Showing papers on "Orthorhombic crystal system published in 2010"

A study of ternary Cu2SnS3 and Cu3SnS4 thin films prepared by sulfurizing stacked metal precursors

Abstract: Thin films of Cu2SnS3 and Cu3SnS4 were grown by sulfurization of dc magnetron sputtered Sn–Cu metallic precursors in a S2 atmosphere. Different maximum sulfurization temperatures were tested which allowed the study of the Cu2SnS3 phase changes. For a temperature of 350 °C the films were composed of tetragonal (I-42m) Cu2SnS3. The films sulfurized at a maximum temperature of 400 °C presented a cubic (F-43m) Cu2SnS3 phase. On increasing the temperature up to 520 °C, the Sn content of the layer decreased and orthorhombic (Pmn21) Cu3SnS4 was formed. The phase identification and structural analysis were performed using x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) analysis. Raman scattering analysis was also performed and a comparison with XRD and EBSD data allowed the assignment of peaks at 336 and 351 cm−1 for tetragonal Cu2SnS3, 303 and 355 cm−1 for cubic Cu2SnS3, and 318, 348 and 295 cm−1 for the Cu3SnS4 phase. Compositional analysis was done using energy dispersive spectroscopy and induced coupled plasma analysis. Scanning electron microscopy was used to study the morphology of the layers. Transmittance and reflectance measurements permitted the estimation of absorbance and band gap. These ternary compounds present a high absorbance value close to 104 cm−1. The estimated band gap energy was 1.35 eV for tetragonal (I-42m) Cu2SnS3, 0.96 eV for cubic (F-43m) Cu2SnS3 and 1.60 eV for orthorhombic (Pmn21) Cu3SnS4. A hot point probe was used for the determination of semiconductor conductivity type. The results show that all the samples are p-type semiconductors. A four-point probe was used to obtain the resistivity of these samples. The resistivities for tetragonal Cu2SnS3, cubic Cu2SnS3 and orthorhombic (Pmn21) Cu3SnS4 are 4.59 × 10−2 Ω cm, 1.26 × 10−2 Ω cm, 7.40 × 10−4 Ω cm, respectively.

Universal Behavior and Electric-Field-Induced Structural Transition in Rare-Earth-Substituted BiFeO3

Abstract: The discovery of a universal behavior in rare-earth (RE)-substituted perovskite BiFe0 3 is reported. The structural transition from the ferroelectric rhombohedral phase to an orthorhombic phase exhibiting a double-polarization hysteresis loop and substantially enhanced electromechanical properties is found to occur independent of the RE dopant species. The structural transition can be universally achieved by controlling the average ionic radius of the A-site cation. Using calculations based on first principles, the energy landscape of BiFe0 3 is explored, and it is proposed that the origin of the double hysteresis loop and the concomitant enhancement in the piezoelectric coefficient is an electric-field-induced transformation from a paraelectric orthorhombic phase to the polar rhombohedral phase.

Enhanced Photocatalytic Activity and Ferromagnetism in Gd Doped BiFeO3 Nanoparticles

Abstract: BiFeO3 (BFO) is of considerable interest because of its potential applications in the design of devices combining magnetic, electronic, and optical functionalities. Effects of the Gd dopant on the structural, photocatalytic activity, and ferromagnetic properties of BFO nanoparticles have been studied. X-ray diffraction and Raman spectra results of Bi1−xGdxFeO3 (BGFOx, x = 0, 0.05, 0.1, and 0.15) reflect that the crystal structure of the samples remain stable for x < 0.1, while compositional-driven phase transition from rhombohedral to orthorhombic is observed at x = 0.1. The photocatalytic activity to decompose Rhodamine-B under visible-light illumination increases in BGFOx as x increases from zero to 0.1 and then decreases for x = 0.15. The maximum in photocatalytic activity near the phase boundary of x = 0.1 is associated with the changing of the polar behavior of the nanoparticles. Comparing with the linear magnetization−magnetic field (M−H) relation in pure BFO nanoparticles, obvious M−H loops can be ...

