Showing papers on "Orthorhombic crystal system published in 2018"
TL;DR: In this paper, a structural refinement of room-temperature black-phase CsPbI3 in an orthorhombic polymorph is presented, which is adopted by both powders and thin films of black- phase CsPsPbII3, fabricated either by high- or lowtemperature processes.
Abstract: Room-temperature films of black-phase cesium lead iodide (CsPbI3) are widely thought to be trapped in a cubic perovskite polymorph. Here, we challenge this assumption. We present structural refinement of room-temperature black-phase CsPbI3 in an orthorhombic polymorph. We demonstrate that this polymorph is adopted by both powders and thin films of black-phase CsPbI3, fabricated either by high- or low-temperature processes. We perform electronic band structure calculations for the orthorhombic polymorph and find agreement with experimental data and close similarities with orthorhombic methylammonium lead iodide. We investigate the structural transitions and thermodynamic stability of the various polymorphs of CsPbI3 and show that the orthorhombic polymorph is the most stable among its other perovskite polymorphs, but it remains less stable than the yellow nonperovskite polymorph.
397 citations
TL;DR: This study provides a novel and fundamental perspective to overcome the Achilles' heel of the inorganic lead iodide perovskite and opens it up for high-performance optoelectronic devices.
Abstract: All-inorganic lead halide perovskites demonstrate improved thermal stability over the organic–inorganic halide perovskites, but the cubic α-CsPbI3 with the most appropriate bandgap for light harvesting is not structurally stable at room temperature and spontaneously transforms into the undesired orthorhombic δ-CsPbI3 Here, we present a new member of black-phase thin films of all-inorganic perovskites for high-efficiency photovoltaics, the orthorhombic γ-CsPbI3 thin films with intrinsic thermodynamic stability and ideal electronic structure Exempt from introducing organic ligands or incorporating mixed cations/anions into the crystal lattice, we stabilize the γ-CsPbI3 thin films by a simple solution process in which a small amount of H2O manipulates the size-dependent phase formation through a proton transfer reaction Theoretical calculations coupled with experiments show that γ-CsPbI3 with a lower surface free energy becomes thermodynamically preferred over δ-CsPbI3 at surface areas greater than 8600 m
267 citations
TL;DR: La:HfO2 appears to be a material with a broad window of process parameters, and accordingly, by optimization of the La content in the layer, it is possible to improve the performance of the material significantly.
Abstract: Recently simulation groups have reported the lanthanide series elements as the dopants that have the strongest effect on the stabilization of the ferroelectric non-centrosymmetric orthorhombic phas...
211 citations
TL;DR: It is discovered that polar solvent molecules can induce the lattice distortion of ligand-stabilized cubic CsPbI3, leading to the phase transition into orthorhombic phase, which is unfavorable for photovoltaic applications.
Abstract: Despite the recent surge of interest in inorganic lead halide perovskite nanocrystals, there are still significant gaps in their stability disturbance and the understanding of their destabilization, assembly, and growth processes. Here, we discover that polar solvent molecules can induce the lattice distortion of ligand-stabilized cubic CsPbI3, leading to the phase transition into orthorhombic phase, which is unfavorable for photovoltaic applications. Such lattice distortion triggers the dipole moment on CsPbI3 nanocubes, which subsequently initiates the hierarchical self-assembly of CsPbI3 nanocubes into single-crystalline nanowires. The systematic investigations and in situ monitoring on the kinetics of the self-assembly process disclose that the more amount or the stronger polarity of solvent can induce the more rapid self-assembly and phase transition. These results not only elucidate the destabilization mechanism of cubic CsPbI3 nanocrystals, but also open up opportunities to synthesize and store cub...
198 citations
TL;DR: It was found that the large activation barrier for the transition from the tetragonal/orthorhombic to the monoclinic phase, which is the stable phase at room temperature, suppresses the phase transition, and thus, plays a critical role in the emergence of ferroelectricity.
