Catálogo de publicaciones - revistas

<jats:p>The magnetocaloric effect of Mn, Ni, and Mn–Ni-doped EuTiO<jats:sub>3</jats:sub> compounds are studied in the near-liquid-helium-temperature range. The Eu(Ti<jats:sub>0.9375</jats:sub>Mn<jats:sub>0.0625</jats:sub>)O<jats:sub>3</jats:sub>, Eu(Ti<jats:sub>0.975</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub>, and Eu(Ti<jats:sub>0.9125</jats:sub>Mn<jats:sub>0.0625</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub> are prepared by the sol–gel method. The Eu(Ti<jats:sub>0.9375</jats:sub>Mn<jats:sub>0.0625</jats:sub>)O<jats:sub>3</jats:sub> and Eu(Ti<jats:sub>0.9125</jats:sub>Mn<jats:sub>0.0625</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub> exhibit ferromagnetism with second-order phase transition, and the Eu(Ti<jats:sub>0.975</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub> displays antiferromagnetic behavior. Under the magnetic field change of 10 kOe (1 Oe = 79.5775 A⋅m<jats:sup>−1</jats:sup>), the values of magnetic entropy change are 8.8 J⋅kg<jats:sup>−1</jats:sup>⋅K<jats:sup>−1</jats:sup>, 12 J⋅kg<jats:sup>−1</jats:sup>⋅K<jats:sup>−1</jats:sup>, and 10.9 J⋅kg<jats:sup>−1</jats:sup>⋅K<jats:sup>−1</jats:sup> for Eu(Ti<jats:sub>0.9375</jats:sub>Mn<jats:sub>0.0625</jats:sub>)O<jats:sub>3</jats:sub>, Eu(Ti<jats:sub>0.975</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub>, and Eu(Ti<jats:sub>0.9125</jats:sub>Mn<jats:sub>0.0625</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub>, respectively. The co-substitution of Mn and Ni can not only improve the magnetic entropy change, but also widen the refrigeration temperature window, which greatly enhances the magnetic refrigeration capacity. Under the magnetic field change of 10 kOe, the refrigerant capacity value of Eu(Ti<jats:sub>0.9125</jats:sub>Mn<jats:sub>0.0625</jats:sub>Ni<jats:sub>0.025</jats:sub>)O<jats:sub>3</jats:sub> is 62.6 J⋅kg<jats:sup>−1</jats:sup> more than twice that of EuTiO<jats:sub>3</jats:sub> (27 J⋅kg<jats:sup>−1</jats:sup>), indicating that multi-component substitution can lead to better magnetocaloric performance.</jats:p>

<jats:p>The ternary rare-earth aluminum germanide GdAlGe with tetragonal structure is systematically studied by x-ray diffraction, magnetic and electric measurements. The magnetic and electric properties of GdAlGe are strongly related to its special magnetic structure formed by magnetic Gd3 isosceles triangles △s. The GdAlGe orders ferromagnetically at 21 K due to the exchanging interaction of Gd3 △ ↑ – △ ↑ Gd3. The mechanism of magnetic transport originates from the slip scattering induced by Stoner spin fluctuation in the magnetic ordering region and the spin wave scattering induced by the thermal photon excitation and phonon scattering in the paramagnetic region. The positive magnetoresistance is observed in GdAlGe, which might be due to the disordered magnetic scatter induced by magnetic anisotropy in GdAlGe.</jats:p>

<jats:p>A novel p-GaN gate GaN high-electron-mobility transistor (HEMT) with an AlGaN buffer layer and hybrid dielectric zone (H-HEMT) is proposed. The hybrid dielectric zone is located in the buffer and composed of horizontal arranged HfO<jats:sub>2</jats:sub> zone and SiN<jats:sub> <jats:italic>x</jats:italic> </jats:sub> zone. The proposed H-HEMT is numerically simulated and optimized by the Silvaco TCAD tools (ATLAS), and the DC, breakdown, <jats:italic>C</jats:italic>–<jats:italic>V</jats:italic> and switching properties of the proposed device are characterized. The breakdown voltage of the proposed HEMT is significantly improved with the introduction of the hybrid dielectric zone, which can effectively modulate the electric field distribution in the GaN channel and the buffer. High breakdown voltage of 1490 V, low specific on-state resistance of 0.45 mΩ⋅cm<jats:sup>2</jats:sup> and high Baliga’s figure of merit (FOM) of 5.3 GW/cm<jats:sup>2</jats:sup>, small <jats:italic>R</jats:italic> <jats:sub>on</jats:sub> <jats:italic>Q</jats:italic> <jats:sub>oss</jats:sub> of 212 mΩ⋅nC, high turn-on speed 627 V/ns and high turn-off speed 87 V/ns are obtained at the same time with the gate-to-drain distance <jats:italic>L</jats:italic> <jats:sub>gd</jats:sub> of 6 μm.</jats:p>

