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Showing papers on "Orthorhombic crystal system published in 2009"


Journal ArticleDOI
TL;DR: High resolution electron microscopy at low temperatures further reveals an unexpected additional modulation of the crystal structure of the superconducting phase that involves displacements of the Fe atoms, and that the nonsuperconducting composition shows a different, complex nanometer-scale structural modulation.
Abstract: In this Letter we show that superconducting ${\mathrm{Fe}}_{1.01}\mathrm{Se}$ undergoes a structural transition at 90 K from a tetragonal to an orthorhombic phase but that nonsuperconducting ${\mathrm{Fe}}_{1.03}\mathrm{Se}$ does not. High resolution electron microscopy at low temperatures further reveals an unexpected additional modulation of the crystal structure of the superconducting phase that involves displacements of the Fe atoms, and that the nonsuperconducting composition shows a different, complex nanometer-scale structural modulation. Finally, we show that magnetism is not the driving force for the phase transition in the superconducting phase.

428 citations


Journal ArticleDOI
TL;DR: In this article, a detailed investigation using variable temperature powder neutron diffraction demonstrates that BiFeO3 undergoes a phase transition from the ferroelectric alpha phase (rhombohedral, R3c) to a paraelectric beta phase (orthorhombic, Pbnm) between 820 degrees C and 830 degrees C.
Abstract: A detailed investigation using variable temperature powder neutron diffraction demonstrates that BiFeO3 undergoes a phase transition from the ferroelectric alpha phase (rhombohedral, R3c) to a paraelectric beta phase (orthorhombic, Pbnm) between 820 degrees C and 830 degrees C. Coexistence of both phases over a finite temperature interval, together with abrupt changes in key structural parameters, confirms that the transition is first order. The beta phase corresponds to a GdFeO3-type perovskite structure.

265 citations


Journal ArticleDOI
TL;DR: These materials show higher thermal stability than other metal-organic perovskite series of [AmineH][M(HCOO)(3)] templated by the organic monoammonium cations as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework.
Abstract: We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal-organic perovskite ABX(3), [C(NH(2))(3)][M(II)(HCOO)(3)], in which A = C(NH(2))(3) is guanidinium, B = M is a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO(-). The compounds could be synthesized by either diffusion or hydrothermal methods from water or water-rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna2(1). In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti-anti formate bridges, thus forming the anionic NaCl-type [M(HCOO)(3)](-) frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn-Teller effect of Cu(2+) results in a distorted anionic Cu-formate framework that can be regarded as Cu-formate chains through short basal Cu-O bonds linked by the long axial Cu-O bonds. These materials show higher thermal stability than other metal-organic perovskite series of [AmineH][M(HCOO)(3)] templated by the organic monoammonium cations (AmineH(+)) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin-canted antiferromagnetism, with a Neel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin-canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin-flop and a spin-flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.

227 citations


Journal ArticleDOI
TL;DR: In this paper, the crystal structure and luminescence properties of Eu 2+ -doped Sr x Ca 1−− x AlSiN 3 (0.2 ǫ −1) red phosphor were characterized.

181 citations


Journal ArticleDOI
TL;DR: The transition from rhombohedral BiFeO3 to the antiferroelectric PbZrO3-like structure implies a modification from polar to antipolar behavior as mentioned in this paper.
Abstract: Bi1−xNdxFeO3 (0≤x≤0.2) ceramics have been investigated using x-ray diffraction (XRD) and electron diffraction (ED). XRD patterns for x≤0.1 were consistent with rhombohedral BiFeO3, whereas those for x=0.15 and x=0.2 exhibited peak splitting and superlattice reflections representative of orthorhombic, antiferroelectric PbZrO3. ED for the latter samples confirmed the presence of 14(hk0) superlattice reflections typical of a PbZrO3-like structure but additional superlattice reflections were observed at 14(00l) yielding a √2a,2√2a,4a (where a is the pseudocubic lattice parameter) unit cell. The transition from rhombohedral BiFeO3 to the PbZrO3-like structure implies a modification from polar to antipolar behavior.