Abstract: Hf1-xZrxO2 (x ∼ 0.5-0.7) has been the leading candidate of ferroelectric materials with a fluorite crystal structure showing highly promising compatibility with complementary metal oxide semiconductor devices. Despite the notable improvement in device performance and processing techniques, the origin of its ferroelectric crystalline phase (space group: Pca21) formation has not been clearly elucidated. Several recent experimental and theoretical studies evidently showed that the interface and grain boundary energies of the higher symmetry phases (orthorhombic and tetragonal) contribute to the stabilization of the metastable non-centrosymmetric orthorhombic phase or tetragonal phase. However, there was a clear quantitative discrepancy between the theoretical expectation and experiment results, suggesting that the thermodynamic model may not provide the full explanation. This work, therefore, focuses on the phase transition kinetics during the cooling step after the crystallization annealing. It was found that the large activation barrier for the transition from the tetragonal/orthorhombic to the monoclinic phase, which is the stable phase at room temperature, suppresses the phase transition, and thus, plays a critical role in the emergence of ferroelectricity.
138 citations
TL;DR: In this article, the authors introduce the origin, synthesis, crystal structure and phase transitions of the four polymorphic phases of BiVO4: orthorhombic (pucherite), zircon (dreyerite), scheelite monoclinic (clinobisvanite) and tetragonal.
Abstract: The BiVO4 material has attracted much attention in recent years due to its active photocatalytic properties under visible light, bright yellow color as a nontoxic pigment, and its high relative permittivity (er) and Qf (quality factor, Q × resonant frequency, f) as a potential microwave dielectric ceramic. In this review, we introduce the origin, synthesis, crystal structure and phase transitions of the four polymorphic phases of BiVO4: orthorhombic (pucherite), zircon (dreyerite), scheelite monoclinic (clinobisvanite) and scheelite tetragonal. We then precis recent studies on doped BiVO4 ceramics in terms of A site, B site and A/B site complex substitutions. Low sintering temperature (<800 °C) and high er values could be obtained in some solid solution ceramics and near zero temperature coefficient of resonant frequency (TCF/τf) values could be achieved in layered or granulated particle composite ceramics. Besides, a series of temperature stable high er microwave dielectric ceramics can also be obtained for many co-fired composite ceramics, such as BiVO4–TiO2, and BiVO4–TiO2–Bi2Ti4O11. The high er, high Qf value, low sintering temperature and chemical compatibility with some base metals suggest that BiVO4-based materials are strong candidates for both LTCC and other microwave device applications in current 4G and future 5G technologies.
132 citations
TL;DR: In this paper, a colloidal route was used to synthesize uniform Cs3Sb2Cl9 perovskite nanowires with lengths up to several microns.
Abstract: All-inorganic perovskite nanocrystals are emergent alternative of organolead halide perovskites. Cesium antimony halide (Cs3Sb2X9, X = Cl, Br, I) all-inorganic perovskites nanocrystals possessing analogous electronic configuration to the organolead halide perovskites are promising materials for optoelectronic applications. We report on a colloidal route to synthesis uniform Cs3Sb2Cl9 perovskite nanowires with lengths up to several microns. We have synthesized aspect ratio controlled nanorods with the same ∼20 nm diameter of nanowires by tuning the precursors and ligands in the reaction. The crystallinity of the nanocrystals is significantly altered from the pristine bulk trigonal and orthorhombic phases owing to the one-dimensional shape of the nanocrystals. Rietveld refinement carefully separates out orthorhombic phase from the trigonal phase revealing a coexistence of both the phases in a minor and major ratio in the nanocrystals. The functionality in the form of fast photodetector demonstrates Cs3Sb2Cl...
121 citations
TL;DR: The temperature-dependent structure evolution of the hybrid halide perovskite compounds, FASnI3 and FAPbBr3, has been monitored using high-resolution synchrotron X-ray powder diffraction to suggest dynamic motion is occurring in the inorganic sublattice due to the flexibility of the in organic network and dynamic lone pair stereochemical activity on the B-site.