Anomalous Suppression of the Orthorhombic Lattice Distortion in Superconducting Ba ( Fe 1 − x Co x ) 2 As 2 Single Crystals

Abstract: High-resolution x-ray diffraction measurements reveal an unusually strong response of the lattice to superconductivity in $\mathrm{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2}$. The orthorhombic distortion of the lattice is suppressed and, for Co doping near $x=0.063$, the orthorhombic structure evolves smoothly back to a tetragonal structure. We propose that the coupling between orthorhombicity and superconductivity is indirect and arises due to the magnetoelastic coupling, in the form of emergent nematic order, and the strong competition between magnetism and superconductivity.

Gas sensing properties of thermally evaporated lamellar MoO3

Abstract: In this work, MoO 3 was thermally evaporated onto gold interdigital fingers on quartz substrates and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques The deposited MoO 3 consist of stratified long rectangles (average length of 50 μm width of 5 μm and thickness of 500 nm) which are predominantly orthorhombic (α-MoO 3 ) Each of these plates was composed of many nano-thick layers (average ∼30 nm) placed by Van der Waals forces on top of each other forming lamellar patterns The devices were used as sensors and exhibited considerable change in surface conductivity when exposed to NO 2 and H 2 gases at elevated temperature of 225 °C The structural and gas sensing properties of thermally evaporated MoO 3 thin films were investigated

Nb2O5 Photoelectrodes for Dye-Sensitized Solar Cells: Choice of the Polymorph

Abstract: Nanowires of Nb2O5 were developed in three polymorphic forms, namely, pseudo-hexagonal, orthorhombic, and monoclinic, by electrospinning a polymeric solution and by subsequent annealing. The materials were characterized by X-ray and electron diffraction, scanning and transmission electron microscopy, BET surface area measurements, absorption spectrometry, and cyclic voltammometry. These characterizations indicate that the monoclinic phase has a higher conduction band edge compared with the other two and is likely to display higher open circuit voltage in solar cells. Dye-sensitized solar cells were fabricated using the above polymorphs, and the device performances were studied. The pseudo-hexagonal phase showed higher device performance owing to its higher specific surface area compared with the others. However, when normalized, the device performances with respect to the dye-loading, the monoclinic phase gave superior performance. Studies on the charge transport properties using electrochemical impedance...

Uniaxial-strain mechanical detwinning of CaFe 2 As 2 and BaFe 2 As 2 crystals: Optical and transport study

Abstract: The parent compounds of iron-arsenide superconductors, AFe2As2 (A=Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at a temperature TTO in the range 135 to 205 K depending on the alkaline earth element. Below TTO the free standing crystals split into equally populated structural domains, which mask intrinsic, in-plane, anisotropic properties of the materials. Here we demonstrate a way of mechanically detwinning CaFe2As2 and BaFe2As2. The detwinning is nearly complete, as demonstrated by polarized light imaging and synchrotron X-ray measurements, and reversible, with twin pattern restored after strain release. Electrical resistivity measurements in the twinned and detwinned states show that resistivity, �, decreases along the orthorhombic ao-axis but increases along the orthorhombic bo-axis in both compounds. Immediately below TTO the ratio �bo/�ao = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to CaFe2As2, BaFe2As2 reveals an anisotropy in the nominally tetragonal phase, suggesting that either fluctuations play a larger role above TTO in BaFe2As2 than in CaFe2As2, or that there is a higher temperature crossover or phase transition.

Antimony Tuned Rhombohedral-Orthorhombic Phase Transition and Enhanced Piezoelectric Properties in Sodium Potassium Niobate

Abstract: It has been reported that the rhombohedral–orthorhombic low-temperature polymorphic phase transition in (Na,K)NbO3 can be tuned close to room temperature by substituting Sb for Nb, such that enhanced piezoelectric properties are induced based on the theory of two-phase coexistence. A diagram of phase structures changing with Sb content and temperature has been generalized for (Na,K)(Nb,Sb)O3 (NKNS) compositions. The thermal stability of piezoelectric properties of NKNS ceramics was evaluated considering the existence of successive phase transition above room temperature. The microstructure, dielectric, and ferroelectric properties of NKNS ceramics were discussed from a crystallographic point of view.

