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1.
The smart meta-superconductor MgB2 and Bi(Pb)SrCaCuO increase the superconducting transition temperature (TC), but the changes in the transport critical current density (JC) and Meissner effect are still unknown. Here, we investigated the JC and Meissner effect of smart meta-superconductor MgB2 and Bi(Pb)SrCaCuO. The use of the standard four-probe method shows that Y2O3:Eu3+ and Y2O3:Eu3++Ag inhomogeneous phase significantly increase the JC, and JC decreases to a minimum value at a higher temperature. The Meissner effect was measured by direct current magnetization. The doping of Y2O3:Eu3+ and Y2O3:Eu3++Ag luminescent inhomogeneous phase causes a Meissner effect of MgB2 and Bi(Pb)SrCaCuO at a higher temperature, while the non-luminescent dopant reduces the temperature at which samples have Meissner effect. The introduction of luminescent inhomogeneous phase in conventional MgB2 and copper oxide high-temperature Bi(Pb)SrCaCuO superconductor increases the TC and JC, and Meissner effect is exerted at higher temperature. Therefore, smart meta-superconductivity is suitable for conventional and copper oxide high-temperature superconductors. 相似文献
2.
Magdalena Krupska-Klimczak Przemyslaw Gwizd Irena Jankowska-Sumara Dorota Sitko Piotr Jele 《Materials》2022,15(15)
Ferroelectric ceramics BaTiO3:x%Eu (x = 0, 0.1, 1, 2, 3) were synthesized by a conventional method. Structural investigation confirmed that all ceramics possessed tetragonal (P4mm) symmetries at room temperature for the undoped ceramics as well as for the doped ceramics. Furthermore, a slight downshifting of the Curie temperature (TC) with an increasing Eu3+ doping amount has been noted. The Raman spectra unveiled the existence of new modes for higher-doped BaTiO3:x%Eu (BTEx) which are related to local disorders and defects. The ferroelectric properties were found to depend on both doping and the microstructure. The electrocaloric effect was also studied for those ceramics. It was observed that ΔT decreases with doping; however, the temperature range of its occurrence widens considerably. 相似文献
3.
Joseph Longji Dadiel Sugali Pavan Kumar Naik Pawe Pczkowski Jun Sugiyama Hiraku Ogino Naomichi Sakai Yokoyama Kazuya Tymon Warski Anna Wojcik Tetsuo Oka Masato Murakami 《Materials》2021,14(23)
In this study, high-density magnesium diboride (MgB2) bulk superconductors were synthesized by spark plasma sintering (SPS) under pressure to improve the field dependence of the critical current density (Jc-B) in MgB2 bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and Jc-B using two methods, ex situ (sintering MgB2 synthesized powder) and in situ (reaction sintering of Mg and B powder), respectively. As a result, we found that higher density with suppressed particle growth and suppression of the formation of coarse particles of MgB4 and MgO were found to be effective in improving the Jc-B characteristics. In the ex situ method, the degradation of MgB2 due to pyrolysis was more severe at temperatures higher than 850 °C. The sample that underwent SPS treatment for a short time at 850 °C showed higher density and less impurity phase in the bulk, which improved the Jc-B properties. In addition, the in situ method showed very minimal impurity with a corresponding improvement in density and Jc-B characteristics for the sample optimized at 750 °C. Microstructural characterization and flux pinning (fP) analysis revealed the possibility of refined MgO inclusions and MgB4 phase as new pinning centers, which greatly contributed to the Jc-B properties. The contributions of the sintering conditions on fP for both synthesis methods were analyzed. 相似文献
4.
Jiahao Wu Zhe Wang Bin Li Baoshun Liu Xiujian Zhao Gen Tang Dawen Zeng Shouqin Tian 《Materials》2023,16(1)
VO2-based film, as a very promising thermochromic material for smart windows, has attracted extensive attention but has not been widely applied because it is difficult to simultaneously improve in terms of both solar-modulation efficiency (ΔTsol) and visible transmittance (Tlum) when made using the magnetron-sputtering method, and it has poor durability when made using the wet chemical method. Herein, island-like ZrO2-VO2 composite films with improved thermochromic performance (ΔTsol: 12.6%, Tlum: 45.0%) were created using a simple approach combining a dual magnetron-sputtering and acid-solution procedure. The film’s ΔTsol and Tlum values were increased initially and subsequently declined as the sputtering power of the ZrO2 target was raised from 30 W to 120 W. ΔTsol achieved its maximum of 12.6% at 60 W, and Tlum reached its maximum of 51.1% at 90 W. This is likely the result of the interaction of two opposing effects: Some VO2 nanocrystals in the composite film were isolated by a few ZrO2 grains, and some pores could utilize their surface-plasmon-resonance effect at high temperature to absorb some near-infrared light for an enhanced ΔTsol and Tlum. More ZrO2 grains means fewer VO2 grains in the composite film and increased film thickness, which also results in a decrease in ΔTsol and Tlum. As a result, this work may offer a facile strategy to prepare VO2-based films with high thermochromic performance and promote their application in smart windows. 相似文献
5.
