PhD Research Work
PhD Thesis Title: "Electroactive Ceramic Filled Flexible Poly(dimethylsiloxane) and Polyurethane Composites for Dielectric and Piezoelectric Applications".
PhD Research Areas: (i) Smart polymer-ceramic micro/nano composites, (ii) Preparation of electroceramic simple/complex oxides (powders) via solid state reaction and chemical route, (iii) Surface modification of ceramic nanoparticles to improve dielectric properties, and (iv) Doping of transition/rare earth elements to the base oxide via solid state and chemical method.
Few of my PhD works are given below.
PhD Research Areas: (i) Smart polymer-ceramic micro/nano composites, (ii) Preparation of electroceramic simple/complex oxides (powders) via solid state reaction and chemical route, (iii) Surface modification of ceramic nanoparticles to improve dielectric properties, and (iv) Doping of transition/rare earth elements to the base oxide via solid state and chemical method.
Few of my PhD works are given below.
Title: Flexible Nanocomposites Comprised of Poly(dimethylsiloxane) and High-Permittivity TiO2 Nanoparticles Doped with La3+/Cu+ for Dielectric Applications (Link)
Abstract: Highly ordered spherical titania (TiO2) and La3+/Cu+-doped TiO2nanoparticles with particle sizes of ≤∼20 nm are prepared by the sol–gel method using titanium isopropoxide [Ti(O-iPr)4] as the main raw material. The prepared nanoparticles are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Both undoped and doped materials exhibit frequency-dependent permittivity, which increases with a decrease in the frequency, and attain very high values of 105 order at the low-frequency end (∼10 Hz). The doping of TiO2 with La3+/Cu+ has a strong influence on its dielectric behavior, and the permittivity of doped samples increases significantly compared to that of undoped samples. The crystal phase of TiO2 (rutile) remains unaffected even after La3+/Cu+ doping, as evidenced from XRD analysis. There is a bathochromic shift (red shift) of the UV–visible peak due to La3+/Cu+ doping in TiO2. Three different ceramic/polymer composites are prepared using three types of nanoparticles (TiO2, La-TiO2, Cu-TiO2) using a poly(dimethylsiloxane) elastomer as the base matrix. These flexible composites show some unique features like good temperature- and frequency-independent dielectric properties, thereby making them suitable candidates for flexible electronic materials. Further, their processing can be accomplished at low temperature (∼150 °C) and is more economical compared to ceramic dielectrics.
Abstract: Highly ordered spherical titania (TiO2) and La3+/Cu+-doped TiO2nanoparticles with particle sizes of ≤∼20 nm are prepared by the sol–gel method using titanium isopropoxide [Ti(O-iPr)4] as the main raw material. The prepared nanoparticles are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Both undoped and doped materials exhibit frequency-dependent permittivity, which increases with a decrease in the frequency, and attain very high values of 105 order at the low-frequency end (∼10 Hz). The doping of TiO2 with La3+/Cu+ has a strong influence on its dielectric behavior, and the permittivity of doped samples increases significantly compared to that of undoped samples. The crystal phase of TiO2 (rutile) remains unaffected even after La3+/Cu+ doping, as evidenced from XRD analysis. There is a bathochromic shift (red shift) of the UV–visible peak due to La3+/Cu+ doping in TiO2. Three different ceramic/polymer composites are prepared using three types of nanoparticles (TiO2, La-TiO2, Cu-TiO2) using a poly(dimethylsiloxane) elastomer as the base matrix. These flexible composites show some unique features like good temperature- and frequency-independent dielectric properties, thereby making them suitable candidates for flexible electronic materials. Further, their processing can be accomplished at low temperature (∼150 °C) and is more economical compared to ceramic dielectrics.
Title: Facile preparation of uniform barium titanate (BaTiO3) multipods with high permittivity: impedance and temperature dependent dielectric behavior (Link)
Abstract: Perovskite barium titanate (BaTiO3) multipods were prepared via high temperature solid state reaction. The crystal structure and morphology of BaTiO3 particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). The XRD analysis of the crystal structure revealed that a single-phase compound was formed having tetragonal crystal structure. Calorimetric study (DSC) over room to high temperature was used to find the energy involved in different steps of synthesis especially during the initiation and the termination process for the formation of BaTiO3. These multipods have high average aspect ratio (10, where average diameter 300 nm and average length 3 μm) as seen from FESEM. UV-Vis spectroscopy reveals that the prepared material is UV active. The bulk and surface chemical composition of these BaTiO3 particles as investigated by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra reveals that in the prepared BaTiO3, the titanium ions exist in two different oxidation states, namely Ti3+ and Ti4+. The BaTiO3 multipod exhibits high permittivity with relatively low dielectric loss. From impedance analysis of the material, the dual resistivity characteristics, one for grain and the other for grain-boundary can be distinguished. An equivalent circuit has been proposed through analysis of the complex impedance plot (Nyquist plot) for BaTiO3 multipods. This material has perfect capacitative nature as seen from the Bode plot, and can be used for charge storage devices and other electronic applications. From temperature dependent dielectric analysis, the Curie temperature of BaTiO3 multipods is found to be 85 °C.
