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The aim of this proposal is to develop lead free relaxor ferroelectric materials with enhanced power density, very short discharge time, high breakdown strength for possible pulsed capacitor applications.

Materials with high power density and energy density are becoming gradually significant due to swift growth of advanced pulsed power systems for applications such as hybrid electric vehicles, high frequency inverters, space vehicle power systems, medical devices, electromagnetic rail guns etc, Energy storage devices mainly comprise of Fuel cells, lithium ion batteries, electrochemical capacitors and electrostatic capacitors. Batteries possess enormously high energy density but their output power is limited by the low mobility of charge carriers, which further restricts their application in pulsed power systems. Due to fast polarization response under an applied external electric field, dielectric materials exhibit very high charge/discharge speed which further results in a huge output power density of the order of MW.

From the last decade, relaxor ferroelectrics possess negligible Pr (remnant polarization), low coercive field and high Pmax (maximum polarization) due to their characteristic polar nano regions (PNRs), which further results in high energy density and efficiency. Therefore, the relaxor ferroelectrics are appreciated candidates in the field of energy storage applications. It is experimentally evidenced that DBS of bulk ceramic is associated with the microstructure, such as grain size, grain boundary condition, porosity etc. Among these, grain size contribution is quite prominent. Tunkasiri calculated the effect of grain size on DBS of the ceramic; E_DBS∝1/√G where, EDBS is the DBS of the ceramic and G is the grain size of the ceramic. To achieve our goal, the proposed research will concentrate on the following specific objectives:

• To optimize the composition for the lead free (Bi0.5Na0.5)TiO3–BaTiO3 [NBT-BT] based solid solutions to achieve high value of breakdown strength > 200 kV/cm and recoverable energy density > 2 J/cm3.
• To study the effect of aging on power density and energy storage efficiency.
• To design and develop a pulse power capacitor with capacity ~1000 pF, operating temperature range -30 to +100°C, Vmax (DC) ~30kV.

We have synthesized the PZT and Nb doped PZT samples using solid state reaction method. XRD studies clearly depict that there is no impurity phase present in the samples. Dielectric measurements show that the dielectric constant was below 500 as required for ferroelectric generator (FEG) applications. Ferroelectric measurements show that the remnant polarization for all samples is above 25 µC/cm2. We have also achieved high density to samples to become good candidate for FEG applications.

Magnetoelectric composites have sparked a lot of interest in order to produce high magnetoelectric coefficients in bulk and layered composites using different techniques. A wide range of magnetostrictive and piezoelectric phase combinations have been studied in the past, with lead (Pb) based materials being used as the piezoelectric component due to their strong piezoelectric response. However, many investigations focused on developing lead-free ferroelectric systems with electrical properties equal to those of lead-based systems due to environmental concerns.

The objective of this project is to achieve the requirements for a good magnetoelectric effect in a lead-free composite. In this study, phase structure, dielectric properties, magnetic properties and magnetodielectric have been investigated and analyzed the magnetoelectric coupling coefficient of the composites. In layered composites, we also discovered the self-biasing phenomenon, which allows considerable ME coupling in the absence of a DC magnetic field. The elimination of the necessity for DC magnetic bias in ME composites opens up a lot of opportunities for the development of components for a variety of applications. The ME coefficient is also greatly influenced by the thickness fractions of the two phases, thus we optimised the longitudinal and transverse ME response by altering the thickness of both BCZT and NZCF layers in the next work.

In this project, we have synthesized a non-Pb piezoelectric system BZT-BCT, which exhibits a very high piezoelectric coefficient (d33) of 512 pC/N at MPB, which is comparable even with high-end PZT. Lead-free BZT-xBCT samples were prepared using the solid-state reaction technique. Structural analysis shows the presence of orthorhombic and tetragonal phases in the prepared samples. We observed that with an increase in x content, the tetragonal phase increases which further results in higher d33. Sintering temperature plays a very important role to achieve desired density, which further leads to good piezoelectric properties.

Meanwhile, we have also introduced a novel method to obtain high piezoelectric coefficient and electromechanical coupling coefficient in BZT-BCT by introducing a novel synthesis procedure. We observed high d33~ 520 pC/N and electromechanical coupling coefficient ~ 57.5% in 0.5BZT-0.5BCT synthesized by novel synthesis procedure.

