The application of ferroelectric materials (i.e. solids that exhibit spontaneous electric polarisation) in solar cells has a long and controversial history. This includes the first observations of the anomalous photovoltaic effect (APE) and the bulk photovoltaic effect (BPE). The recent successful application of inorganic and hybrid perovskite structured materials (e.g. BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors can be used in conventional photovoltaic architectures. We review developments in this field, with a particular emphasis on the materials known to display the APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical analysis is complemented with first-principles calculation of the underlying electronic structure. In addition to discussing the implications of a ferroelectric absorber layer, and the solid state theory of polarisation (Berry phase analysis), design principles and opportunities for high-efficiency ferroelectric photovoltaics are presented.

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Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited

Thermal stability of ZnO thin films fabricated by pulsed laser deposition

Degradation of acetaminophen in aqueous solution under visible light irradiation by Bi-modified titanate nanomaterials: morphology effect, kinetics and mechanism

In the present study, the potential of microwave irradiation as an innovative energy- efficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration.

https://iopscience.iop.org/article/10.1088/1757-899X/161/1/012068/pdf

Microwave sintering of ceramic materials

In the present study, ferroelectric and piezoelectric nature of La substituted lead zirconate titanate was investigated to decide the optimum La content. (Pb1−xLax)(Zr0.60Ti0.40)O3 (hereinafter PLZT x/60/40) ceramics were synthesized using novel processing approach of high energy ball milling and cold isostatic pressing (CIP). This study deals with two types of hysteresis loops, polarization (P–E) and strain vs. electric field (S–E) loops. Energy density properties, remanent polarization (Pr), coercive field (Ec), piezoelectric charge coefficient (d33), internal macroscopic electric field (Ein), domain switching current (Imax) and strain hysteresis, normalized strain coefficient (Smax/Emax) were also calculated to study the behaviour of PLZT x/60/40 ferroelectrics. In addition, current vs. electric field (I–E) curves were traced not only to support P–E studies and determination of the Ec but also to confirm the ferroelectricity and domain switching characteristics studies. The PLZT 8/60/40 electro-ceramics not only show the highest Pr ~ 29.1 μC/cm2, Imax ~ 2 mA, unipolar strain ~ 0.25% and average d33 ~ 632 pm/V but also the lowest Ec ~ 9.4 kV/cm and strain hysteresis loss ~ 4%.

Composition dependent ferro-piezo hysteresis loops and energy density properties of mechanically activated (Pb 1−x La x )(Zr 0.60 Ti 0.40 )O 3 ceramics

Fine powders of lanthanum modified (Pb 0.92 La 0.08 )(Zr 0.60 Ti 0.40 )O 3 (PLZT 8/60/40) were processed by high energy mechanical ball milling. The ceramic pellets from these powders were sintered by using microwave sintering. Microwave processed ceramics were further investigated for their sintering behaviour, microstructure, dielectric and piezoelectric properties. The XRD pattern of PLZT shows a single phase formation except for the ceramics sintered at 1200 °C. Higher density and more uniform grain distribution were found for PLZT ceramics, microwave sintered at 1150 °C, in spite of having much shorter sintering time. As a result, comparable dielectric and piezoelectric properties were obtained for microwave sinterd PLZT ceramics. These show the grain size ∼1.2 μm, and the highest relative density ∼99.46%. The dielectric constant for the unpoled PLZT ceramics was found to be ∼2100. The piezoelectric charge (d 33 ) and electromechanical coupling coefficient (k p ) value for the PLZT ceramics were found to be, ∼574 pC/N and ∼67% respectively.

Microwave sintering of fine grained PLZT 8/60/40 ceramics prepared via high energy mechanical milling

Thin films of CaBi4Ti4O15 (CBTi) were deposited at different substrate temperatures (550–700 °C) using pulsed laser ablation technique. Structural, morphological and linear optical properties of the same were investigated. The CBTi thin films crystallize above 550 °C and forms single phase is confirmed by XRD and Raman spectroscopy. The lattice strain induced during deposition, controls the unit cell volume, grain size and crystallite size. The refractive index, real and imaginary parts of optical dielectric constant and optical band gap were extracted from transmission spectra (190–2500 nm). Tauc’s plot confirmed the direct band gap nature ranging from 3.4 to 3.6 eV. The study on CBTi thin films and their optical properties opens up a new window for optical applications.

Effect of substrate temperature on the optical properties of CaBi 4 Ti 4 O 15 thin films deposited by pulsed laser ablation

We have investigated the optical and microwave dielectric properties of lead-free perovskite ferroelectric Na0.5Bi0.5TiO3 (NBT) thin films deposited on fused silica substrate using pulsed laser deposition at different substrate temperatures. The refractive index over a wide range of wavelength fits well with the single effective oscillator model. The XRD pattern shows polycrystalline nature with very small crystallite size. Dielectric properties of materials in microwave frequency range are measured by a resonant method. High transmittance shown by the NBT thin films along with their superior optical characteristics makes NBT a promising candidate for various photonic and microwave device applications.

Optical properties of sodium bismuth titanate thin films

In this study, (Pb0.92La0.08) (Zr0.60Ti0.40) O3 (PLZT 8/60/40) ceramics were synthesized using a high-energy ball-milling technique followed by microwave sintering at different temperatures from 900 °C to 1200 °C. The optimal microwave sintering temperature for the PLZT 8/60/40 ceramics was found to be 1150 °C, which is relatively low compared with conventional sintering temperature. The sintered ceramics show the pure perovskite phase, uniform grain microstructure (1.2 µm) and high density (~99.5%). The polarization vs. electric field (P-E) hysteresis curves were used to investigate the ferroelectric and energy storage properties. The switching characteristic in P-E loops and occurrence of domain switching current in current vs. electric field (I-E) loops confirms their ferroelectric nature. The PLZT ceramics, which were sintered at 1150 °C, show the highest remnant polarization (Pr) of ~32.18 μC/cm2 and domain switching current (Imax) of ~0.91 mA with a low coercive field (Ec) of ~10.17 kV/cm. The bipolar and unipolar strain vs. electric field (S-E) hysteresis loops were also measured and the highest unipolar strain was found to be ~0.26% for the PLZT ceramics sintered at 1150 °C. The unipolar S-E curves were used to derive the piezoelectric coefficient (d33~495 pm/V) and a strain hysteresis loss (~5.8%).

https://www.mdpi.com/1996-1073/13/23/6457/pdf

Investigation of the Effects of Reduced Sintering Temperature on Dielectric, Ferroelectric and Energy Storage Properties of Microwave-Sintered PLZT 8/60/40 Ceramics

Sivanagi Reddy Emani

Papers

Microwave sintering of fine grained PLZT 8/60/40 ceramics prepared via high energy mechanical milling

Effect of substrate temperature on the optical properties of CaBi 4 Ti 4 O 15 thin films deposited by pulsed laser ablation

Optical properties of sodium bismuth titanate thin films

Investigation of the Effects of Reduced Sintering Temperature on Dielectric, Ferroelectric and Energy Storage Properties of Microwave-Sintered PLZT 8/60/40 Ceramics

Effect of oxygen partial pressure on structural and optical properties of pulsed laser deposited CaBi4Ti4O15 thin films