<jats:p>Iron (Fe) was successfully doped in CuWO<jats:sub>4</jats:sub> photoanode films with a combined liquid-phase spin-coating method via the dopant sources of Fe(NO<jats:sub>3</jats:sub>)<jats:sub>3</jats:sub>, FeSO<jats:sub>4</jats:sub> and FeCl<jats:sub>3</jats:sub>. The microstructure of the prepared films was characterized by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The light absorption and photoelectric conversion properties were evaluated by the UV-visible absorption spectra and monochromatic incident photon-to-electron conversion efficiency. The chemical composition and element combination of the samples were examined by x-ray photoelectron spectroscopy. A linear sweep voltammetric and stability test (<jats:italic>I</jats:italic>–<jats:italic>t</jats:italic>) were performed with an electrochemical workstation. The results show that the samples are uniform with a thickness of approximately 800 nm and that the photoelectrochemical performance of the doped films is heavily dependent on the Fe source and dopant concentration. Upon optimizing the doping conditions of Fe(NO<jats:sub>3</jats:sub>)<jats:sub>3</jats:sub> and the optimal source, the photocurrent density in the Fe-doped CuWO<jats:sub>4</jats:sub> photoanode film is improved by 78% from 0.267 mA/cm<jats:sup>2</jats:sup> to 0.476 mA/cm<jats:sup>2</jats:sup> at 1.23 V vs reversible hydrogen electrode. The underlying causes are discussed.</jats:p>

<jats:p>Photoluminescence (PL) characteristics of the structure consisting of green InGaN/GaN multiple quantum wells (MQWs) and low indium content InGaN/GaN pre-wells are investigated. Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed. The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature. In addition, the differences in the carrier localization effect, defect density, and phonon–exciton interaction between the pre-wells and green InGaN/GaN MQWs, and the internal quantum efficiency of the sample are studied. The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.</jats:p>

<jats:p>Densification is a major feature of silica glass that has received widespread attention. This work investigates the fracture behavior of densified silica glass upon uniaxial tension based on atomistic simulations. It is shown that the tensile strength of the silica glass approximately experiences a parabolic reduction with the initial density, while the densified samples show a faster power growth with the increase of strain rate. Meanwhile, the fracture strain and strain energy increase significantly when the densification exceeds a certain threshold, but fracture strain tends to the same value and strain energy becomes closer for different densified samples at extreme high strain rate. Microscopic views indicate that all the cracks are formed by the aggregation of nanoscale voids. The transition from brittleness fracture to ductility fracture can be found with the increase of strain rate, as a few fracture cracks change into a network distribution of many small cracks. Strikingly, for the high densified sample, there appears an evident plastic flow before fracture, which leads to the crack number less than the normal silica glass at the high strain rate. Furthermore, the coordinated silicon analysis suggests that high strain rate tension will especially lead to the transition from 4- to 3-fold Si when the high densified sample is in plastic flow.</jats:p>

<jats:p>We observed morphological modification of rod-shaped C<jats:sub>60</jats:sub> solvate crystals using a facile hydrothermal method. The initial C<jats:sub>60</jats:sub> rods were changed from smooth rods to rough rods, porous rods or pieces under different hydrothermal conditions. During the hydrothermal treatment, the initial samples underwent a decomposition-recrystallization process, which can be tuned by the content of alcohol in the hydrothermal solution, thereby leading to modification of the morphological properties of the initial C<jats:sub>60</jats:sub> rods. In addition, the rough and porous C<jats:sub>60</jats:sub> rods prepared in our work exhibit excellent photoluminescence intensities that are approximately 7 and 3 times higher than those of pure C<jats:sub>60</jats:sub> powders, respectively. Our results suggest that the hydrothermal method is a potential route for fabricating fullerene materials with controllable morphologies and novel functions.</jats:p>

