Abstract:Although nanoscale deformation, such as nanostrain in iron chalcogenide FST) thin films, has attracted attention owing to the enhancement of general superconducting properties, including critical current density (Jc) and critical transition temperature, its formation has proven to be an extremely challenging and complex process thus far. Herein, we successfully fabricated an epitaxial FST thin film with uniformly distributed nanostrain by injection of a trace amount of CeO2 inside FST matrix using sequenti… Show more
“…Since the discovery of superconductivity in LaFeAsO in 2008, iron-based superconductors (IBS) have attracted widespread attention due to their unique properties compared with both traditional low-temperature and high- T c cuprate superconductors. − Among all the IBS, FeSeTe, known as the “11”-family IBS, has the advantages of simple structure, nontoxicity (without As), high current-carrying density, and low anisotropy, making it have great potential for high-field applications. − The critical transition temperature ( T c ) of a bulk FeSeTe superconductor is relatively low compared with the other family of IBS. It has been found, from the FeSe x Te 1– x phase diagram, that the optimal doping is observed at x = 0.5 with the maximum T c of 15 K .…”
By
preparing a series of high-quality Fe1.1Se0.8Te0.2 films on the CaF2 substrate via pulsed
laser deposition, we reveal the evolution of the structure as well
as the superconductivity with the film thickness. We have found that
there exists a threshold thickness above which the critical temperature T
c reaches its optimal value of 23.18 K with
large activation energy, promising for high-field technological applications.
Most importantly, the thick films have been found in a metastable
state due to the fragile balance between the increased strain energy
and the large compressive stress. Once the balance is broken by an
external perturbation, a unique structure avalanche happens with a
large part of the film exfoliated from the substrate and curves out.
The exfoliated part of the film remains a single phase, with its lattice
parameter and T
c recovering the bulk values.
Our results clearly demonstrate the close relation between the compressive
stress of the film/substrate interface and the high critical temperature
observed in FeSeTe films. Moreover, this also provides an efficient
way to fabricate free-standing single-phase FeSeTe crystals in the
phase-separation regime.
“…Since the discovery of superconductivity in LaFeAsO in 2008, iron-based superconductors (IBS) have attracted widespread attention due to their unique properties compared with both traditional low-temperature and high- T c cuprate superconductors. − Among all the IBS, FeSeTe, known as the “11”-family IBS, has the advantages of simple structure, nontoxicity (without As), high current-carrying density, and low anisotropy, making it have great potential for high-field applications. − The critical transition temperature ( T c ) of a bulk FeSeTe superconductor is relatively low compared with the other family of IBS. It has been found, from the FeSe x Te 1– x phase diagram, that the optimal doping is observed at x = 0.5 with the maximum T c of 15 K .…”
By
preparing a series of high-quality Fe1.1Se0.8Te0.2 films on the CaF2 substrate via pulsed
laser deposition, we reveal the evolution of the structure as well
as the superconductivity with the film thickness. We have found that
there exists a threshold thickness above which the critical temperature T
c reaches its optimal value of 23.18 K with
large activation energy, promising for high-field technological applications.
Most importantly, the thick films have been found in a metastable
state due to the fragile balance between the increased strain energy
and the large compressive stress. Once the balance is broken by an
external perturbation, a unique structure avalanche happens with a
large part of the film exfoliated from the substrate and curves out.
The exfoliated part of the film remains a single phase, with its lattice
parameter and T
c recovering the bulk values.
Our results clearly demonstrate the close relation between the compressive
stress of the film/substrate interface and the high critical temperature
observed in FeSeTe films. Moreover, this also provides an efficient
way to fabricate free-standing single-phase FeSeTe crystals in the
phase-separation regime.