Large strain and high energy storage density in orthorhombic perovskite (Pb0.97La0.02)(Zr1−x−ySnxTiy)O3 antiferroelectric thin films

Abstract: Antiferroelectric (Pb0.97La0.02)(Zr1−x−ySnxTiy)O3 (PLZST) thin films with orthorhombic perovskite structure were prepared on Si substrates by a chemical solution deposition process. A secondary pyrochlore phase, which was not detectable with x-ray diffraction, was revealed with transmission electron microscopy. The pyrochlore phase was effectively suppressed by the introduction of polyethylene glycol (PEG) in the precursor solution and applying PbO capping layer on the surface of the films. With the persistent and detrimental pyrochlore phase removed completely, our PLZST antiferroelectric thin films exhibited excellent electrical and electromechanical properties. A large energy storage density up to 13.7 J/cm3 was exhibited from the polarization measurement, and a strain of 0.49% under the clamping of the substrate was also achieved in the thin film with high Zr content.

The polar phase of NaNbO(3): a combined study by powder diffraction, solid-state NMR, and first-principles calculations.

Abstract: A polar phase of NaNbO(3) has been successfully synthesized using sol-gel techniques. Detailed characterization of this phase has been undertaken using high-resolution powder diffraction (X-ray and neutron) and (23)Na multiple-quantum (MQ) MAS NMR, supported by second harmonic generation measurements and density functional theory calculations. Samples of NaNbO(3) were also synthesized using conventional solid-state methods and were observed to routinely comprise of a mixture of two different polymorphs of NaNbO(3), namely, the well-known orthorhombic phase (space group Pbcm) and the current polar phase, the relative quantities of which vary considerably depending upon precise reaction conditions. Our studies show that each of these two polymorphs of NaNbO(3) contains two crystallographically distinct Na sites. This is consistent with assignment of the polar phase to the orthorhombic space group P2(1)ma, although peak broadenings in the diffraction data suggest a subtle monoclinic distortion. Using carefully monitored molten salt techniques, it was possible to eradicate the polar polymorph and synthesize the pure Pbcm phase.

Piezoelectric and Dielectric Properties of (Ba1−xCax)(Ti0.95Zr0.05)O3 Lead-Free Ceramics

Abstract: Lead-free (Ba1−xCax)(Ti0.95Zr0.05)O3 (x=0.02–0.20) ceramics were prepared successfully using a solid-state reaction technique. The polymorphic phase transitions from orthorhombic to tetragonal phase around room temperature were identified in the composition range of 0.06

Bi(1-x)R(x)FeO(3)(R=rare earth): a family of novel magnetoelectrics

Abstract: Crystals of solid solutions Bi(1-x)R(x)FeO(3),here R= La, Dy, Gd, were obtained with x <=0.7. Solid solutions of the stated rare earths, as x is increased from 0 to 0.7, have one and the same sequence of five crystal structures (rhombohedral C3v 6, triclinic C1 1,orthorhombic D2 6,orthorhombic D2 5, orthorhombic C2v 9). The ferroelectric-paraelectric transition occurs in rhombohedral and triclinic crystals at T=810-560{\deg}C.The high temperature modifications are orthorhombic and cubic. The orthorhombic structure C2v 9 holds up to 1180{\deg}C.The ferroelectric domain structure was distinguished in all types of crystals. No magnetoelectric effect (MEE) was detected in the orthorhombic crystals with the D2 (222) symmetry class. But the mm2 crystals were found to have both quadratic and linear MEE.The value of the quadratic effect is considerably smaller than that ofthe linear one. Magnetoelectric hysteresis takes place in the crystals. The tensorial properties of the obtained crystals are analyzed from the viewpoint of crystal symmetry.

