242 research outputs found
Cova de Can SadurnĂ, la transformaciĂł dâun jaciment. Lâepisodi sepulcral del neolĂtic postcardial
The
present study deals with the structural characterization and classification
of the novel compounds <b>1</b>â<b>8</b> into perovskite
subclasses and proceeds in extracting the structureâband gap
relationships between them. The compounds were obtained from the employment
of small, 3â5-atom-wide organic ammonium ions seeking to discover
new perovskite-like compounds. The compounds reported here adopt unique
or rare structure types akin to the prototype structure perovskite.
When trimethylammonium (TMA) was employed, we obtained TMASnI<sub>3</sub> (<b>1</b>), which is our reference compound for a âperovskitoidâ
structure of face-sharing octahedra. The compounds EASnI<sub>3</sub> (<b>2b</b>), GASnI<sub>3</sub> (<b>3a</b>), ACASnI<sub>3</sub> (<b>4</b>), and IMSnI<sub>3</sub> (<b>5</b>)
obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium
(ACA), and imidazolium (IM) cations, respectively, represent the first
entries of the so-called âhexagonal perovskite polytypesâ
in the hybrid halide perovskite library. The hexagonal perovskites
define a new family of hybrid halide perovskites with a crystal structure
that emerges from a blend of corner- and face-sharing octahedral connections
in various proportions. The small organic cations can also stabilize
a second structural type characterized by a crystal lattice with reduced
dimensionality. These compounds include the two-dimensional (2D) perovskites
GA<sub>2</sub>SnI<sub>4</sub> (<b>3b</b>) and IPA<sub>3</sub>Sn<sub>2</sub>I<sub>7</sub> (<b>6b</b>) and the one-dimensional
(1D) perovskite IPA<sub>3</sub>SnI<sub>5</sub> (<b>6a</b>).
The known 2D perovskite BA<sub>2</sub>MASn<sub>2</sub>I<sub>7</sub> (<b>7</b>) and the related all-inorganic 1D perovskite âRbSnF<sub>2</sub>Iâ (<b>8</b>) have also been synthesized. All
compounds have been identified as medium-to-wide-band-gap semiconductors
in the range of <i>E</i><sub>g</sub> = 1.90â2.40
eV, with the band gap progressively decreasing with increased corner-sharing
functionality and increased torsion angle in the octahedral connectivity
Subtle Roles of Sb and S in Regulating the Thermoelectric Properties of NĂą Type PbTe to High Performance
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/1/aenm201700099.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/2/aenm201700099-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/3/aenm201700099_am.pd
The Faraday effect and phase transition in the CH 3 NH 3 PbI 3 halide perovskite single crystal
The spin degree of freedom of charge carriers in halide-perovskite
semiconductors can be highly useful for information photonics applications. The
Faraday effect is known to be the best indicator of paramagnetism of the
material and of the spin-light interaction. In this work, the Faraday effect is
demonstrated, for the first time, in a hybrid organic-inorganic halide
perovskite MAPbI3 (MA+=CH3NH+3). The Faraday rotation and birefringence were
measured across the tetragonal-cubic phase transition at 327 K. The Faraday
rotation is strongly suppressed below the phase transition temperature due to
anisotropy (linear birefringence) of the tetragonal crystal phase. The
situation changes drastically above the phase transition temperature, when the
crystal becomes optically isotropic. The emerging Faraday rotation obeys the
Curie law, demonstrating its population-related paramagnetic nature. This
observation opens new prospects for application of these systems and for their
investigations using methods of the polarization noise spectroscopy applicable
to optically anisotropic materials.Comment: 12 pages, 5 figure
Hybrid OrganicâInorganic Halide Post-Perovskite 3-Cyanopyridinium Lead Tribromide for Optoelectronic Applications
2D halide perovskite-like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to lasing. To date, the most studied families of such low-dimensional halide perovskite-like compounds are RuddlesdenâPopper, DionâJacobson, and other phases that can be derived from 3D halide perovskites by slicing along different crystallographic directions, which leads to the spatially isotropic corner-sharing connectivity type of metal-halide octahedra in the 2D layer plane. In this work, a new family of hybrid organicâinorganic 2D lead halides is introduced, by reporting the first example of the hybrid organicâinorganic post-perovskite 3-cyanopyridinium lead tribromide (3cp)PbBr3. The post-perovskite structure has unique octahedra connectivity type in the layer plane: a typical âperovskite-likeâ corner-sharing connectivity pattern in one direction, and the rare edge-sharing connectivity pattern in the other. Such connectivity leads to significant anisotropy in the material properties within the inorganic layer plane. Moreover, the dense organic cation packing results in the formation of 1D fully organic bands in the electronic structure, offering the prospects of the involvement of the organic subsystem into material's optoelectronic properties. The (3cp)PbBr3 clearly shows the 2D quantum size effect with a bandgap around 3.2Â eV and typical broadband self-trapped excitonic photoluminescence at temperatures below 200 K
An assessment of sputtered nitrogen-doped nickel oxide for all-oxide transparent optoelectronic applications: The case of hybrid NiO:N/TiO2 heterostructure
ransition metal oxides present a unique category of materials due to their versatile optical, electrical and mechanical properties. Nickel oxide (NiO) is an intrinsic p-type oxide semiconductor. P-NiO with controllable and reproducible physico-chemical properties, if combined with transparency and low temperature (low-T) fabrication processes, can be fully exploited in many transparent and/or flexible devices for applications, like energy management (production, manipulation, storage), sensing, wearable and health care electronics, etc. Reproducibility, transparency and low-T fabrication processes of p-type NiO are the motivation of this work. Nitrogen is one of the dopants used for modifying the properties of NiO. Until now, nitrogen-doped NiO, has shown inferior properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO. The NiO:N films were grown by sputtering on room-temperature substrates in plasma containing 50% Ar and 50% (O2+N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having transmittance less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50-2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheungâs methods. The diodeâs transparency and characteristics were further enhanced upon thermal treatment and this was attributed to improved NiO:N properties with annealing. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices
Transparent all-oxide hybrid NiON/TiO2 heterostructure for optoelectronic applications
Nickel oxide (NiO) is a p-type oxide and nitrogen is one of the dopants used for modifying its properties. Until now, nitrogen-doped NiO has shown inferior optical and electrical properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO thin film. The NiO:N films were grown at room temperature by sputtering using a plasma containing 50% Ar and 50% (O2 + N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having a transmittance of less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50â2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheungâs methods, which were further improved upon thermal treatment. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices
Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping
Superionic thermoelectric materials have been shown to have high figure-of-merits, leading to expectations for efficient high-temperature thermoelectric generators. These compounds exhibit extremely high cation diffusivity, comparable to that of a liquid, which is believed to be associated with the low thermal conductivity that makes superionic materials good for thermoelectrics. However, the superionic behavior causes cation migration that leads to device deterioration, being the main obstacle for practical applications. It has been reported that lithium doping in superionic Cu_(2âx)Se leads to suppression of the Cu ion diffusivity, but whether the material will retain the promising thermoelectric properties had not yet been investigated. Here, we report a maximum zT>1.4 from Li_(0.09)Cu_(1.9)Se, which is higher than what we find in the undoped samples. The high temperature effective weighted mobility of the doped sample is found higher than Cu_(2âx)Se, while the lattice thermal conductivity remains similar. We find signatures of suppressed bipolar conduction due to an enlarged band gap. Our findings set forth a possible route for tuning the stability of superionic thermoelectric materials
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