Showing papers on "Orthorhombic crystal system published in 2012"
TL;DR: A structural investigation revealed the orthorhombic phase to be of space group Pbc2(1), whose noncentrosymmetric nature is deemed responsible for the spontaneous polarization in this novel, nanoscale ferroelectrics.
Abstract: The transition metal oxides ZrO2 and HfO2 as well as their solid solution are widely researched and, like most binary oxides, are expected to exhibit centrosymmetric crystal structure and therewith linear dielectric characteristics. For this reason, those oxides, even though successfully introduced into microelectronics, were never considered to be more than simple dielectrics possessing limited functionality. Here we report the discovery of a field-driven ferroelectric phase transition in pure, sub 10 nm ZrO2 thin films and a composition- and temperature-dependent transition to a stable ferroelectric phase in the HfO2–ZrO2 mixed oxide. These unusual findings are attributed to a size-driven tetragonal to orthorhombic phase transition that in thin films, similar to the anticipated tetragonal to monoclinic transition, is lowered to room temperature. A structural investigation revealed the orthorhombic phase to be of space group Pbc21, whose noncentrosymmetric nature is deemed responsible for the spontaneous...
1,161 citations
TL;DR: The synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI(3), coupled with ab initio first-principles density functional theory (DFT) calculations are described.
Abstract: CsSnI3 is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI3 have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI3, coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI3. The black orthorhombic form of CsSnI3 demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior w...
810 citations
TL;DR: A new nanocrystalline sensitizer with the chemical formula (CH3CH2NH3)PbI3 is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated.
Abstract: A new nanocrystalline sensitizer with the chemical formula (CH3CH2NH3)PbI3 is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a = 8.7419(2) A, b = 8.14745(10) A, and c = 30.3096(6) A, which can be described as 2 H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6 eV versus vacuum and the optical bandgap of ca. 2.2 eV. A spin coating of the CH3CH2NH3I and PbI2 mixed solution on a TiO2 film yields ca. 1.8-nm-diameter (CH3CH2NH3)PbI3 dots on the TiO2 surface. The (CH3CH2NH3)PbI3-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5 G one sun (100 mW/cm2) illumination.
245 citations
TL;DR: In this article, the effects of crystal structure and electronic structure on the photocatalytic activities of cubic NaNbO3 have been investigated by H2 evolution from aqueous methanol solution and CO2 photoreduction in gas phase.
Abstract: Cubic and orthorhombic NaNbO3 were fabricated to study the effects of crystal structure and electronic structure on the photocatalytic activities in detail. The samples were characterized by X-ray diffraction, field emission transmission electron microscopy, high-resolution transmission electron microscopy, UV–visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the two phases of NaNbO3 have been assessed by H2 evolution from aqueous methanol solution and CO2 photoreduction in gas phase. The photocatalytic H2 evolution and CO2 reduction activities over cubic NaNbO3 were nearly twice of those over orthorhombic NaNbO3. The first-principles calculation reveals that the higher activity over cubic NaNbO3 can be attributed to its unique electronic structure, which is beneficial for electron excitation and transfer.
241 citations
TL;DR: In this article, a simple probe ultrasonic approach was used to synthesize hexagonal molybdenum oxide (h -MoO 3 ) and an irreversible phase transition occurred to form orthorhombic α-MoO3 after annealing at 436°C.
Abstract: Molybdenum oxide nanorods have been successfully synthesized by a simple probe ultrasonic approach. A possible growth mechanism of the MoO 3 nanorods and the influence of ultrasonic times on morphologies have been investigated. The characterization results of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and differential thermal analysis (DTA) demonstrate that the nanorods exhibits hexagonal molybdenum oxide ( h -MoO 3 ) and an irreversible phase transition occurs to form orthorhombic α-MoO 3 after annealing at 436 °C. The gas sensing tests indicate that the MoO 3 based sensor has high response to NO 2 and the response is not interfered by CO and CH 4 at operating temperature of 290 °C. The intrinsic sensing performance arises from the non-stoichiometry of MoO 3 due to the presence of Mo 5+ ions in the lattice of oxide, which has been confirmed by the results of X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis.
173 citations
TL;DR: In this article, a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth R3+ cations (R = Y, La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) is presented.
Abstract: We report a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth R3+ cations (R = Y, La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu). The room-temperature Raman spectra and the associated phonon mode assignment provide reference data for structural investigation of the whole series of RCrO3 orthochromites and phonon ab-initio calculations. The assignment of the chromite spectra and comparison with Raman data on other orthorhombic perovskites allows correlating the phonon modes with the structural distortions in the RCrO3 series. In particular, two Ag modes are identified as octahedra rotation soft modes, as their positions scale linearly with the octahedra tilt angle of the CrO6 octahedra.
164 citations
TL;DR: Theoretical analysis of the electronic structure allows us to elucidate the origin of this nonstoichiometry and the attendant mixed ion-electron conductor character so important for intermediate temperature fuel cell operation.
Abstract: We characterize experimentally and theoretically the promising new solid oxide fuel cell electrode material Sr2Fe1.5Mo0.5O6−δ (SFMO). Rietveld refinement of powder neutron diffraction data has determined that the crystal structure of this material is distorted from the ideal cubic simple perovskite, instead belonging to the orthorhombic space group Pnma. The refinement revealed the presence of oxygen vacancies in the as-synthesized material, resulting in a composition of Sr2Fe1.5Mo0.5O5.90(2) (δ = 0.10(2)). DFT+U theory predicts essentially the same concentration of oxygen vacancies. Theoretical analysis of the electronic structure allows us to elucidate the origin of this nonstoichiometry and the attendant mixed ion–electron conductor character so important for intermediate temperature fuel cell operation. The ease with which SFMO forms oxygen vacancies and allows for facile bulk oxide ion diffusivity is directly related to a strong hybridization of the Fe d and O p states, which is also responsible for ...
156 citations
TL;DR: In this paper, an orthorhombic CZnSnS4 (CZTS) was synthesized via an ethylenediamine-assisted hydrothermal method.
Abstract: Cu2ZnSnS4 (CZTS) is acknowledged as an alternative to traditional p-type semiconductors. Traditionally obtained CZTS, however, is mostly kesterite or stannite phase, which features a tetragonal crystal cell. Herein, novel orthorhombic CZTS has been synthesized via an ethylenediamine-assisted hydrothermal method. Ethylenediamine plays an important part in the construction of the orthorhombic phase. Kesterite CZTS was also obtained in an ultrapure water system without ethylenediamine. The structure was confirmed by XRD, XPS and HRTEM. The band gap of the orthorhombic CZTS is about 1.45 eV, which approaches the optimum value for solar photoelectric conversion. What's more, we found that this orthorhombic CZTS is metastable. After annealing at 500 °C, a phase transformation from the orthorhombic structure to the tetragonal kesterite structure was achieved. The photoelectric response was also characterised, which demonstrated its potential for application in photovoltaic devices.
132 citations
TL;DR: In this article, the authors found that poly(l-lactide) (PLLA) chains take the left-handed 103) helical conformation and are packed in the orthorhombic lattice.
Abstract: By screening examinations for a wide variety of organic solvents, we found that poly(l-lactide) (PLLA) forms the crystalline complex (e-form) with the specific organic solvents such as tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) below room temperature. It was revealed that PLLA has high selectivity for low molecular weight compounds to form the e-crystals. By fiber diagram analyses for the e-forms, it was found that PLLA chains take the 107 (left-handed 103) helical conformation and are packed in the orthorhombic lattice (a = 1.5–1.6 nm, b = 1.2–1.3 nm, c = 2.8–2.9 nm, and α = β = γ = 90°). Based on R-factor and packing energy calculations, the plausible crystal structure of PLLA–DMF complex was proposed, in which four PLLA chains and eight guest solvents are packed in the unit cell.
127 citations
TL;DR: In this article, the effects of sintering temperature on the crystalline structure and piezoelectric properties of BaTiO 3 ceramics have been investigated using XRD patterns.
Abstract: BaTiO 3 ceramics were prepared by conventional sintering technique with a special emphasis on the effects of sintering temperature (1100–1230 °C) on the crystalline structure and piezoelectric properties. XRD patterns indicated that the crystallographic structure changed from tetragonal phase to orthorhombic one with raising sintering temperature from 1160 °C to 1180 °C. Domains were shaped in a stripe and a herringbone in orthorhombic samples for BaTiO 3 ceramics. The domain width and domain density increased with raising sintering temperature. The BaTiO 3 ceramic sintered at 1190 °C showed the excellent electrical properties, d 33 = 355 pC/N, k p = 40%, P r = 10.2 μC/cm 2 , respectively, which are originated to the contributions of both the crystallographic structure transition and nano-domain.
115 citations
TL;DR: In this article, Orthorhombic α-MoO3 microplates were produced from (NH4)6Mo7O24ċ4H2O solid powder by a 900 W microwave plasma for 40, 50, and 60min.
Abstract: Orthorhombic α-MoO3 microplates were produced from (NH4)6Mo7O24ċ4H2O solid powder by a 900 W microwave plasma for 40, 50, and 60min. Phase, morphologies, and vibration modes were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and Raman and Fourier transform infrared (FTIR) spectroscopy. Sixty min processing resulted in the best crystallization of the α-MoO3 phase, with photoluminescence (PL) in a wavelength range of 430-440 nm.
TL;DR: The new compound LiGaGe(2)Se(6) has been synthesized and melts congruently at a rather low temperature of 710 °C, which indicates that bulk crystals can be obtained by the Bridgman-Stockbarger technique.
Abstract: The new compound LiGaGe2Se6 has been synthesized. It crystallizes in the orthorhombic space group Fdd2 with a = 12.501(3) A, b = 23.683(5) A, c = 7.1196(14) A, and Z = 8. The structure is a three-dimensional framework composed of corner-sharing LiSe4, GaSe4, and GeSe4 tetrahedra. The compound exhibits a powder second harmonic generation signal at 2 μm that is about half that of the benchmark material AgGaSe2 and possesses a wide band gap of about 2.64(2) eV. LiGaGe2Se6 melts congruently at a rather low temperature of 710 °C, which indicates that bulk crystals can be obtained by the Bridgman–Stockbarger technique. According to a first-principles calculation, there is strong hybridization of the 4s and 4p orbitals of Ga, Ge, and Se around the Fermi level. The calculated birefractive index is Δn = 0.04 for λ ≥ 1 μm, and the calculated major SHG tensor elements are d15 = 18.6 pm/V and d33 = 12.8 pm/V. This new material is promising for application in IR nonlinear optics.
TL;DR: The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method.
Abstract: The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature. An accuracy of the order of 10−5 has been achieved by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method. The results on cubic SrTiO3 [a = 3.905268 (98) A], orthorhombic DyScO3 [a = 5.442417 (54), b = 5.719357 (52) and c = 7.904326 (98) A], and orthorhombic NdGaO3 [a = 5.428410 (54), b = 5.498407 (55) and c = 7.708878 (95) A] are discussed in view of possible systematic errors as well as non-stoichiometry in the crystals.
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TL;DR: In this paper, a tensile-strained orthorhombic phase of the multiferroic BiFeO 3 was created via strain engineering by growing it on a NdScO 3 substrate.
Abstract: A new orthorhombic phase of the multiferroic ${\mathrm{BiFeO}}_{3}$ has been created via strain engineering by growing it on a ${\mathrm{NdScO}}_{3}(110{)}_{o}$ substrate. The tensile-strained orthorhombic ${\mathrm{BiFeO}}_{3}$ phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane $⟨110{⟩}_{\mathrm{pc}}$ directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism.
TL;DR: Li2B3O4F3 was obtained by a solid state reaction from LiBO2 and LiBF4 at 553 K and crystallizes in the acentric orthorhombic space group P212121 (no. 19) with the cell parameters a=4.8915(9), b=8.734(2), and c=12.301(2) A as discussed by the authors.
TL;DR: In this article, a noncentrosymmetric (NCS) compound, MgTeMoO6, has been synthesized using the high temperature solution method with TeO2-MoO3 mixture as a flux.
