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particles still has diameters less than 100 nm.
The size distribution of these nanoparticles is shown in Figure(6), The distribution seems to be symmetric about 22 
nm, The particles of sizesis in the range of 5 - 45 nm in diameter for this specimen. 
 
Fig.6. the particle-size distribution of the nano-sized ZnO 
3.3. Electrical measurement
The Electrical characteristic (I-V)was measuredby using V-I source/ measuring unit(MEGOHMMETER-M1500P 
(1500 V,20 mA)),an Ampere meter and a Voltmeter. A summary of the electrical properties was listed in Table2. 
The breakdown voltage was measured at V(1mA) and the leakage current (I
L
) was measured at 0.75V(1mA). The 
non-linearity coefficient defined by empirical formula: 
I=KV
α
.................................................................(2) 
Where I is the current, V is the applied electric Voltage; α is the nonlinearity coefficient and K is constant. 
howeverNon-linearity coefficient determined by the formula: 
)
1
log
2
/(log
)
1
log
2
(log
V
V
I
I




..............(3) 
 
Khalaf AL ABDULLAH, Sahar AWDE/ Energy Procedia 00 (2017) 000–000 
5 
and it is identified in the range of 1.0 mA to 10 mA. Where V1 and V2 are the electric voltage at I1=1 mA and 
I2=10 mA, respectively. The voltage gradient E(1mA) is calculated by E(1mA)= V(1mA)/h, where h is the sample 
thickness. The breakdown voltage per grain boundary (Vgb), given by the equation (Anas et al. 2010): E = Vgb/d, 
where d is the average of grain size[14-16], and equal to 4um in this study after sintering. 
Table 2. Summary of the electrical properties of pure ZnO Varistor.
Nonlinearity
coefficient(α) 
Breakdown
Voltage
Voltage(V)
gradient(V/mm) 
Leakage current 
(I
L
) (uA) 
The breakdown voltage 
per grain boundary (Vgb) 
(V) 
30
450 
225 
100 
0.9 
Figure (7) shows the current as a function of the electric voltage for theSample. The curve can be divided into two 
regions: the first one (the ohmic region) is known as a high resistance region and the second one (the non-ohmic 
region) is known as a very low resistance region. The electrical properties (breakdown voltage, non-linear 
coefficient,etc) are typically related to grain size. A smaller grain size can effectively increase nonlinearity 
coefficient α and the breakdown voltage because the number of grain boundaries per unit thickness of varistor 
increases[16]. 
Fig.7.( I-V) characteristic of pureZnO Varistor prepared at 1050
o
C 
Fig.8. (I-V) Experimental characteristics of pure ZnO Varistor at various temperatures

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Khalaf AL ABDULLAH et al. / Energy Procedia 119 (2017) 565–570 
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4 
Khalaf AL ABDULLAH, Sahar AWDE/ Energy Procedia 00 (2017) 000–000 
Figure(5) shows the synthesized AFM image of ZnO nanoparticles in 2-dimension. Data are collectedover a selected 
area of the surface of the sample,Areas ranging from approximately (0-7) microns and (0-2) microns in width.Most 
of the particles appear spherical in shape, however some elongated particles and moderately agglomerated particles 
are also present as shown in the AFM images. see Fig(5.a) andFig(5.b). 
Fig.5.AFM images of the prepared ZnO nanoparticle in 2D, (a)7microns area ; (b)2 microns area 
Agglomeration is understood to increase linearly with annealing temperature and hence some degree of 
agglomeration at this temperature (500
o
C) appears unavoidable [7]. But as noticed, most of the agglomerated