Yuan Ma

Bio: Yuan Ma is an academic researcher from Northwestern Polytechnical University. The author has contributed to research in topics: Nanorod & Dielectric. The author has an hindex of 4, co-authored 5 publications receiving 333 citations.

Ni-doped ZnO nanorods gas sensor: Enhanced gas-sensing properties, AC and DC electrical behaviors

Abstract: Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150 °C. The morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy. Gas-sensing testing results demonstrated that Ni-doped ZnO nanorods had enhanced gas-sensing performance. Furthermore, AC impedance spectroscopy and DC current–voltage curves were observed to investigate the gas-sensing mechanism. Current–voltage curves are approximately close to a linear function, indicating the potential barriers formed at the electron-depleted surface layer occupy a dominant when carriers transport in the gas sensor, and AC impedance spectra indicates the potential barriers height of the electron-depleted surface layer.

The electrocaloric effect and thermal stability of 0.94(Bi 0.5 Na 0.5 )TiO 3 –0.06BaTiO 3 modified by WO 3

Abstract: The solid-state reaction method is used to prepare the 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 modified by WO3 lead-free ceramic. The unpoled (Bi0.5Na0.5)0.94Ba0.06Ti1−(3/2)x W x O3 with pseudo-cubic structure undergoes transition from ferroelectric to relaxor ferroelectric that happens in the T d. The maximum reversible temperature change |ΔT| = 0.8 K occurs at the room temperature due to the decline of temperature. In addition, |ΔT| = 0.15 K at the (Bi0.5Na0.5)0.94Ba0.06Ti1−(3/2)x W x O3 with x = 0.75 mol% exhibits good thermal stability at the temperature range of 303–413 K.

Superior energy storage properties and excellent stability of novel NaNbO3-based lead-free ceramics with A-site vacancy obtained via a Bi2O3 substitution strategy

Abstract: This study presents an innovative strategy to improve the energy storage properties of NaNbO3 lead-free ceramics by the addition of Bi2O3. The introduction of Bi2O3 can effectively increase the breakdown strength and decrease the remnant polarization of NaNbO3 ceramics. Meanwhile, hybridization between the O2− 2p and Bi3+ 6p orbitals can enhance the polarization. The novel NaNbO3-based (Na0.7Bi0.1NbO3) ceramics demonstrate ultrahigh energy storage efficiency of 85.4% and remarkably high energy storage density (4.03 J cm−3) at 250 kV cm−1 simultaneously, which are superior to the results of almost all recently reported lead-free alternatives. The outstanding stability of energy storage characteristics in terms of frequency (1–1000 Hz), temperature (20–120 °C) and fatigue (cycle number: 105) is also observed in Na0.7Bi0.1NbO3 ceramics. Furthermore, additional pulsed charge–discharge measurements for Na0.7Bi0.1NbO3 ceramics are also carried out to evaluate actual operation performance. The Na0.7Bi0.1NbO3 ceramics exhibit extremely high power density (62.5 MW cm−3) and current density (1250 A cm−2) and release all stored energy rapidly (∼155 ns) under various electric fields and temperatures. These properties qualify these environment-friendly Na0.7Bi0.1NbO3 ceramics as innovative and most promising alternatives for energy storage applications, especially for high power and pulsed power system applications.

Phase transitions in bismuth-modified silver niobate ceramics for high power energy storage

Abstract: Ag(Nb0.8Ta0.2)O3 is used here as a model system to shed light on the nature of the low temperature phase behavior of the unsubstituted parent compound AgNbO3, which is an important material for high-power energy storage applications. The three dielectric anomalies previously identified as M1 ↔ M2, Tf and M2 ↔ M3 transitions in AgNbO3 ceramics are found to be intimately related to the polarization the behavior of the B-site cations. In particular, the M1 ↔ M2 transition is found to involve the disappearance of original ferroelectric polar structure in the M1 phase. Analysis of weak-field and strong field hysteresis loops in the M2 region below Tf suggests the presence of a weakly-polar structure exhibiting antipolar behavior (i.e., a non-compensated antiferroelectric), which can be considered as ferrielectric (FIE). Modeling of the permittivity data using the Curie–Weiss law indicates that the Curie temperature is close to the freezing temperature, Tf, which can be regarded as the Curie point of the FIE phase. Substitution by Ta5+ in this system enhances the stability of the weakly polar/antiferroelectric state, giving rise to an increased energy storage density of 3.7 J cm−3 under an applied field of 27 MV m−1, one of the highest values ever reported for a dielectric ceramic. Furthermore, the energy storage capability remains approximately constant at around 3 J cm−3 up to 100 °C, at an applied field of 22 MV m−1.