Autonomous Design of Photoferroic Ruddlesden-Popper Perovskites for Water Splitting Devices

The use of ferroelectric materials for light-harvesting applications is a possible solution for increasing the efficiency of solar cells and photoelectrocatalytic devices. In this work, we establish a fully autonomous computational workflow to identify light-harvesting materials for water splitting devices based on properties such as stability, size of the band gap, position of the band edges, and ferroelectricity. We have applied this workflow to investigate the Ruddlesden-Popper perovskite class and have identified four new compositions, which show a theoretical efficiency above 5%.

Negative capacitance devices: sensitivity analyses of the developed TCAD ferroelectric model for HZO

This work aims to investigate the suitability of innovative negative capacitance (NC) devices to be used in High Energy Physics experiments detection systems, featuring self-amplified, segmented, high granularity detectors. Within this framework, MFM (Metal-Ferroelectric-Metal) and MFIM (Metal-Ferroelectric-Insulator-Metal) structures have been investigated within the Technology-CAD environment. The strength of this approach is to exploit the behavior of a simple capacitor to accurately ad-hoc customize the TCAD library aiming at realistically modeling the polarization properties of devices fabricated with ferroelectric materials. The comparison between simulations and measurements in terms of polarization as a function of the applied electric field for both MFM and MFIM devices has been used for modeling and methodologies validation purposes. The analyses and results obtained for MFIM capacitors can be straightforwardly extended to the study of NC-FETs. This work would support the use of the TCAD modeling approach as a predictive tool to optimize the design and the operation of the new generation NC-FET devices for the future High Energy Physics experiments in the HL-LHC scenario. The NC working principle will be employed for particle detection applications in order to exceed the limits imposed by current CMOS technology in terms of power consumption, signal detectability and switching speed.

Electrical and structural properties of pure and self-defected Bi1/2Na1/2TiO3 system: A DFT study

The structural and electronic properties of the rhombohedral phase of the A-site-substituted perovskite Sodium bismuth titanate Bi1/2Na1/2TiO3 (BNT) were investigated via the density functional theory (DFT) that implemented in the CASTEP module in the Materials Studio software. I also investigated the impacts of atoms vacancy and oxygen-dopants on dielectric, electrical conductivity, and ferroelectric properties. The author expected that the defected on lead-free ferroelectric materials could extend the functional materials for innovative electronic applications.

Advanced Magnetic and Dielectric Nanomaterials

<p>Abstract: Multiferroics are a novel class of next generation multifunctional materials that exhibit simultaneous magnetic spin, electric dipole, and ferroelastic ordering. It gives an additional degree of freedom to design new devices. Magnetoelectric effect in these materials result in the manipulation of magnetic spins via applied electric field and vice versa, making them suitable for next generation applications. Single phase multiferroics show low magnetoelectric coefficient, hence there is a need to look at composite multiferroic structures with respective magnetic and ferroelectric phase. The magnetoelectric coefficient in the composite structures depends on the magnitude of strain induced by one phase to the other. This requires the need to study suitable magnetic and ferroelectric materials that can be combined to create magnetoelectric multiferroic composite structures. Also, higher surface to volume ratio at the nanoscale should enhance the interaction between the two phases. Here, in we synthesised and studied magnetic and ferroelectric structures that have potential to be used as the respective phases of multiferroic magnetoelectric composites. Magnetic materials with high magnetostriction and low coercivity are suitable candidates for the formation of multiferroic composite. The size dependent and tuneable magnetic properties of cobalt ferrite and nickel-iron composites, respectively fulfil the above-mentioned criteria. Herein, the properties of the above magnetic materials were explored at nanoscale where efficient techniques such as thermal decomposition and electrospinning were applied. Cobalt ferrite nanoparticles with varying sizes were synthesised at the nanoscale and magnetic studies were performed to study their size dependent suitability to be used as a potential magnetic material in multiferroic composite formation. The nanoparticle synthesis by thermal decomposition of metal oleate precursors displayed reaction time dependent growth. The nanoparticles sized below superparamagnetic limit showed a negligible coercivity fulfilling an essential requirement to display magnetoelectric effect. Alongside, a successful synthesis of novel cobalt iron oxide (Co0.33Fe0.67O) nanoparticles was also performed. This displayed a synthesis dependent ferrimagnetic to antiferromagnetic phase transition in Co Fe-O structure at nanoscale. A controlled oxidation of Co0.33Fe0.67O could lead to the formation of antiferromagnetic-ferrimagnetic core-shell nanostructure that can overcome the superparamagnetic limit in nanoparticles system. They are potential materials in ME-RAMs. 1-D magnetic nanostructure show a sharp shape anisotropy and hence can be used as magnetic components of composite multiferroic structures. Nickel-iron composites in FCC phase were studied at the nanoscale in the form of fibres. Electrospinning of suitable metal precursors with PVP polymer followed by the reduction of nanofibres in H2 led to the formation of Ni0.47Fe0.53 fibre mats. They were ferromagnetic and displayed high saturation magnetisation along with low coercivity fulfilling the requirement to be used in magnetoelectric applications. 1-D flexible ferroelectric composite structures were studied alongside to be used as the ferroelectric component of multiferroic composites. Polyvinylidene fluoride was doped with DIPAB at varying ratios to study the improvement in the ferroelectric properties of the composite structure in comparison to just PVDF with low dielectric constant. Electrospinning of composite polymer solution led to the formation of DIPAB doped PVDF nanofibres. They displayed improved relative dielectric constant and low loss tangent and find use in composite magnetoelectric materials formation. The ease of processability of DIPAB doped PVDF nanofibres aids in incorporating the above studied magnetic materials. The studies proved the worth of as-synthesised magnetic and ferroelectric materials at the nanoscale for the formation of magnetoelectric multiferroic composite nanomaterials. The cobalt ferrite nanoparticles doped in DIPAB-PVDF nanofibres can result in core-sheath ME composite structure. A coating of DIPAB-PVDF composite on the formed Ni0.47Fe0.53 fibres will result to the formation of 1-D magnetoelectric structures.</p>

