The improvement of ferromagnetic properties is critical for the practical application of multiferroic materials, to be exact, BiFeO3 (BFO). Herein, we have investigated the evolution in the structure and morphology of Ho or/and Mn-doped thin films and the related diversification in ferromagnetic behavior. BFO, Bi0.95Ho0.05FeO3 (BHFO), BiFe0.95Mn0.05O3 (BFMO) and Bi0.95Ho0.05Fe0.95Mn0.05O3 (BHFMO) thin films are synthesized via the conventional sol-gel method. Density, size and phase structure are crucial to optimize the ferromagnetic properties. Specifically, under the applied magnetic field of 10 kOe, BHFO and BFMO thin films can produce obvious magnetic properties during magnetization and, additionally, doping with Ho and Mn (BHFMO) can achieve better magnetic properties. This enhancement is attributed to the lattice distortions caused by the ionic sizes difference between the doping agent and the host, the generation of the new exchange interactions and the inhibition of the antiferromagnetic spiral modulated spin structure. This study provides key insights of understanding the tunable ferromagnetic properties of co-doped BFO.

https://www.mdpi.com/2079-4991/8/9/711/pdf

Enhanced Magnetic Properties of BiFeO3 Thin Films by Doping: Analysis of Structure and Morphology

Enhanced piezoelectric properties of 0.7BiFeO3-0.3BaTiO3 lead-free piezoceramics with high Curie temperature by optimizing Bi self-compensation

Electrospinning preparation of Sn4+-doped BiFeO3 nanofibers as efficient visible-light-driven photocatalyst for O2 evolution

Recently the solar energy, an inevitable part of green energy source, has become a mandatory topics in frontier research areas. In this respect, non-centrosymmetric ferroelectric perovskites with open circuit voltage (VOC) higher than the bandgap, gain tremendous importance as next generation photovoltaic materials. Here a non-toxic co-doped Ba1−x(Bi0.5Li0.5)
 x
 TiO3 ferroelectric system is designed where the dopants influence the band topology in order to enhance the photovoltaic effect. In particular, at the optimal doping concentration (x
 opt
  ~ 0.125) the sample reveals a remarkably high photogenerated field EOC = 320 V/cm (VOC = 16 V), highest ever reported in any bulk polycrystalline non-centrosymmetric systems. The band structure, examined through DFT calculations, suggests that the shift current mechanism is key to explain the large enhancement in photovoltaic effect in this family.

/pdf/giant-photovoltaic-response-in-band-engineered-ferroelectric-1sesrvplpt.pdf

Giant photovoltaic response in band engineered ferroelectric perovskite

Here, we have successfully designed a photonic crystal structure to improve the light absorption by increasing the optical path length of the incident light inside the absorbing material to enhance the efficiency of a thin film silicon solar cell. The current design is based on the high temperature superconducting-dielectric photonic crystals (HTcSD PCs). We have substituted the indium tin oxide as a front contact and antireflection coating in the conventional cell by HTcScD PCs. Also, we have substituted the back contact and the back reflector of the conventional cell construction by HTcScD PCs. The aim of these substitutions is to reduce the power dissipation in a thin film silicon solar cell. Numerical results of the proposed structure are obtained based on the transfer matrix method, the finite element method, and COMSOL Multiphysics software. The HTcScD PCs reduced the power dissipation in the thin film silicon solar cell due to the increase of the optical generation term of electron–hole pairs. Finally, using high temperature superconducting photonic crystals in photovoltaic applications is promising and may be of potential use in the future.

Enhancement of the solar cell based on nanophotonic crystals

Crystal structure refinement, ferroelectric and ferromagnetic properties of Ho3+ modified BiFeO3 multiferroic material

We report remarkable photovoltaic effect in YBa2Cu3O6.96 (YBCO) ceramic between 50 and 300 K induced by blue-laser illumination, which is directly related to the superconductivity of YBCO and the YBCO-metallic electrode interface. There is a polarity reversal for the open circuit voltage Voc and short circuit current Isc when YBCO undergoes a transition from superconducting to resistive state. We show that there exists an electrical potential across the superconductor-normal metal interface, which provides the separation force for the photo-induced electron-hole pairs. This interface potential directs from YBCO to the metal electrode when YBCO is superconducting and switches to the opposite direction when YBCO becomes nonsuperconducting. The origin of the potential may be readily associated with the proximity effect at metal-superconductor interface when YBCO is superconducting and its value is estimated to be ~10–8 mV at 50 K with a laser intensity of 502 mW/cm2. Combination of a p-type material YBCO at normal state with an n-type material Ag-paste forms a quasi-pn junction which is responsible for the photovoltaic behavior of YBCO ceramics at high temperatures. Our findings may pave the way to new applications of photon-electronic devices and shed further light on the proximity effect at the superconductor-metal interface.

/pdf/origin-of-photovoltaic-effect-in-superconducting-yba2cu3o6-3eqcb4g393.pdf

Origin of photovoltaic effect in superconducting YBa2Cu3O6.96 ceramics

Crystal structural, dielectrical properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x=0–0.3)

We investigate the room temperature microstructure and high temperature magnetic properties of Ca2+-substituted Bi1–xCaxFeO3 (0 ≤ x ≤ 0.2) ceramics. The Bi1–xCaxFeO3 compound transforms from rhombohedral into tetragonal structure with the phase boundary lying around x = 0.1. Based on this, the magnetic modulation becomes significant and the strongest remnant magnetization Mr is obtained at x = 0.1 compound. An important observation is the ferromagnetic-like phase transition revealed at TFM = 878 K in pure BiFeO3. The TFM of Bi1–xCaxFeO3 varies with Ca concentration and is close to the TAFM when x = 0.1. The convergence between TFM and TAFM implies the severe competition between Fe3+−O2−−Fe3+ and unbalanced Fe3+−O2−−Fe2+ antiferromagnetic exchange interactions, which leads to the dramatic change around TAFM in the M-T curve of x = 0.1 compound. The structure-related modulation of magnetic structure and complex interaction between Fe3+ and Fe2+ may be the driving force for the excellent magnetic properties ...

High temperature magnetic behavior of multiferroics Bi1–xCaxFeO3

I-V characteristics of YBCO-Ag system under blue laser (λ = 450 nm) illumination were studied from 100 to 300 K and obvious photovoltaic effects were observed. All the I-V curves in the temperature range intersect at a point in the first quadrant while the laser points to the cathode electrode, indicating a zero temperature coefficient of resistivity. This implies that the outputting voltage keeps constant in a broad temperature range when a critical bias current is assigned. The intersection points of different laser intensities fall in a straight line, the slope of which (Rc) is independent of temperature and laser intensity.

F.G. Chang

Papers

Crystal structure refinement, ferroelectric and ferromagnetic properties of Ho3+ modified BiFeO3 multiferroic material

Origin of photovoltaic effect in superconducting YBa2Cu3O6.96 ceramics

Crystal structural, dielectrical properties and high temperature magnetic phase transition of Sm1-xCaxFeO3 (x=0–0.3)

High temperature magnetic behavior of multiferroics Bi1–xCaxFeO3

Zero temperature coefficient of resistivity induced by photovoltaic effect in Y Ba2Cu3O6.96 ceramics