A combustion synthesis method has been developed for synthesis of Eu2+ doped CaAlSiN3 phosphor and its photoluminescence properties were investigated. Ca, Al, Si, and Eu2O3 powders were used as the Ca, Al, Si and Eu sources. The addition of NaN3, NH4Cl and Si3N4 powders was found to increase significantly the product yield. These powders were mixed and pressed into a compact, which was then wrapped up with an igniting agent (i.e., Mg+Fe3O4). The compact was ignited by electrical heating under a N2 pressure of ≤1.0 MPa. Effects of these experimental parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized CaAlSiN3:Eu2+ phosphor absorbs light in the region of 200–600 nm and shows a broad band emission in the region of 500–800 nm due to the 4f65d1 → 4f7 transition of Eu2+. The sample doped with Eu2+ at the optimized molar ratio of 0.04 is efficiently excited by the blue light (460 nm) and generates emission peaking at ~650 nm with peak emission intensity ~106% of a commercially available phosphor, YAG:Ce3+(P46-Y3).The internal quantum efficiency of the synthesized phosphor was measured to be 71%, compared to 69% of the YAG:Ce3+ (P46-Y3). 相似文献
6.
VO2, as a promising material for smart windows, has attracted much attention, and researchers have been continuously striving to optimize the performance of VO2-based materials. Herein, nitrogen-incorporated VO2 (M1) thin films, using a polyvinylpyrrolidone (PVP)-assisted sol–gel method followed by heat treatment in NH3 atmosphere, were synthesized, which exhibited a good solar modulation efficiency (ΔTsol) of 4.99% and modulation efficiency of 37.6% at 2000 nm (ΔT2000 nm), while their visible integrated transmittance (Tlum) ranged from 52.19% to 56.79% after the phase transition. The crystallization, microstructure, and thickness of the film could be regulated by varying PVP concentrations. XPS results showed that, in addition to the NH3 atmosphere-N doped into VO2 lattice, the pyrrolidone-N introduced N-containing groups with N–N, N–O, or N–H bonds into the vicinity of the surface or void of the film in the form of molecular adsorption or atom (N, O, and H) filling. According to the Tauc plot, the estimated bandgap of N-incorporated VO2 thin films related to metal-to-insulator transition (Eg1) was 0.16–0.26 eV, while that associated with the visible transparency (Eg2) was 1.31–1.45 eV. The calculated Eg1 and Eg2 from the first-principles theory were 0.1–0.5 eV and 1.4–1.6 eV, respectively. The Tauc plot estimation and theoretical calculations suggested that the combined effect of N-doping and N-adsorption with the extra atom (H, N, and O) decreased the critical temperature (τc) due to the reduction in Eg1. 相似文献
7.
Xinhong Chu Qiusheng Xie Xiaoming Zhang Bingfeng Guo Jianqing Liao Xiujian Zhao 《Materials》2022,15(9)
In this paper, VO2 thin films with good optical properties are fabricated on practical float glass by magnetron sputtering and a professional annealing method. The near-infrared switching efficiency (NIRSE) of the prepared film reaches 39% (@2000 nm), and its near-infrared energy modulation ability (ΔTir) reaches 10.9% (780–2500 nm). Further, the highest integral visible transmittance Tlum is 63%. The proposed method exhibits good reproducibility and does not cause any heat damage to the magnetron sputtering machine. The crystalline structure of the VO2 film is characterized by X-ray diffraction (XRD). The lattice planes (011) and (−211) grow preferentially (JCPDS 65-2358), and a large number of NaV2O5 crystals are detected simultaneously. The microstructures are characterized by scanning electron microscopy (SEM), and a large number of long sheet crystals are identified. The phase transition temperature is significantly reduced by an appropriate W doping concentration (Tc = 29 °C), whereas excessive W doping causes distortion of the thermal hysteresis loop and a reduction in the NIRSE. Oxygen vacancies are created by low pressure annealing, due to which the phase transition temperature of VO2 film decreases by 8 °C. The addition of an intermediate SiO2 layer can prevent the diffusion of Na+ ions and affect the preparation process of the VO2 thin film. 相似文献
8.
Jae Wook Kim S. Y. Haam Y. S. Oh S. Park S.-W. Cheong P. A. Sharma M. Jaime N. Harrison Jung Hoon Han Gun-Sang Jeon P. Coleman Kee Hoon Kim 《Proceedings of the National Academy of Sciences of the United States of America》2009,106(37):15573-15576
The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a “metaelectric” critical end point, has been rarely studied. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (H) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn2O5, in which the electric polarization (P) switches polarity along with a concomitant Mn spin–flop transition at a critical magnetic field Hc. The simultaneous metaelectric and spin–flop transitions become sharper upon cooling but remain a continuous cross-over even down to 0.5 K. Near the P = 0 line realized at μ0Hc ≈ 18 T below 20 K, the dielectric constant (ɛ) increases significantly over wide field and temperature (T) ranges. Furthermore, a characteristic power-law behavior is found in the P(H) and ɛ(H) curves at T = 0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn2O5 near zero temperature. 相似文献
9.
Magnetic and magnetocaloric properties of the amorphous Fe92−xZr8Bx ribbons were studied in this work. Fully amorphous Fe89Zr8B3, Fe88Zr8B4, and Fe87Zr8B5 ribbons were fabricated. The Curie temperature (Tc), saturation magnetization (Ms), and the maximum entropy change with the variation of a magnetic field (−ΔSmpeak) of the glassy ribbons were significantly improved by the boron addition. The mechanism for the enhanced Tc and −ΔSmpeak by boron addition was studied. 相似文献
10.