161 citations


Journal ArticleDOI
TL;DR: In this article, the phase diagram of lead-free piezoelectric KxNa1−xNbO3 has been studied, with particular focus on the proposed morphotropic phase boundaries, by powder and single crystal x-ray diffraction.
Abstract: The phase diagram of lead-free piezoelectric KxNa1−xNbO3 has been studied, with particular focus on the proposed morphotropic phase boundaries, by powder and single crystal x-ray diffraction. The tilt system and cation displacement has been mapped out as a function of temperature and composition, highlighting changes in the oxygen octahedra at x=0.2 and x=0.4 at room temperature. The orthorhombic to monoclinic boundary at x=0.5 has been investigated, with a subtle change in the structure observed. The conclusion is that KxNa1−xNbO3 does not display a morphotropic phase boundary comparable with that in lead zirconate titanate, and that the most significant structural change as a function of composition occurs at x=0.2 because of the change of the tilt system.

143 citations


Journal ArticleDOI
TL;DR: An orthorhombic (space group Pnnm) boron phase was synthesized at pressures above 9GPa and high temperature, and it was demonstrated to be stable at least up to 30GPa as discussed by the authors.
Abstract: An orthorhombic (space group Pnnm) boron phase was synthesized at pressures above 9GPa and high temperature, and it was demonstrated to be stable at least up to 30GPa. The structure, determined by single-crystal x-ray diffraction, consists of B12 icosahedra and B2 dumbbells. The charge density distribution obtained from experimental data and abinitio calculations suggests covalent chemical bonding in this phase. Strong covalent interatomic interactions explain the low compressibility value (bulk modulus is K300=227GPa) and high hardness of high-pressure boron (Vickers hardness HV=58GPa), after diamond the second hardest elemental material. © 2009 The American Physical Society.

139 citations


Journal ArticleDOI
TL;DR: In this paper, the authors identify the phase lines corresponding to transitions among the ambient-pressure paramagnetic tetragonal (T), the antiferromagnetic orthorhombic (O), and the nonmagnetic collapsed tetragon (cT) phases of a single-crystal neutron and high-energy x-ray diffraction.
Abstract: Single-crystal neutron and high-energy x-ray diffraction measurements have identified the phase lines corresponding to transitions among the ambient-pressure paramagnetic tetragonal (T), the antiferromagnetic orthorhombic (O), and the nonmagnetic collapsed tetragonal (cT) phases of ${\text{CaFe}}_{2}{\text{As}}_{2}$. We find no evidence of additional structures for pressures of up to 2.5 GPa (at 300 K). Both the T-cT and O-cT transitions exhibit significant hysteresis effects, and we demonstrate that coexistence of the O and cT phases can occur if a nonhydrostatic component of pressure is present. Measurements of the magnetic diffraction peaks show no change in the magnetic structure or ordered moment as a function of pressure in the O phase, and we find no evidence of magnetic ordering in the cT phase. Band-structure calculations show that the transition into the cT phase results in a strong decrease in the iron $3d$ density of states at the Fermi energy, consistent with a loss of the magnetic moment.

139 citations


Journal ArticleDOI
TL;DR: It is shown that well-defined, highly crystalline nanowires of a rigid rod conjugated polymer, a poly(para-phenylene ethynylene)s derivative with thioacetate end groups (TA-PPE), can be obtained by self-assembling from a dilute solution.
Abstract: In this paper, we show that well-defined, highly crystalline nanowires of a rigid rod conjugated polymer, a poly(para-phenylene ethynylene)s derivative with thioacetate end groups (TA-PPE), can be obtained by self-assembling from a dilute solution. Structural analyses demonstrate the nanowires with an orthorhombic crystal unit cell wherein the lattice parameters are a ≈ 13.63 A, b ≈ 7.62 A, and c ≈ 5.12 A; in the nanowires the backbones of TA-PPE chains are parallel to the nanowire long axis with their side chains standing on the substrate. The transport properties of the nanowires examined by organic field-effect transistors (OFETs) suggest the highest charge carrier mobility approaches 0.1 cm2/(V s) with an average value at ∼10−2 cm2/(V s), which is 3−4 orders higher than that of thin film transistors made by the same polymer, indicating the high performance of the one-dimensional polymer nanowire crystals. These results are particular intriguing and valuable for both examining the intrinsic properties ...