“…Selenium has been a point of focus in materials research over the past few decades, owing to its high photoconductivity and use for the synthesis of a wealth of chemicals. − Particularly interesting are metal selenides, which find applications in thermoelectrics, semiconductor quantum dots, photovoltaics, magnetic semiconductors, and superconductors. − The ubiquitous applications of selenide materials prompt the need to develop facile, simple, and nontoxic means of synthesis. The conventional syntheses of transition metal selenides usually involve solid-state reactions of elements and precursors, chemical vapor deposition, and gas phase reactions. , These reactions require high temperatures, which are energy intensive and may restrict the control of products.…”
Section: Introductionmentioning
confidence: 99%
“…Trialkylphosphine selenides have also been used as precursors to synthesize high-quality transition metal selenide nanocrystals. − It has been demonstrated that the phosphine route may be suitable for materials where surface passivation is required to minimize surface recombination sites; − however, for materials with applications in photovoltaics and sensors, the presence of bulky surface-bound organic species may impede device performance. , Furthermore, the reaction of Se with alkyl phosphines such as trioctylphosphine (TOP) and tributylphosphine (TBP) results in unstable and hazardous products, which are difficult to control even under inert atmospheres. − This led to the adoption of phosphine-free precursors, which are formed by dissolving Se in high-boiling-point solvents such as oleylamine, octadecene, olive oil, and paraffin. − It has been demonstrated that these phosphine-free selenium precursors are more reactive toward particle growth when compared to their phosphine counterparts. , Unfortunately, this strategy is usually associated with the formation of H 2 Se, which acts as a major deactivation pathway during precursor formation and also poses health concerns . Another strategy involves the use of selenourea and elemental Se under a reductive atmosphere (NaBH 4 , hydrazine, concentrated NaOH/KOH), alkyl thiol reduction, and reaction of SeO 2 in coordinative solvents. ,,− Most of the aforementioned reducing agents are unstable in air, and their mechanisms of action are complicated .…”
The inertness of elemental selenium is a significant obstacle in the synthesis of selenium-containing materials at low reaction temperatures. Over the years, several recipes have been developed to overcome this hurdle; however, most of the methods are associated with the use of highly toxic, expensive, and environmentally harmful reagents. As such, there is an increasing demand for the design of cheap, stable, and nontoxic reactive selenium precursors usable in the low-temperature synthesis of transition metal selenides with vast applications in nanotechnology, thermoelectrics, and superconductors. Herein, a novel synthetic route has been developed for activating elemental selenium by using a solvothermal approach. By comprehensive 77 Se NMR, Raman, and infrared spectroscopies and gas chromatography−mass spectrometry, we show that the activated Se solution contained HSe − , [Se−Se] 2− , and Se 2− ions, as well as dialkyl selenide (R 2 Se) and dialkyl diselenide (R−Se−Se−R) species in dynamic equilibrium. This also corresponded to the first observation of naked Se 2 2− in solution. The versatility of the developed Se precursor was demonstrated by the successful synthesis of (i) the polycrystalline room-temperature modification of the β-Ag 2 Se thermoelectric material; (ii) large single crystals of superconducting β-FeSe; (iii) CdSe nanocrystals with different particle sizes (3−10 nm); (iv) nanosheets of PtSe 2 ; and (v) mono-and dibenzyl selenides and diselenides at room temperature. The simplicity and diversity of the developed Se activation method holds promise for applied and fundamental research.
“…Transition-metal chalcogenides display astounding properties ranging from electronic, thermal, optical properties to novel forms of superconductivity and magnetism. − Among various prominent transition-metal chalcogenides, silver-based ones are comparatively less well-explored in the literature. Among them, silver selenide (Ag 2 Se) is an n-type chalcogenide with a phase transition at atmospheric pressure from semiconducting orthorhombic to superionic cubic where Ag + becomes mobile within a rigid lattice of Se.…”
Herein, we have successfully synthesized
binary Ag2Se,
composite Ag0:Ag2Se, and ternary Cu+:Ag2Se through an ambient aqueous-solution-based approach
in a one-pot reaction at room temperature and atmospheric pressure
without involving high-temperature heating, multiple-processes treatment,
and organic solvents/surfactants. Effective controllability over phases
and compositions/components are demonstrated with feasibility for
large-scale production through an exquisite alteration in reaction
parameters especially pH for enhancing and understanding thermoelectric
properties. Thermoelectric ZT reaches 0.8–1.1
at near-room-temperature for n-type Ag2Se and Cu+ doping further improves to 0.9–1.2 over a temperature range
of 300–393 K, which is the largest compared to that reported
by wet chemistry methods. This improvement is related to the enhanced
electrical conductivity and the suppressed thermal conductivity due
to the incorporation of Cu+ into the lattice of Ag2Se at very low concentrations (x%Cu+:Ag2Se, x = 1.0, 1.5, and 2.0).
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