The influence of boron doping on the structural and mechanical characterization of ZnO

Article abstract of DOI:10.1016/j.jallcom.2019.05.140

In this study, we have reported the structural and mechanical properties of B-doped ZnO (Zn_1-xB_xO, x = 0.00, 0.05, 0.07, 0.09, 0.11)by using XRD, SEM, EDS and static Vickers micro-hardness measurements. All nanopowder samples were prepared by hydrothermal method. From the XRD measurements, we have found that all the samples crystalize in hexagonal wurtzite structure and crystallite sizes were found to be 61.50, 36.97, 36.65, 36.59 and 34.85 nm for x = 0.00, 0.05, 0.07, 0.09, 0.11 samples, respectively. From the SEM measurements, the irregular appearance and size distribution of the particles were observed for all samples. The chemical composition of Zn_1-xB_xO nanopowders were investigated by EDX spectroscopy. Zn,O and B peaks are clearly seen and the content of Zn, O and B are consistent with preparation of samples. From the load dependent indentation diagonal length measurements, load dependent (apparent)hardness, elastic modulus, yield strength, and fracture toughness values of the samples were computed. The hardness values increase with increasing the boron content and the applied load. In addition, the apparent hardness values were analyzed by using the various theoretical models to evaluate the load independent (true)hardness values. The IIC model was found to be sufficient for our investigations. The possible reasons for the observed changes in mechanical, structural properties due to B-doping in ZnO were discussed.

Full text of DOI:10.1016/j.jallcom.2019.05.140

Journal of Alloys and Compounds 797 (2019) 717e726
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
The influence of boron doping on the structural and mechanical
characterization of ZnO
,
Sevim Demirozu Senol a *, Rıfkı Terzioglu b, Ozgur Ozturk c
a Department of Chemistry, Bolu Abant Izzet Baysal University, 14280 Bolu, Turkey
b Department of Electrical and Electronics Engineering, Bolu Abant Izzet Baysal University, 14280 Bolu, Turkey
c Department of Electrical and Electronics Engineering, Kastamonu University, 37100 Kastamonu, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, we have reported the structural and mechanical properties of B-doped ZnO (Zn1-xBxO,
x ¼ 0.00, 0.05, 0.07, 0.09, 0.11) by using XRD, SEM, EDS and static Vickers micro-hardness measurements.
All nanopowder samples were prepared by hydrothermal method. From the XRD measurements, we
have found that all the samples crystalize in hexagonal wurtzite structure and crystallite sizes were
found to be 61.50, 36.97, 36.65, 36.59 and 34.85 nm for x ¼ 0.00, 0.05, 0.07, 0.09, 0.11 samples, respec-
tively. From the SEM measurements, the irregular appearance and size distribution of the particles were
observed for all samples. The chemical composition of Zn1-xBxO nanopowders were investigated by EDX
spectroscopy. Zn,O and B peaks are clearly seen and the content of Zn, O and B are consistent with
preparation of samples. From the load dependent indentation diagonal length measurements, load
dependent (apparent) hardness, elastic modulus, yield strength, and fracture toughness values of the
samples were computed. The hardness values increase with increasing the boron content and the applied
load. In addition, the apparent hardness values were analyzed by using the various theoretical models to
evaluate the load independent (true) hardness values. The IIC model was found to be sufficient for our
investigations. The possible reasons for the observed changes in mechanical, structural properties due to
B-doping in ZnO were discussed.
Received 27 February 2019
Received in revised form
7 May 2019
Accepted 13 May 2019
Available online 16 May 2019
Keywords:
B-doped ZnO
Hydrothermal method
Vickers microhardness
HK approach
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
Therefore, one of the procedure used in the literature to increase
the mechanical properties of ZnO-based semiconductor materials is
ZnO is an important technological material because of its
considerable performance in electronics, optics and photonics [1,2].
Since ZnO has strong piezoelectric and pyroelectric properties
arising from the absence in its wurtzite structure with a hexagonal
lattice, wide band gap (3.37eV) and large electrochemical coupling,
it is widely used in piezoelectric sensors, mechanical actuators
[3,4]. In addition, it has an extensive application in the photo-
electrical devices, photovoltaic applications and solar cell hetero-
junction [5e8].