133 citations


Journal ArticleDOI
TL;DR: In this article, a novel SnWO4 visible-light active photocatalysts with two polymorphs (orthorhombic α and cubic β phases) were prepared by a conventional solid-state reaction method, and their optical properties, electronic band structure, and photocatalysis activities were investigated.
Abstract: Novel SnWO4 visible-light active photocatalysts with two polymorphs (orthorhombic α and cubic β phases) were prepared by a conventional solid-state reaction method, and their optical properties, electronic band structure, and photocatalytic activities were investigated. It was found that the low-temperature phase, α-SnWO4 with corner-shared WO6 octahedra, exhibited a dark-red color and indirect band gap of 1.64 eV, whereas the high-temperature phase, β-SnWO4 with unshared WO4 tetrahedra, exhibited a light-yellow color and direct band gap of 2.68 eV. The Mott−Schottky plots obtained using a thick film electrode in 1 M NaCl electrolyte revealed the n-type semiconductive properties of the SnWO4 polymorphs; i.e., the flat-band potential values of α- and β-SnWO4 were −0.61 and −0.66 V (SCE), respectively. From the electronic band structure calculations performed using density functional theory, the Sn 5p and O 2p orbitals were hybridized to construct the valence band in both SnWO4 polymorphs. However, the cons...

130 citations


Journal ArticleDOI
TL;DR: A photodegradation study on Procion Red MX 5B was carried out, showing that the hexagonal WO3nanowire clusters had the highest photodegrades efficiency.
Abstract: Tungsten trioxide (WO3) nanostructures were synthesized by hydrothermal method using sodium tungstate (Na2WO4·2H2O) alone as starting material, and sodium tungstate in presence of ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] or cobalt chloride (CoCl2·6H2O) as structure-directing agents. Orthorhombic WO3having a rectangular slab-like morphology was obtained when Na2WO4·2H2O was used alone. When ferrous ammonium sulfate and cobalt chloride were added to sodium tungstate, hexagonal WO3nanowire clusters and hexagonal WO3nanorods were obtained, respectively. The crystal structure and orientation of the synthesized products were studied by X-ray diffraction (XRD), micro-Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM), and their chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). The optical properties of the synthesized products were verified by UV–Vis and photoluminescence studies. A photodegradation study on Procion Red MX 5B was also carried out, showing that the hexagonal WO3nanowire clusters had the highest photodegradation efficiency.

Journal ArticleDOI
TL;DR: Structural analysis of the crystal under various stages of tensile strain reveals that the deformation behavior manifests itself mainly in the rotation of the PO(4) tetrahedron with concomitant movements of both the columnar and axial Ca ions.

Journal ArticleDOI
TL;DR: The correlation between structural distortion and superconductivity in FeSe(1-x) thin films with different preferred growth orientations is reported, suggesting that the low temperature structural distortion is closely associated with thesuperconductivity of this material.
Abstract: Superconductivity was recently found in the tetragonal phase FeSe. A structural transformation from tetragonal to orthorhombic (or monoclinic, depending on point of view) was observed at low temperature, but was not accompanied by a magnetic ordering as commonly occurs in the parent compounds of FeAs-based superconductors. Here, we report the correlation between structural distortion and superconductivity in ${\mathrm{FeSe}}_{1\ensuremath{-}x}$ thin films with different preferred growth orientations. The films with preferred growth along the $c$ axis show a strong thickness dependent suppression of superconductivity and low temperature structural distortion. In contrast, both properties are less affected in the films with (101) preferred orientation. These results suggest that the low temperature structural distortion is closely associated with the superconductivity of this material.