Abstract: A noncentrosymmetric (NCS) compound, MgTeMoO6, has been synthesized using the high temperature solution method with TeO2–MoO3 mixture as a flux. MgTeMoO6 crystalizes in the orthorhombic space group P21212 (No. 18) with cell parameters a = 5.03780(10) A, b = 5.26910(10) A, c = 8.8985(2) A, and Z = 2. The compound exhibits a novel neutral layered structure consisting of asymmetric MgO6 octahedra, TeO4 polyhedra and MoO4 tetrahedra. Thermal stability measurements revealed an incongruent melting point of 682.35 °C. The crystal exhibits a very broad transmission range from 360 nm to 5.2 μm. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicates that the crystal exhibits a strong SHG efficiency of ∼1.5 × KTiOPO4. Additional SHG measurements indicate the material is type-I phase-matchable. Furthermore, calculations on the local dipole moment indicates that the strong SHG response of MgTeMoO6 is mainly caused by the three types of NLO-active units (TeO4, MoO4 and MgO6).
TL;DR: In this paper, an orthorhombic carbon (O$-carbon) in $Pbam$ (${D}_{2h}^{9}$) symmetry was identified for compressed graphite in AA stacking, which is formed via a distinct one-layer by one layer slip and buckling mechanism along the [210] direction.
Abstract: We identify by ab initio calculations an orthorhombic carbon ($O$-carbon) in $Pbam$ (${D}_{2h}^{9}$) symmetry for compressed graphite in AA stacking, which is formed via a distinct one-layer by one-layer slip and buckling mechanism along the [210] direction. It is dynamically stable and energetically more favorable than other known compressed graphite phases, albeit its slightly higher kinetic barrier. The $O$-carbon is comparable to diamond in ultralow compressibility, has a band gap wider than that of diamond, and is compatible with experimental x-ray diffraction data. The present results offer insights for understanding the complex structural landscape of compressed graphite and the versatile nature of carbon in forming a rich variety of structures under pressure.
TL;DR: In this article, a new package for calculating the elastic constants of orthorhombic structure is proposed, which is compatible with the highly accurate all-electron full-potential (linearized) augmented plane-wave plus local orbital [FP-(L)APW+lo] method implemented in WIEN2k code.
TL;DR: In this paper, the microstructure and crystallography of eutectic borides and secondary precipitations in 18.5% C steel have been investigated extensively, and the results show that the as-cast micro-structure of Cr-Ni-Mo-containing Fe-B steel is composed of a dendritic martensite with large interdendritic eutectoric borsides.
TL;DR: In this article, the crystal structure of melted CaZrO 3 was compared with a conventionally synthesized material and it was found that the obtained material has an orthorhombic perovskite-like structure.
Abstract: Calcium zirconate (CaZrO 3 ), because of its high melting point, low thermal expansion coefficient, high strength and excellent corrosion resistance against alkali oxides, is a good candidate for a novel refractory material. CaZrO 3 is mostly synthesized by the reaction in the solid state but the material obtained in such a way often suffers low bulk density, high porosity and other defects which lower its potential application value. To overcome these obstacles a novel synthesis method by an electric arc melting technique was proposed. The crystal structure of melted CaZrO 3 was compared with a conventionally synthesized material. According to X-ray measurements the obtained material has an orthorhombic perovskite-like structure. Its stoichiometry was confirmed by the scanning electron microscope and EDS analysis. The material is almost poreless with its density close to theoretical. The estimated crystal structure parameters were used to calculate the electronic structure of CaZrO 3 using the full potential linear augmented plane wave (FLAPW) method. It has been found that CaZrO 3 is an insulator with the energy band gap of 4.1 eV. The Ca–O bond is typically ionic while Zr–O bond is of a significant covalent character.
TL;DR: In this paper, the authors used the density functional theory to calculate the band structures and density of states (DOS) of an ANbO 3 (A=Na, K) photocatalysts, which are indirect band gap semiconductors with an orthorhombic system.
TL;DR: A novel carbon polymorph with an orthorhombic Cmcm symmetry is predicted, named as C carbon, which has the lowest enthalpy among the previously proposed cold-compressed graphite phases.
Abstract: Based on an ab initio evolutionary algorithm, a novel carbon polymorph with an orthorhombic Cmcm symmetry is predicted, named as C carbon, which has the lowest enthalpy among the previously proposed cold-compressed graphite phases.