Morever, the mechanical properties of ZnO-based semi-
conductors such as hardness, elastic modulus, fracture toughness,
brittleness and yield strength play an important role in production
of optoelectronic devices. The variations in mechanical properties is
directly related to interatomic bounding force of the materials.
to add different types of atoms into the ZnO structure [9e12].
It has been suggested that B doped ZnO might enhance its
mechanical properties; for example, hardness of the undoped ZnO
films is much lower than that of B-doped ZnO sample [13].
Although the study on properties of electrical, magnetic and optical
of B-ZnO is intensively studied, the mechanical properties is rarely
studied in the literature.
One of the most common used methods to determine the me-
chanical properties of materials is the Vickers hardness test. The
method was developed as an alternative to the Brinell method in
1921 by British researchers Vickers, Smith and Sandland [14]. The
system is based on the optical measurement of the 136ꢀ diamond
pyramid tip, with specific loads selected depending on the material
type and thickness. In addition, Vickers hardness is similar to the
Brinell method because it is an optical hardness measurement
method. Vickers hardness test can be performed for all specimens
due to having the largest scales among the hardness
measurements.
* Corresponding author.
E-mail address: demirozu_s@ibu.edu.tr (S.D. Senol).
https://doi.org/10.1016/j.jallcom.2019.05.140
0925-8388/© 2019 Elsevier B.V. All rights reserved.

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S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
It is well known that the microhardness of the solids is load
3. Results and discussion
dependent. The microhardness decreases with increasing the
applied test-load which is called the Indentation Size Effect (ISE)
while it increases with the increase in the applied load which is
named Reverse Indentation Size Effect (RISE) behavior [15]. The
determination of these behaviors of materials is very important in
terms of usage in technological applications.
The main objective of this study is to investigate the effect of
boron concentration on the structural and mechanical properties of
Zn1ꢁxBxO (x ¼ 0, 0.05, 0.07, 0.09, 0.11) samples prepared by using
the hydrothermal method. In this study, the mechanical properties
of the samples were evaluated and the load dependent Vickers
micro-hardness data were analyzed by using the most widely used
methods in the literature such as Meyer's Law, the Proportional
Sample Resistance, Elastic/Plastic Deformation, Indentation-
Induced Cracking (IIC) and Hays-Kendall (HK) models. To the best
of our knowledge, no detailed study on the effects of B addition on
the structural and mechanical properties of ZnO has been published
in the literature.
3.1. XRD, SEM and EDS analyses
Fig. 1 shows the XRD patterns of the Zn1-xBxO nanoparticles
with x ¼ 0.00, 0.05, 0.07, 0.09, 0.11 boron content. Some of the
Miller indices are indicated in Fig. 1. The XRD patterns of all the
samples are analyzed with the standard card for bulk ZnO with a
hexagonal wurtzite structure (ICDD Card no.36-1451) and all
samples crystallize in hexagonal wurtzite structure. It was found
that there is no characteristic peaks related to B and impurity
phases, that is, the B atom entered into the ZnO crystal structure.
Fig. 2 shows the superposition of the experimental and the calcu-
lated pattern for each samples. The bottom curve shows the dif-
ference between the observed and calculated profiles. The quality
factors (Rp, Rwp) and the goodness of fit (GOF) values are obtained
from the Rietveld analysis [16] of the X-rays data and are listed in
Table 1. All characteristic peaks of the ZnO are covered by the
calculated curve. The fitting results show that the cell parameters
are very close to those reported by many groups for the ZnO sam-
ples [4,18e20]. It was observed from the XRD results that crystal
structure unchanged but intensity of (100) and (200) changed with
the B content. One can see from the figure that the main peaks (100)
and (200) intensity of the Z5 sample decreased in comparison with
the Z0 sample. The decrease in the peak intensities may point out
the decrease in grain growth and orientation in the presence of the
B content, leading to the decrease of the microhardness value
which is in good agreement with our microhardness measure-
ments. Then, the intensity of the peaks increased with increasing
the B concentration, leading to the increase in microhardness
values. The decrease of intensity and the increase of full width at
half maximum (FWHM) for Z5 sample indicate that crystallite size
became smaller when compared with undoped sample Z0.