Journal ArticleDOI
TL;DR: In this article, the relationship between the crystal structure, charge doping and magnetism in AFe2As2 systems was analyzed using first-principle band structure calculations, and the tetragonal to orthorhombic structural distortion along with the associated magnetic order and anisotropy, the influence of doping on the A site and the Fe site were analyzed.
Abstract: The electronic structure and physical properties of the pnictide compound families REOFeAs (RE = La, Ce, Pr, Nd, Sm), AFe2As2 (A = Ca, Sr, Ba, Eu), LiFeAs and FeSe are quite similar. Here, we focus on the members of the AFe2As2 family whose sample composition, quality and single-crystal growth are more controllable compared with the other systems. Using first-principles band structure calculations, we focus on understanding the relationship between the crystal structure, charge doping and magnetism in AFe2As2 systems. We will elaborate on the tetragonal to orthorhombic structural distortion along with the associated magnetic order and anisotropy, the influence of doping on the A site and the Fe site and the changes in the electronic structure as a function of pressure. Experimentally, we investigate the substitution of Fe in SrFe2 xTMxAs2 by other 3d transition metals, TM = Mn, Co or Ni. In contrast to a partial substitution of Fe by Co or Ni (electron doping), a corresponding Mn partial substitution does not lead to the suppression of the antiferromagnetic order or the appearance of superconductivity. Most of the calculated properties agree well with the measured properties, but several of them are sensitive to the As z position. For a microscopic understanding of the electronic structure of this new family of superconductors, this structural feature related to the Fe-As interaction is crucial, but its correct ab initio treatment still remains an open question.

Journal ArticleDOI
TL;DR: In this article, the crystal structures of four isostructural orthorhombic carbonates, CaCO{sub 3} (aragonite), SrCO{ sub 3}(strontianite), PbCO {sub 3] (cerussite), and BaCO{-sub 3}, were obtained by Rietveld refinements using data acquired by high-resolution powder X-ray diffraction (HRPXRD).
Abstract: The crystal structures of four isostructural orthorhombic carbonates, CaCO{sub 3} (aragonite), SrCO{sub 3} (strontianite), PbCO{sub 3} (cerussite), and BaCO{sub 3} (witherite), were obtained by Rietveld refinements using data acquired by synchrotron high-resolution powder X-ray diffraction (HRPXRD). For BaCO{sub 3}, powder neutron-diffraction data were obtained and refined by the Rietveld method. For aragonite, we also carried out a refinement of the structure by single-crystal X-ray diffraction. These carbonates belong to the space group Pmcn, with Z = 4. The CO{sub 3} group is slightly non-planar, and the two independent C-O distances are slightly different. The CO{sub 3} group becomes more symmetrical and less aplanar from CaCO{sub 3} to BaCO{sub 3} (M{sub radii}{sup 2+}: Ca and distances, average angle, and aplanarity. These linear trends are the result of the effective size of the divalent ionic radius of the M cations thatmore » are coordinated to nine oxygen atoms. The geometrical features of the CO{sub 3} group can be obtained reliably only by using neutron-diffraction data, especially in the presence of other heavy atoms.« less

Journal ArticleDOI
01 Apr 2009-EPL
TL;DR: In this paper, the structural and superconducting properties of β-FeSe under pressure up to 26 GPa were studied using synchrotron radiation and diamond anvil cells.
Abstract: We have studied the structural and superconducting properties of β–FeSe under pressures up to 26 GPa using synchrotron radiation and diamond anvil cells. The bulk modulus of the tetragonal phase is 28.5(3) GPa, much smaller than the rest of Fe based superconductors. At 12 GPa we observe a phase transition from the tetragonal to an orthorhombic symmetry. The high-pressure orthorhombic phase has a higher Tc reaching 34 K at 22 GPa.

Journal ArticleDOI
TL;DR: In this article, the polycrystalline samples of BaTi1−xMnxO3 (BMT) ferroelectric ceramics with x=0, 004, 007, 010 have been prepared using a solid-state reaction technique.

Journal ArticleDOI
TL;DR: BaSi2O2N2 is a promising host lattice for rare-earth doped luminescent materials in phosphor-converted (pc)-LEDs as mentioned in this paper.