Rubrene micro-crystals from solution routes: their crystallography, morphology and optical properties

Abstract: A series of rubrene micro-crystals (MCs) with controllable sizes and shapes, ranging from one-dimensional (1D) ribbons to 2D rhombic and hexagonal plates, have bee prepared by employing the reprecipitation method Based on X-ray diffraction analysis, the crystal structures of 1D ribbons and 2D plates have been identified to be triclinic and monoclinic phases, respectively, rather than the commonly reported orthorhombic phase for vacuum-deposited rubrene crystals In our system, adjustment of the monomer concentration of rubrene, which in turn determines the supersaturation (β) for crystallization, paved the way for kinetic control over the nucleation and growth processes Combining with theoretical calculations, we found that transformation from a triclinic phase at low supersaturation to a monoclinic phase at high supersaturation was responsible for the morphology change from 1D ribbons to 2D plates Both ensemble and single-particle spectroscopy clarifies that 1D ribbons and 2D plates show distinct optical properties, probably related to their different solid-state structures in triclinic and monoclinic crystals Moreover, scanning near-field optical microscopy reveals that the ribbons show waveguiding along a 1D direction, and the plates in a 2D plane

Lattice, elastic, polarization, and electrostrictive properties of BaTiO3 from first-principles

Abstract: Predicting the domain structures and properties in both bulk single crystal and thin film ferroelectrics using the phase-field approach requires the knowledge of fundamental mechanical, electrical, and electromechanical coupling properties of a single-domain state. In this work, the elastic properties and structural parameters of cubic single crystals as well as tetragonal, orthorhombic, and rhombohedral BaTiO3 single domain states are obtained using first-principles calculations under the local density approximation. The calculated lattice constants, bulk modulus, and elastic constants are in good agreement with experiments for both the cubic paraelectric phase and the low-temperature ferroelectric phases. Spontaneous polarizations for all three ferroelectric phases and the electrostrictive coefficients of cubic BaTiO3 are also computed using the Berry’s phase approach, and the results agree well with existing experimentally measured values.

Insights into the Origin of Cooperative Effects in the Spin Transition of [Fe(NH2trz)3](NO3)2: the Role of Supramolecular Interactions Evidenced in the Crystal Structure of [Cu(NH2trz)3](NO3)2·H2O

Abstract: The thermally induced hysteretic spin transition (ST) that occurs in the polymeric chain compound [Fe(NH2trz)3](NO3)2 (1) above room temperature (Tc↑ = 347 K, Tc↓ = 314 K) has been tracked by 57Fe Mossbauer spectroscopy, SQUID magnetometry, differential scanning calorimetry (DSC), and X-ray powder diffraction (XPRD) at variable temperatures. From the XRPD pattern indexation, an orthorhombic primitive cell was observed with the following cell parameters: a = 11.83(2) A, b = 9.72(1) A, c = 6.361(9) A at 298 K (low-spin state) and a = 14.37(2) A, b = 9.61(4) A, c = 6.76(4) A at 380 K (high-spin state). The enthalpy and entropy variation associated to the ST of 1, have been evaluated by DSC as ΔH = 23(1) kJ mol−1 and ΔS = 69.6(1) J mol−1 K−1. These thermodynamic data were used within a two-level Ising like model for the statistical analysis of First Order Reversal Curve (FORC) diagram that was recorded for 1, in the cooling mode. Strong intramolecular cooperative effects are witnessed by the derived interacti...

CuxSnSx+1 (x = 2, 3) thin films grown by sulfurization of metallic precursors deposited by dc magnetron sputtering

Abstract: We report the results of the growth of Cu-Sn-S ternary chalcogenide compounds by sulfurization of dc magnetron sputtered metallic precursors. Tetragonal Cu2SnS3 forms for a maximum sulfurization temperature of 350 °C. Cubic Cu2SnS3 is obtained at sulfurization temperatures above 400 °C. These results are supported by XRD analysis and Raman spectroscopy measurements. The latter analysis shows peaks at 336 cm-1, 351 cm-1 for tetragonal Cu2SnS3, and 303 cm-1, 355 cm-1 for cubic Cu2SnS3. Optical analysis shows that this phase change lowers the band gap from 1.35 eV to 0.98 eV. At higher sulfurization temperatures increased loss of Sn is expected in the sulphide form. As a consequence, higher Cu content ternary compounds like Cu3SnS4 grow. In these conditions, XRD and Raman analysis only detected orthorhombic (Pmn21) phase (petrukite). This compound has Raman peaks at 318 cm-1, 348 cm-1 and 295 cm-1. For a sulfurization temperature of 450 °C the samples present a multi-phase structure mainly composed by cubic Cu2SnS3 and orthorhombic (Pmn21) Cu3SnS4. For higher temperatures, the samples are single phase and constituted by orthorhombic (Pmn21) Cu3SnS4. Transmittance and reflectance measurements were used to estimate a band gap of 1.60 eV. For comparison we also include the results for Cu2ZnSnS4 obtained using similar growth conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polymorphic phase transition and piezoelectric properties of (Ba1−xCax)(Ti0.9Zr0.1)O3 lead-free ceramics