2. Experimental
Zn1ꢁxBxO were prepared as polycrystalline nanopowders with
various compositions (x ¼ 0, 0.05, 0.07,0.09,0.11) using hydrother-
mal method. In synthesis process, Zinc acetatedihydrate,
(Zn(CH3COO)22H2O) (Merck), hexamethylenetetramine, (HMT)
(Merck), were mixed thoroughly in an appropriate proportion and
dissolved in deionized (DI) water to obtain equimolar aqueous
solution. Then, boric acid, (H3BO3) Merck, was added with different
concentrations (x ¼ 0.0, 0.05, 0.07, 0.09, 0.11) and was stirred using
the magnetic stirrer at room temperature for 2 h until a transparent
solution was obtained. After this step, 80 mL of prepared solution
transferred to 100 mL autoclaves. The fraction was conducted in an
electric oven at 100 ꢀC for 12 h. The vessel was cooled to RT and the
precipitate was collected by centrifugation and washed with DI
water and dried air. The five different powder materials obtained
are Z0, Z5, Z7, Z9, Z11 as the names mentioned in Table 2. Finally,
these samples were pressed under 4 tons for 5 min into disk shaped
compacts with a thickness of 2 mm and a diameter of 5 mm. Finally,
the pressed samples were annealed at 750 ꢀC for 2 h in air.
The average crytallite sizes were evaluated for the main peaks of
(101), (002) and (100), and are embedded in Table 1. It was obtained
from the table that the crystallite size values decrease with the
increase in B amount. This result is consistent with microhardness
measurements in the present study.
To investigate the surface morphologies of the samples SEM
micrographs are taken and depicted in Fig. 3. The irregular
appearance and the size distribution of the particles are observed
for all samples. From the SEM images, uniform granularity was
In this work, the samples are used for investigation of XRD, SEM
and Vickers hardness measurements. Zn1ꢁxBxO (x ¼ 0.00, 0.05,
0.07, 0.09, 0.11) pellet samples were identified by means of X-ray
diffraction (XRD) using Rigaku Multiflex at room temperature with
CuK
a
(
l
q
¼ 1.5418 Å). The XRD data were collected over the range
20ꢀ < 2
< 80ꢀ in a scan speed of 3ꢀ/min and a step increment of
0.02ꢀ. The refinement of cell parameters was performed by use of
Jana 2006 software [16]. The average crystallite size is estimated
from XRD data using Debye-Scherer's formula, 〈D〉 ¼ kl
where 〈D〉 is average crystallite size in Å, is the shape factor,
the wavelength of the X-ray (lCu-K ¼ 1.5418 Å) and
/
b
cos
q
k
l
is
b
is the cor-
q is the Bragg angle
a
rected full width at half maximum (FWHM) and
of diffraction [17]. The surface morphologies of the samples were
performed by scanning electron microscopy (SEM) (FEI Quanta Feg
250).
Vickers microhardness measurements of the samples were
performed with Vickers microhardness meter (SHIMADZU) at room
temperature to study the effect of the additives on the mechanical
properties of the samples. The load was applied for 10 s and varied
in the range of 0.245e2.940 N. All measurements were averaged by
pressing the notch on five different surfaces of the sample so that
the marks were not overlapped.
Fig. 1. XRD patterns for undoped and Zn1ꢁxBxO (x ¼ 0, 0.05, 0.07, 0.09, 0.11)
nanopowders.

S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
719
Fig. 2. Jana2006 refinement patterns for undoped ZnO, Zn0.95B0.05O, Zn0.93B0.07O, Zn0.91B0.09O and Zn0.89B0.11O samples.
Table 1
Details of Jana2006 refinement of undoped ZnO, Zn0.95B0.05O, Zn0.93B0.07O, Zn0.91B0.09O and Zn0.89B0.11O samples (GOF, RP, RWP, agreement factors).
