Abstract
The effects of La
2
O
3
on the behaviours of ZnO nanoparticle-Bi
2
O
3
-Mn
2
O
3
varistors were determined. The discs with various La
2
O
3
compositions (0.0-3.0 mol%) were prepared via traditional ceramic techniques and their characteristics were investigated. The results demonstrate that La
2
O
3
remarkably affects the varistor samples, in which the size of grain diminished from 29.3 to 8.5 µm according to increasing La
2
O
3
content from 0.0 to 3.0 mol%. The significant response within the varistor sample fabricated from ZnO nanoparticles through sintering process at 1200
o
C perhaps caused by the surface properties of the powdered ZnO nanoparticles. X-ray diffraction results show that the addition of La
2
O
3
to the varistor resulted in additional peaks, which can be attributed to the construction of La-based phases through the sintering process at high temperature. The spinal phases of the (Bi
48
ZnO
73
) and (Mn
3
O
4
) diminish with the 3.0 mol% content of La
2
O
3
. The varistor samples with 2.0 mol% La
2
O
3
show a superior spinal phase construction of (Bi
48
ZnO
73
) and (Mn
3
O
4
) and La-based phases, resulting in homogeneous grain size. La
2
O
3
doping substantially enhanced the electrical behaviours of the disc sample with a notable increase in breakdown voltage from 2614.8 to 5730.7 V/mm caused by the increase in La
2
O
3
doping concentration from 0.0% to 3.0 mol%. The improvement was associated with the potential lanthanide ion segregation caused by its greater ionic radius to the boundaries between ZnO grains, thus enhancing its electrical properties. Moderate La
2
O
3
doping concentration at 1.0 mol% improved the non-linear characteristics of the sample (α = 66) and 4400 V/mm breakdown voltage was introduced, while a significant amount of La
2
O
3
doping concentration (more than 1.0 mol%) caused its deterioration (α = 35). The increase in donor concentration N
d
to 2.1 × 10
20
cm
−3
for the varistor doped with 1.0 mol% La
2
O
3
is accompanied by a decrease of interfacial states density N
IS
to 2.2 × 10
12
cm
−2
eV
−1
, in addition to decrease in depletion layer ω to 3.9 nm. The leakage currents of the sample decreased from 0.473 to 0.310 mA/cm
2
with the increase of La
2
O
3
doping contents from 0.0% to 2.0 mol% and then increased to 0.596 mA/cm
2
at 3.0 mol% La
2
O
3
doping concentration. Therefore, La
2
O
3
may be added to dominate the microstructural characteristics and electrical behaviours of ZnO-Bi
2
O
3
-Mn
2
O
3
varistor manufactured using powdered ZnO nanoparticles.