Abstract: Lead-free (Ba 1− x Ca x )(Ti 0.9 Zr 0.1 )O 3 ( x =0.12–0.18) (BCZT) ceramics were prepared successfully using a solid-state reaction technique. The polymorphic phase transitions (PPT) from rhombohedral to orthorhombic phase around room temperature were identified in the composition range 0.14 x x =0.16, showing coexistence of rhombohedral and orthorhombic phase, exhibit enhanced piezoelectric and dielectric properties of d 33 =328 pC/N, k p =37.6% and e ′=4800. With the increase of Ca content, the polymorphic phase transitions shift to lower temperature and cannot be observed above room temperature at x ≥0.18.

Structure and Hydrogen Storage Properties of Calcium Borohydride Diammoniate

Abstract: A new type of hydrogen storage material—namely, calcium borohydride diammoniate (Ca(BH4)2·2NH3), is synthesized by reacting calcium borohydride and 2 equiv of ammonia. Structural analyses show that this complex has an orthorhombic structure (space group Pbcn) with unit-cell parameters of a = 6.4160 A, b = 8.3900 A, c = 12.7020 A, and V = 683.75 A3, in which Ca2+ coordinates with four −BH4 groups two −NH3 groups. The presence of NH3 in the crystal lattice facilitates the formation of B−H···H−N dihydrogen bonding. As a consequence, the bond lengths of B−H and N−H are increased with comparison to Ca(BH4)2 and NH3, respectively. Our experimental results show that more than 11.3 wt % hydrogen can be released exothermically from Ca(BH4)2·2NH3 in a closed vessel at a temperature as low as 250 °C.

Structure and Characterization of KSc(BH4)4

Abstract: A new potassium scandium borohydride, KSc(BH4)4, is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH4)4, forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl3 together with a new ternary chloride K3ScCl6, which is also structurally characterized. This indicates that the formation of KSc(BH4)4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (∼31 mol %) can be obtained with a reactant ratio KBH4:ScCl3 of 2:1. KSc(BH4)4 crystallizes in the orthorhombic crystal system, a = 11.856(5), b = 7.800(3), c = 10.126(6) A, V = 936.4(8) A3 at RT, with the space group symmetry Pnma. KSc(BH4)4 has a BaSO4 type structure where the BH4 tetrahedra take the oxygen positions. Regarding the packing of cations, K+, and complex anions, [Sc(BH4)4]−, the structure of KSc(BH4)4 can be seen as a distorted variant of orthorhombi...

Rhombohedral-to-orthorhombic transition and multiferroic properties of Dy-substituted BiFeO3

Abstract: Investigation of crystal structure, ferroelectric, and magnetic properties of polycrystalline Bi1−xDyxFeO3 (0.1≤x≤0.2) samples was carried out. X-ray diffraction study revealed composition-driven rhombohedral-to-orthorhombic R3c→Pnma phase transition at x∼0.15. Both structural phases were found to coexist in a broad concentration range. Piezoresponse force microscopy found suppression of the parent ferroelectric phase upon dysprosium substitution. Magnetometric study confirmed that the A-site doping induces appearance of a weak ferromagnetic behavior. Both the ferroelectric and magnetic properties were shown to correlate with a structural evolution.

Mixed azide and 5-(pyrimidyl)tetrazole bridged Co(II)/Mn(II) polymers: synthesis, crystal structures, ferroelectric and magnetic behavior.