Samples
Undoped ZnO
Zn0.95B0.05
O
Zn0.93B0.07
O
Zn0.91B0.09
O
Zn0.89B0.11O
Symmetry
Space Group
a(Å)
Hexagonal
P63/mmc
3.2483
5.2043
90.000
90.000
120.000
Rigaku
CuKa
Hexagonal
P63/mmc
3.2483
5.2029
90.000
90.000
120.000
Rigaku
CuKa
Hexagonal
P63/mmc
3.2460
5.1995
90.000
90.000
120.000
Rigaku
CuKa
Hexagonal
P63/mmc
3.2478
5.2019
90.000
90.000
120.000
Rigaku
CuKa
Hexagonal
P63/mmc
3.2463
5.1990
90.000
90.000
120.000
Rigaku
CuKa
c(Å)
o
a
b
d
(
(
(
degree)
o degree)
o degree)
Diffractometer
Radiation type
Monochromator
Wavelength (Å)
Graphite
1.5406
20.00e80.00ꢀ
0.02
Graphite
1.5406
20.00e80.00ꢀ
0.02
Graphite
1.5406
20.00e80.00ꢀ
0.02
Graphite
1.5406
20.00e80.00ꢀ
0.02
Graphite
1.5406
20.00e80.00ꢀ
0.02
Refined profile range (2Qo
)
Step size (2Qo
)
GOF
RP
3.66
12.77
2.78
10.17
3.65
11.14
2.59
13.16
3.26
10.31
RWP
V
20.73
47.6
17.80
47.5
21.95
47.5
18.31
47.5
19.06
47.4
observed, grains were brightly visible and the particle boundaries
are irregular but almost clear for all the samples. As can be clearly
seen from the micrographs, its distribution in the ZnO
microstructure becomes denser and more compact as the B con-
centration increases. This may be related to the reduction in grain
size, which was confirmed by the XRD results. Porosity and

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S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
Table 2
microstructure. The SEM images reveals that the average grain size
significantly depends on the B concentration. The boron atoms act
as nucleation centers in the vacancy sites of ZnO. So, B atoms might
result in a decrease of the average grain size. Based on the XRD and
SEM results, it is expected that the smaller grain size, less number
and size of voids, better grain connectivity and denser surface with
increasing the B addition would make the hardness value higher
which is what we observe and discuss below in Section 3.2. The
morphology of ZnO samples enhanced by boron concentration and
this enhancement makes the microhardness value increase.
EDS spectra of Zn1-xBxO nanoparticles are shown in Fig. 4. The
EDS experimental results indicate that the B concentration level
tends to increase systematically with the increase of dopant level,
verifying the introduction of B impurities into the bulk ZnO crystal
structures.
The average crytallite sizes of the Zn1-xBxO nanoparticle at different boron
concentrations.
Samples
Called as
D (nm)
ZnO
Z0
Z5
Z7
Z9
61.50
36.97
36.65
36.59
34.85
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
Z11
intergranular voids are observed to be more frequent in the Z5
sample, as shown in Fig. 3b. It is concluded that stronger grain
connectivity could be obtained with increasing B concentration
owing to a reduction in intergranular voids [21]. The denser and
more compact structure could be attributed to
a harder
Fig. 3. SEM images of the Zn1-xBxO powders prepared at different B concentrations (a) undoped (b) 5%, (c) 7%, (d) 9% and (e) 11%.

S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
721
3.2. Vickers microhardness measurements
and d is the indentation size in
mm. In order to evaluate the Vickers
microhardness values of the materials various loads in the range of
0.245, 0.480, 0.980, 1.960 and 2.940 N are applied to each samples.
Average value of indentation diagonal lengths are determined by
taking five different locations on each specimen the surface. The
values of the load-dependent elastic modulus, (E), and yield
strength (Y), were calculated for all samples using the following
The Vickers hardness of the materials can be calculated as
ꢀ .
ꢁ
Hv ¼ 1854:4 P d2
ðGPaÞ
(1)
where Hv is the Vickers hardness in GPa, P is the applied load in N
Fig. 4. SEM attached EDS spectra of undoped ZnO, Zn0.95B0.05O, Zn0.93B0.07O, Zn0.91B0.09O and Zn0.89B0.11O.