P. Ryan Steed Kaitlin A. Kraft Robert H. Fillingame 《Proceedings of the National Academy of Sciences of the United States of America》2014,111(47):16730-16735
H+-transporting F1F0 ATP synthase catalyzes the synthesis of ATP via coupled rotary motors within F0 and F1. H+ transport at the subunit a–c interface in transmembranous F0 drives rotation of a cylindrical c10 oligomer within the membrane, which is coupled to rotation of subunit γ within the α3β3 sector of F1 to mechanically drive ATP synthesis. F1F0 functions in a reversible manner, with ATP hydrolysis driving H+ transport. ATP-driven H+ transport in a select group of cysteine mutants in subunits a and c is inhibited after chelation of Ag+ and/or Cd+2 with the substituted sulfhydryl groups. The H+ transport pathway mapped via these Ag+(Cd+2)-sensitive Cys extends from the transmembrane helices (TMHs) of subunits a and c into cytoplasmic loops connecting the TMHs, suggesting these loop regions could be involved in gating H+ release to the cytoplasm. Here, using select loop-region Cys from the single cytoplasmic loop of subunit c and multiple cytoplasmic loops of subunit a, we show that Cd+2 directly inhibits passive H+ transport mediated by F0 reconstituted in liposomes. Further, in extensions of previous studies, we show that the regions mediating passive H+ transport can be cross-linked to each other. We conclude that the loop-regions in subunits a and c that are implicated in H+ transport likely interact in a single structural domain, which then functions in gating H+ release to the cytoplasm.The F1F0-ATP synthase of oxidative phosphorylation uses the energy of a transmembrane electrochemical gradient of H+ or Na+ to mechanically drive the synthesis of ATP via two coupled rotary motors in the F1 and F0 sectors of the enzyme (1). H+ transport through the transmembrane F0 sector is coupled to ATP synthesis or hydrolysis in the F1 sector at the surface of the membrane. Homologous ATP synthases are found in mitochondria, chloroplasts, and many bacteria. In Escherichia coli and other eubacteria, F1 consists of five subunits in an α3β3γδε stoichiometry. F0 is composed of three subunits in a likely ratio of a1b2c10 in E. coli and Bacillus PS3 (2, 3) or a1b2c11 in the Na+ translocating Ilyobacter tartaricus ATP synthase (1, 4) and may contain as many as 15 c subunits in other bacterial species (5). Subunit c spans the membrane as a hairpin of two α-helices, with the first transmembrane helix (TMH) on the inside and the second TMH on the outside of the c ring (1, 4). The binding of Na+ or H+ occurs at an essential, membrane-embedded Glu or Asp on cTMH2. High-resolution X-ray structures of both Na+- and H+-binding c-rings have revealed the details and variations in the cation binding sites (4–8). In the H+-translocating E. coli enzyme, Asp-61 at the center of cTMH2 is thought to undergo protonation and deprotonation, as each subunit of the c ring moves past the stationary subunit a. In the functioning enzyme, the rotation of the c ring is thought to be driven by H+ transport at the subunit a/c interface. Subunit γ physically binds to the cytoplasmic surface of the c-ring, which results in the coupling of c-ring rotation with rotation of subunit γ within the α3β3 hexamer of F1 to mechanically drive ATP synthesis (1).E. coli subunit a folds in the membrane with five TMHs and is thought to provide aqueous access channels to the H+-binding cAsp-61 residue (9, 10). Interaction of the conserved Arg-210 residue in aTMH4 with cTMH2 is thought to be critical during the deprotonation–protonation cycle of cAsp-61 (1, 11, 12). At this time, very limited biophysical or crystallographic information is available on the 3D arrangement of the TMHs in subunit a. TMHs 2–5 of subunit a pack in a four-helix bundle, which was initially defined by cross-linking (13), but now, such a bundle, packing at the periphery of the c-ring, has been viewed directly by high-resolution cryoelectron microscopy in the I. tartaricus enzyme (14). Previously published cross-linking experiments support the identification of aTMH4 and aTMH5 packing at the periphery of the c-ring and the identification of aTHM2 and aTMH3 as the other components of the four-helix bundle seen in these images (13, 15, 16). More recently, published cross-linking experiments identify the N-terminal α-helices of two b subunits, one of which packs at one surface of aTMH2 with close enough proximity to the c-ring to permit cross-linking (17). The other subunit b N-terminal helix packs on the opposite peripheral surface of aTMH2 in a position where it can also be cross-linked to aTMH3 (17). The last helix density shown in Hakulinen and colleagues (14) packs at the periphery of the c-ring next to aTMH5 and is very likely to be aTMH1.The aqueous accessibility of Cys residues introduced into the five TMHs of subunit a has been probed on the basis of their reactivity with and inhibitory effects of Ag+ and other thiolate-reactive agents (18–20). Two regions of aqueous access were found with distinctly different properties. One region in TMH4, extending from Asn-214 and Arg-210 at the center of the membrane to the cytoplasmic surface, contains Cys substitutions that are sensitive to inhibition by both N-ethylmaleimide (NEM) and Ag+ (18–20; Fig. 1). These NEM- and Ag+-sensitive residues in TMH4 pack at or near the peripheral face and cytoplasmic side of the modeled four-helix bundle (11, 13). A second set of Ag+-sensitive substitutions in subunit a mapped to the opposite face and periplasmic side of aTMH4 (18, 19), and Ag+-sensitive substitutions were also found in TMHs 2, 3, and 5, where they extend from the center of the membrane to the periplasmic surface (19, 20). The Ag+-sensitive substitutions on the periplasmic side of TMHs 2–5 cluster at the interior of the four-helix bundle predicted by cross-linking and could interact to form a continuous aqueous pathway extending from the periplasmic surface to the central region of the lipid bilayer (11, 13, 19, 20). We have proposed that the movement of H+ from the periplasmic half-channel and binding to the single ionized Asp61 in the c-ring is mediated by a swiveling of TMHs at the a–c subunit interface (16, 21–24). This gating is thought to be coupled with ionization of a protonated cAsp61 in the adjacent subunit of the c-ring and with release of the H+ into the cytoplasmic half-channel at the subunit a–c interface. The route of aqueous access to the cytoplasmic side of the c subunit packing at the a–c interface has also been mapped by the chemical probing of Cys substitutions and, more recently, by molecular dynamics simulations (22, 25, 26).Open in a separate windowFig. 