Nanoscale materials exhibit properties that are quite distinct from those of bulk materials because of their size restricted nature. Here, we investigated the high-pressure structural stability of ...cubic (C−type) nano-Eu2O3 using in situ synchrotron X−ray diffraction (XRD), Raman and luminescence spectroscopy, and impedance spectra techniques. Our high-pressure XRD experimental results revealed a pressure-induced structural phase transition in nano−Eu2O3 from the C−type phase (space group: Ia-3) to a hexagonal phase (A−type, space group: P-3m1). Our reported transition pressure (9.3 GPa) in nano-Eu2O3 is higher than that of the corresponding bulk-Eu2O3 (5.0 GPa), which is contrary to the preceding reported experimental result. After pressure release, the A−type phase of Eu2O3 transforms into a new monoclinic phase (B−type, space group: C2/m). Compared with bulk−Eu2O3, C-type and A-type nano−Eu2O3 exhibits a larger bulk modulus. Our Raman and luminescence findings and XRD data provide consistent evidence of a pressure-induced structural phase transition in nano-Eu2O3. To our knowledge, we have performed the first high-pressure impedance spectra investigation on nano-Eu2O3 to examine the effect of the structural phase transition on its transport properties. We propose that the resistance inflection exhibited at ∼12 GPa results from the phase boundary between the C−type and A−type phases. Besides, we summarized and discussed the structural evolution process by the phase diagram of lanthanide sesquioxides (Ln2O3) under high pressure.
•Nano Eu2O3 transformed from C-type to A-type as the pressure increasing.•A-type transformed into B-type after the pressure releasing to 0 GPa.•Nano Eu2O3 exhibits the higher transition pressure than in the bulk.•The Raman and luminescence results provide consistent evidence with XRD data.•Transport properties were affected by structural phase transition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this work, compared with the corresponding pure CsPbCl3 nanocrystals (NCs) and Mn2+-doped CsPbCl3 NCs, Mn2+/Cu2+-codoped CsPbCl3 NCs exhibited improved photoluminescence (PL) and photoluminescence ...quantum yields (PL QYs) (57.6%), prolonged PL lifetimes (1.78 ms), and enhanced thermal endurance (523 K) as a result of efficient Mn2+ doping (3.66%) induced by the addition of CuCl2. Furthermore, we applied pressure on Mn2+/Cu2+-codoped CsPbCl3 NCs to reveal that a red shift of photoluminescence followed by a blue shift was caused by band gap evolution and related to the structural phase transition from cubic to orthorhombic. Moreover, we also found that under the preheating condition of 523 K, such phase transition exhibited obvious morphological invariance, accompanied by significantly enhanced conductivity. The pressure applied to the products treated with high temperature enlarged the electrical difference and easily intensified the interface by closer packaging. Interestingly, defect-triggered mixed ionic and electronic conducting (MIEC) was observed in annealed NCs when the applied pressure was 2.9 GPa. The pressure-dependent ionic conduction was closely related to local nanocrystal amorphization and increased deviatoric stress, as clearly described by in situ impedance spectra. Finally, retrieved products exhibited better conductivity (improved by 5–6 times) and enhanced photoelectric response than those when pressure was not applied. Our findings not only reveal the pressure-tuned optical and electrical properties via structural progression but also open up the promising exploration of more amorphous all-inorganic CsPbX3-based photoelectric applications.
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It is known that metallization can greatly facilitate chemical reactions and dramatically change electric transport properties of materials. The search for materials displaying metallization at low ...pressure is one of the most urgent challenges. In this paper, pressure-induced metallization of molybdenum diselenide (MoSe2) under nonhydrostatic compression has been studied experimentally using Hall effect and X-ray diffraction measurements combined with diamond anvil cell techniques. In situ conductivity and Hall effect measurements under pressure reveal a monotonic decrease of resistivity mostly related to a significant increase of the carrier density by a factor of 4. Above 35.7 GPa, the sample acquires a metallic character with a characteristic increase of the mobility from 9.9 to 16.2 cm2 V–1·s–1 and saturation of the carrier concentration at 5.1 × 1020 cm–3. These results show that the metallization of powder MoSe2 can be initiated by a reduced pressure of 35.7 GPa under nonhydrostatic compression, compared to that above 40 GPa with a single-crystal sample under hydrostatic compression Nat. Commun. 2015, 6, 7312 . The mechanisms of anisotropic-stress-induced metallization for such reduced initiation pressure have been discussed.
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High-pressure behaviors of wurtzite CdS and CdS:Eu
3+
nanoparticles (8-10 nm) were investigated by synchrotron radiation X-ray diffraction, Raman spectroscopy, and photoluminescence under high ...pressure at ambient temperature. The doping of Eu ions increases the phase transition pressure from wurtzite structure to rocksalt structure (CdS = 4.76 GPa and CdS:Eu = 5.22 GPa) and so does the bulk modulus (
B
0
) of the initial and high pressure phases. This phenomenon can be attributed to the great impact on tensile strain along the
c
-axis of CdS nanoparticles, which is identified by the relationship of lattice contraction and the pressure obtained from Raman 1LO. The phase transitions of all samples are partly reversible. The Eu
3+
ions luminescence from
5
D
0
→
7
F
J
(
J
= 1, 2) transition in CdS:Eu nanoparticles emerges obviously and changes during the phase transformation, which indicate the variation of the local symmetry of the Eu
3+
ions. The new peak of
5
D
0
→
7
F
3
emerges at 7.26 GPa, persisting until the end of the whole experiment. The obtained CdS nanoparticles will hold promising potential in the fabrication of effective biological sensors and photodetectors for practical application under high pressure.
