Showing papers on "Orthorhombic crystal system published in 1999"
TL;DR: In this paper, a mixture of SnCl4 with H2S at 300−545 °C was used for the deposition of SnS2, SnS3, and SnSS3.
Abstract: Atmospheric pressure chemical vapor deposition of SnS2, Sn2S3, and SnS has been achieved onto glass substrates from the reaction of SnCl4 with H2S at 300−545 °C. The films show good uniformity and surface coverage, adherence, and a variety of colors (black, yellow, brown, and gray) dependent on deposition temperature and film thickness. Growth rates were on the order of 1−2 μm min-1. All the films were crystalline. For substrate temperatures of up to 500 °C single phase films with the hexagonal SnS2 structure (a = 3.65(1) A, c = 5.88(1) A) were formed. At 525 °C a film of mixed composition containing predominantly orthorhombic Sn2S3 (a = 8.83(1) A, b = 3.76(1) A, c = 14.03(1) A) was formed together with some SnS2. At 545 °C films with orthorhombic SnS structure (a = 4.30(1) A, b = 11.20(1) A, c = 3.99(1) A) were formed. Scanning electron microscopy (SEM) revealed a variety of different film thicknesses and morphologies, including needles, plates, and ovoids, dependent on the deposition temperature and tim...
381 citations
TL;DR: The single phase La-doped BaTiO3 with the formula Ba 1−xLaxTi1−x/4O3: 0.20 was prepared by solid state reaction of oxide mixtures at 1350°C, 3 days, in O2.
Abstract: Single phase La-doped BaTiO3 with the formula Ba1−xLaxTi1−x/4O3: 0⩽x⩽0.20 was prepared by solid state reaction of oxide mixtures at 1350 °C, 3 days, in O2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x⩾0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x∼0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from ∼10 000 for x=0 at 130 °C to ∼25 000 for x=0.06 at ∼−9 °C. At larger x, the permittivity maximum broadened, showed “relaxor”-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss.
331 citations
TL;DR: The structure of CaTiO3 has been studied at high temperatures by powder neutron diffraction methods as mentioned in this paper, and two phase transitions are evident, with an intermediate tetragonal (I/mcm) structure forming near 1500 K and a primitive cubic structure above 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthorhombic Cmcm structure around 1380 K, which is a remarkable feature of the results.
Abstract: The structure of CaTiO3 has been studied at high temperatures by powder neutron diffraction methods. From inspection of the diffraction data two phase transitions are evident, with an intermediate tetragonal (I/mcm) structure forming near 1500 K and a primitive cubic structure above 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthorhombic Cmcm structure around 1380 K. A remarkable feature of the results is the regular variation in the out-of-phase octahedral tilt angle over the entire temperature range.
277 citations
TL;DR: In this paper, the dielectric and piezoelectric properties of BaTiO3 single crystals polarized along the 〈001〉 crystallographic axes were investigated as a function of temperature and dc bias.
Abstract: Dielectric and piezoelectric properties of BaTiO3 single crystals polarized along the 〈001〉 crystallographic axes were investigated as a function of temperature and dc bias. Electromechanical coupling (k33)∼85% and piezoelectric coefficients (d33)∼500 pC/N, better or comparable to those of lead-based Pb(Zr, Ti)O3 (PZT), were found from 〈001〉-oriented orthorhombic crystals at 0 °C, as a result of crystallographic engineering. A rhombohedral BaTiO3 crystal polarized along 〈001〉 also exhibited enhanced piezoelectric performance, i.e., k33∼79% and d33∼400 pC/N at −90 °C, superior to PZTs at the same temperature. It was found that the crystal structure determined the (in)stability of the engineered domain state in BaTiO3 single crystals. Rhombohedral (3m) crystals at −100 °C exhibited a stable domain configuration, whereas depoling occurred in crystals in the adjacent orthorhombic phase upon removal of the E field.
258 citations
TL;DR: In this paper, the authors performed electron crystallographic studies on small submicron single crystal domains of restacked WS2 and MoS2 to solve their superstructure and found that what initially seems to be a trigonal crystal is actually a triplet of three individual orthorhombic crystals.