1.The predicted topology of subunit a in the E. coli inner membrane. The location of the most Ag+-sensitive Cys substitutions are highlighted in red (>85% inhibition) or orange (66–85% inhibition). The five proposed TMHs are shown in boxes, each with a span of 21 amino acids, which is the minimum length required to span the hydrophobic core of a lipid bilayer. The α-helical segments shown in loops 1–2 and 3–4 are consistent with the predictions of TALOS, based on backbone chemical shifts seen by NMR (29). Others have also predicted extensive α-helical regions in these loops (12, 30), but the possible positions remain largely speculative. aArg210 is highlighted in green. Figure is modified from those shown previously (21, 23, 24, 27).We have also reported Ag+-sensitive Cys substitutions in two cytoplasmic loops of subunit a (27) and, more recently, in the cytoplasmic loop of subunit c (28). The mechanism by which Ag+ inhibited F1F0-mediated H+ transport was uncertain. Several of these substitutions were also sensitive to inhibition by Cd+2, and these substitutions provided a means of testing whether Cd+2 directly inhibits passive H+ transport through F0 (28). In the case of two subunit c loop substitutions, Cd+2 was shown to directly inhibit passive F0-mediated transport activity. In this study, we have extended the survey to Cd+2-sensitive Cys substitutions in cytoplasmic loops of subunit a. We report four loop substitutions in which Cd+2 inhibits passive F0-mediated H+ transport. Further, in two cases, we show cross-linking between pairs of Cys substitutions, which lie in subunits a and c, respectively, and which individually mediate passive H+ transport activity. These results suggest that the a and c loops, which gate H+ release to the cytoplasm, fold into a single domain at the surface of F0. 相似文献
11.
Yixuan He Yuhao Wu Fan Bu Yiyuan Zhang Yifan Zhang Bo Hei Jianbao Zhang Haifeng Wang 《Materials》2022,15(4)
The undercooling (∆T) dependencies of the solidification pathways, microstructural evolution, and recalescence behaviors of undercooled Co-18.5at.%B eutectic alloys were systematically explored. Up to four possible solidification pathways were identified: (1) A lamellar eutectic structure consisting of the FCC–Co and Co3B phase forms, with extremely low ΔT; (2) The FCC–Co phase primarily forms, followed by the eutectic growth of the FCC–Co and Co2B phases when ΔT < 100 K; (3) As the ΔT increases further, the FCC–Co phase primarily forms, followed by the metastable Co23B6 phase with the trace of an FCC–Co and Co23B6 eutectic; (4) When the ΔT increases to 277 K, the FCC–Co phase primarily forms, followed by an FCC–Co and Co3B eutectic, which is similar in composition to the microstructure formed with low ΔT. The mechanisms of the microstructural evolution and the phase selection are interpreted on the basis of the composition segregation, the skewed coupled zone, the strain-induced transformation, and the solute trapping. Moreover, the prenucleation of the primary FCC–Co phase was also detected from an analysis of the different recalescence behaviors. The present work not only enriches our knowledge about the phase selection behavior in the undercooled Co–B system, but also provides us with guidance for controlling the microstructures and properties practically. 相似文献
12.
Yoshinori Imai Yuichi Sawada Fuyuki Nabeshima Atsutaka Maeda 《Proceedings of the National Academy of Sciences of the United States of America》2015,112(7):1937-1940
We demonstrate the successful fabrication on CaF2 substrates of FeSe1−xTex films with 0 ≤ x ≤ 1, including the region of 0.1 ≤ x ≤ 0.4, which is well known to be the “phase-separation region,” via pulsed laser deposition that is a thermodynamically nonequilibrium method. In the resulting films, we observe a giant enhancement of the superconducting transition temperature, Tc, in the region of 0.1 ≤ x ≤ 0.4: The maximum value reaches 23 K, which is ∼1.5 times as large as the values reported for bulk samples of FeSe1−xTex. We present a complete phase diagram of FeSe1−xTex films. Surprisingly, a sudden suppression of Tc is observed at 0.1 < x < 0.2, whereas Tc increases with decreasing x for 0.2 ≤ x < 1. Namely, there is a clear difference between superconductivity realized in x = 0 ? 0.1 and in x ≥ 0.2. To obtain a film of FeSe1−xTex with high Tc, the controls of the Te content x and the in-plane lattice strain are found to be key factors.Since the discovery of superconductivity in LaFeAs(O,F) (1), many studies concerning iron-based superconductors have been conducted. FeSe is the iron-based superconductor with the simplest crystal structure (2). The Tc of FeSe is ∼8 K, which is not very high in comparison with other iron-based superconductors. However, the value of Tc strongly depends on the applied pressure, and the temperature at which the resistivity becomes zero, , reaches as high as ~ 30 K at 6 GPa (3). This suggests that FeSe samples with higher Tc are available by the fabrication of thin films because we can introduce lattice strain. Indeed, we have previously reported that FeSe films fabricated on CaF2 substrates exhibit Tc values ∼1.5 times higher than those of bulk samples because of in-plane compressive strain (4). On the other hand, superconductivity with Tc of 65 K has recently been reported in a monolayer FeSe film on SrTiO3 (5, 6). It is unclear whether this superconductivity results from the characteristics of the interface. However, this finding indicates that FeSe demonstrates potential as a very-high-Tc superconductor.The partial substitution of Te for Se in FeSe also raises Tc to a maximum of 14 K at x = 0.5 ? 