Abstract: Perovskite barium titanate (BaTiO3) multipods were prepared via high temperature solid state reaction. The crystal structure and morphology of BaTiO3 particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). The XRD analysis of the crystal structure revealed that a single-phase compound was formed having tetragonal crystal structure. Calorimetric study (DSC) over room to high temperature was used to find the energy involved in different steps of synthesis especially during the initiation and the termination process for the formation of BaTiO3. These multipods have high average aspect ratio (10, where average diameter 300 nm and average length 3 μm) as seen from FESEM. UV-Vis spectroscopy reveals that the prepared material is UV active. The bulk and surface chemical composition of these BaTiO3 particles as investigated by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra reveals that in the prepared BaTiO3, the titanium ions exist in two different oxidation states, namely Ti3+ and Ti4+. The BaTiO3 multipod exhibits high permittivity with relatively low dielectric loss. From impedance analysis of the material, the dual resistivity characteristics, one for grain and the other for grain-boundary can be distinguished. An equivalent circuit has been proposed through analysis of the complex impedance plot (Nyquist plot) for BaTiO3 multipods. This material has perfect capacitative nature as seen from the Bode plot, and can be used for charge storage devices and other electronic applications. From temperature dependent dielectric analysis, the Curie temperature of BaTiO3 multipods is found to be 85 °C.
Title: Development of polyurethane–titania nanocomposites as dielectric and piezoelectric material (Link)
Abstract: Polyurethane (PU)–titania nanocomposites of different compositions are prepared by a melt-mixing technique. Two different sequences of mixing method are adapted to prepare two different sets of composites. All these composites show composition-dependent dielectric properties, and composites with tunable dielectric properties can be obtained through judicial adjustment of composition. The morphology of these composites has been investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). Dielectric properties at low frequency regions are found to depend on morphology. These composites show excellent piezoelectric behaviour, where the dielectric constant and conductivity of these flexible composites change appreciably with changes in applied stress. The dielectric breakdown strength of these composite is also measured. To understand the thermal stability of these composites, thermogravimetric analysis has been applied and it was found that a composite containing 12.49 vol% titania shows higher thermal stability, beyond which, stability decreases due to the photocatalytic effect of titania.
Abstract: Polyurethane (PU)–titania nanocomposites of different compositions are prepared by a melt-mixing technique. Two different sequences of mixing method are adapted to prepare two different sets of composites. All these composites show composition-dependent dielectric properties, and composites with tunable dielectric properties can be obtained through judicial adjustment of composition. The morphology of these composites has been investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). Dielectric properties at low frequency regions are found to depend on morphology. These composites show excellent piezoelectric behaviour, where the dielectric constant and conductivity of these flexible composites change appreciably with changes in applied stress. The dielectric breakdown strength of these composite is also measured. To understand the thermal stability of these composites, thermogravimetric analysis has been applied and it was found that a composite containing 12.49 vol% titania shows higher thermal stability, beyond which, stability decreases due to the photocatalytic effect of titania.
Title: Development of Flexible Piezoelectric Poly(dimethylsiloxane)–BaTiO3 Nanocomposites for Electrical Energy Harvesting (Link)
Abstract: Flexible poly(dimethylsiloxane)–BaTiO3 (PDMS-BaTiO3) nanocomposites of different compositions are prepared via room-temperature mixing for possible sensor and electrical energy-generation applications. The effect of BaTiO3 particles (multipods) on electrical properties is extensively studied, and it is found that permittivity of composites is increased significantly whereas the volume resistivity is decreased with the increase in BaTiO3 concentration. The mechanical properties of PDMS-BaTiO3 composites are also composition-dependent where both tensile strength and percent elongation at break decreases with increase in BaTiO3 particle concentration because of the nonreinforcing nature of BaTiO3 particles, as is apparent from Kraus plots. These composites have excellent piezoelectric behavior, where the dielectric properties of these composites changed substantially with the change in the applied stress. The temperature-dependent dielectric properties reveal that dielectric properties increased with a rise in temperature up to a certain limit and decreased thereafter. Filler shape, dispersion, and distribution in the matrix polymer were observed through field emission scanning electron microscopy.
Abstract: Flexible poly(dimethylsiloxane)–BaTiO3 (PDMS-BaTiO3) nanocomposites of different compositions are prepared via room-temperature mixing for possible sensor and electrical energy-generation applications. The effect of BaTiO3 particles (multipods) on electrical properties is extensively studied, and it is found that permittivity of composites is increased significantly whereas the volume resistivity is decreased with the increase in BaTiO3 concentration. The mechanical properties of PDMS-BaTiO3 composites are also composition-dependent where both tensile strength and percent elongation at break decreases with increase in BaTiO3 particle concentration because of the nonreinforcing nature of BaTiO3 particles, as is apparent from Kraus plots. These composites have excellent piezoelectric behavior, where the dielectric properties of these composites changed substantially with the change in the applied stress. The temperature-dependent dielectric properties reveal that dielectric properties increased with a rise in temperature up to a certain limit and decreased thereafter. Filler shape, dispersion, and distribution in the matrix polymer were observed through field emission scanning electron microscopy.