Ferroelectrics of
ABO3 type perovskite structure like PbTiO3 and BaTiO3,
and those synthesized with a varied concentration of other divalent,
tetravalent and pentavalent atoms are important because of their application as
dielectric materials and the study of phase change in such materials is
interesting. In the same series SrTiO3 is cubic at room temperature
with no ferroelectric property and it can serve as a reference lattice. Mössbauer,
EPR and IR studies of FexSr1-xTiO3 (x ≤ 0.3) ceramics have indicated structural change. The variation of
the specific heat with temperature shows a peak at around 157 K, which
indicates phonons occupying two energy states and a phase change. The specific
heat of 7.5 R deg-1 mole-1 at 500°C is much
greater than 3R for simple elemental systems (metals), which indicates that
other internal modes of vibrations are excited or anharmonic movements of atoms
are present. The XRD intensity peaks are quite sharp that indicates that
samples are made of well-grown crystallites mostly in single phase. The samples
have orthorhombic structure though there are significant changes in unit cell
volumes. For example, the sample with x
= 0.3 has a = 6.3853, b = 4.7769 Å, c = 3.9039 Å.
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