TL;DR: Room temperature lasing was stably observed in air from an orthorhombic crystal of 5,5'-bis(4'-methoxybiphenyl-4-yl)-2,2'-bithiophene (BP2T-OMe) indicating a promising potential of BP2T -OMe for organic laser media.
Abstract: Room temperature lasing was stably observed in air from an orthorhombic crystal of 5,5'-bis(4'-methoxybiphenyl-4-yl)-2,2'-bithiophene (BP2T-OMe). A pair of parallel {110} facets of the single crystal acted as effective Fabry-Perot mirrors. This prominent lasing is based on high group refractive index (3.5) and Q factor (4500) of the orthorhombic crystal resonator indicating a promising potential of BP2T-OMe for organic laser media.
TL;DR: In this paper, a series of Nb2O5-doped mixed conducting materials have been synthesized by the solid-state reaction method and the crystal structure, phase stability, oxygen desorption behavior, thermal expansion behavior, electrical conductivity and oxygen permeability of the prepared materials were systematically investigated.
TL;DR: In this article, single phase hexagonal and orthorhombic YFeO3 were prepared by a citric acid assisted sol-gel process, and the prepared samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area measurement, transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and UV-Vis diffuse reflectance spectroscopy (DRS).
TL;DR: In this article, the structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R 3 ¯ c structure of LaFeO3 is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes.
TL;DR: V(2)O(5) NBs display a high electrochemical performance in a non-aqueous electrolyte as a cathode material for lithium ion batteries and field emission properties are investigated which shows that a low turn-on field is required to draw the emission current density.
Abstract: High-quality self-assembled V2O5 nanofiber-bundles (NBs) are synthesized by a simple and direct hydrothermal method using a vanadium(V) hydroxylamido complex as a vanadium source in the presence of HNO3. The possible reaction pathway for the formation of V2O5 NBs is discussed and demonstrated that HNO3 functions both as an oxidizing and as an acidification agent. V2O5 NBs are single-crystals of an orthorhombic phase that have grown along the [010] direction. A bundle is made of indefinite numbers of homogeneous V2O5 nanofibers where nanofibers have lengths up to several micrometres and widths ranging between 20 and 50 nm. As-prepared V2O5 NBs display a high electrochemical performance in a non-aqueous electrolyte as a cathode material for lithium ion batteries. Field emission properties are also investigated which shows that a low turn-on field of ∼1.84 V μm−1 is required to draw the emission current density of 10 μA cm−2.
TL;DR: It is demonstrated in BaFe2As2 samples detwinned via uniaxial strain that the in-plane C4 symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures.
Abstract: We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$. Our data show that modest strain fields along the in-plane orthorhombic $b$ axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ samples detwinned via uniaxial strain that the in-plane ${C}_{4}$ symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material.
TL;DR: In this article, a Monte Carlo random walk model was developed to simulate the chain structure of amorphous layers in polyethylene, and the chains emerging from the orthorhombic crystal lamellae were either folding bac...
TL;DR: Initial second harmonic generation (SHG) experiments showed crystalline K(4)GeP( 4)Se(12) outperforms the other alkali metal analogues and exhibits the strongest second harmonicgeneration response among reported quaternary chalcophosphates, ~30 times that of AgGaSe(2) at 730 nm.
Abstract: A new series of germanium chalcophosphates with the formula A4GeP4Q12 (A = K, Rb, Cs; Q = S, Se) have been synthesized. The selenium compounds are isostructural and crystallize in the polar orthorhombic space group Pca21. The sulfur analogues are isostructural to one another but crystallize in the centrosymmetric monoclinic space group C2/c. All structures contain the new molecular anion [GeP4Q12]4–; however, the difference between the sulfides and selenides arises from the change in crystal packing. Each discrete molecule is comprised of two ethane-like P2Q6 units that chelate to a central tetrahedral Ge4+ ion in a bidentate fashion. The selenides were synthesized pure by stoichiometric reaction of the starting materials, whereas the sulfides contained second phases. The band gaps of the molecular salts are independent of the alkali metal counterions and have a value of 2.0 eV for the selenides and 3.0–3.1 eV for the sulfides. All A4GeP4Se12 compounds melt congruently, and the potassium analogue can be q...