Journal ArticleDOI
TL;DR: The results of structural studies of pure-phase perovskite thin films of BiFeO3-10% RMnO3 (R=La, Eu, Gd, Tb, and Dy) are presented in this article.
Abstract: The results of structural studies of pure-phase perovskite thin films of BiFeO3–10% RMnO3 (R=La, Eu, Gd, Tb, and Dy) are presented. Raman scattering studies show line broadening similar to what is reported for RMnO3; they were attributed to Jahn–Teller distortion and orthorhombic structural change. Evidence of an anomaly of the orthorhombic distortion at GdMnO3 could be obtained. Interestingly the addition of GdMnO3 leads to a substantial increase in magnetization, combined with moderate ferroelectric polarization. All other compositions are characterized by higher ferroelectric polarization but almost no magnetization.

Journal ArticleDOI
TL;DR: Compound {Fe(3-Clpy)(2)[Pd(CN)(4)]} represents a new example of a "re-entrant" two-step spin transition by showing the Pnma space group in the intermediate phase (IP) and the Pnc2 space group on the low-spin (LS) and high-spin(HS) phases.
Abstract: Twelve coordination polymers with formula {Fe(3-Xpy)(2)[M(II)(CN)(4)]} (M(II): Ni, Pd, Pt; X: F, Cl, Br, I; py: pyridine) have been synthesised, and their crystal structures have been determined by single-crystal or powder X-ray analysis. All of the fluoro and iodo compounds, as well as the chloro derivative in which M(II) is Pt, crystallise in the monoclinic C2/m space group, whereas the rest of the chloro and all of the bromo derivatives crystallise in the orthorhombic Pnc2 space group. In all cases, the iron(II) atom resides in a pseudo-octahedral [FeN(6)] coordination core, with similar bond lengths and angles in the various derivatives. The major difference between the two kinds of structure arises from the stacking of consecutive two-dimensional {Fe(3-Xpy)(2)[M(II)(CN)(4)]}(infinity) layers, which allows different dispositions of the X atoms. The fluoro and chloro derivatives undergo cooperative spin crossover (SCO) with significant hysteretic behaviour, whereas the rest are paramagnetic. The thermal hysteresis, if X is F, shifts toward room temperature without changing the cooperativity as the pressure increases in the interval 10(5) Pa-0.5 GPa. At ambient pressure, the SCO phenomenon has been structurally characterised at different significant temperatures, and the corresponding thermodynamic parameters were obtained from DSC calorimetric measurements. Compound {Fe(3-Clpy)(2)[Pd(CN)(4)]} represents a new example of a "re-entrant" two-step spin transition by showing the Pnma space group in the intermediate phase (IP) and the Pnc2 space group in the low-spin (LS) and high-spin (HS) phases.

Journal ArticleDOI
TL;DR: In this article, the authors review neutron scattering investigations of the crystal structures, magnetic structures, and spin dynamics of the iron-based RFe(As, P)(O, F) (R = La, Ce. Pr, Nd), (Ba,Sr, Ca)Fe2As2, and Fe1+x(Te-Se) systems.
Abstract: We review neutron scattering investigations of the crystal structures, magnetic structures, and spin dynamics of the iron-based RFe(As, P)(O, F) (R = La, Ce. Pr, Nd), (Ba,Sr,Ca)Fe2As2, and Fe1+x(Te-Se) systems. On cooling from room temperature all the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic/monoclinic structural transition Occurs, below which the systems become antiferromagnets. For the first two classes of materials the magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direction, with an ordered moment typically less than one Bohr magneton. Hence these are itinerant electron magnets, with a spin structure that is consistent with Fermi-surface nesting and a very energetic spin wave bandwidth similar to 0.2 eV. With doping, the structural and magnetic transitions are suppressed in favor of superconductivity, with Superconducting transition temperatures up to approximate to 55 K. Magnetic correlations are observed in the Superconducting regime, With a Magnetic resonance that follows the Superconducting order parameter just like the cuprates. The rare earth moments order antiferromagnetically at low T like 'conventional' Magnetic Superconductors, while the Cc crystal field linewidths are affected when superconductivity sets in. The application of pressure in CaFe2As2 transforms the system from a magnetically ordered orthorhombic material to a 'collapsed' non-magnetic tetragonal system. Tetragonal Fe1+xTe transforms to a low T monoclinic structure at small x that changes to orthorhombic at larger x, which is accompanied by a crossover from commensurate to incommensurate magnetic order. Se doping Suppresses the magnetic order, while incommensurate magnetic correlations are observed in the superconducting regime. (C) 2009 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: In this article, a series of solid-solution semiconductors (AgNbO3)1−x(SrTiO3x) were developed as highly visible-light-active photocatalysts for efficient O2 evolution and decomposition of organic pollutants.
Abstract: A novel series of solid-solution semiconductors (AgNbO3)1−x(SrTiO3)x (0 ≤ x ≤ 1) have been developed as highly visible-light-active photocatalysts for efficient O2 evolution and decomposition of organic pollutants. Rietveld refinement reveals that the perovskite-type solid solutions (AgNbO3)1−x(SrTiO3)x are crystallized in an orthorhombic system (0 ≤ x < 0.9) or a cubic system (0.9 ≤ x ≤ 1). In the mixed valent perovskites (AgNbO3)1−x(SrTiO3)x, the hybridization behaviors between the Ag 4d and O 2p orbitals and between the Nb 4d and Ti 3d orbitals play a crucial role in tuning the energy band structure (band gap, band edge, and bandwidth, etc.) and, thus, in tailoring the photophysical and photocatalytic properties. As a result of competition between the absorption ability to visible-light and the reductive/oxidative abilities, the highest visible-light activities for both O2 evolution and decomposition of gaseous 2-propanol (IPA) are realized over (AgNbO3)0.75(SrTiO3)0.25. In addition, very fine Ag parti...

