z Materials Science inc. Nanomaterials & Polymers
Temperature Stable Dielectric Properties in BaTiO
3
–Bi
(Mg
2/3
Nb
1/3
)O
3
–NaNbO
3
Solid Solution
Raz Muhammad,*
[a]
Asif Ali,
[a]
Javier Camargo,
[b]
and Miriam S. Castro
[b]
0.5BaTiO
3
–(0.5–x)Bi(Mg
2/3
Nb
1/3
)O
3
–xNaNbO
3
(x = 0.1, 0.2 and 0.3)
samples were processed via solid-state sintering route. Phase
identification of the samples showed the formation of a single-
phase cubic perovskite-structure (space group Pm-3 m) which
was further confirmed using Raman spectroscopy. Microstruc-
tural analysis of the samples revealed some voids in the
samples while grain size was observed to decrease with
increasing NaNbO
3
concentration. The addition of NaNbO
3
shifted T
m
to below room temperature and the stability range
of 0.5BaTiO
3
–0.5Bi(Mg
2/3
Nb
1/3
)O
3
ceramics was enhanced. The
sample with x = 0.20 exhibited ε
r(mid)
= 400 � 15% stable over a
wide temperature range from 85 to 500 °C and most
importantly a low dielectric loss of < 0.05 stable across a wide
temperature range 100 to 426 °C was maintained. The
thermally stable dielectric properties of sample x = 0.2 suggests
that it could be useful candidate material for capacitor
applications in both low (X9R) as well as harsh environment
applications.
Introduction
BaTiO
3
(BT) is used as a base material in various applications
such as multi-layer ceramic capacitor (MLCCs), transducer,
thermistor, pyroelectric sensor and non-volatile memory
devices.
[1]
The major drawback of BT is its sharp Curie point (T
c
)
near ∼ 120 °C. At temperature above T
c
, it has a cubic structure
(paraelectric phase) while below T
c
the structure is tetragonal
(ferroelectric phase). It has a high ε
r
value at the Curie point
and a high refractive index value of (n � 2.4) in its cubic phase.
It is insulating in nature but when doped with some other
metal like sodium, neodymium, samarium, yttrium etc. behaves
like a semiconducting material. The semiconducting BT may
exhibit positive temperature coefficient of resistivity (PTCR) in
some cases which is important for some practical application.
The single crystal of BT has been reported
[2]
to exhibit a
negative temperature coefficient of resistivity (NTCR). Although,
in modern electronic devices, capacitors are widely used. The
challenge for capacitor industries is to find a material which
can be sintered at low temperature so that they can lower the
cost of electrodes. In addition, other important parameters
such as the use of low cast raw materials, easy fabrication
method and environmental friendliness are also taken into
consideration for the fabrication of new materials for the
capacitor applications.
[3]
Capacitor operating at high temperature > 200 °C are
required for harsh environment applications. BT would be an
interesting material due to its high relative permittivity, but at
the cost of its low T
c
. The Curie point is shifted by modify the
lattice of BT through adding different dopants to achieve the
desired properties. Ceramic solid solution (1–x)BT–xBi(Mg
0.5
Zr
0.5
)
O
3
(BT–BMZ) has been investigated for high temperature
applications.
[4]
Optimum dielectric properties were obtained for
the composition 0.4BT–0.06BMZ i.e. ε
r
= 7000 with low
dielectric losses of < 0.025 across the temperature range 200–
300 °C. Similarly, single phase ceramic solid solution (1 x)BT–
Bi(Mg
0.5
Zr
0.5
)O
3
at x = 0.4 has an ε
r
= 600 � 10% across a wide
temperature range of 25–400 °C, tanδ < 0.02 in temperature
range from 55–280 °C and high value of dc resistivity 10
6
Ω-m
at 400 °C.
[5]
(1 x)BT–xBi(Li
1/3
Zr
2/3
)O
3
at x = 0.1 showed a high ε
r
= 1726 with a variation of < � 15% across 70 to 144 °C with
a low dielectric loss of < 0.02 across from 21 to 200 °C.
[6]
By
introducing the Ba vacancies in the ceramic 0.8BT–0.2Bi(Zn
1/
2
Ti
1/2
)O
3
(0.8BT–0.2BZT), the dielectric properties were strongly
affected i.e. 2 mol.% Ba deficiency.
[7]
The solid solution
possesses a high ε
r
= 1150 with a low tanδ (< 0.045) which was
maintained up to a high temperature range of 460 °C. The
dielectric properties of the solid solution (1-x)BT–xBi(Mg
0.5
Sn
0.5
)
O
3
(BT–BMS) for x = 0.1 had ε
r
= 2918 with a variation of less
than � 15% across 56 to 248 °C with a low dielectric tanδ <
0.025 across 54 to125 °C, which also showed energy storage
of 0.12 J/cm
3
) and low J
loss
(0.04 J/cm
3
).
[8]
Ma et al.
[9]
reported
the dielectric properties of (1–x)BT–xBi(Mg
2/3
Ta
1/3
)O
3
(BT–BMTa)
and found a high ε
r
(∼ 1000-2000 � 15%) in a wide temper-
ature range of 30 to 150 °C with low tanδ < 0.02. Lead-free
ceramic solid solution 0.5BT–0.5Bi(Mg
1/2 +x/6
T
i(1-x)/2
Nb
x/3
)O
3
with
x = 0.01–0.25 has been reported to exhibit a high ε
r
= 1100 in
the wide temperature range of 55–500 °C with a variation of �
15% and low dielectric losses � 0.025 in the temperature range
of 102–425 °C.
[10]
The dielectric properties of the ceramic (1–x)
BT–xBi(Mg
2/3
Nb
1/3
)O
3
(BT–BMN) for x = 0.1 were reported to
[a] Dr.R.Muhammad,A.Ali
Department of Physics
Abdul Wali Khan University Mardan
Garden Campus, KP, Pakistan
E-mail: raz@awkum.edu.pk
[b] Dr.J.Camargo,Dr.M.S.Castro
Institute of Research in Materials Science and Technology, National
University of Mar del Plata
Av. Colon 10850 (B7606BVZ), Mar del Plata, Argentina
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/slct.202000243
Full Papers DOI: 10.1002/slct.202000243
3730 ChemistrySelect 2020, 5,3730–3734 © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim