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•Thermal decomposition of Schiff base complexes provides a convenient and effective pathway to fabricate CuO and NiO NPs.•The electrical conduction in CuO NPs and NiO NPs is governed ...by intrinsic band-to-band type and large polarons conduction mechanism, respectively.•The thermoelectric measurements confirm that the NPs are P-type degenerate semiconductors.•The NPs show weak ferromagnetic ordering at room temperature and antiferromagnetic to paramagnetic transition with high dipolar interaction.
In this study, CuO and NiO NPs have been synthesized by facile thermal decomposition of Schiff base complexes and their physical properties have been examined. The synthesized CuO and NiO NPs are crystallized in polycrystalline monoclinic and cubic structures with average particle size 17 ± 0.4 and 62 ± 1 nm, respectively. The electrical conductivity measurements confirm that the conduction in the CuO NPs is a band-to-band type while the conduction in the NiO NPs is governed by the large polaron conduction mechanism. The thermoelectric measurements confirm that the CuO and NiO NPs are P-type degenerate semiconductors with room temperature Seebeck coefficients equal to 89.9 and 12.1 mV/K, respectively. The magnetic measurements exhibit that the NPs have weak ferromagnetic ordering and antiferromagnetic to paramagnetic transition with high dipolar interaction.
The introduction of transition metal doping, particularly Fe3+, into high‐performance microwave dielectrics can make “smart” materials that switch between a high‐Q, low loss state and a low‐Q, high ...loss state using a small external magnetic field. In this study, the dielectric and magnetic properties of the high permittivity host material LaAlO3 (εr = 22.5), when doped with Fe3+, are reported. Spin losses dominate the loss tangent at cryogenic temperatures and survive up to room temperature. Peaks in the loss tangent versus temperature relation are observed near 40, 75, and 215 K. Additional measurements of samples exposed to annealing in varying environments, combined with Debye analysis and the results of native defect energy predictions from density functional calculationsPhys Rev B. 2009;80:104115, allows us to associate the 40, 75, and 215 K peaks to the following reactions, Oix+VOx→Oi′+VO·, FeAlx+VAl″→FeAl′+VAl′, and Alix+Ali··→2Ali·, respectively.
The distinct physical properties of hybrid organic–inorganic materials can lead to unexpected nonequilibrium phenomena that are difficult to characterize due to the broad range of length and time ...scales involved. For instance, mixed halide hybrid perovskites are promising materials for optoelectronics, yet bulk measurements suggest the halides reversibly phase separate upon photoexcitation. By combining nanoscale imaging and multiscale modeling, we find that the nature of halide demixing in these materials is distinct from macroscopic phase separation. We propose that the localized strain induced by a single photoexcited charge interacting with the soft, ionic lattice is sufficient to promote halide phase separation and nucleate a light-stabilized, low-bandgap, ∼8 nm iodide-rich cluster. The limited extent of this polaron is essential to promote demixing because by contrast bulk strain would simply be relaxed. Photoinduced phase separation is therefore a consequence of the unique electromechanical properties of this hybrid class of materials. Exploiting photoinduced phase separation and other nonequilibrium phenomena in hybrid materials more generally could expand applications in sensing, switching, memory, and energy storage.
Polypyrrole (PPy) nanorods (NRs) and nanoparticles (NPs) are synthesized via electrochemical and chemical methods, respectively, and tested upon ammonia exposure using Raman and X-ray photoelectron ...spectroscopy (XPS). Characterization of both nanomaterials via Raman spectroscopy demonstrates the formation of PPy, displaying vibration bands consistent with the literature. Additionally, XPS reveals the presence of neutral PPy species as major components in PPy NRs and PPy NPs, and other species including polarons and bipolarons. Raman and XPS analysis after ammonia exposure show changes in the physical/chemical properties of PPy, confirming the potential of both samples for ammonia sensing. Results demonstrate that the electrochemically synthesized NRs involve both proton and electron transfer mechanisms during ammonia exposure, as opposed to the chemically synthesized NPs, which show a mechanism dominated by electron transfer. Thus, the different detection mechanisms in PPy NRs and PPy NPs appear to be connected to the particular morphological and chemical composition of each film. These results contribute to elucidate the mechanisms involved in ammonia detection and the influence of the synthesis routes and the physical/chemical characteristics of PPy.
CuFeO2 is recognized as a potential photocathode for photo(electro)chemical water splitting. However, photocurrents with CuFeO2‐based systems are rather low so far. In order to optimize charge ...carrier separation and water reduction kinetics, defined CuFeO2/Pt, CuFeO2/Ag, and CuFeO2/NiOx(OH)y heterostructures are made in this work through a photodeposition procedure based on a 2H CuFeO2 hexagonal nanoplatelet shaped powder. However, water splitting performance tests in a closed batch photoreactor show that these heterostructured powders exhibit limited water reduction efficiencies. To test whether Fermi level pinning intrinsically limits the water reduction capacity of CuFeO2, the Fermi level tunability in CuFeO2 is evaluated by creating CuFeO2/ITO and CuFeO2/H2O interfaces and analyzing the electronic and chemical properties of the interfaces through photoelectron spectroscopy. The results indicate that Fermi level pinning at the Fe3+/Fe2+ electron polaron formation level may intrinsically prohibit CuFeO2 from acquiring enough photovoltage to reach the water reduction potential. This result is complemented with density functional theory calculations as well.
Heterostructured Pt/CuFeO2, Ag/CuFeO2, and NiOxOHy/CuFeO2 hexagonal nanoplatelets made through photodeposition are tested for photochemical water reduction. However, these heterostructures demonstrate limited water reduction efficiencies. Interface experiments show that Fermi level pinning at the Fe3+/Fe2+ charge transition level intrinsically limits the CuFeO2 Fermi level from rising above the H+/H2 redox level, thus inhibiting water reduction.
We present an experimental system to study the Bose polaron by immersion of single, well-controllable neutral Cs impurities into a Rb Bose-Einstein condensate (BEC). We show that, by proper optical ...traps, independent control over impurity and BEC allows for precision relative positioning of the two sub-systems as well as for dynamical studies and independent read-out. We furthermore estimate that measuring the polaron binding energy of Fröhlich-type Bose polarons in the low and intermediate coupling regime is feasible with our experimental constraints and limitations discussed, and we outline how a parameter regime can be reached to characterize differences between Fröhlich and Bose-polaron in the strong coupling regime.
Detailed ac electrical investigations within the frequency range 100 Hz-1 MHz have been conducted on the polycrystalline YFe0·9Cr0·1O3 samples prepared via solid state reaction route, in a broad ...thermal interval of 298–673 K. A systematic development of grain, grain boundary and electrode polarization contribution have been observed with increasing temperature. The thermal variation of the grain resistance (R g) and grain boundary resistances (R gb) followed the non-adiabatic small polaron hopping (SPH) model and is responsible for the long-range conduction with different values of the activation energies at different thermal regimes. The ac conductivity of the material exhibited series of dispersive regions with broad region, where the slope changes occurred up to 473 K. Above 473 K, appreciable dc conductivity in the material can be seen. Different dispersive regions in the conductivity spectrum obeyed single power law and power law variation (Aωn).
Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons, significantly affecting electronic charge‐transport properties. ...Understanding the formation and (de)localization of polarons is therefore critical for further developing organic semiconductors as a future electronics platform. However, there are very few studies reported in this area. In particular, there is no direct in situ monitoring of polaron formation and identification of its dependence on molecular structure and impact on electrical properties, limiting further advancement in organic electronics. Herein, how a minor modification of side‐chain density in thiophene‐based conjugated polymers affects the polaron formation via electrochemical doping, changing the polymers’ electrical response to the surrounding dielectric environment for gas sensing, is demonstrated. It is found that the reduction in side‐chain density results in a multistep polaron formation, leading to an initial formation of localized polarons in thiophene units without side chains. Reduced side‐chain density also allows the formation of a high density of polarons with fewer polymer structural changes. More numerous but more localized polarons generate a stronger analyte response but without the selectivity between polar and non‐polar solvents, which is different from the more delocalized polarons that show clear selectivity. The results provide important molecular understanding and design rules for the polaron formation and its impact on electrical properties.
A small modification of side‐chain density in thiophene‐based conjugated polymers affects the polaron formation via electrochemical doping. In situ monitoring of polaron formation allows identification of its dependence on molecular structures. Understanding of the polaron formation mechanism is important for molecular design rules and its impact on electrical properties.
Despite more than 20 years of research, the root cause of the impractically short lifetimes of blue phosphorescent organic light‐emitting diodes (PHOLEDs) has remained unclear. To overcome this, the ...authors investigate how the electrical properties of the emission layer (EML) of blue PHOLEDs affect degradation of the devices. It is found that a large density of dopant carriers is the dominant factor triggering triplet‐polaron annihilation (TPA), which is a major defect‐generation and hence lifetime‐reduction mechanism. In order to reduce the generation of the TPA‐induced defects to ensure long device lifetimes, the dopant carrier density should be minimized by suppressing the spontaneous charge transfer from the host to the dopant initially and by supplying sufficient charges with opposite polarity into the EML. However, there exists another critical factor that offsets the low overall density of defects against device lifetimes—that is, the non‐uniform distribution of defects leading to intense exciton quenching. These two degradation factors are predetermined, and hence can be controlled, by the charge mobilities of the PHOLED EML. Given these considerations, it is demonstrated that the long‐lifetime blue PHOLEDs can be realized.
A high density of dopant carriers is found to be the primary cause of the degradation of blue phosphorescent organic light‐emitting diodes (PHOLEDs) by inducing defect‐generation process. Accordingly, the authors demonstrate that the lifetimes of blue PHOLEDs can be enhanced by minimizing the dopant carrier density and by alleviating the detrimental interactions between charges, excitons and defects.
Sintering of composites constituted by two nonstoichiometric phases (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) and Gd0.1Ce0.9O2 (GDC) under constant electric field in constant heating rate experiment is ...studied in this work. The requirements of field and temperature for composite systematically increase with GDC amounts this indicating the importance of material conductivity. Sintering/grain growth rate is higher in the composite compared to pure LSCF phase. Flash‐sintering phenomenon in the composite is explained on the basis of three factors: (1) large and continuous increase in conductivity of LSCF acts as source of defects, (2) maintenance of sufficient local temperature because of GDC during continuous conductivity increase facilitates the cationic diffusion, and (3) reduction reactions of LSCF, during polaron hopping conduction, and of GDC phase at higher temperature activate the sintering process.
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