For energy storage efficiency, we prepared BZT-BCT by sol-gel technique. The different parameters like dielectric constant, dielectric loss, polarization, coercive field, the efficiency of energy storage were found to be optimum for the (1-x)BZT-xBCT ceramics at x =0.55. We estimated the energy storage density W~ 189 mJ/cm3 and high efficiency η ~ 75.6% for BZT-0.55BCT ceramic composition. Therefore, this work suggested that 0.45BZT-0.55BCT ceramics are potential candidates for energy storage capacitor.

Furthermore, we investigated the temperature stability of 5% (Mg1/3Nb2/3)4+ doped BZT-BCT composition at 50kV/cm. We observed Wrec ~ 235 mJ/cm3and ultra-high η~ 94.3% at room temperature. The η of ceramic increases to 94.6% and Wrec to 187 mJ/cm3 as the temperature rises to 110°C.

A design concept for making sandwich panel for blast mitigation was developed such that the designed material should be able to absorb the maximum of blast energy by undergoing elastic, plastic and fracture. Design concept include the specifically designed perforated face sheet so that after interacting with blast wave it doesn’t leave any splinters off. The specific light weight alloy of aluminum (AA6061-T6) was selected for making front and back sheet (both of 2mm thickness) of sandwich panel. Closed cell Aluminum alloy foam (AA6061) was used as central soft core. The foam was synthesized on stir casting furnace by melt route. The synthesized foam was cut into slices and sandwiched between face sheet and back sheet. The pressure value correspond to equivalent quantity of TNT and stand-off distance was investigated by simulation method. Quasi-static compression test and High strain rate test on Split Hopkinson Pressure Bar apparatus for face sheet material, central foam and back sheet material was performed to know the compressive strength. Face sheet and back sheet was tested individually on Shock tube at 46 bar reflected pressure and were analyzed. A sandwich panel was designed (11mm thick foam) and tested on shock tube which completely deformed plastically thereby absorbing some part of incident energy. Its blast mitigation capacity was increased by increasing the central foam thickness to 22 mm which resulted in very little deformation and 75.84% increase in mitigated transmitted pressure was recorded. The stress wave and strain behavior due to shock wave interaction were studied by Ansys fluent software.

The project is synthesis sintering and characterization of sesquioxides like YAG and yttrium oxide ceramics, particularly in the field of advance ceramics. YAG and Y2O3 is known for its excellent chemical stability, high melting point, thermal conductivity, and transparency in a wide spectral range. The traditional method of growing single crystals of Y2O3 faces challenges due to its high melting point, so polycrystalline transparent ceramics (PTCs) are used as an alternative, offering advantages such as easy fabrication and the ability to create complex structures. To lower the sintering temperature sesquioxides could be doped with sintering additives in a limited quantity so as not interfere with basic properties of sesquioxides. To enhance and observe altering the physical and chemical properties sesquioxides could be doped with Rare earth elements (REEs) can be doped. The project is about the development and compilation of various studies that focus on doping Y2O3 with REEs like erbium (Er3+), ytterbium (Yb3+), samarium (Sm3+), and europium (Eu3+), which significantly affect the characteristics of the material.

For development and implementation of analog computing system, recently, Brain inspired computing, also known as nueromorphic computing has received much attention as it exhibits many features needed for design and development of energy efficient, fast and, highly parallel analog computing system. However, like all other new and emerging technologies, neuromorphic computing is also facing difficulties and challenges in terms of hardware design and implementation [3]-[4]. Hence, in this project we are focusing to generate indigenous tools which can be further used to solve the challenges in brain inspired electronics system design.