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S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
formulas, respectively;
E ¼ 81:9635Hv
(2)
(3)
YzHv=3
Fracture toughness can be determined from.
pffiffiffiffiffiffiffiffiffiffiffi
KIC ¼ c 2Ej
a
j
(4)
where
a
is the surface energy, c can be positive or negative value
depending on ISE or RISE behavior, respectively. Brittleness (Bi) and
ductility (D) parameters for each sample were calculated from the
following equations:
Bi ¼ Hv=KIC and D ¼ 1=Bi
(5)
The load-dependent Hv, E, Y, KIC, Bi and D values for all the
samples are displayed in Table 3. Fig. 5 depictes the applied load
dependence of hardness for all the samples. As seen from Fig. 5, the
microhardness of the samples decreases with both decreasing the
boron amount and applied load and reaches a saturated region at
about 1.96 N which indicates that all the samples show RISE
behavior. Among the samples, the Z0 sample has the greatest
hardness value. Among the B-doped samples, the Z5 sample has the
smallest hardness value. The Z5 sample has the larger grain, crys-
tallite sizes and the worser grain connectivity which is in good
agreement with the XRD and SEM analyses. One can see from the
figure that the microhardness value of the Z5 sample decreased in
comparison with the Z0 sample. B addition is found to degrade the
hardness of the samples which might be result of either phase
segregation due to impurities and/or an increase in voids because of
boron incorporation or as it is also observed a changes in the grain
boundaries from SEM and XRD data. Then, the value of micro-
hardness increases with the increase in boron content. We have
also observed from the XRD and SEM results that the smaller grain
size, less number and size of voids, better grain connectivity and
denser surface with increasing the B content make the hardness
value higher. The morphology of ZnO samples enhanced by boron
Fig. 5. Variations of microhardness with load for the samples.
concentration and this enhancement makes the microhardness
value increase.
In recently, mechanical properties of Al, Mg,Y doped ZnO were
investigated [21e24]. It was found that both Al and Mg concen-
trations decreased the microhardness value in comparision with
ZnO [22e24]. In the present study, the value of microhardness of Z5
sample is 0.535 GPa while the value of Al doped ZnO sample is
0.580 GPa at 0.245 N. Kaya et al. found that the microhardness value
increased with increasing Yttrium content in ZnO. The value of ZnO
was found ton be 0.0253 GPa and the present study value is
1.490 GPa at 2.0 N. This difference can be related to the sample
preparation route. The present study sample preparation is hy-
drothermal method and that of previous study is sol-gel.
Moreover, The E, Y, KIC, Bi and D values depend on both load and
boron content. The behavior of these values has the same as
hardness value, that is, these values increased when the applied
load and B concentration increased.
Table 3
Hv, E, Y and KIC load-dependent values of the samples.
ꢁ1/2
Samples
F (N)
Hv (GPa)
E (GPa)
Y (GPa)
KIC(MPa/m1/2
)
Bi(m
)
D(m 1/2
)
Undoped ZnO
0.245
0.490
0.980
1.960
2.940
0.245
0.490
0.980
1.960
2.940
0.245
0.490
0.980
1.960
2.940
0.245
0.490
0.980
1.960
2.940
0.245
0.490
0.980
1.960
2.940
0.820
1.172
1.270
1.490
1.497
0.535
0.652
0.956
1.065
1.100
0.566
0.807
1.144
1.157
1.185
0.761
1.042
1.214
1.406
1.460
0.770
1.122
1.239
1.435
1.440
67.210
96.060
104.090
122.120
122.690
43.850
53.440
78.350
87.290
90.16
46.390
66.220
93.760
94.830
97.120
62.370
85.400
99.500
115.150
119.66
63.11
0.273
0.390
0.423
0.496
0.499
0.178
0.217
0.318
0.355
0.366
0.188
0.269
0.381
0.385
0.395
0.253
0.347
0.404
0.468
0.486
0.256
0.374
0.413
0.478
0.480
40.925
48.926
50.930
55.165
55.294
37.306
41.184
49.868
52.636
53.494
35.193
42.048
50.033
50.318
50.922
42.558
49.799
53.753
57.826
58.948
34.900
42.128
44.342
47.643
47.726
20.036
23.954
24.936
27.009
27.073
14.340
15.831
19.170
20.233
20.563
16.082
19.192
22.864
22.993
23.270
17.881
20.924
22.584
24.314
24.767
22.063
26.633
27.941
30.119
30.172
0.049
0.041
0.040
0.037
0.036
0.069
0.063
0.052
0.049
0.048
0.062
0.052
0.044
0.043
0.042
0.055
0.047
0.044
0.041
0.040
0.045
0.037
0.035
0.033
0.033
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
91.96
101.55
117.61
118.02

S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
723
3.3. Analyses and modeling
in Fig. 7. Increasing the range of loads was found to a nonlinear
relation between F/d versus d data. The true hardness values are
evaluated according to the PSR model as;
In this section, the load dependent microhardness values of the
nanopowder samples were analyzed by using Meyer's law, the
proportional sample resistance (PSR), elastic/plastic deformation
(EPD), indentation-induced cracking (IIC), and the HayseKendall
(HK) models [25e27].