0.6 (7). In FeSe1−xTex, it is well known that we cannot obtain single-phase samples with 0.1 < x < 0.4 because of phase separation (7). Here, we focus on this region of phase separation. Generally, the process of film deposition involves crystal growth in a thermodynamically nonequilibrium state. Thus, film deposition provides an avenue for the synthesis of a material with a metastable phase. In this paper, we report the fabrication of epitaxial thin films of FeSe1−xTex with 0 ≤ x ≤ 1 on CaF2 substrates, using the pulsed laser deposition (PLD) method. We demonstrate that single-phase epitaxial films of FeSe1−xTex with 0.1 ≤ x ≤ 0.4 are successfully obtained and that the maximum value of Tc is as large as 23 K, which is higher than the previously reported values for bulk and film samples of FeSe1−xTex (7–12), except for those of the monolayer FeSe films (5, 6). Our results clearly show that the optimal Te content for the highest Tc for FeSe1−xTex films on CaF2 is different from the widely believed value for this system.Fig. 1A presents the X-ray diffraction patterns of FeSe1−xTex films for x = 0 ? 0.5 on CaF2. Here and hereafter, the Te content x of our films represents the nominal Te composition of the polycrystalline target. With the exception of an unidentified peak in the FeSe0.5Te0.5 film, only the 00l reflections of a tetragonal PbO-type structure are observed, which indicates that these films are well oriented along the c axis. Fig. 1 B and C presents enlarged segments of these plots near the 001 and 003 reflections, respectively. The 2θ values of the peak positions decrease with increasing x in a continuous manner, which is consistent with the fact that the c-axis length increases with increasing x. It should be noted that the values of the full widths at half maximum (FWHM), δ(2θ), of the FeSe1−xTex films with x = 0.1 ? 0.4, which is known as the region of phase separation in the bulk samples (7), are δ(2θ) = 0.2°?0.3° for the 001 reflection and δ(2θ) = 0.4°?0.6° for the 003 reflection, which are nearly the same as the values for the FeSe and FeSe0.5Te0.5 films. This result is in sharp contrast to the previously reported result that the FWHM was broad only in films of FeSe1−xTex with x = 0.1 and 0.3 (13), where phase separation has been believed to occur. The results presented in Fig. 1 A–C indicate the formation of a single phase in our FeSe1−xTex films with x = 0.1 ? 0.4.Open in a separate windowFig. 1.(A) Out-of-plane X-ray diffraction patterns of FeSe1−xTex thin films for x = 0 ? 0.5 with film thicknesses of 120–147 nm. The # symbols represent peaks associated with the substrate. The * represents an unidentified peak. Enlarged segments of the plots presented in A near the 001 and 003 peaks are shown in B and C, respectively. (D) The c-axis lengths of FeSe1−xTex films, where the x value indicated on the horizontal axis is the nominal Te content. (E) Relations between the a-axis and c-axis lengths in FeSe1−xTex films. The colors and shapes of the symbols correspond to the Te content x, as shown. The dashed lines are guides for the eye. The data for x = 0 and 0.5 presented in A–E are cited from refs. 4, 9, and 14.In Fig. 1D, the c-axis lengths of 29 films of FeSe1−xTex are plotted as a function of x. The values of the c-axis lengths vary almost linearly with the nominal Te contents of the targets in the whole range of x, including both end-member materials. The evident formation of a single phase and the systematic change in the c-axis length strongly indicate that the nominal Te content of the polycrystalline target is nearly identical to that of the final FeSe1−xTex film. Note that the compositional analysis of grown films using scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis is impossible for FeSe1−xTex films on CaF2 substrates because the energies of the K edge of Ca and the L edge of Te are very close to each other. The above-mentioned features indicate that phase separation is suppressed in our FeSe1−xTex films with x = 0.1 ? 0.4 on CaF2 substrates. To our knowledge, this result is the first manifestation of the suppression of phase separation in FeSe1−xTex with x = 0.1 ? 0.4.Fig. 1E presents the relations between the a-axis and c-axis lengths in films of FeSe1−xTex. At first glance, there seem to be no relations between the a-axis length and x, in sharp contrast to the behavior of the c-axis length. The a-axis and c-axis lengths of films with the same x show a weak negative correlation. This behavior cannot be explained by a difference in Te content of a film, which should result in a positive correlation. By contrast, if variations in c are caused by a difference in in-plane lattice strain, this behavior can be explained in terms of the Poisson effect. Indeed, the a-axis lengths of films of FeSe and FeSe0.5Te0.5 are smaller than those of bulk samples with the same composition. Thus, we consider that the a-axis length predominantly depends on the in-plane lattice strain rather than the Te content x. One might think that this behavior looks strange, because the lattice constant of CaF2 is longer than the a of FeSe1−xTex, which usually leads to a tensile strain. In a previous paper, the penetration of F− ions from the CaF2 substrates into the films was proposed as a possible mechanism for nontrivial compressive strain in FeSe1−xTex films on CaF2 substrates (15). Because of the smaller ionic radius of F− than that of Se2−, this peculiar compressive strain can be explained by the partial substitution of F− for Se2− near the interface between a film and a substrate.Fig. 2 A–D presents the temperature dependences of the electrical resistivities, ρ, of 16 films of FeSe1−xTex for x = 0.1 ? 