There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.

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Room-temperature ferroelectricity in strained SrTiO3.

Abstract PVDF-based compounds are one of the most promising materials for technological application. In this work, structural and optical techniques have been used to study PVDF-based lead-free ceramic composites, considering the inclusion of the ferroelectric BaTiO3 (BT) and magnetic BaFe12O19 (BHF) and SrFe12O19 (SHF) phases. Results obtained from X-Ray diffraction measurements revealed the formation of the PVDF/ceramic composites with the respective ferroelectric and magnetic phases related to the BT and BHF and SHF ceramics. On the other hand, from the analyses of the Raman and FT-IR spectroscopies, it was possible to confirm the incorporation of the ceramics into the PVDF matrix. It was observed that the β-phase % decreased with the increase of doping content, except for the PVDF/BHF composite, which showed to remains almost constant. The results reveal that the studied hybrid PVDF/ceramic samples could be considered potential candidates for electronic applications.

Synthesis and structural characterization of PVDF-based lead-free ceramic composites

The enhancement of photovoltage and photocurrent of material is fundamentally significant owing to the many interesting phenomena found and the potential applications. However, vast altering of magnitude-orders of photoelectricity has been technologically challenging. Here we report two dielectric materials Li2ZnSiO4 and Li2SiO3 showing high photovoltage and photocurrent tunability. When magnetic field increasing from 0.00015T up to 0.44T,it is found that 3850% of photovoltage tunability and 3841 % of photocurrent tunability in Li2ZnSiO4 , and 132.8% of photovoltage tunability and 132.5% of photocurrent tunability in Li2SiO3. A simple model that considers the effects of spin mixing/interaction and magnetically-tunable charge gradient is used to explain this interaction between magnetic field and the photoelectricity. This result indicates a magnetic approach can be potentially used for energy efficiency.

Giant magnetic pumping of photovoltage and photocurrent using dielectric lossy material

Single crystal fibre growth of magnetoplumbite family of materials and their properties

Laser Heated Pedestal Growth of Lead Magnesium Niobate–Lead Titanate Crystals and Their Characterization

Relaxor ferroelectrics are one of the important classes of self-assembled nanostructure composite materials. Interesting features associated with the nanoregions give rise to the most interesting device related characteristics and unusual properties in these materials. Besides, they possess the largest property coefficients by themselves or when modified with lead titanate (PT). In this report, a detailed temperature dependent study has been carried out on (1-x)PZN-xPT relaxors with compositions x = 0.05 and 0.085 using polarized Raman scattering under optical and E-field variables and inferred the structure-property relations in order to obtain information to characterize the material for matching the application criteria. In addition, phase transitions associated with the relaxors have also been investigated to understand the polarization mechanism(s) for the unpoled and poled specimens.

Ruyan Guo

Papers

Synthesis and structural characterization of PVDF-based lead-free ceramic composites

Giant magnetic pumping of photovoltage and photocurrent using dielectric lossy material

Single crystal fibre growth of magnetoplumbite family of materials and their properties

Laser Heated Pedestal Growth of Lead Magnesium Niobate–Lead Titanate Crystals and Their Characterization

Micro-Raman Study of Self-Assembled Nanostructures: (1−x)PZN:xPT Solid Solution