HPSR ¼ 1854:4
b
(9)
The obtained
a,
b
and HPSR values are given in Table 5. It was
observed from the table that
confirming that all materials show plastic deformation and the RISE
behavior. The constant decreases with the increasing of boron
concentration while the value is not monotonus for all the sam-
a values for all samples were negative,
3.3.1. Meyer's law
One of the simple methods of defining ISE behavior is the
Meyer's Law, which is defined by the following formula.
b
a
ples. These obtained values show that the surface of the material
after the identer has been dipped and removed has not been
relaxed.
F ¼ Adn
(6)
It was observed from the table that the true hardness value
increases with increasing the applied load and the B fraction which
is consistent with the apparent hardness value for each sample.
However, the true hardness according to the PSR model is higher
than the saturation value in the plateau region. For the Z0 sample,
true hardness according to the PSR model is 1.910 GPa which is
higher than the saturation value (Hv ¼ 1.490e1.497 GPa) in the
plateau region. All the other samples, also, display the same trend
which shows that the hardness values deduced from the PSR model
are all greater than the saturation value.
where n is the Meyer number while A is the hardness constant. If n
< 2 (n > 2), material shows the ISE (the RISE) behavior. When n ¼ 2
the hardness is the load independent and gives Kick's Law as follow.
F ¼ AIK d2
(7)
The ln d dependence of ln F graphs of the samples are plotted in
Fig. 6. Slope of this figure is related to n and the vertical intercept is
related to AIK. The obtained n and AIK values are given in Table 4.
Meyer's number of all samples are greater than 2 which confirms
the RISE behavior.
3.3.2. PSR model
3.3.3. EPD model
In Refs. [29,30], the applied load dependent indentation size for
the elastic or plastic deformation model is given by
Li and Bradt developed a model which is called PSR to evaluate
the true hardness value of materials having ISE behavior [28]. This
model is formulated as:
À
Á
2
F ¼ A2 dp þ de
(10)
F
d
¼
a
þ
b
d
(8)
where A2 is a constant and dp is related to plastic deformation. A2
and de values can be obtained from F1/2 versus of dp graph as dis-
played in Fig. 8. The true hardness value can be evaluated as;
where
tively.
a
a
and
and
b
are apparent and true hardness constants, respec-
b are extracted from d dependent F/d graph as shown
Fig. 6. Variation of applied load ln F with diagonal ln d for the samples.
Fig. 7. Plots of F/d versus d for the samples.
Table 4
The extracted and calculated data according to Meyer's Law.
Table 5
The extracted and calculated data according to PSR model.
Samples
lnAIK (N/
m
m2)
Meyer member (n)
Samples
a
(N/
m
m)
b
(N/
m
m2)
HPSR(GPa) Hv(GPa)in plateu region
Undoped ZnO
ꢁ9.407
ꢁ10.989
ꢁ10.447
ꢁ9.831
ꢁ9.309
2.574
2.858
2.760
2.668
2.548
Undoped ZnO ꢁ0.01246 0.00103
1.9100
1.490e1.497
0.956e1.100
1.144e1.185
1.214e1.460
1.239e1.440
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
ꢁ0.01587 8.316 ꢂ 10ꢁ4 1.5421
ꢁ0.01335 8.551 ꢂ 10ꢁ4 1.5856
ꢁ0.01452 8.987 ꢂ 10ꢁ4 1.6665
ꢁ0.00965 9.592 ꢂ 10ꢁ4 1.7787

724
S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
Fig. 9. Graph of the applied load against the square of the diagonal length for the
samples.