Eu dopant increases the phase transition pressure from wurtzite to rocksalt structure compared with CdS nanoparticles. The PL peaks of the Eu
3+
ions can used as pressure probe after the quenching of the PL peaks of rocksalt structure CdS.
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In this work, we report the pressure-dependent electrical transport and structural properties of SnSe. In our experiments an electronic transition from a semiconducting to semimetallic state was ...observed at 12.6 GPa, followed by an orthorhombic to monoclinic structural transition. Hall effect measurements indicate that both the carrier concentration and mobility vary abnormally accompanied by the semimetallic electronic transition. First-principles band structure calculations confirm the semiconducting-semimetallic transition, and reveal that the semimetallic character of SnSe can be attributed to the enhanced coupling of Sn-5s, Sn-5p, and Se-3p orbitals under compression that results in the broadening of energy bands and subsequently the closure of the band gap. The pressure modulated variations of electrical transport and structural properties may provide an approach to improving the thermoelectric properties of SnSe.
A semiconducting-semimetallic transition was observed to occur at 12.6 GPa, followed by an orthorhombic to monoclinic structural transition.
The intercalation of Li+ ions into layer structured compounds montmorillonite (MMT) clay was investigated. It is demonstrated that the interlayer water acting as ion transportation channel could ...affect the electrochemical performance. Before and after dehydration, initial capacities of 95 mAh g−1 and 105 mAh g−1 at current density of 0.5 A g−1 were recorded, respectively. Similar capacity changing trends in electrochemical cycle performance was observed before and after dehydration. Both cycle profiles could be divided into three zones: the capacity decrease zone I (1–40 cycles), the capacity increase zone II (40–400 cycles) and the stabilized capacity zone III (>400 cycles). Before and after dehydration reversible capacities of 80 and 36 mAh g−1 was recorded at 1000 cycle at current density of 0.2 A g−1, respectively. The interlayer water facilitates faster ion transfer and better kinetics in the MMT electrode. This work indicates that MMT clay could be a promising material in lithium ion battery application.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We measured the compressibility of La
2Mg
16Ni, LaMg
2Ni, LaMg
3, and
γ-La to 30.1 GPa by synchrotron X-ray diffraction. The bulk moduli are respectively determined to be 54, 67, 57, and 47.5 GPa. ...The strengthening of the compounds by the addition of nickel is insignificant. The compressibility is dominantly determined by that of La and Mg. The strength increases of the compounds relative to pure La and Mg elements is comparable to that caused by solid solution strengthening.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The electrical transport properties of CH3NH3PbBr3 (MAPbBr3) polycrystals were in situ investigated by alternating-current impedance spectroscopy under high pressures up to 5.6 GPa. It is confirmed ...that ionic and electronic conductions coexist in MAPbBr3. As pressure below 3.3 GPa ions migration is the predominant process, while above 3.3 GPa electronic conduction becomes the main process. An obvious ionic-electronic transition can be observed. The pressure dependent photo responsiveness of MAPbBr3 was also studied by in situ photocurrent measurements up to 3.8 GPa. The mixed conduction can be clearly seen in photocurrent measurement. Additionally, the photocurrents remain robust below 2.4 GPa, while they are suppressed with pressure-induced partial amorphization. Interestingly, the photoelectric response of MAPbBr3 can be enhanced by high pressure, and the strongest photocurrent value appears in the high-pressure phase II at 0.7 GPa, which is similar to previous results in both MAPbI3 and MASnI3.
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Searching for the polymorphic semiconductor nanocrystals would provide precise and insightful structure-spin polarization correlations and meaningful guidance for designing and synthesizing high ...spin-polarized spintronic materials. Herein, the high spin polarization is achieved in polymorphic CdS:Y semiconductor nanocrystals. The high-pressure polymorph of rock-salt CdS:Y nanocrystals has been recovered at ambient conditions synthesized by the wurtzite CdS:Y nanocrystals as starting material under 5.2 GPa and 300 °C conditions. The rock-salt CdS:Y polymorph displays more robust room-temperature ferromagnetism than wurtzite sample, which can reach the ferromagnetic level of conventional semiconductors doped with magnetic transition-metal ions, mainly due to the significantly enhanced spin configuration and defect states. Therefore, crystal structure directly governs the spin configuration, which determines the degree of spin polarization. This work can provide experimental and theoretical methods for designing the high spin-polarized semiconductor nanocrystals, which is important for applications in semiconductor spintronics.
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Synchrotron x-ray diffraction measurements of CdCu{sub 3}Ti{sub 4}O{sub 12} (CDCTO) were performed up to 55.5 GPa. There is no structural phase transformation in this pressure range. The irregular ...curvature shifts of the P V curve are attributed to the grain surface effect. Analysis indicates that the grain surface of CDCTO is stiffer than the grain interior at higher pressures. We point out that the atoms on grain surfaces must be either densely packed or have a strong correlation with the gain interior in order to have a high dielectric constant, as in CaCu{sub 3}Ti{sub 4}O{sub 12}. The derived bulk modulus K of CDCTO is approximately 235 {+-} 7 GPa with K = 5.1 {+-} 0.4.
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