203 research outputs found
Stabilization of Polar Nano Regions in Pb-free ferroelectrics
Formation of polar nano regions through solid-solution additions are known to
enhance significantly the functional properties of ferroelectric materials.
Despite considerable progress in characterizing the microscopic behavior of
polar nano regions, understanding their real-space atomic structure and
dynamics of formation remains a considerable challenge. Here, using the method
of dynamic pair distribution function, we provide direct insights into the role
of solid-solution additions towards the stabilization of polar nano regions in
the Pb-free ferroelectric of Ba(Zr,Ti)O3. It is shown that for an optimum level
of substitution of Ti by larger Zr ions, the dynamics of atomic displacements
for ferroelectric polarization are slowed sufficiently, which leads to
increased local correlation among dipoles below THz frequencies. The dynamic
pair distribution function technique demonstrates unique capability to obtain
insights into locally correlated atomic dynamics in disordered materials,
including new Pb-free ferroelectrics, which is necessary to understand and
control their functional properties
Biomimetic synthesis of hybrid nanocomposite scaffolds by freeze-thawing and freeze-drying
The aim of this study is to biomimetically synthesize hydroxyapatite - hydrophilic polymer scaffolds for biomedical applications. This organic-inorganic hybrid has been structurally characterized and reveals a good microstructural control as seen by the SEM analysis and the nanosize of the particulates is confirmed by AFM microscopy. The characterization of such nano-structured composites would allow researchers to design new systems, tailoring properties for different applications. © Indian Academy of Sciences
Growth of carbon nanotubes on quasicrystalline alloys
We report on the synthesis of carbon nanotubes on quasicrystalline alloys.
Aligned multiwalled carbon nanotubes (MWNTs) on the conducting faces of
decagonal quasicrystals were synthesized using floating catalyst chemical vapor
deposition. The alignment of the nanotubes was found perpendicular to the
decagonal faces of the quasicrystals. A comparison between the growth and tube
quality has also been made between tubes grown on various quasicrystalline and
SiO2 substrates. While a significant MWNT growth was observed on decagonal
quasicrystalline substrate, there was no significant growth observed on
icosahedral quasicrystalline substrate. Raman spectroscopy and high resolution
transmission electron microscopy (HRTEM) results show high crystalline nature
of the nanotubes. Presence of continuous iron filled core in the nanotubes
grown on these substrates was also observed, which is typically not seen in
MWNTs grown using similar process on silicon and/or silicon dioxide substrates.
The study has important implications for understanding the growth mechanism of
MWNTs on conducting substrates which have potential applications as heat sinks
Point defect induced incommensurate dipole moments in the KCa2Nb3O10 Dion-Jacobson layered perovskite
Local structural distortions due to isolated atomic defects and defect complexes strongly affect the macroscopic properties of oxide ceramics. While the characterization of local defect structures is more common in simple ABO3 perovskites, unambiguous determination of the same in layered perovskites is more difficult due to their complex crystal structures. Here, we combined x-ray pair distribution function and density functional theory calculations to characterize the structure of cation-oxygen divacancy pairs in a Dion-Jacobson (D-J) layered perovskite. Our results indicate that local incommensurate dipole moments with polarization density in the range of ∼0.1–17μC/cm2 are created due to divacancy-induced structural distortions in the D-J phase KCa2Nb3O10. This is comparable with defect dipole moments observed in well-known perovskite ferroelectrics. The current results imply that controlling the atomic defects can potentially lead to significant control of dielectric properties in D-J layered perovskites
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