0.4. The value of Tc depends on the film thickness, even in films with the same x. The highest , which is defined as the temperature where the electrical resistivity deviates from the normal-state behavior, and the of the FeSe1−xTex films are 13.2 K and 11.5 K, respectively, for x = 0.1; 22.8 K and 20.5 K, respectively, for x = 0.2; 20.9 K and 19.9 K, respectively, for x = 0.3; and 20.9 K and 20.0 K, respectively, for x = 0.4. Compared with the results for bulk samples, a drastic enhancement of Tc is observed in these FeSe1−xTex films. Surprisingly, the values of in the films with x = 0.2 and 0.4 exceed 20 K. These values are larger than those reported for FeSe0.5Te0.5 films (8, 10, 11, 14). In particular, the Tc of the FeSe0.8Te0.2 film with a thickness of 73 nm is ∼1.5 times as high as those of bulk crystals of FeSe1−xTex with the optimal composition, x ≈ 0.5 (7). Based on the measurement of the ρ of the FeSe0.8Te0.2 film under a magnetic field applied along the c axis, we estimate an upper critical field at 0 K of μ0Hc2 = 55.4 T, using the Werthamer–Helfand–Hohenberg (WHH) theory (16), which yields a Ginzburg–Landau coherence length at 0 K of ξab(0) ~ 24.4 Å (SI Appendix). This value of μ0Hc2 is approximately half the value for an FeSe0.5Te0.5 film on CaF2 with a Tc of ∼16 K (9).Open in a separate windowFig. 2.Temperature dependences of the electrical resistivities, ρ, of FeSe1−xTex thin films for (A) x = 0.1, (B) x = 0.2, (C) x = 0.3, and (D) x = 0.4 with different film thicknesses. Insets present enlarged views of the plots near the superconducting transition.Using the data shown above, we present the phase diagram of FeSe1−xTex films on CaF2 substrates in Fig. 3. For comparison, the data for bulk samples of FeSe1−xTex (7, 17) are also plotted in Fig. 3. In bulk crystals, the optimal Te content to achieve the highest Tc is considered to be x ≈ 0.5, and phase separation occurs in the region of 0.1 ≤ x ≤ 0.4 (7). However, our data clearly demonstrate that this phase separation is absent and that the optimal composition for an FeSe1−xTex film on a CaF2 substrate is not x ≈ 0.5 but x ≈ 0.2. It should be noted that the dependence of Tc on x suddenly changes at the boundary defined by 0.1 < x < 0.2. Unlike the “dome-shaped” phase diagram that is familiar in iron-based superconductors, the values of Tc in films with 0.2 ≤ x ≤ 1 increase with decreasing x, whereas the strong suppression of Tc is observed at 0.1 < x < 0.2. The behavior in films with x ≥ 0.2 can be explained by the empirical law that shows the relation between Tc and structural parameters. In iron-based superconductors, it is well accepted that the bond angle of (Pn, Ch)-Fe-(Pn, Ch) (Pn, ?Pnictogen; Ch, ?Chalcogen), α (18, 19), and/or the anion height from the iron plane, h (20), are the critical structural parameters that determine the value of Tc. In bulk samples of FeSe1−xTex, α and h approach their optimal values, i.e., α = 109.47° (18, 19) and h = 1.38 Å (20), with decreasing x (down to x = 0), which should be the same in FeSe1−xTex films. Therefore, the increase of Tc in films with 0.2 ≤ x ≤ 1 with decreasing x can be explained by the optimization of α and/or h based on the empirical law. However, the sudden suppression of Tc in films with 0 ≤ x < 0.2 is not consistent with this scenario, and its origin should be sought among other factors. We consider there are two candidates for this origin from the structural analysis of bulk samples of FeSe1−xTex. One is the effect of the orthorhombic distortion. In a bulk sample of FeSe, a structural phase transition from tetragonal to orthorhombic occurs at 90 K (21). However, in bulk samples of FeSe1−xTex with x ~ 0.4 ? 0.6 where Tcs take optimum values, there are papers with different conclusions on the presence/absence of a similar type of structural transition to that of FeSe (22–24). It should be noted that a structural transition temperature is lower and that the orthorhombicity is much smaller than those of FeSe even in the report where the structural transition is present (24). These results on crystal structures suggest that the orthorhombic distortion results in a suppression of Tc. This scenario is applicable to the behavior of our films, if a large orthorhombic distortion is observed only in films with x = 0 ? 0.1. The other candidate is the change in the distance between the layers of Fe-Ch tetrahedra, δ. As shown in SI Appendix, in polycrystalline samples of FeSe1−xTex, the δ value of FeSe is much smaller than those of FeSe1−xTex with x ≥ 0.5 where δ is nearly independent of x (22). We speculate that the decrease of δ in FeSe is related with the suppression of Tc. Indeed, in polycrystalline samples, FeSe exhibits smaller values of δ and Tc than does FeSe0.5Te0.5 (7, 22), and the intercalation of alkali metals and alkaline earths into FeSe results in the c-axis length as large as ∼20 Å and Tc as high as 45 K (25, 26). At this moment, the origin of the suppression of Tc at 0.1 < x < 0.2 is unclear. Regardless of its origin, we believe that it is reasonable to distinguish between superconductivity in x = 0 ? 0.1 and in x ≥ 0.2. In other words, our phase diagram in Fig. 3 provides a previously unidentified view for superconductivity in FeSe1−xTex, that is, a discontinuity in superconductivity of FeSe1−xTex. We are able to come to this picture only after the data for x = 0.1 ? 0.4 become available in this study. If we remove a cause for the suppression of Tc in in some way, a further increase in Tc can be expected because of the optimization of structural parameters.Open in a separate windowFig. 3.Dependence of Tc on x. The red and blue circles represent the and values of the FeSe1−xTex thin films, respectively. The black triangles represent the values obtained in measurements of the magnetic susceptibility of bulk samples (7, 17). The dashed curve is a guide for the eye.In conclusion, we prepared high-quality epitaxial thin films of FeSe1−xTex on CaF2 substrates, using the pulsed laser deposition method. We successfully obtained FeSe1−xTex films with 0.1 ≤ x ≤ 0.4, which has long been considered to be the “phase-separation region,” using a thermodynamically nonequilibrium growth of film deposition. From the results of electrical resistivity measurements, a complete phase diagram is presented in this system, in which the maximum value of Tc is as high as 23 K at x = 0.2. Surprisingly, a sudden suppression of Tc is observed at 0.1 < x < 0.2, whereas Tc increases with decreasing x for 0.2 ≤ x < 1. This behavior is different from that of the dome-shaped phase diagram that is familiar in iron-based superconductors. 相似文献
13.