Advanced Magnetic and Dielectric Nanomaterials

<p>Abstract: Multiferroics are a novel class of next generation multifunctional materials that exhibit simultaneous magnetic spin, electric dipole, and ferroelastic ordering. It gives an additional degree of freedom to design new devices. Magnetoelectric effect in these materials result in the manipulation of magnetic spins via applied electric field and vice versa, making them suitable for next generation applications. Single phase multiferroics show low magnetoelectric coefficient, hence there is a need to look at composite multiferroic structures with respective magnetic and ferroelectric phase. The magnetoelectric coefficient in the composite structures depends on the magnitude of strain induced by one phase to the other. This requires the need to study suitable magnetic and ferroelectric materials that can be combined to create magnetoelectric multiferroic composite structures. Also, higher surface to volume ratio at the nanoscale should enhance the interaction between the two phases. Here, in we synthesised and studied magnetic and ferroelectric structures that have potential to be used as the respective phases of multiferroic magnetoelectric composites. Magnetic materials with high magnetostriction and low coercivity are suitable candidates for the formation of multiferroic composite. The size dependent and tuneable magnetic properties of cobalt ferrite and nickel-iron composites, respectively fulfil the above-mentioned criteria. Herein, the properties of the above magnetic materials were explored at nanoscale where efficient techniques such as thermal decomposition and electrospinning were applied. Cobalt ferrite nanoparticles with varying sizes were synthesised at the nanoscale and magnetic studies were performed to study their size dependent suitability to be used as a potential magnetic material in multiferroic composite formation. The nanoparticle synthesis by thermal decomposition of metal oleate precursors displayed reaction time dependent growth. The nanoparticles sized below superparamagnetic limit showed a negligible coercivity fulfilling an essential requirement to display magnetoelectric effect. Alongside, a successful synthesis of novel cobalt iron oxide (Co0.33Fe0.67O) nanoparticles was also performed. This displayed a synthesis dependent ferrimagnetic to antiferromagnetic phase transition in Co Fe-O structure at nanoscale. A controlled oxidation of Co0.33Fe0.67O could lead to the formation of antiferromagnetic-ferrimagnetic core-shell nanostructure that can overcome the superparamagnetic limit in nanoparticles system. They are potential materials in ME-RAMs. 1-D magnetic nanostructure show a sharp shape anisotropy and hence can be used as magnetic components of composite multiferroic structures. Nickel-iron composites in FCC phase were studied at the nanoscale in the form of fibres. Electrospinning of suitable metal precursors with PVP polymer followed by the reduction of nanofibres in H2 led to the formation of Ni0.47Fe0.53 fibre mats. They were ferromagnetic and displayed high saturation magnetisation along with low coercivity fulfilling the requirement to be used in magnetoelectric applications. 1-D flexible ferroelectric composite structures were studied alongside to be used as the ferroelectric component of multiferroic composites. Polyvinylidene fluoride was doped with DIPAB at varying ratios to study the improvement in the ferroelectric properties of the composite structure in comparison to just PVDF with low dielectric constant. Electrospinning of composite polymer solution led to the formation of DIPAB doped PVDF nanofibres. They displayed improved relative dielectric constant and low loss tangent and find use in composite magnetoelectric materials formation. The ease of processability of DIPAB doped PVDF nanofibres aids in incorporating the above studied magnetic materials. The studies proved the worth of as-synthesised magnetic and ferroelectric materials at the nanoscale for the formation of magnetoelectric multiferroic composite nanomaterials. The cobalt ferrite nanoparticles doped in DIPAB-PVDF nanofibres can result in core-sheath ME composite structure. A coating of DIPAB-PVDF composite on the formed Ni0.47Fe0.53 fibres will result to the formation of 1-D magnetoelectric structures.</p>

Investigation of the dielectric fatigue on the example of lead titanate films PbTiO3

The phenomenon of dielectric fatigue of active dielectrics, which consists in a decrease in the residual polarization depending on the number of switching cycles, is researched. A model of the dependence of the residual polarization of ferroelectric materials on the number of switching cycles is proposed. The model is based on piecewise - linear approximation of the results of measurements of the hysteresis loops of thin films PbTiO3 at a temperature T = 470 (°C), the electric field strength E = 100 (kV/cm). The developed model was used in the development of a technique for studying dielectric fatigue, depending on different modes of material switching.