Biomedical Engineering Reference
In-Depth Information
14.1 Introduction
h e group of materials with ABO
3
type perovskite structure is also very
important due to their attractive electrical and magnetic properties for
technological applications and the richness of physical and chemical
aspects they possess. h e perovskite lead zirconate titanate Pb (Zr
x
Ti
1-x
)
O
3
, abbreviated as PZT, is known to have excellent piezoelectric proper-
ties [1, 2]. Oxides with complex perovskite structures and high dielectric
constants play an important role in microelectronics and have numerous
technological applications. h ey have been used as memory devices and
capacitors. For both types of applications, materials of high dielectric con-
stants are required. For many of the technological applications, composi-
tionally modii ed PZT ceramics are used. h ese modii ed PZT ceramics
still show superior piezoelectric properties [3]. h ese compositional modi-
i cations may be incorporated either by chemical substitution at A-site or
B-sites of the perovskite structure or by using of -valent element as an
additive. In the miniaturization era of technological advancement, there is
an ever-pressing need for light, ei cient, reliable, and long-lasting devices
for power supply as well. h is requires new generation of electric compo-
nents like transformers, capacitors, transistors, etc. h e most commonly
used tiny piezoelectric transformers are based on PT and PZT composi-
tions. h e hard and sot PZTs have their own advantages. h e former has
a low dielectric loss factor and a high mechanical quality factor (Q
m
) [4,
5], while the latter has a high piezoelectric constant and a high coupling
coei cient.
In order to obtain proper ceramics which combine the advantages of
both hard and sot PZTs, dif erent modii cations have been investigated.
Similar to Fe
3+
, Mn
2+
is generally known as hard additive to generate O
2-
vacancies. h e Sr
2+
cation replaces Pb
2+
on the A-site. In the same way Mn
2+
cation replaces Zr
4+
or Ti
4+
on the B-site. O-site vacancies lead to contrac-
tion of the grain body. At the same time, defects complex which consists
of impurity ions and O-site vacancies along with the domain boundaries
are generated to make a long-range polar order. For the above reasons,
the motion of domain walls is getting harder. Consequently, weak-i eld
dielectric and piezoelectric constants and weak-i eld dielectric losses are
reduced, whereas coercive i eld and mechanical quality factor increase. In
this paper we have therefore concentrated on a hard piezoelectric ceramic
composition [Pb
0.94
Sr
0.06
] [(Mn
1/3
Sb
2/3
)
0.05
(Zr
0.495
Ti
0.505
)
0.95
]O
3
to explain the
mechanism of dielectric relaxation [6, 7] in the framework of conductivity
and impedance spectroscopy. It is also known that the piezoelectric prop-
erties of Sr
2+
substituted PZT are most pronounced for x = 0.06. However