Journal ArticleDOI
TL;DR: In this paper, the in-plane magnetic easy and hard directions of these films have been determined from the dependence of the remnant magnetization on the angle of the inplane applied field, determined by the crystal directions of the substrate surface.
Abstract: Epitaxial La0.67Sr0.33MnO3 (LSMO) ferromagnetic thin films were coherently grown on NdGaO3 (NGO) substrates with different crystal orientations of the surface plane. On the (110)o- and (001)o-oriented substrates, the film grows in the (001)pc orientation, and on the (100)o-, (010)o-, and (112)o-oriented substrates the film is (011)pc oriented (we will use subindices o and pc for the orthorhombic and pseudocubic crystal structures, respectively). The lattice parameters and pseudocube angles of the deformed LSMO pseudocube have been determined from x-ray diffraction measurements. The in-plane magnetic easy and hard directions of these films have been determined from the dependence of the remnant magnetization on the angle of the in-plane applied field. For all substrate orientations there is a strong in-plane uniaxial magnetic anisotropy, determined by the crystal directions of the substrate surface. The easy and hard magnetic-anisotropy directions are explained consistently by the (bulk) inverse magnetostriction model, except for the film on NGO (112)o.

Journal ArticleDOI
TL;DR: In this paper, the atomic and electronic properties of cubic and orthorhombic LaMnO3 perovskite surfaces were investigated using the GGA-plane wave approach.

Journal ArticleDOI
TL;DR: In this article, the synthesis of superconducting single crystals of FeSe and their characterization by x-ray diffraction, magnetization and resistivity were reported, showing that the tetragonal PbO structure undergoes a structural transition to a hexagonal structure.
Abstract: We report on the synthesis of superconducting single crystals of FeSe and their characterization by x-ray diffraction, magnetization and resistivity. We have performed ac susceptibility measurements under high pressure in a hydrostatic liquid argon medium up to 14 GPa and we find that TC increases up to 33–36 K in all samples, but with slightly different pressure dependences on different samples. Above 12 GPa no traces of superconductivity are found in any sample. We have also performed a room temperature high pressure x-ray diffraction study up to 12 GPa on a powder sample, and we find that, between 8.5 and 12 GPa, the tetragonal PbO structure undergoes a structural transition to a hexagonal structure. This transition results in a volume decrease of about 16% and is accompanied by the appearance of an intermediate, probably orthorhombic, phase.

