Xiangli Zhong

Cubic and hexagonal structures of diamond nanocrystals formed upon pulsed laser induced liquid–solid interfacial reaction

Abstract Diamond nanocrystals with cubic and hexagonal structures have been prepared by pulsed laser induced liquid–solid (acetone1–graphite) interfacial reaction (PLIIR) at normal temperature and pressure. The structure and morphology of the resulted diamond nanocrystals were characterized by transmission electron microscopy (TEM). The Raman spectroscopy analysis of the obtained diamond nanocrystals showed that three diamond Raman lines, i.e., 1307, 1100, and 623 cm −1 were observed. Interestingly, the Raman line at 1100 cm −1 was identified to be original from nano-diamond. In addition, a new Raman line at 926 cm −1 due to diamond was observed in the Raman spectra (RS).

Sizable electrocaloric effect in a wide temperature range tuned by tensile misfit strain in BaTiO3 thin films

The effects of misfit strain on the electrocaloric (EC) properties of BaTiO3 thin films arestudied by using the Landau-Devonshire thermodynamic theory. The “misfit-strain temperature” phase diagrams for different electric fields are constructed. It was found that the EC effect of a BaTiO3 thin film is strongly dependent on misfit strain. More interestingly, we found that BaTiO3 thin films with tensile misfit strain exhibit a sizable EC effect in a wider temperature range in comparison with those with compressive misfit strain.

Explosion Phase Formation of Nanocrystalline Boron Nitrides Upon Pulsed-Laser-Induced Liquid/Solid Interfacial Reaction

Boron nitride (BN) nanocrystals with explosion (E) phase were prepared by a novel laser-assisted materials fabrication, i.e., pulsed-laser-induced liquid (acetone)/solid (hexagonal boron nitride bulk) interfacial reaction at normal temperature and pressure. Typical diameters of these synthesized quasi-spherical BN nanocrystals were in the range of 30 to 80 nm. Transmission electron microscopy, x-ray diffraction, and Fourier transformed infrared spectroscopy were used to identify the morphologies and structures of the synthesized nanocrystals. Additionally, we proposed the formation mechanism of cubic-BN and E-BN nanocrystals upon pulsed-laser-induced liquid/solid interfacial reaction, in which both liquid and solid were simultaneously involved.

Shape-controlled hydrothermal synthesis of ferroelectric Bi4Ti3O12 nanostructures

Single-crystalline Bi4Ti3O12 (BIT) nanostructures with various morphologies including nanoplates, lamellae, nanobelts and nanorods have been controllably synthesized by a facile hydrothermal process. The structure and morphology characterizations of BIT were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The type of mineralizer and concentration play an important role on the structure and morphology of BIT products. A possible growth mechanism has been proposed by time-dependent experiments. In addition, UV-Vis absorption spectra have shown that the as-synthesized BIT samples have a slightly red-shift behavior. The piezoelectricity of BIT nanoplates and lamellae are confirmed by piezoresponse force microscopy. Local piezoresponse force measurements display a typical butterfly curve, indicating good ferroelectric property of the BIT nanoplates and lamellae.

Organic–Inorganic Copper(II)-Based Material: A Low-Toxic, Highly Stable Light Absorber for Photovoltaic Application

Lead halide perovskite solar cells have recently emerged as a very promising photovoltaic technology due to their excellent power conversion efficiencies; however, the toxicity of lead and the poor stability of perovskite materials remain two main challenges that need to be addressed. Here, for the first time, we report a lead-free, highly stable C6H4NH2CuBr2I compound. The C6H4NH2CuBr2I films exhibit extraordinary hydrophobic behavior with a contact angle of ∼90°, and their X-ray diffraction patterns remain unchanged even after 4 h of water immersion. UV/vis absorption spectrum shows that C6H4NH2CuBr2I compound has an excellent optical absorption over the entire visible spectrum. We applied this copper-based light absorber in printable mesoscopic solar cell for the initial trial and achieved a power conversion efficiency of ∼0.5%. Our study represents an alternative pathway to develop low-toxic and highly stable organic-inorganic hybrid materials for photovoltaic application.

Strain effects on formation and migration energies of oxygen vacancy in perovskite ferroelectrics: A first-principles study

Oxygen vacancies (VO) and their migration and redistribution are believed to be the dominant factors resulting in the degradation of ferroelectrics. Thus, suppressing the formation and mobility of VO is quite crucial for the physical properties of ferroelectric materials. In this paper, the ab-biaxial strain effects on VO and their migration process in prototype perovskite ferroelectric BaTiO3 were studied by first principles total energy calculation. It is found that the formation energies for the two symmetrically inequivalent VO are enhanced under compressive strain. VO migration path between Vc (VO is located along the c-axis) and Vab (VO is located in the ab-plane) shows an “S” shape. The VO migration barrier between Vc and Vab is enhanced by the compressive strain while lowered by the tensile strain. These results suggest that the ferroelectricity degradation induced by VO and their migration can be effectively mitigated by applying compressive strain.

A ferroelectric tunnel junction based on the piezoelectric effect for non-volatile nanoferroelectric devices

A ferroelectric tunnel junction based on the piezoelectric effect mechanism, which not only overcomes the drawbacks concerning retention time and polarization switching in the ferroelectric tunnel junction based on the electrostatic effect, but also suggests a new design concept for compact ferroelectric tunnel junction solid-state memories for next-generation information technology devices.

Enhanced room temperature electrocaloric effect in barium titanate thin films with diffuse phase transition

Diffuse phase transition was found in barium titanate (BT) thin films with a thickness of 300 nm prepared by a sol–gel method. The electrocaloric effect of these BT thin films was also investigated under a sweep electrical field of 216.7 kV cm−1. Interestingly, it was found that the electrocaloric temperature change (ΔT) increased with a decrease in temperature when the temperature was below 310 K. The novel electrocaloric phenomenon observed in BT thin films with a diffuse phase transition is significant in studying the room temperature electrocaloric effect, which is promising in the refrigeration industry.

A ferroelectric memristor based on the migration of oxygen vacancies

Ferroelectric resistive switching memory is a non-destructive and easy to achieve multilevel storage, which is a breakthrough for further improving the density in the random access memory. However, the application of ferroelectric resistive switching memory is limited by the high operating voltage, the low switching ratio or slow write/read speed. Herein, we show a type of memristor with a thin ferroelectric film, the device can switch its resistance states by controlling the oxygen vacancy migration in the effect of an external electric field. The device still exhibits stable resistive switching phenomena after an endurance test of about 100 cycles and has high switch ratio about 108% and good retention about 1.7 × 105 s. Furthermore, the device has the potential of being a multi-states memory with a low write voltage below 2 V and a fast write/read speed of about 5 μs. Our results suggest new opportunities for the development of high storage density nonvolatile memory.

Enhancing the electrocaloric effect of PbZr0.4Ti0.6O3/PbTiO3 superlattices via composition tuning

A thermodynamic model is developed to investigate the electrocaloric effect (ECE) of the PbZr0.4Ti0.6O3/PbTiO3 ferroelectric superlattices. The ECE of a superlattice consisting of ferroelectric layers A and B with thickness hA and hB is calculated as a function of the thickness fraction βA=hA/(hA+hB). An ECE anomaly could be found at the specific composition. In particular, we found that a maximum adiabatic temperature change (ΔT=5.3 K) appears for the critical thickness of PbTiO3. This large ECE is attributed to the large change in spontaneous polarization associated with the phase transform, caused by the misfit strain between the ferroelectric sublayers.