Abstract: The temperature-dependent structure evolution of the hybrid halide perovskite compounds, formamidinium tin iodide (FASnI3, FA+ = CH[NH2]2+) and formamidinium lead bromide (FAPbBr3), has been monitored using high-resolution synchrotron X-ray powder diffraction between 300 and 100 K. The data are consistent with a transition from cubic Pm3m (No. 221) to tetragonal P4/mbm (No. 127) for both materials upon cooling; this occurs for FAPbBr3 between 275 and 250 K, and for FASnI3 between 250 and 225 K. Upon further cooling, between 150 and 125 K, both materials undergo a transition to an orthorhombic Pnma (No. 62) structure. The transitions are confirmed by calorimetry and dielectric measurements. In the tetragonal regime, the coefficients of volumetric thermal expansion of FASnI3 and FAPbBr3 are among the highest recorded for any extended inorganic crystalline solid, reaching 219 ppm K–1 for FASnI3 at 225 K. Atomic displacement parameters of all atoms for both materials suggest dynamic motion is occurring in the...
120 citations
TL;DR: In this article, the authors used a hard template method to encapsulate hollow nanospheres of Orthorhombic Nb2O5 hollow nanosphere into sulfur-doped graphene networks (denoted as S-Nb 2O5 HNS@S-rGO) and achieved a reversible capacity 215 mAh g−1 at 0.5 C over 100 cycles.
Abstract: Orthorhombic Nb2O5 (T-Nb2O5) has recently attracted great attention for its application as an anode for sodium ion batteries (NIBs) owing to its patulous framework and larger interplanar lattice spacing. Sulfur-doped T-Nb2O5 hollow nanospheres (diameter:180 nm) uniformly encapsulate into sulfur-doped graphene networks (denoted: S-Nb2O5 HNS@S-rGO) using hard template method. The 3D ordered porous structure not only provides good electronic transportation path but also offers outstanding ionic conductive channels, leading to an improved sodium storage performance. In addition, the introduction of sulfur to graphene and Nb2O5 leads to oxygen vacancy and enhanced electronic conductivity. The sodium storage performance of S-Nb2O5 HNS@S-rGO is unprecedented. It delivers a reversible capacity 215 mAh g−1 at 0.5 C over 100 cycles. In addition, it also possesses a great high-rate capability, retaining a stable capacity of 100 mAh g−1 at 20 C after 3000 cycles. This design demonstrates the potential applications of Nb2O5 as anode for high performance NIBs.
115 citations
TL;DR: High-resolution photoluminescence (PL) spectroscopy of single bromide-based NCs reveals the exciton fine structure in the form of sharp peaks that are linearly polarized and grouped in doublets or triplets, which directly mirror the adopted crystalline structure, tetragonal (D4h symmetry) or orthorhombic (D2h symmetry).
Abstract: All inorganic CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) belong to the novel class of confined metal–halide perovskites which are currently arousing enthusiasm and stimulating huge activity across several fields of optoelectronics due to outstanding properties. A deep knowledge of the band-edge excitonic properties of these materials is thus crucial to further optimize their performances. Here, high-resolution photoluminescence (PL) spectroscopy of single bromide-based NCs reveals the exciton fine structure in the form of sharp peaks that are linearly polarized and grouped in doublets or triplets, which directly mirror the adopted crystalline structure, tetragonal (D4h symmetry) or orthorhombic (D2h symmetry). Intelligible equations are found that show how the fundamental parameters (spin–orbit coupling, ΔSO, crystal field term, T, and electron–hole exchange energy, J) rule the energy spacings in doublets and triplets. From experimental data, fine estimations of each parameter are obtained. The analysis of the absorption spectra of an ensemble of NCs with a “quasi-bulk” behavior leads to ΔSO = 1.20 ± 0.06 eV and T = −0.34 ± 0.05 eV in CsPbBr3. The study of individual luminescence responses of NCs having sizes comparable to the exciton Bohr diameter, 7 nm, allows us to estimate the value of J to be around ≈3 meV in both tetragonal and orthorhombic phases. This value is already enhanced by confinement.
