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.

/pdf/room-temperature-ferroelectricity-in-strained-srtio3-4u1ustezxf.pdf

Room-temperature ferroelectricity in strained SrTiO3.

This research is focused on piezoelectric energy harvesting at high pressure fields and low frequency applications. Lead Zirconate Titanate (PZT) is the primary piezoelectric evaluated with a focus...

Assessment of PZT (Soft/Hard) Composites for Energy Harvesting

This study presents and discusses the use of a specific methodology combining experimental and theoretical generation of electron density maps in order to investigate the electronic structure of tetragonal BaTiO3. The experimental maps were obtained from Rietveld structural refinement of X-ray powder diffraction data, and the theoretical values were obtained from ab initio calculations using the Density Functional Theory. From the results, an explanation for the origin of room-temperature electrical polarization in tetragonal BaTiO3 is proposed.

Study of the BaTiO3 electronic structure using the maximum entropy method and density functional theory calculations

Disclosed are various embodiments of a terahertz wave modulator The wave modulator can include one or more layers of piezoelectric/ferroelectric single crystal or polycrystalline material The crystalline material can be configured to resonate when a low-energy external excitation is applied An incident terahertz waveform can be dynamically controlled when the incident terahertz waveform interacts with the at least one layer of piezoelectric crystalline material while the at least one layer of piezoelectric crystalline material is resonating The dynamic control of the incident terahertz waveform can be with respect to at least one of a phase shift and an amplitude modulation of the waveform

Piezoelectric resonance controlled terahertz wave modulators

(Ba1-xSrx)TiO3 single crystal fibers with x = 0.35 and 0.40 were grown, using the laser heated pedestal growth (LHPG) technique, in order to investigate the dielectric properties under dc bias for potential tunable capacitor application at room temperature. Temperature dependences of the dielectric constant and loss factor as a function of dc-bias field were measured. At room temperature and 5000V/cm, the changes on the dielectric constant were 45% and 20% for x = 0.35 (Tc≈20°C) and x = 0.40 (Tc≈4°C), respectively. Low dielectric loss (10−3-10−2) around RT, with and without the bias field, were observed for the composition x = 0.40. This composition although, showed distribution of phases generated during the melt growth process and that disturbed, to some extent, the field dependence behavior in the para-electric phase.

Field dependence of dielectric properties of bst single crystals

The dependence of frequency and applied magnetic field in the magnetoelectric effect (ME) of the composites 0.68Pb(Mg1/3Nb2/3)-0.32PbTiO3/CoFe2O4 (PMN-PT/CFO) and 0.68Pb(Mg1/3Nb2/3)-0.32PbTiO3/NiFe2O4 (PMN-PT/NFO) are investigated. The results for PMN-PT/CFO composite, show a hysteretic behavior for the ME coefficient, at low temperatures (5 K), for frequencies higher than 1000 Hz. Contrasting with these results, the ME coefficient for the PMN-PT/NFO shows a well-known peak-peak related with the magnetostriction coefficient. Based on energy levels of stabilization for each ferromagnetic phase, it was possible to explain the ME hysteretic distinct behavior of PMN-PT/CFO, because of the degeneracy in the energy levels, due to the spin-orbit coupling causing changes in the dynamic properties of the magnetoelastic interactions.

https://iopscience.iop.org/article/10.1088/1361-648X/aad151/pdf

Ruyan Guo

Papers

Assessment of PZT (Soft/Hard) Composites for Energy Harvesting

Study of the BaTiO3 electronic structure using the maximum entropy method and density functional theory calculations

Piezoelectric resonance controlled terahertz wave modulators

Field dependence of dielectric properties of bst single crystals

Dynamic magnetization on the low temperature magnetoelectric effect in multiferroic composites