Fig. 8. Plots of diagonal lengths versus the square root of the applied loads for the
samples.
Table 7
The extracted and calculated data according to HK model.
HEPD ¼ 1854:4A2
(11)
Samples
AHK (N/(m
m)2) WHK(N) HHK (GPa) Hv(GPa)in plateu region
From Fig. 8, the A12/2, de and HEPD values are extracted and
tabulated in Table 6. As can be seen from Table 6, the de values of all
the samples are negative which indicates that plastic deformation
is observed for all the samples. It was obtained that the extracted
true hardness values according to this model are greater than that
for apparent hardness and are greater than that of the PSR model.
Undoped ZnO 8.74 ꢂ 10ꢁ4
ꢁ0.22
ꢁ0.35
ꢁ0.26
ꢁ0.27
ꢁ0.14
1.620
1.238
1.299
1.596
1.526
1.490e1.497
0.956e1.100
1.144e1.185
1.214e1.460
1.239e1.440
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
6.68 ꢂ 10ꢁ4
7.01 ꢂ 10ꢁ4
8.61 ꢂ 10ꢁ4
8.23 ꢂ 10ꢁ4
based on the following explanations; the applied indentation test
load at the point of maximum penetration during the loading half-
cycle will be balanced by the total specimen resistance. Therefore,
3.3.4. HK model
Hays and Kendall [31] modified the Kick's law [32] as follows
WHK ꢁ F ¼ AHKd2
(12)
where AHK is a load-independent constant and WHK is the mini-
mum load to initiate plastic deformation. Fig. 9 exhibits F(N) versus
d2 (
mm) graphs for all the samples. The values of AHK and WHK were
extracted by fitting our data with this model and tabulated in
Table 7. According to this model, the true hardness values are
calculated from following relation
HHK ¼ 1854:4AHK
(13)
The calculated hardness HHK (GPa) values are summarized in
Table 7. Since the WHK values are negative, it can be said that all the
samples show RISE behavior. Again, it was found that the extracted
true hardness values according to this model are greater than that
for apparent hardness and are lower than that of the PSR and EPD
model.
3.3.5. IIC model
Indentation-Induced Cracking (IIC) model is advanced to explain
the RISE behavior by proposed Li and Bradt [28]. RISE behavior is
Fig. 10. Variation of lnHv versus ln (F5/3/d3), according to the IIC model.
Table 6
The extracted and calculated data according to EPD model.
Samples
A12/2(N1/2
/m
m)
de
(
m
m)
HEPD (GPa)
Hv (GPa) in plateu region
Undoped ZnO
0.0328
0.0300
0.0302
0.0330
0.0316
ꢁ0.244
ꢁ0.375
ꢁ0.304
ꢁ0.292
ꢁ0.197
1.995
1.668
1.691
2.019
1.851
1.490e1.497
0.956e1.100
1.144e1.185
1.214e1.460
1.239e1.440
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O

S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
725
Table 8
The extracted and calculated data according to IIC model.
Samples
m
lnK (N(3e5m)/3
/m
m(2e3m)
HIIC (GPa)
Hv(GPa)in plateu region
Undoped ZnO
0.46137
0.49593
0.49924
0.47015
0.43914
5.2753
5.5562
5.6252
5.3527
4.9937
1.249
0.861
0.972
1.176
1.208
1.490e1.497
0.956e1.100
1.144e1.185
1.214e1.460
1.239e1.440
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
Table 9
The results of apparent microhardness at the plateau region and true hardness values extracted by using IIC, HK, EPD and PSR models.