96 citations
TL;DR: The experiments reveal the decomposition route for the CsPbX3 perovskites in high vacuum, with a much higher stability than their hybrid organic-inorganic MAPb X3 counterparts.
Abstract: We present the growth, phase transitions, and thermal decomposition of CsPbX3 (X = I, Br) thin films monitored by in situ X-ray diffraction (XRD). The perovskite films are prepared in vacuum via co-evaporation of PbX2 and CsX (X = I, Br) onto glass substrates. In situ X-ray diffraction allows the observation of phase transitions and decomposition while the samples are heated with a linear temperature ramp. Our experiments reveal the decomposition route for the CsPbX3 perovskites in high vacuum, with a much higher stability than their hybrid organic–inorganic MAPbX3 counterparts. We also observe the response of a black CsPbI3 thin film to exposure to ambient air at room temperature using the same XRD system. Exposing the black CsPbI3 to ambient air leads to the formation of yellow orthorhombic δ-CsPbI3, whose crystal structure could be identified by its X-ray diffraction pattern. Additionally, the linear coefficients of expansion are determined for δ-CsPbI3 and the (020)-orientation of CsPbBr3.
TL;DR: In this article, the authors carried out first-principles calculations of bandgaps of 260 all-inorganic halide perovskites belonging to the class ABX3, with Li, Na, K, Rb, Cs, B = Pb, Sn, and Ge, and X = F, Cl, Br, I.
Abstract: In order to address an all-inorganic halide lead-free perovskite for potential photovoltaic applications, we carried out first-principles calculations of bandgaps of 260 all-inorganic halide perovskites belonging to the class ABX3, with A = Li, Na, K, Rb, Cs, B = Pb, Sn, and Ge, and X = F, Cl, Br, I. Three most common crystal symmetries were chosen, including cubic, tetragonal, and two orthorhombic phases. The bandgap exhibited increase with the decreasing of the anions radius (I, Br, Cl, F) and lowering the symmetry of the structures. With consideration of multiple factors forming perovskites, we reported three all-inorganic lead-free halides perovskites including cubic-KSnCl3, cubic-RbSnCl3, and trigonal-NaGeBr3 as candidates with desirable bandgap (1.24–1.44 eV) for photovoltaic applications.
TL;DR: In this article, a stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution.
TL;DR: In this paper, a solution combustion method was used to synthesize nanorod-like structure with a size of about 50nm dia and few microns long, which exhibited high specific capacitance with good cycle stability.
TL;DR: In this article, the Nb2O5 catalyst was used as a solid acid catalyst for the formation of lactic acid from 1,3-dihydroxyacetone and pyruvaldehyde in water at 373 K, and was determined to be a highly active and selective catalyst.
Abstract: Hydrothermal treatment of NH4[NbO(C2O4)2(H2O)2]·nH2O in water at 448 K for 3 days produced crystalline Nb2O5 with a deformed orthorhombic structure and a high surface area (208 m2 g–1). Fourier-transform infrared spectroscopy measurements of pyridine adsorption revealed that the Nb2O5 catalyst has both high densities of Bronsted and Lewis acid sites that can work in the presence of water. One feature of the Nb2O5 catalyst is its high density of water-compatible Lewis acid sites (0.21 mmol g–1), which is much larger than that of Nb2O5·nH2O (0.03 mmol g–1). The Nb2O5 catalyst was studied as a solid acid catalyst for the formation of lactic acid from 1,3-dihydroxyacetone and pyruvaldehyde in water at 373 K, and was determined to be a highly active and selective catalyst, compared with typical acid catalysts (H2SO4, Sc(OTf)3, and Nb2O5·nH2O). A high Lewis acid density with moderate acid strength is a crucial factor for the high catalytic performance exhibited for the former reaction. High densities of both Br...
