure
ZnO), unlike Y2O3-doped 5-component-based ceramics, in
which the ρ decreased with an increase in the amount of Y2O3.
It is assumed that this is attributed to the effect of La2O3 in this
composition. The average grain size (d) decreased from 4.1,
3.9, and 3.7 μm with an increase in the amount of Y2O3
Fig. 1 shows the SEM micrographs of the samples fordifferent amount of Y2O3. On the whole, the grains of thesamples were uniformly distributed and one of the features ofsurface morphology is some little porosity. It was obvious thatthe porosity decreased with an increase in the amount of Y2O3.All the samples revealed the presence of Pr-rich (Pr6O11 andPr2O3) and Y-rich intergranular layer (whitish bulk) as minorsecondary phases, in addition to major phase of ZnO (blackish)by the XRD patterns as indicated in Fig. 2, whereas no La-richphase was detected within detection limit of XRD. As a result,this system shows simple microstructure consisted of onlymajor phase and intergranular layer [4,6–8], unlike multiphases in ZnO–Bi2O3-based varistor ceramics. As the amountof Y2O3 increased, the densities (ρ) sintered pellets noticeablyincreased from 4.97, 5.18, and 5.20 g/cm3 (5.78 g/cm3 in pureZnO), unlike Y2O3-doped 5-component-based ceramics, inwhich the ρ decreased with an increase in the amount of Y2O3.It is assumed that this is attributed to the effect of La2O3 in thiscomposition. The average grain size (d) decreased from 4.1,3.9, and 3.7 μm with an increase in the amount of Y2O3
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