Mateusz Petrus Jarosaw Wo
niak Tomasz Cygan Artur Lachowski Dorota Moszczyska Bogusawa Adamczyk-Cielak Anita Rozmysowska-Wojciechowska Tomasz Wojciechowski Wanda Ziemkowska Agnieszka Jastrzbska Andrzej Olszyna 《Materials》2021,14(13)
This article presents new findings related to the problem of the introduction of MXene phases into the silicon carbide matrix. The addition of MXene phases, as shown by the latest research, can significantly improve the mechanical properties of silicon carbide, including fracture toughness. Low fracture toughness is one of the main disadvantages that significantly limit its use. As a part of the experiment, two series of composites were produced with the addition of 2D-Ti3C2Tx MXene and 2D-Ti3C2Tx surface-modified MXene with the use of the sol-gel method with a mixture of Y2O3/Al2O3 oxides. The composites were obtained with the powder metallurgy technique and sintered with the Spark Plasma Sintering method at 1900 °C. The effect adding MXene phases had on the mechanical properties and microstructure of the produced sinters was investigated. Moreover, the influence of the performed surface modification on changes in the properties of the produced composites was determined. The analysis of the obtained results showed that during sintering, the MXene phases oxidize with the formation of carbon flakes playing the role of reinforcement. The influence of the Y2O3/Al2O3 layer on the structure of carbon flakes and the higher quality of the interface was also demonstrated. This was reflected in the higher mechanical properties of composites with the addition of modified Ti3C2Tx. Composites with 1 wt.% addition of Ti3C2Tx M are characterized with a fracture toughness of 5 MPa × m0.5, which is over 50% higher than in the case of the reference sample and over 15% higher than for the composite with 2.5 wt.% addition of Ti3C2Tx, which showed the highest fracture toughness in this series. 相似文献
14.
Zhe Wang Bin Li Shouqin Tian Baoshun Liu Xiujian Zhao Xuedong Zhou Gen Tang Aimin Pang 《Materials》2021,14(17)
As a typical thermochromic material, VO2 coatings can be applied to smart windows by modulating the transmission of near infrared (NIR) light via phase transition. However, the inherent undesirable luminous transmittance (Tlum) and solar modulation efficiency (ΔTsol) of pure VO2 impede its practical application. In order to solve this problem, the porous VO2 based composite film was prepared by magnetron sputtering and subsequent acid solution process with Zn2V2O7 particles used as a sacrificial template to create pores, which showed excellent Tlum (72.1%) and enhanced ΔTsol (10.7%) compared with pure VO2 film. It was demonstrated that the porous structure of the film caused by acid solution process could improve the Tlum obviously and the isolated VO2 nanoparticles presented strong localized surface plasmon resonance (LSPR) effects to enhance the ΔTsol. Therefore, this method will provide a facile way to prepare VO2 based films with excellent thermochromic performance and thus promote the application of the VO2 based films in smart windows. 相似文献
15.
Joo A. O. Santos Alessandra M. G. Mutti Airton G. Bispo-Jr Ana M. Pires Sergio A. M. Lima 《Materials》2020,13(23)
Luminescent organic-inorganic hybrids containing lanthanides (Ln3+) have been prominent for applications such as luminescent bio-probes in biological assays. In this sense, a luminescent hybrid based on dense silica (SiO2) nanospheres decorated with Eu3+ β–diketonate complexes using dibenzoylmethane (Hdbm) as a luminescent antenna was developed by using a hierarchical organization in four steps: (i) anchoring of 3-aminopropyltriethoxysilane (APTES) organosilane on the SiO2 surface, (ii) formation of a carboxylic acid ligand, (iii) coordination of Eu3+ to the carboxylate groups and (iv) coordination of dbm− to Eu3+. The hybrid structure was elucidated through the correlation of thermogravimetry, silicon nuclear magnetic resonance and photoluminescence. Results indicate that the carboxylic acid-Eu3+-dbm hybrid was formed on the surface of the particles with no detectable changes on their size or shape after all the four steps (average size of 32 ± 7 nm). A surface charge of −27.8 mV was achieved for the hybrid, assuring a stable suspension in aqueous media. The Eu3+ complex provides intense red luminescence, characteristic of Eu3+ 5D0→7FJ electronic transitions, with an intrinsic emission quantum yield of 38%, even in an aqueous suspension. Therefore, the correlation of luminescence, structure, particle morphology and fluorescence microscopy images make the hybrid promising for application in bioimaging. 相似文献
16.