TL;DR: In this paper, the fundamental properties of MAPbBr3 single crystal were investigated by applying temperature-dependent x-ray diffraction and photoluminescence (PL) measurements from 10 K to 270 K.
Abstract: We investigated the fundamental properties of MAPbBr3 single crystal by applying temperature-dependent x-ray diffraction and photoluminescence (PL) measurements from 10 K to 270 K. The structural and spectral analyses illustrate the phase transitions of MAPbBr3 single crystal from cubic phase (-MAPbBr3) to tetragonal phases (-MAPbBr3 and -MAPbBr3), and then to orthorhombic phase (-MAPbBr3) at ~230 K, ~160 K and ~150 K, respectively. The Time-resolved PL results show that both free excitons (FE) and bound excitons (BE) have contributions to the PL emissions. The PL at high temperature mainly originates from the BE transitions, while the PL at low temperature (-MAPbBr3 phase) comes from both BE and FE transitions, and the FE related PL becomes more and more dominant at lower temperatures. The first-principle calculation at zero temperature reveals that the BE-related PL was caused by defects from the anti-site substitution of MA and Br ions.
TL;DR: In this paper, a low temperature, one pot solution combustion synthesis approach using glycine as the fuel is used to synthesize a nanophosphor with Eu3+ doping, which exhibits high chemical, thermal and structural stability.
TL;DR: In this article, the XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe2O3-added (0.995-x)K0.48Na0.5Na 0.5ZrO3 0.005BiScO3 ceramics.
Abstract: Although phase boundary engineering has made notable progress in improving the electrical properties of (K,Na)NbO3-based piezoceramics, lattice distortion and spontaneous polarization of multiphase coexisting systems are a few of the remaining concerns. Here, new research employing XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe2O3-added (0.995-x)K0.48Na0.52NbO3-xBi0.5Na0.5ZrO3-0.005BiScO3 ceramics. The distortion of the oxygen octahedron and the spontaneous polarization were presented. Central cation displacement provides a much larger contribution to polarization and the electric dipole moment in orthorhombic phase is much larger than that in tetragonal phase. Benefiting from tetragonal-orthorhombic phase coexistence and lattice distortion, optimized ferroelectric and piezoelectric properties (d33 ∼ 381 pC/N, Pr ∼ 20.47 μC/cm2) were obtained. The ceramic still holds a large d33 (313 pC/N) after up to 300 ℃ of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.
TL;DR: The realization of n-type Ge chalcogenides is elusive owing to intrinsic Ge vacancies that make them p-type semiconductors, but the interplay of positive and negative chemical pressure anomalously changes the band gap of GeSe with increasing the AgBiSe2 concentration.
Abstract: The realization of n-type Ge chalcogenides is elusive owing to intrinsic Ge vacancies that make them p-type semiconductors GeSe crystallizes into a layered orthorhombic structure similar to SnSe at ambient conditions The high-symmetry cubic phase of GeSe is predicted to be stabilized by applying 7 GPa external pressure or by enhancing the entropy by increasing to temperature to 920 K Stabilization of the n-type cubic phase of GeSe at ambient conditions was achieved by alloying with AgBiSe2 (30-50 mol %), enhancing the entropy through solid solution mixing The interplay of positive and negative chemical pressure anomalously changes the band gap of GeSe with increasing the AgBiSe2 concentration The band gap of n-type cubic (GeSe)1-x (AgBiSe2 )x (030≤x≤050) has a value in the 03-04 eV range, which is significantly lower than orthorhombic GeSe (11 eV) Cubic (GeSe)1-x (AgBiSe2 )x exhibits an ultralow lattice thermal conductivity (κL ≈043 W m-1 K-1 ) in the 300-723 K range The low κL is attributed to significant phonon scattering by entropy-driven enhanced solid-solution point defects
TL;DR: In this article, single crystals of the methylammonium (MA) lead halides MAPbI3, MAPbBr3, and MAPbCl3 have been investigated using infrared spectroscopy with the aim of analyzing structural and dynamical aspects of processes that enable the ordering of the MA molecule in the orthorhombic crystal structure of these hybrid perovskites.
