Xuanhu Chen

Bio: Xuanhu Chen is an academic researcher from Nanjing University. The author has contributed to research in topics: Pulsed laser deposition & Thin film. The author has an hindex of 14, co-authored 51 publications receiving 1698 citations.

Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

Abstract: Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.

Review of gallium-oxide-based solar-blind ultraviolet photodetectors

Abstract: Solar-blind photodetectors are of great interest to a wide range of industrial, civil, environmental, and biological applications. As one of the emerging ultrawide-bandgap semiconductors, gallium oxide (Ga2O3) exhibits unique advantages over other wide-bandgap semiconductors, especially in developing high-performance solar-blind photodetectors. This paper comprehensively reviews the latest progresses of solar-blind photodetectors based on Ga2O3 materials in various forms of bulk single crystal, epitaxial films, nanostructures, and their ternary alloys. The basic working principles of photodetectors and the fundamental properties and synthesis of Ga2O3, as well as device processing developments, have been briefly summarized. A special focus is to address the physical mechanism for commonly observed huge photoconductive gains. Benefitting from the rapid development in material epitaxy and device processes, Ga2O3-based solar-blind detectors represent to date one of the most prospective solutions for UV detection technology towards versatile applications.

Solar-blind Photodetector with High Avalanche Gains and Bias-tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures

Abstract: The metastable α-phase Ga2O3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga2O3 remains challenging. To this end, single crystalline α-Ga2O3 epilayers are achieved on nonpolar ZnO (1120) substrates for the first time and a high performance Au/α-Ga2O3/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 103 and a detectivity of 9.66 × 1012 cm Hz1/2 W–1. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W–1 at −5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga2O3 and Ga2O3/ZnO heterointerfaces. The device also allows avalanche multiplication processes in...

Low-field magnetoresistance in nanosized La0.7Sr0.3MnO3/Pr0.5Sr0.5MnO3 composites

Abstract: Nanosized La07Sr03MnO3/Pr05Sr05MnO3 (LSMO1−xPSMOx) ceramic composites are prepared using solid-sate sintering Their microstructural, electro- and magnetotransport properties are characterized by means of various techniques It is found that the antiferromagnetic/ferromagnetic coupling between PSMO/LSMO at low temperature and the weak ferromagnetic order of PSMO at high temperature results in enhanced low-field magnetoresistance (LFMR) of the composites With increasing temperature up to 250 K the observed LFMR decays more slowly than that for pure LSMO and this behavior may be explained by the spin coupling near boundaries between LSMO and PSMO grains

Multiferroicity: the coupling between magnetic and polarization orders

Abstract: Multiferroics, defined for those multifunctional materials in which two or more kinds of fundamental ferroicities coexist, have become one of the hottest topics of condensed matter physics and materials science in recent years. The coexistence of several order parameters in multiferroics brings out novel physical phenomena and offers possibilities for new device functions. The revival of research activities on multiferroics is evidenced by some novel discoveries and concepts, both experimentally and theoretically. In this review, we outline some of the progressive milestones in this stimulating field, especially for those single-phase multiferroics where magnetism and ferroelectricity coexist. First, we highlight the physical concepts of multiferroicity and the current challenges to integrate the magnetism and ferroelectricity into a single-phase system. Subsequently, we summarize various strategies used to combine the two types of order. Special attention is paid to three novel mechanisms for multiferroicity generation: (1) the ferroelectricity induced by the spin orders such as spiral and E-phase antiferromagnetic spin orders, which break the spatial inversion symmetry; (2) the ferroelectricity originating from the charge-ordered states; and (3) the ferrotoroidic system. Then, we address the elementary excitations such as electromagnons, and the application potentials of multiferroics. Finally, open questions and future research opportunities are proposed.

First-principles study of spontaneous polarization in multiferroic Bi Fe O 3

Abstract: The ground-state structural and electronic properties of ferroelectric $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ are calculated using density functional theory within the local spin-density approximation (LSDA) and the $\mathrm{LSDA}+U$ method. The crystal structure is computed to be rhombohedral with space group $R3c$, and the electronic structure is found to be insulating and antiferromagnetic, both in excellent agreement with available experiments. A large ferroelectric polarization of $90--100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{C}∕{\mathrm{cm}}^{2}$ is predicted, consistent with the large atomic displacements in the ferroelectric phase and with recent experimental reports, but differing by an order of magnitude from early experiments. One possible explanation is that the latter may have suffered from large leakage currents. However, both past and contemporary measurements are shown to be consistent with the modern theory of polarization, suggesting that the range of reported polarizations may instead correspond to distinct switching paths in structural space. Modern measurements on well-characterized bulk samples are required to confirm this interpretation.

Greatly reduced leakage current and conduction mechanism in aliovalent-ion-doped BiFeO3

Abstract: Transport properties of aliovalent-ion-doped BiFeO3 (BFO) thin films have been studied in order to identify the cause of high leakage currents Doping of 2at% Ti4+ ions increased the dc resistivity by more than three orders of magnitude In contrast, doping of 2+ ions such as Ni2+ reduced the dc resistivity by two orders of magnitude Current–voltage (I–V) characteristics indicated that the main conduction mechanism for pure and Ni2+ doped BFO was space charge limited, which was associated with the free-carriers trapped by the oxygen vacancies, whereas in the Ti4+ doped BFO, field-assisted ionic conduction was dominant

Visible-Light Photocatalytic Properties of Weak Magnetic BiFeO3 Nanoparticles

Abstract: Polycrystalline BiFeO3 nanoparticles (size 80-120 nm) are prepared by a simple sol-gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 mu(B)/Fe at room temperature, in good agreement with theoretical calculations.