Abstract: There has been a lot of confusion about the nature of restacked MoS2 and WS2. The structure has been proposed to be trigonal TiS2 type with octahedral M4+ and called 1T-MoS2. The presence of a distortion in the metal plane that gives rise to a superstructure has been suggested. We have performed electron crystallographic studies on small (submicron) single crystal domains of restacked WS2 and MoS2 to solve their superstructure. We find that what initially seems to be a trigonal crystal is actually a “triplet” of three individual orthorhombic crystals. Using two-dimensional hk0 data from films for both “triple” and “single” crystals we calculated corresponding Patterson projections, which reveal a severe distortion in the Mo/W plane, forming infinite zigzag chains. The projection of the structure suggests M−M distances of 2.92 and 2.74 A for MoS2 and WS2, respectively. Least-squares refinement from the single-crystal data gives R1 = 13.3% for WS2 and R1 = 15.3% for MoS2. Therefore, we submit that restacked...
232 citations
TL;DR: In this paper, single crystals of Ba(ZrxTi1−x)O3 were grown by templated grain growth (TGG) for 30 h at 1350°C.
Abstract: Single crystals of Ba(ZrxTi1−x)O3 were grown by templated grain growth (TGG). Millimeter size single crystals of Ba(ZrxTi1−x)O3 were produced by heating a BaTiO3 crystal in contact with a sintered polycrystalline matrix of 4.5, 5.0, or 8.5 mol % Zr-doped barium titanate for 30 h at 1350 °C. To facilitate boundary migration, the ceramic compact was made 3 mol % TiO2 excess. The 4.5 and 5.0 mol % Zr-doped crystals were orthorhombic at room temperature, and for a pseudocubic (001) orientation, they showed remanent polarizations of 13 μC/cm2 and a high field d33 of 340–355 pC/N. The 8.5 mol % Zr-doped crystal [again oriented along the pseudocubic (001)] was rhombohedral at room temperature with a remanent polarization of 10 μC/cm2. A k33 value of 0.74 from resonance measurements was observed for the 4.5 mol % Zr-doped crystal.
220 citations
TL;DR: In this paper, high-temperature, high-resolution neutron powder diffraction experiments were performed to investigate the phases of WO 3 between room temperature and 850°C, and two phases were found and characterized by Rietveld refinements.
218 citations
TL;DR: In this paper, the high pressure phase γ-MgH2 was formed by heating the low-pressure phase MgH 2 in a multianvil press at 2 GPa pressure to 1070 K for 120 min and successive rapid quenching.
216 citations
TL;DR: In this article, powder neutron diffraction has been used to pinpoint the nature of the ferroelectric-paraelectric phase transition in Bi4Ti3O12, and the structure has been refined in orthorhombic spa.
Abstract: Powder neutron diffraction has been used to pinpoint the nature of the ferroelectric-paraelectric phase transition in Bi4Ti3O12. Below Tc (675 °C) the structure has been refined in orthorhombic spa...
199 citations
TL;DR: The fit of the magnetic susceptibility for 2 using a molecular field correction, which takes into consideration antiferromagnetic interactions between chains via the tp ligand, yields J'/k(B) = -0.13 K.
Abstract: The reaction between CuCl2·2H2O and disodium terephthalate, Na2tp, in aqueous solution simultaneously produces chain, bis(aqua)[μ-(terephthalato-κO:κO‘)]copper(II), monohydrate, Cutp(OH2)2·H2O (1), and layered, bis(aqua)[μ-(terephthalato-κO)]copper(II), Cutp(OH2)2 (2), structured materials. 1 (C8H10CuO7) belongs to the orthorhombic P21212 space group [a = 6.3015(4) A, b = 6.8743(4) A, c = 22.9972(14) A, and Z = 4] and incorporates tp in a bridging bis-monodentate binding mode and Cu(II) in a tetragonally elongated octahedron. 2 (C8H10CuO6) which belongs to the orthorhombic Pmc21 space group [a = 10.7421(8) A, b = 7.2339(10) A, c = 5.7143(13) A, and Z = 2] incorporates tp in a mono-bidentate binding mode and Cu(II) in a distorted square pyramid. 1 and 2 exhibit axial X-band powder EPR spectra with g⊥ = 2.08, g∥ = 2.29 (1) and g⊥ = 2.07, g∥ = 2.29 (2) at 300 K. 1 obeys the Curie−Weiss law at high temperatures (θ = −7.2 K) and at low temperatures behaves as 1-D magnetic chains with an exchange-coupling const...