<jats:p>We report the effects of MgSiO<jats:sub>3</jats:sub> addition on the crystal growth and characteristics of type-Ib diamonds synthesized in Fe–Ni–C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385 °C–1405 °C, and duration of 23.1 h. As MgSiO<jats:sub>3</jats:sub> increases from 0.0 wt% to 3.0 wt%, the diamond growth temperature increases from 1385 °C to 1405 °C, the addition of MgSiO<jats:sub>3</jats:sub> and the movement of <jats:italic>P</jats:italic>–<jats:italic>T</jats:italic> diagram toward the higher temperature direction result in a series of effects to the Fe–Ni–C system and crystal growth. Firstly, it increases the content of metastable recrystallized graphite and accelerates the competition with the carbon source needed for diamond growth, thus causing the decreased crystal growth rate. Diamond crystals exhibit the combination form of {111}, {100}, {113}, and {110} sectors, the decreased {100} and {113} sectors, dominated {111} sector are all attributed to the higher growth rate in [100] direction caused by the synergy of MgSiO<jats:sub>3</jats:sub> and the movement of <jats:italic>P</jats:italic>–<jats:italic>T</jats:italic> diagram. The higher growth rate in [100] direction also increases the metal catalyst and graphite inclusions and leads to the increase of residual tensile stress on the crystal surface. Accompanying with the high growth rate, a higher dissolution rate along [100] and [113] directions than [111] direction occurs at the microstructure and forms the significantly developed (111) stepped growth layer. In addition to the movement of <jats:italic>P</jats:italic>–<jats:italic>T</jats:italic> diagram, the addition of MgSiO<jats:sub>3</jats:sub> poisons the catalyst and increases the nitrogen content of diamond from 120 ppm to 227 ppm.</jats:p>

<jats:p>Twisted moiré superlattice receives tremendous interests since the discovery of correlated insulating states and superconductivity in magic angle twist bilayer graphene (MA-TBG) [<jats:italic>Nature</jats:italic> <jats:bold>556</jats:bold> 80 (2018), <jats:italic>Nature</jats:italic> <jats:bold>556</jats:bold> 43 (2018)], even gives arise to a new field “twistronics” [<jats:italic>Science</jats:italic> <jats:bold>361</jats:bold> 690 (2018)]. It is a new platform hosting strong electron correlations, providing an alternative for understanding unconventional superconductivity. In this article, we provide a review of recent experimental advances in the twisted moiré superlattice, from MA-TBG to twisted double bilayer graphene and other two-dimensional materials based moiré superlattice, covering correlated insulating states, superconductivity, magnetism, <jats:italic>et al</jats:italic>.</jats:p>

<jats:p>A three-dimensional (3D) multiple phase field model, which takes into account the grain boundary (GB) energy anisotropy caused by texture, is established based on real grain orientations and Read–Shockley model. The model is applied to the grain growth process of polycrystalline Mg (ZK60) alloy to investigate the evolution characteristics in different systems with varying proportions of low-angle grain boundary (LAGB) caused by different texture levels. It is found that the GB energy anisotropy can cause the grain growth kinetics to change, namely, higher texture levels (also means higher LAGB proportion) result in lower kinetics, and <jats:italic>vice versa</jats:italic>. The simulation results also show that the topological characteristics, such as LAGB proportion and distribution of grain size, undergo different evolution characteristics in different systems, and a more serious grain size fluctuation can be caused by a higher texture level. The mechanism is mainly the slower evolution of textured grains in their accumulation area and the faster coarsening rate of non-textured grains. Therefore, weakening the texture level is an effective way for implementing a desired homogenized microstructure in ZK60 Mg alloy. The rules revealed by the simulation results should be of great significance for revealing how the GB anisotropy affects the evolution of polycrystalline during the grain growth after recrystallization and offer the ideas for processing the alloy and optimizing the microstructure.</jats:p>