The Aim of this project is to design, develop and fabricate an integrated frequency multiplier utilizing a novel self-switching diode (SSD) based on GaN two-dimensional heterostructures. The SSD has an entirely different working principal which does not require any p-n junction and /or Schottky barrier to operate eliminating the requirement of an additional bias circuit than that of conventional and commercially available diodes. Due to planar and single-layered device architecture, SSD exhibits low parasitics resulting in a zero-bias rectification up to 1.5 THz at room temperatures with responsivity and NEP comparable to commercially available Schottky diodes. The SSD can easily be fabricated utilizing a single-step lithography followed by an etching process from using wide variety of materials varying from conventional Silicon to III-V heterostructures to novel graphene. On the other hand, commercially available Schottky barrier diodes, have multi-layered and vertical structure, and require an additional bias high enough to overcome the built-in electric field and to allow current flow. It further introduces the parasitic capacitance which in turn limits the operating speed and high frequency performance restricting to utilise a Schottky diode to generate very high microwave/ Terahertz frequencies. Schottky barrier diodes are commonly being utilised in array i.e. parallel or anti-parallel configuration for frequency multipliers to improve input/output power handling capacity. However, they suffer from excessive heat at the Schottky junctions leading to the performance degradation and require novel materials and challenging fabrication techniques to achieve ultra-low charge carrier transit time and parasitics at room temperature to generate high microwave/terahertz signals. Utilising excellent properties of GaN, SSD can be implemented for frequency multipliers to generate signals with hundreds of gigahertz frequencies with improved efficiency and high power handling capacity. Planar structure of device is more suitable as more number of SSDs in array configuration can be easily integrated without interconnects reducing overall device impedance exhibiting better noise properties at high frequencies. Further, heat dissipation can be managed efficiently by correct design of SSD channel. Therefore, developing GaN SSD based integrated frequency multiplier is timely given the rapid progress in the GaN technology and development of high frequency microwave/terahertz sources for wide variety of applications such as future generation communications, medical and security imaging etc. Additionally, training of early career researchers in this project will provide India with the scientists and engineers with the skills to transfer GaN-based technologies from academia to industry for industrial and/or strategic applications in line with Government of India’s Semiconductor Mission, Make in India, Aatmnirbhar Bharat, and Skill India Missions.

The aim of this project is to design and develop a novel nanoelectronic rectifier, also known as self-switching diode (SSD), from van der Waals hetrostructure consisting of graphene/h-BN/MoS2 layers. Due to excellent material properties, proposed SSDs can operate with ultra-fast switching speed than that of electronic rectifiers fabricated from conventional semiconductors for a wide variety of applications such as signal detection, future generation communications, medical and security imaging etc. Recently, emerging two-dimensional (2D)-layered semiconductors including graphene, hexagonal boron nitride (h-BN) and molybdenum disulphide (MoS2) have shown considerable potential for designing next-generation integrated electronic and optoelectronic devices, due to their excellent unique physical and structural properties. Particularly, the 2D-layered semiconductors of graphene, h-BN and MoS2 can be flexibly combined to form different configurations of vertical van der Waals heterostructures with atomically sharp interfaces and tunable band alignment, opening up vast opportunities for fundamental investigation of novel electronic properties at the limit of single atom thickness and potential applications in novel devices concept such as self-switching diode. The working of conventional rectifying diodes depend either upon a pn doped junction or a Schottky barrier, that also determines the limitations. An applied bias high enough is generally required to overcome the built-in electric field and to allow a significant current flow, introducing the parasitic capacitance which in turn limits the operating speed and high frequency performance. The novel nanodiode concept proposed in this project is entirely different and it has a single‐layered device architecture that is ideally‐suited to graphene and/or graphene based van der Waals heterostructures. Moreover, it operates on new working principle enabling zero threshold voltage, thus eliminating the need for a bias circuit. Developing SSD in graphene/h-BN/MoS2 is timely given the rapid progress in graphene and/or 2d van der Waals material engineering. Since the device speed generally scales with the carrier mobility, the proposed SSDs are expected to operate at very high frequencies possibly up to THz.

In this research, a semi-classical drift-diffusion 3D modeling have been developed to predict the rectification behavior and noise spectra of both the ballistic rectifiers considered in this research. Furthermore, the developed model predicts that minimum low frequency noise for both the devices which depends upon carrier concentration inside device active region rather than mobility, enables potential applications as THz detectors for imaging.

Further, it has been demonstrated that symmetric geometry of both type of ballistic rectifiers, i.e. three terminals and four terminals, can be utilized as a thermoelectric rectifier for wide variety of applications to produce rectified output voltage converting thermal energy radiated from the electronic devices/ICs. Prototypes of ballistic rectifiers with and without antidot have been developed demonstrating rectification of microwave/RF signals.

The development of this novel technology of Ballistic Rectifier can be used for various applications including future generation communications, signal detection, medical and security imaging.