Journal ArticleDOI
TL;DR: In this paper, the structural and superconducting properties of tetragonal FeSe under pressure up to 26GPa were studied using synchrotron radiation and diamond anvil cells.
Abstract: We have studied the structural and superconducting properties of tetragonal FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller than the rest of Fe based superconductors. At 12GPa we observe a phase transition from the tetragonal to an orthorhombic symmetry. The high pressure orthorhombic phase has a higher Tc reaching 34K at 22GPa.

Journal ArticleDOI
Yue Wang1, Jing Chen1, Peng Wang1, Ling Chen1, Yu-Biao Chen1, Li-Ming Wu1 
TL;DR: In this paper, the growth direction of Bi2S3 nanorods is intrinsically governed by the crystal structure motif and the high surface energy of the (001) plane of orthorhombic Bi 2S3 according to the CASTEP calculations.
Abstract: Uniform Bi2S3 nanorods growing along [001] have been synthesized from the precursor of Bi[S2CN(C8H17)2]3 by two different approaches: solventless and solvothermal methods. The structure, morphology, and formation process of the nanorods have been investigated by SEM, TEM, HRTEM, XRD, and EDX analyses. The growth direction is intrinsically governed by the crystal structure motif and the high surface energy of the (001) plane of orthorhombic Bi2S3 according to the CASTEP calculations. Besides, some important factors that influence the growth of Bi2S3 nanorods, such as the length of alkyl group in the precursor and the reaction temperature are investigated. The optical band gap of the as-synthesized Bi2S3 nanorods is measured to be 1.50 eV indicating a slightly blue shift owing to the quantum size effect.

Journal ArticleDOI
TL;DR: In this article, a limit of Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry.
Abstract: The structure of orthorhombic (α″) martensitic phase of Ti–8Nb, Ti–12Nb, and Ti–16Nb alloys has been investigated using Rietveld refinement of x-ray diffraction data. The chemical analysis data have been used to determine the site occupancy of initial models. A limit of the Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry. This has also been incorporated in the initial models of experimental alloys, and accordingly Wyckoff positions have been refined. It has been observed that the atoms move along the Y-axis (parallel to the b-axis) and the movement of atoms increases with increase in Nb concentration. The formation of orthorhombic (α″) phase has been explained based on the movement of atoms along the Y-axis. This in turn breaks the hexagonal symmetry and forms an orthorhombic phase.

Journal ArticleDOI
TL;DR: In this article, a single crystal of Bi2Znob2O6 has been grown with sizes up to 18 x 13 x 6 mm(3) by the top-seeded growth method with high quality.
Abstract: A single crystal of Bi2ZnOB2O6 has been grown with sizes up to 18 x 13 x 6 mm(3) by the top-seeded growth method for the First time with high quality. It crystallizes in the orthorhombic system, space group Pba2 with unit-cell parameters a = 10.8200(7) angstrom, b = 11.00 14(7) angstrom, c = 4.8896(3) angstrom, Z = 4, V = 582.03(6) angstrom(3). Bi2ZnOB2O6 has a three-dimensional network consisting of ZnB2O76- layers alternating with six-coordinated Bi3+ cations along the c axis. Transmission spectrum of Bi2ZnOB2O6 crystal was reported. The refractive indices of the crystal were measured by the minimum deviation technique and fitted to the Sellmeier equations. The powder second-harmonic generation (SHG) properties measured by the Kurtz-Perry method indicate that Bi2ZnOB2O6 is phasematchable.

Journal ArticleDOI
TL;DR: In this paper, a congruent melting compound, Bi2ZnOB2O6, was grown by the Kyropoulos method from stoichiometric ratio compound melt.
Abstract: Sizable single crystals of a nonlinear optical (NLO) material, Bi2ZnOB2O6, were grown by the Kyropoulos method from stoichiometric ratio compound melt. It is a congruent melting compound and crystallizes in the orthorhombic system, space group Pba2. The morphologies and habits of Bi2ZnOB2O6 crystals grown using [100], [010], and [001] seeds were studied. The SHG efficiency of Bi2ZnOB2O6 is 3−4 times that of KDP (KH2PO4). Its birefringence is pretty large (0.085−0.106). The experiments prove that Bi2ZnOB2O6 crystal is nonhygroscopic and excellently deliquescence resistant.