Yiting Liu

Bio: Yiting Liu is an academic researcher from Shenyang University of Technology. The author has contributed to research in topics: Materials science & Ultimate tensile strength. The author has an hindex of 1, co-authored 1 publications receiving 16 citations.

Ambient Drying Route to Aramid Nanofiber Aerogels with High Mechanical Properties for Low-k Dielectrics

Abstract: Polymeric aerogels with low dielectric constant (low-k) are an important material solution for applications in high-frequency terminal electronic devices. However, most aerogels are prepared using high-cost supercritical drying or freeze-drying methods and typically exhibit poor mechanical properties and low thermal stability, which limits their use in practical applications. Here, we report the fabrication of aerogels with layered structure and hierarchical nanopores based on aramid nanofibers (ANFs), using a vacuum-assisted filtration method followed by low-cost ambient drying. The porosity of the ANF aerogels can be controlled from 38 to 79% by rationally selecting solvents with different surface tension for solvent exchange, tuning the affinity between solvents and ANF skeletons as well as controlling the solvent evaporation rate during the ambient drying process. The ANF aerogels have an ultralow and tunable dielectric constant as low as 1.56 while exhibiting a low dielectric loss between 0.0040 to 0.0055 at 1 MHz. The advantageous low-k property can be preserved at high temperatures up to 300 °C, and an inherent flame retardancy is achieved due to the rigid and all-aromatic backbone structure of poly(p-phenylene terephthalamide). Moreover, the nanoporous ANF layers with relatively lower porosity compared with the overall porosity of the aerogel provide strong mechanical strength and modulus, while the presence of larger nanopores from the interspacing of ANF layers ensures a high porosity for the entire aerogel, which endows the aerogel film with superior tensile strength and modulus compared with their conventional counterparts containing homogeneous porous structures. Collectively, these ANF aerogels exhibit low-k, outstanding mechanical properties, high thermal stability, and inherent flame retardancy, enabling them to become very promising next-generation dielectric materials.

Thickness-dependent, tunable anomalous Hall effect in hydrogen-reduced PdCoO$_2$ thin films

Abstract: It was recently reported that hydrogen-reduced PdCoO$_2$ films exhibit strong perpendicular magnetic anisotropy (PMA) with sign tunable anomalous Hall effect (AHE). Here, we provide extensive thickness-dependent study of this system, and show that the electronic and magnetic properties are strongly dependent on the thickness and annealing conditions. Below a critical thickness of 25 nm, AHE shows clear PMA with hysteresis, and its sign changes from positive to negative, and back to positive as the annealing temperature increases from 100 $^\circ$C to 400 $^\circ$C. Beyond the critical thickness, both PMA and AHE hysteresis disappear and the AHE sign remains positive regardless of the annealing parameters. Our results show that PMA may have a large role on AHE sign-tunability and that below the critical thickness, competition between different AHE mechanisms drives this sign change.

First-principles investigation of structural stability, electronic and optical properties of suboxide (Zr3O)

Abstract: Zirconium oxides (Zr-O) has been widely used in energy storage system, catalyst, microelectronic, optoelectronics, and high-temperature ceramics etc. Unfortunately, the ground state structure, electronic and optical properties of Zr3O are unclear until now. Here, we apply the first-principles calculations to study the structure, electronic and optical properties of Zr3O. Three Zr3O oxides: rhombohedral (R32), rhombohedral (R-3c) and hexagonal (P6322) phase are studied. The results show that three Zr3O oxides are thermodynamic and dynamical stabilities. The calculated phonon density of state (PhDOS) further demonstrates the stable of Zr3O oxides. In particular, it is found that the rhombohedral (R-3c) Zr3O is slightly more stable than the other two Zr3O oxides. Unlike ZrO2, the Zr3O oxides exhibit better electronic properties due to the electronic jump between Zr- excitation band and Zr- conduction band near the Fermi level. Compared to the hexagonal Zr3O, the host peak of the rhombohedral Zr3O move into the low energy region, which leads to the red shift phenomenon occurs. In addition, it is found that the rhombohedral (R32, No.155) Zr3O oxide has better storage optical properties compared to the other two Zr3O oxides.

The vacancy defects and oxygen atoms occupation effects on mechanical and electronic properties of Mo5Si3 silicides

Abstract: Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials. By means of first-principles calculations, in this paper, we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo5Si3. Four vacancies (Si–Va1, Si–Va2, Mo–Va1, Mo–Va2) and oxygen occupation models (O–Mo1, O–Mo2, O–Si1, O–Si2) are selected for research. It is found that Mo–Va2 vacancy has the stronger structural stability in the ground state in comparison with other vacancies. Besides, the deformation resistance and hardness of the parent Mo5Si3 are weakened due to the introduction of different vacancy defects and oxygen occupation. The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo5Si3. These vacancies and the oxygen atoms occupation change the localized hybridization between Mo–Si and Mo–Mo atoms. The weaker O–Mo bond is a contributing factor for the excellent ductile behavior in the O-Si2 model for Mo5Si3.

Monte Carlo study of the magnetic properties and magnetocaloric effect of an AFM/FM BiFeO3/Co bilayer

Abstract: The magnetic properties and magnetocaloric effect of an antiferromagnetic/ferromagnetic (AFM/FM) BiFeO3/Co bilayer with mixed-spin (5/2, 3/2) have been studied based on Monte Carlo simulation. The magnetization, susceptibility, and critical temperature are investigated under various exchange couplings and an external magnetic field. In particular, the influence of exchange couplings and an external magnetic field on the magnetic entropy change, adiabatic temperature change, and the relative cooling power (RCP) are studied. The simulation results indicated that the decrease of the exchange coupling and the increase of external magnetic fields can cause an increase of magnetic entropy change, adiabatic temperature change, and RCP. In addition, the hysteresis loops of the system are presented for different exchange couplings and temperatures.