الفهرس 
Definition of a ceramicOnly 14 pages are availabe for public view
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Abstract
Ferroelectric ceramics, un-doped Ba1-xSrxTiO3 (BST) where x has the
values: 0.0, 0.1, 0.15, 0.25, 0.3 and 0.5 mol. %, rare earth–doped [(1-x)
(B0.75 Sr0.25 TiO3)+ 0.2 mol. % Sm2O3 +x Dy2O3] (BSTR), where x = 0,
0.1, 0.3 and 0.5, respectively were all prepared by a solid state reaction
technique.
X-ray diffraction (XRD) patterns confirmed the formation of the
perovskite phase for all prepared un-doped and doped samples. Also, size
of crystallites and the parameter, a, c and c/a ratio were found to be
decreased with increasing of Sr content in un- doped samples, but they
are increased for Dy2O3 doped BSTR ceramics.
Field emission scanning electron microscopy (FESEM) of doped samples
confirmed (XRD) results revealed that, as x Dy2O3 content increases,
particle size increases. Energy dispersive X-ray (EDX) analysis for doped
samples indicates that the increase of Dy2O3 content in the sample
resulting in formation of perovskite tetragonal phase of large grains
BSTR and small ones BST residing on the boundaries of the former as
confirmed by SEM micrographs.
Mechanical properties such as ultrasonic attenuation, ultrasonic wave
velocities, and elastic moduli were studied by employing an ultrasonic
pulse echo method at 2 MHz frequency for both doped and un-doped
samples. Obtained results revealed strong compositional dependence of
all previous mechanical properties. Also, high temperature ultrasonic
studies for both Dy2O3-doped and un-doped samples showed the Curie
transition temperatures of tested ceramics in addition to some relaxations
peaks which occur in these materials to be dependent on composition for
both BST and BSTR ceramics.
For un-doped, BST samples, increasing Sr content, resulted in decreasing
bulk density while increasing Dy2O3 in doped samples increased the
density. The ultrasonic attenuation decreased for all tested ceramics and
ultrasonic velocities and elastic moduli are all increased upon increasing
amounts of dopants, Sr in BST and Dy2O3 in BSTR ceramics.
Finally, dielectric investigations are performed on un-doped and rare
earth-doped samples at room temperature in the range of frequency from
0.1 Hz up to one MHz for un-doped samples and from 100 Hz up to one
MHz for doped samples. Variations of all parameters, the complex
impedance Z*, the real and imaginary components of dielectric constant
ε` and ε``, dissipation factor, tan δ and the ac-conductivity with frequency
(log f) revealed the nature of polarization, dielectric loss and types of
conduction mechanisms in tested ceramics. The acquired structural,
mechanical, and electrical results were discussed and correlated.