Terry G. Holesinger Matthew D. Feldmann Boris Maiorov Leonardo Civale John A. Kennison Yates J. Coulter Paul D. Dowden Javier F. Baca Paul H. Tobash Eric D. Bauer Kenneth R. Marken 《Materials》2011,4(11):2042-2056
Many second phase additions to YBa2Cu3O7−x (YBCO) films, in particular those that self-assemble into aligned nanorod and nanoparticle structures, enhance performance in self and applied fields. Of particular interest for additions are Ba-containing perovskites that are compatible with YBCO. In this report, we discuss the addition of Ba2YRuO6 to bulk and thick-film YBCO. Sub-micron, randomly oriented particles of this phase were found to form around grain boundaries and within YBCO grains in bulk sintered pellets. Within the limits of EDS, no Ru substitution into the YBCO was observed. Thick YBCO films were grown by pulsed laser deposition from a target consisting of YBa2Cu3Oy with 5 and 2.5 mole percent additions of Ba2YRuO6 and Y2O3, respectively. Films with enhanced in-field performance contained aligned, self-assembled Ba2YRuO6 nanorods and strained Y2O3 nanoparticle layers. A 0.9 µm thick film was found to have a self-field critical current density (Jc) of 5.1 MA/cm2 with minimum Jc(Θ, H=1T) of 0.75 MA/cm2. Conversely, Jc characteristics were similar to YBCO films without additions when these secondary phases formed as large, disordered phases within the film. A 2.3 µm thick film with such a distribution of secondary phases was found to have reduced self-field Jc values of 3.4 MA/cm2 at 75.5 K and Jc(min, Θ, 1T) of 0.4 MA/cm2. 相似文献
17.
The electronics related to the fifth generation mobile communication technology (5G) are projected to possess significant market potential. High dielectric constant microwave ceramics used as filters and resonators in 5G have thus attracted great attention. The Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramic system has aroused people’s interest due to its underlying excellent microwave dielectric properties. In this paper, the relationships between the dielectric constant, Nd-doped content, sintering temperature and the density of Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramics were studied. The linear regression equation was established by statistical product and service solution (SPSS) data analysis software, and the factors affecting the dielectric constant have been analyzed by using the enter and stepwise methods, respectively. It is found that the model established by the stepwise method is practically significant with Y = −71.168 + 6.946x1 + 25.799x3, where Y, x1 and x3 represent the dielectric constant, Nd content and the density, respectively. According to this model, the influence of density on the dielectric constant is greater than that of Nd doping concentration. We bring the linear regression analysis method into the research field of microwave dielectric ceramics, hoping to provide an instructive for the optimization of ceramic technology. 相似文献
18.
Daniel Gajda Andrzej J. Zaleski Andrzej Morawski Magorzata Maecka Mustafa Akdoan Firat Karaboa Doan Avc Hakan Yeti Ibrahim Belenli Tomasz Czujko 《Materials》2021,14(13)
Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (Birr), critical temperature (Tc), upper magnetic field (Bc2), engineered critical current density (Jec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on Birr, Tc, Bc2, Jec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest Birr, Tc, Bc2, Jec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2. 相似文献
19.
A 28-electron reduced C2h-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo142O429H10(H2O)49(CH3CO2)5(C2H5CO2)]30- (≡{Mo142(CH3CO2)5(C2H5CO2)}) comprising eight carboxylate-coordinated (with disorder) {Mo2} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La3+ in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical Ci-Mo-blue ring of formula [Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2]10- (≡{Mo134La10}), isolated as the Na10[Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2]·144 H2O Na+ salt. The elliptical structure of {Mo134La10} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO9/LaO7Cl2 tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO2(H2O)7 and one LaO2(H2O)2Cl2 TTP geometries (as A-C modes) for each of two inner rings result from the coordination of all three defect pockets of the inner ring for {Mo142(CH3CO2)5(C2H5CO2)}, and two LaO4(H2O)5 TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo2} linkers with La3+ in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La3+]/[{Mo142(CH3CO2)5(C2H5CO2)}] = 6/1 with ΔH = 22 kJ⋅mol-1, ΔS = 172 J⋅K-1⋅mol-1, ΔG = −28 kJ⋅mol-1, and K = 9.9 × 104 M-1 at 293 K, leads to the conclusion that the coordination of the defect pockets to La3+ precedes the replacement of the {Mo2} linkers with La3+. 139La- NMR spectrometry of the coordination of {Mo142(CH3CO2)5(C2H5CO2)} ring to La3+ is also discussed. 相似文献
20.
Daiki Shiozawa Takahide Sakagami Yu Nakamura Takato Tamashiro Shinichi Nonaka Kenichi Hamada Tomoaki Shinchi 《Materials》2021,14(17)
Short fiber reinforced plastics (SFRPs) have excellent moldability and productivity compared to continuous fiber composites. In this study, thermoelastic stress analysis (TSA) was applied to detect delamination defects in short carbon fiber reinforced plastics (SCFRPs). The thermoelastic temperature change ΔTE, phase of thermal signal θE, and second harmonic temperature component ΔTD were measured. In the fatigue test of SCFRP, it was confirmed that changes in ΔTE, θE, and ΔTD appeared in the damaged regions. A staircase-like stress level test for a SCFRP specimen was conducted to investigate the generation mechanism of the ΔTD. The distortion of the temperature change appeared at the maximum tension stress of the sinusoidal load—and when the stress level decreased, the temperature change returned to the original sinusoidal waveform. ΔTD changed according to the change in the maximum stress during the staircase-like stress level test, and a large value of ΔTD was observed in the final ruptured region. A distortion of the temperature change and ΔTD was considered to be caused by the change in stress sharing condition between the fiber and resin due to delamination damage. Therefore, ΔTD can be applied to the detection of delamination defects and the evaluation of damage propagation. 相似文献