Samples
HIIC (GPa)
HHK (GPa)
HEPD (GPa)
HPSR(GPa)
Hv (GPa) in plateu region
Undoped ZnO
1.249
0.861
0.972
1.176
1.208
1.620
1.238
1.299
1.596
1.526
1.995
1.668
1.691
2.019
1.851
1.910
1.542
1.585
1.666
1.778
1.490e1.497
0.956e1.100
1.144e1.185
1.214e1.460
1.239e1.440
Zn0.95B0.05
Zn0.93B0.07
Zn0.91B0.09
Zn0.89B0.11
O
O
O
O
the applied load of the indentation can be expressed by four indi-
vidual space resistances, i.e., the plastic deformation, the elastic
deformation, the friction at the indentor/specimen face interface
and the specimen cracking resistance. In addition, while cracking is
defined as RISE behavior, friction and elastic deformation lead to
normal ISE. In this model, Vickers microhardness values were
calculated by the diamond indenter as given in Ref. [31].
also resulting from the relative predominance of the activity of
either two sets of slip planes of a particular slip system or two slip
systems below and above a particular load [25].
4. Conclusions
!
ꢂ
ꢃ
F5=3
d3
In this study, Zn1-xBx O, (x ¼ 0.00, 0.05, 0.07, 0.09,0.11) nano-
powders were prepared by the hydrothermal method. The in-
vestigations consist of XRD, SEM and static Vickers hardness
measurements. The main findings of the study can be summarized
as follows:
F
Happ
¼
l1K1
þ K2
(14)
d2
where d is the trace's diameter and l1, K1 and K2 are constants. The
K1 is the geometrical conversion factor whose value depends on the
identer while the K2 is load dependent. l1 ¼1 and K2 (F5/3/d3) ¼ 0
for an ideal plastic materials while l1 ¼0 for ideal brittle solids. If
the angle of 148ꢀ between the opposite edges of the Vickers dia-
mond indenter the indentation diagonal (d) should be equal 7 times
indentation depth (h). This relation is well compatible for hardness
data on semiconductors [15,33e36]. In the case of a perfect brittle
material, true hardness can be given by
1) The XRD results proved that Zn1-xBxO crystallize in hexagonal
wurtzite structure without any impurities and additional pha-
ses. In addition, the crystallite size decreases with increasing the
B concentration which is consistent with the micro-hardness
measurements.
2) From the SEM analysis, we have found that the Z5 sample has
smaller grain size, denser surface, better grain connectivity and
low void density compared to the Z7, Z9 and Z11 samples. These
findings are in agreement with the apparent and true hardness
values.
!
m
P5=3
d3
Happ ¼ K
(15)
3) B addition is found to degrade the hardness of the samples
which might be result of either phase segregation due to an
increase in voids because of boron incorporation or as it is, also
observed from SEM and XRD data, a changes in the grain
boundaries.
4) The micro-hardness values increased with increasing both the
applied load and the B content. In our micro-hardness mea-
surements, in contrast to the ISE, a RISE behavior is observed.
5) We have found that the IIC is the most successful model to
explain the load versus indentation data of our samples among
the five models we have used in the fitting.
where m and K are load independent constants. The ln (Hv) versus
ln (F5/3/d3) graphs of all the samples are plotted in Fig. 10. Slope of
this figure is proportional to m while vertical intercept is propor-
tional to lnK. The obtained m, lnK and true hardness HIIC values are
given in Table 8. The exponent m is used to define the ISE or RISE
behavior. If m is greater (less) than 0.6, the ISE behavior (RISE
behavior) is observed [36,37]. As can be seen from Table 9, the m
values of all the samples are less than 0.6 and the RISE behavior is
observed for all the samples. As can be seen from the table, there is
no trend in m and K values for different samples while HIIC of the
samples increase with increasing B fraction close to the plateau
hardness values.
As a summary of the results presented above, we have used
Meyer, PSR, EPD, HK and IIC models to analyze the micro-
indentation data in B doped ZnO samples and the resulting
micro-hardness data are displayed in Table 9. According to the re-
sults, the IIC model is the most appropriate model to address the
RISE behavior for the samples in this work.
Acknowledgements
This research partially supported by Bolu Abant Izzet Baysal
University Scientific Research Projects Coordination Department
under the Grant No. BAPe 2013.03.02.609. The authors would like
to thank to the Kastamonu University Research and Application
Center for the supports.
The RISE behavior generally is due to relative predominance
nucleation and multiplication of dislocations. This behavior can

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S.D. Senol et al. / Journal of Alloys and Compounds 797 (2019) 717e726
(2017) 50527e50536.
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