Abstract: The reaction of pyrimidine-2-carbonitrile, NaN3 in the presence of Co(NO3)2·6H2O or MnCl2·4H2O leads to the formation of complexes [Co(pmtz)(μ1,3-N3)(H2O)]n (1) and [Mn(pmtz)(μ1,3-N3)(H2O)]n (2) respectively, under hydrothermal condition [pmtz =5-(pyrimidyl)tetrazolate]. These two complexes have been fully characterized by single crystal X-ray diffraction. Complex 1 crystallizes in a non-centrosymmetric space group Aba2 in the orthorhombic system and is found to exhibit ferroelectric behavior, whereas complex 2 crystallizes in the P21/c space group in the monoclinic system. Variable temperature magnetic characterizations in the temperature range of 2−300 K indicate that complex 1 is a canted antiferromagnet (weak ferromagnet) with Tc = 15.9 K. Complex 1 represents a unique example of a multiferroic coordination polymer containing tetrazole as a co-ligand. Complex 2 is a one-dimensional chain of Mn(II) bridged by a well-known antiferromagnetic coupler end-to-end azido ligand. In contrast to the role played...

Temperature dependence of the structural parameters in the transformation of aragonite to calcite, as determined from in situ synchrotron powder x-ray-diffraction data

Abstract: The temperature dependency of the crystal structure and the polymorphic transition of CaCO{sub 3} from aragonite to calcite were studied using Rietveld structure refinement and high-temperature in situ synchrotron powder X-ray-diffraction data at ambient pressure, P. The orthorhombic metastable aragonite at room P, space group Pmcn, transforms to trigonal calcite, space group R{bar 3}c, at about T{sub c} = 468 C. This transformation occurs rapidly; it starts at about 420 C and is completed by 500 C, an 80 C interval that took about 10 minutes using a heating rate of 8 C/min. Structurally, from aragonite to calcite, the distribution of the Ca atom changes from approximately hexagonal to cubic close-packing. A 5.76% discontinuous increase in volume accompanies the reconstructive first-order transition. Besides the change in coordination of the Ca atom from nine to six from aragonite to calcite, the CO{sub 3} groups change by a 30{sup o} rotation across the transition.

Crystal and Molecular Structure Analysis of 2-Methylimidazole

Abstract: The crystal structure of the title compound, C4H6N2, has been determined using X-ray diffraction at 100 K The crystal of 2-methylimidazole is in orthorhombic crystal system with space group P212121 (Z = 4), lattice parameters: a = 59957(12) A, b = 81574(16) A and c = 97010(19) A, V = 47447(16) A The molecule of 2-methylimidazole is approximately planar The maximum deviation from the least-squares imidazole plane, calculated for all non-H atoms is 0006(2) A N–H···N hydrogen bonds link the molecules together, forming infinite chains of hydrogen bond pattern C(4) defined by the graph-set analysis Two chains, which are almost antiparallel to each other, pass through each unit cell The dihedral angle between the mean planes of molecules forming these intersecting chains is 7690(4)° No evidence was found for disorder of the hydrogen-bonding proton between the atoms N1 and N3 The significance of this study lies in the analysis of the interactions occurring via hydrogen bonds in this structure, as well as, in the comparison drawn between the molecular structure of 2-methylimidazole and those of several of other imidazole derivatives possessing a hydrogen atom in the N1 position The article presents the detailed description of the crystal structure of 2-methylimidazole including the information on the symmetry of the analyzed crystal, the values of the bond distances and the angles as well as hydrogen bond interaction analysis

Phonon properties of nanosized bismuth layered ferroelectric material—Bi2WO6

Abstract: Nanosized Bi2WO6 was synthesized by a mild hydrothermal crystallization process. This method allowed obtaining plate-like crystallites of very small thickness (down to 3 nm). The effect of particle size on the structure and properties of Bi2WO6 was studied by X-ray diffraction (XRD), transmission electron microscopy, and Raman and infrared spectroscopies. It has been shown that the orthorhombic distortion decreases with decreasing particle size, but the structure of the smallest crystallites is still orthorhombic. Raman studies have also revealed a very strong intensity decrease for those modes that appear mainly for incident and scattered light polarized perpendicular to the layers. This behavior has been attributed to a decrease in the orthorhombic distortion and a plate-like shape of the nanocrystallites. Copyright © 2009 John Wiley & Sons, Ltd.