Abstract: Single crystals of the methylammonium (MA) lead halides MAPbI3, MAPbBr3, and MAPbCl3 have been investigated using infrared spectroscopy with the aim of analyzing structural and dynamical aspects of processes that enable the ordering of the MA molecule in the orthorhombic crystal structure of these hybrid perovskites Our temperature-dependent studies were focused on the analysis of the CH/NH rocking, C–N stretching, and CH/NH bending modes of the MA molecule in the 800–1750 cm–1 frequency range They deliver a direct comparison of the behaviors of the three halides on crossing the orthorhombic–tetragonal phase transition in MA lead halide single crystals Drastic changes of all vibrational modes close to the phase transition were clearly observed Additional spectral features that were not discussed previously are pointed out The transformation of the two-dimensional orthorhombic hydrogen bond layers into a more three-dimensional arrangement in the tetragonal phase seems to be an important feature provid
TL;DR: In this article, alcohol-based bifunctional ammonium cations, 2-hydroxyethylammonium (HEA+), HO(CH2)2NH3+, were introduced into formamidinium (FA+) tin-based perovskites (HEAxFA1-xSnI3; x = 0-1) to absorb light in carbon-based mesoscopic solar cells.
Abstract: Alcohol-based bifunctional ammonium cations, 2-hydroxyethylammonium (HEA+), HO(CH2)2NH3+, were introduced into formamidinium (FA+) tin-based perovskites (HEAxFA1–xSnI3; x = 0–1) to absorb light in carbon-based mesoscopic solar cells. We found that HEA+ cations play a key role to control the crystal structures, the lattice structures altered from orthorhombic (x = 0) to rhombohedral (x = 0.2–0.4) with greater symmetry. When x was increased to 0.6–1.0, tin and iodide vacancies were formed to generate 3D-vacant perovskites (HEAxFA1–xSn0.67I2.33, x ≥ 0.6) with a tetragonal structure. Tin-based perovskites in this series were fabricated into mesoporous solar cells using one-step drop-cast (DC), two-step solvent-extraction (SE), and SE + 3% ethylenediammonium diiodide (EDAI2) as an additive. After optimization of device performance with the SE + 3% EDAI2 approach, the HEA0.4FA0.6SnI3 (HEAI = 40%) device gave the best photovoltaic performance with JSC = 18.52 mA cm–2, VOC = 371 mV, FF = 0.562, and overall effici...
TL;DR: This work provides an effective way to stabilize the cubic CsPbI3- xBr x ( x < 1) phase at low temperature to further improve the performance of all-inorganic perovskite solar cells.
Abstract: All-inorganic cesium lead perovskites have emerged as alternative absorbing layers in solar cells owing to their superb thermal stability compared with the organic-inorganic hybrid perovskites. However, the desired cubic CsPbI3 phase forms at a high temperature and suffers from a phase transition to the orthorhombic yellow phase at room temperature. A developed nonstoichiometric method is applied to fabricate CsPbI3- xBr x ( x < 1) films by adding excess CsBr into the precursor solution. The excess CsBr in the precursor solution helps to produce a microstrain in the lattice to stabilize the cubic CsPbI3 phase at low temperature and incorporate a small part of Br- into the CsPbI3 lattice. At the optimal CsBr concentration (0.5 M), the corresponding solar cell achieves a power conversion efficiency of 10.92%. This work provides an effective way to stabilize the cubic CsPbI3- xBr x ( x < 1) phase at low temperature to further improve the performance of all-inorganic perovskite solar cells.
