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      Articles written in Bulletin of Materials Science

    • Morphology-controlled ultrafine BaTiO$_3$-based PVDF–HFP nanocomposite: synergistic effect on dielectric and electro-mechanical properties

      VAIBHAV KHIRATKAR RADHAMANOHAR AEPURU H S PANDA

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      Perovskite-based flexible nanocomposites were realized by dispersing BaTiO$_3$ and modified monodisperse BaTiO$_3$ in PVDF–HFP matrix. BaTiO$_3$ was modified in situ by the addition of carbon solution, which was prepared electrochemically by using graphite rod. Structural characterization revealed that the decrease in tetragonality due to reductionin particle size of modified BaTiO$_3$ than unmodified BaTiO$_3$. The controlled morphology of treated-BaTiO$_3$ nanoparticles was well dispersed in polymer matrix and exhibited effective dielectric constant.High active surface area of modified BaTiO$_3$ suggested strong interfacial polarization, reduced dielectric loss and induced relaxation as compared to PVDF–HFP/BTnanocomposite. The experimental dielectric behaviour was fitted with theoretical Maxwell–Garnet model and composites followed up to 20 wt.% filler. The polarization effect was further proven by electric modulus studies of nanocomposites in broad frequency (0.1 Hz–1 MHz) and temperature ($−$40 to 130$^{\circ}$C). The results suggested that the shift in relaxation peakstowards higher frequencies with increase in filler content in polymer matrix. Further, a flexible-pressure sensing device was fabricated and evaluated for real applications.

    • BaZrO$_3$ doping in (Na, K)(Nb, Ta)O$_3$: investigating the phase transformation behaviour, piezoelectric, dielectric, ferroelectric properties and their stability

      BHUPENDER RAWAL PRASHANT DIXIT N N WATHORE B PRAVEENKUMAR H S PANDA

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      This study highlights the effect of BaZrO$_3$ doping on (Na$_{0.52}$K$_{0.48}$)(Nb$_{0.95}$Ta$_{0.05}$)O$_3$ lead-free composition. The doping, interestingly, reveals the formation of a new polymorphic phase boundary between rhombohedral and tetragonalphases, while eliminating the orthorhombic phase. Rietveld refinement of temperature dependent X-ray diffraction data, in conjunction with dielectric studies, was utilized to corroborate the findings. The study also addresses in detail the process optimization methodology, involving calcination, sintering and poling process, which is highly relevant to the research community. Two mol% BaZrO$_3$-doped samples exhibited better piezoelectric, ferroelectric and dielectric properties. The doping also substantially improved the stability of properties during ageing, under thermal and cyclic electrical loadings.

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