178 citations
TL;DR: The crystal structure of Si was studied at pressures between 30 and 50 GPa using high-resolution monochromatic synchrotron x-ray diffraction as mentioned in this paper, where powder diffraction patterns of the phase Si VI were indexed on the basis of an orthorhombic unit cell containing 16 atoms.
Abstract: The crystal structure of Si was studied at pressures between 30 and 50 GPa using high-resolution monochromatic synchrotron x-ray diffraction. The powder diffraction patterns of the phase Si VI are indexed on the basis of an orthorhombic unit cell containing 16 atoms. The space group is assigned as $\mathrm{Cmca}$. Full profile refinements reveal that Si VI is isotypic to Cs V; i.e., axial ratios and atomic coordinates are nearly identical for both phases. Thus, formation of the Cs V type structure is not a unique feature of the pressure-driven electronic $s\ensuremath{-}d$ transition in Cs. Instead, the structure type appears to be more common, occurring intermediate between 8- and 12-fold coordinated structures.
TL;DR: In this article, the structural behavior of the three silver halides AgCl, AgBr, and AgI has been investigated to pressures $p\ensuremath{\sim}13\char21{}16\mathrm{GPa}$ using angle-dispersive x-ray diffraction with an image-plate device.
Abstract: The structural behavior of the three silver (I) halides AgCl, AgBr, and AgI has been investigated to pressures $p\ensuremath{\sim}13\char21{}16\mathrm{GPa}$ using angle-dispersive x-ray diffraction with an image-plate device. Principal attention has been paid to the structural characterization of the phase transitions in the pressure range $p\ensuremath{\sim}7\char21{}13\mathrm{GPa}$ observed previously by optical and resistivity techniques. In AgCl, the ambient-pressure rocksalt-structured phase transforms at $p=6.6(6)\mathrm{GPa}$ to a monoclinic structure with a KOH-type arrangement and then to an orthorhombic TlI-type configuration at $p=10.8(8)\mathrm{GPa}.$ Both these structures can be considered to be more densely packed arrangements derived from rocksalt and possess ionic environments intermediate between the octahedrally coordinated rocksalt structure and an eightfold coordinated CsCl-type one adopted at higher pressure. AgBr and AgI both undergo $\mathrm{rocksal}\stackrel{\ensuremath{\rightarrow}}{t}\mathrm{KOH}$-type structural transitions, at $p=7.9(4)\mathrm{GPa}$ and $p=11.3(2)\mathrm{GPa},$ respectively. The nature of the pressure-induced $\mathrm{rocksal}\stackrel{\ensuremath{\rightarrow}}{t}\mathrm{CsCl}$ transformation in the three Ag(I) halides is discussed in relation to the continuous rhombohedral deformation model due to Buerger and to recent theoretical predictions derived from ab initio electronic structure calculations.
TL;DR: In this article, the authors show that the distortion of the orthorhombic perovskite progressively increases along the series, leading for the smallest Ho3+ and Y3+ cations to a subtle monoclinic distortion (space group P21/n) which implies the splitting of the Ni positions in the crystal.
Abstract: RNiO3 nickelates have been prepared under high oxygen pressure (R = Sm, Eu, Gd) or high hydrostatic pressure (R = Dy, Ho, Y) in the presence of KClO4. The samples have been investigated at room temperature (RT) by synchrotron X-ray powder diffraction to follow the evolution of the crystal structures and microstructures along the series. The distortion of the orthorhombic (space group Pbnm) perovskite progressively increases along the series, leading for the smallest Ho3+ and Y3+ cations to a subtle monoclinic distortion (space group P21/n) which implies the splitting of the Ni positions in the crystal. This symmetry was confirmed by neutron powder diffraction; the crystal structures for RHo and Y were refined simultaneously from RT synchrotron and neutron powder diffraction data. In both perovskites the oxygen octahedra around Ni1 and Ni2 positions are significantly distorted, suggesting the manifestation of Jahn−Teller effect, which is almost absent in the nickelates of lighter rare earths. The very dist...