TL;DR: Magnetic properties and the semiconducting nature of the LPCMO nanoparticles will make them as suitable candidate for magnetic semiconductor spintronics.
Abstract: We report on microstructural, magnetic, and optical properties of Pr-doped perovskite manganite (La1 − xPrx)0.67Ca0.33MnO3 (LPCMO, x = 0.0–0.5) nanoparticles synthesized via sol-gel process. Structural characterizations (X-ray and electron diffraction patterns, (high resolution) TEM images) provide information regarding the phase formation and the single-crystalline nature of the LPCMO systems. X-ray and electron diffraction patterns reveal that all the LPCMO samples crystallize in perovskite crystallography with an orthorhombic structure (Pnma space group), where the MnO6 octahedron is elongated along the b axis due to the Jahn-Teller effect. That is confirmed by Raman spectra. Crystallite sizes and grain sizes were calculated from XRD and TEM respectively, and the lattice fringes resolved in the high-resolution TEM images of individual LPCMO nanoparticle confirmed its single-crystalline nature. FTIR spectra identify the characteristic Mn–O bond stretching vibration mode near 600 cm− 1, which shifts towards high wavenumbers with increasing post-annealing temperature or Pr-doping concentration, resulting in further distortion of the MnO6 octahedron. XPS revealed dual oxidation states of Mn3+ and Mn4+ in the LPCMO nanoparticles. UV-vis absorption spectra confirm the semiconducting nature of the LPCMO nanoparticles with optical bandgaps of 2.55–2.71 eV. Magnetic measurements as a function of temperature and magnetic field at field cooling and zero-field cooling modes, provided a Curie temperature around 230 K, saturation magnetization of about 81 emu/g, and coercive field of 390 Oe at 10 K. Such magnetic properties and the semiconducting nature of the LPCMO nanoparticles will make them as suitable candidate for magnetic semiconductor spintronics.
TL;DR: By using ab initio calculations, results of novel phases, average open circuit voltages ( Vocs), and electronic properties of the stable Li2S2 are presented, and two new Li1S2 phases are predicted: orthorhombic ( Cmca) and orthornorthern ( Immm) structures.
Abstract: The intermediate product Li2S2 plays a pivotal role in the charge/discharge process of lithium-sulfur batteries. However, the structural configuration and relevant properties of Li2S2 are unclear. In this work, by using ab initio calculations, we present results of novel phases, average open circuit voltages ( Vocs), and electronic properties of the stable Li2S2. Two new Li2S2 phases are predicted: orthorhombic ( Cmca) and orthorhombic ( Immm) structures. The calculated Vocs of hexagonal ( P63/ mmc), orthorhombic ( Cmca), and orthorhombic ( Immm) are 3.91, 3.95, and 3.88 V, respectively. In particular, the calculated band gap of the Immm structure is about 0.225 eV, which is smaller than that of Li2S. The narrow band gap of Li2S2 derives from the electronic lump between the Li s state and S 3p state for the orthorhombic structure. Therefore, the electronic properties of Li2S2 are markedly influenced by the structural configuration.
TL;DR: In this article, a method was proposed to distinguish between hexagonal and orthorhombic structures on the basis of the relationships between the 2θ and χ angles for these structures, obtained from X-ray diffraction (XRD) -scans.
Abstract: In this study, e-Ga2O3 thin films were grown by mist chemical vapor deposition on a hexagonal (0001) GaN template and a cubic (111) SrTiO3 (STO) substrate. By analyzing the obtained X-ray diffraction (XRD) -scans, it was found that the e-Ga2O3 epitaxial thin films grown on both GaN and STO exhibited an orthorhombic structure. In addition, a method was proposed to distinguish between hexagonal and orthorhombic structures on the basis of the relationships between the 2θ and χ angles for these structures, obtained from the XRD studies. Finally, a mechanism was discussed on the basis of angle relationships, where three rotational domains were observed for orthorhombic e-Ga2O3 on GaN and STO. Transmission electron microscopy was then employed to determine whether the e-Ga2O3 thin films on the GaN template and STO substrate consisted of columnar e-Ga2O3 comprising small domains and intermediate layers between the e-Ga2O3 film and the substrate.
TL;DR: Sodium cadmium orthophosphate NaCdPO4 was prepared by solid-state reaction method at high temperature under air atmosphere as discussed by the authors, where structural, morphology and electrical properties have been investigated.
Abstract: Sodium cadmium orthophosphate NaCdPO4 was prepared by solid-state reaction method at high temperature under air atmosphere. Structural, morphology and electrical properties have been investigated. X-ray powder diffraction analysis indicated that the sample is well crystallized in the orthorhombic maricite structure with Pmnb space group. The composition and morphology of the compound were performed by energy dispersive spectroscopy coupled with scanning electron microscope. Electrical properties were carried out in the frequency range 209 Hz–1 MHz at various temperatures 595–700 K using impedance spectroscopy technique. Nyquist plots analysis revealed the presence of two contributions at different temperatures associated with grain and grain boundary. In order to explain the impedance results an equivalent circuit has been proposed. The AC conductivity was analyzed by Jonscher’s power law of frequency (σ
ac
(ω) ∞ Aω
s
). At high frequency, the conduction mechanism was well interpreted in term overlapping large polaron tunneling.
TL;DR: The structural transformation of cesium lead iodine (CsPbI3) has been investigated in diamond anvil cells up to ∼15 GPa at room temperature by employing synchrotron radiation X-ray diffraction and Raman spectroscopy as mentioned in this paper.
Abstract: The structural transformation of cesium lead iodine (CsPbI3) has been investigated in diamond anvil cells up to ∼15 GPa at room temperature by employing synchrotron radiation X-ray diffraction and Raman spectroscopy. One reversible transformation from orthorhombic (Pnma) to monoclinic (P21/m) phase has been observed at 3.9 GPa. Isothermal pressure–volume relationship of orthorhombic CsPbI3 is well fitted by the third-order Birch–Murnaghan equation of state with K0 = 14(3) GPa, K′0 = 6(2) and V0 = 891(7) A3. The ultralow value of bulk modulus K0 demonstrates the high compressible nature of CsPbI3, similar to those of organic–inorganic metal halide perovskites. The present results provide essential information on the intrinsic properties and stability of CsPbI3, which may be applied in photovoltaic devices.
TL;DR: This work presents a feature of a polar vortex in BiFeO3 films showing morphotropic phase boundary character, which offers a potential degree of manipulating phase components and properties of ferroelectric topological structures.
Abstract: Strongly correlated oxides exhibit multiple degrees of freedoms, which can potentially mediate exotic phases with exciting physical properties, such as the polar vortex recently found in ferroelectric oxide films. A polar vortex is stabilized by competition between charge, lattice, and/or orbital degrees of freedom, which displays vortex–ferroelectric phase transitions and emergent chirality, making it a potential candidate for designing information storage and processing devices. Here, by a combination of controlled film growth and aberration-corrected scanning transmission electron microscopy, we obtain nanoscale vortex arrays in [110]-oriented BiFeO3 films. These vortex arrays are stabilized in ultrathin BiFeO3 layers sandwiched by two coherently grown orthorhombic scandate layers, exhibiting a ferroelectric morphotropic phase boundary constituted by a mixed-phase structure of polar orthorhombic BiFeO3 and rhombohedral BiFeO3. Clear polarization switching and piezoelectric signals were observed in thes...
TL;DR: In this article, the nano-sized niobium pentoxide (Nb2O5) with different morphologies and phase structures are synthesized through a very simple thermal treatment method.
TL;DR: In this paper, hot-filament metal oxide vapor deposition technique was used to obtain one-dimensional nanorods of MoO2, MoO3 and Magneli-phase Mo4O11.