TL;DR: Bis(1, 1, 1-trifluoro-5, 5-dimethyl-5methoxy-acetylacetonato)copper(II) was prepared in two polymorphic modifications as mentioned in this paper.
Abstract: Bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxy-acetylacetonato)copper(II) was prepared in two polymorphic modifications. The orthorhombic α-form is stable and densely packed, with four trans and four c...
TL;DR: In this paper, atomistic simulation techniques have been employed to investigate the energetics of cation formation and migration in cubic, rhombohedral and orthorhombic LaMnO672 3672
Abstract: Atomistic simulation techniques have been employed to investigate the energetics of cation formation and migration in cubic, rhombohedral and orthorhombic LaMnO
3
. The calculations suggest that for rhombohedral and orthorhombic lanthanum manganite, oxidative nonstoichiometry leads to the formation of cation vacancies on both La and Mn sites, though tending towards more La vacancies. The activation energy for lanthanum vacancy migration was found to increase with departure from cubic perovskite symmetry in the order: cubic cubic
directions. Calculated migration energies for this path also increased with distortion from the cubic form. The effect of composition on cation migration energies was also examined.
TL;DR: In this paper, the crystal structure of SrHfO{sub 3} has been studied at high temperatures using powder neutron diffraction and the Rietveld method and it has been shown that at higher temperatures the structure is the ideal cubic perovskite (Pm3{sup -}m).
Abstract: The crystal structure of SrHfO{sub 3} has been studied at high temperatures using powder neutron diffraction and the Rietveld method. From 300 K to approximately 670 K the structure of SrHfO{sub 3} is orthorhombic (Pnma). By 870 K the material adopts a second orthorhombic structure (Cmcm). The material then undergoes a further phase transition and is tetragonal (/4/mcm) from {approx}1000 to 1353 K. At higher temperatures (>1360 K) the structure is the ideal cubic perovskite (Pm3{sup -}m). The angle of rotation of the oxygen octahedron in the tetragonal phase is taken as the order parameter and its temperature variation is consistent with a second order phase transition.
TL;DR: In this article, the authors showed that this transformation is suppressed in spinels of composition up to x ≈ 2 obtained through the electrochemical cycling of orthorhombic LiMnO{sub 2}.
Abstract: Li{sub x}Mn{sub 2}O{sub 4} spinel normally undergoes a transformation from its cubic to tetragonal phase when x exceeds 1 due to a collective Jahn-Teller distortion, resulting in poor cyclability when both the 4 and 3 V intercalation plateaus are utilized. In this study, the authors show that this transformation is suppressed in spinels of composition up to x {approx} 2 obtained through the electrochemical cycling of orthorhombic LiMnO{sub 2}. X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy studies together show the cycling produces a cubic spinel containing partial tetrahedral cation site occupancy and a nanodomain structure (20 to 50 nm size) within parent single-crystalline oxide particles. This structure is responsible for the cycling stability of electrochemically produced spinel. The reversible capacity (272 mAh/g) and energy density (853 Wh/kg) achieved at a low charge-discharge rate (3.33 mA/g) in the present samples are the highest among crystalline LiMnO{sub 2} materials reported to date.
TL;DR: In this paper, the authors show that all three cell edges of orthorhombic Y2W3O12 decrease with increasing temperature, giving an average linear thermal expansion coefficient of −7.0×10−6 K−1.
TL;DR: In this paper, the structural phase transitions in perovskite-like NaTaO3, from room temperature to 933 K, have been examined, and the structure in orthorhombic Cmcm is characterized by simultaneous tilting of the oxygen atom octahedron about two of its tetrad axes.
Abstract: Neutron powder diffraction has been used to examine the structural phase transitions in the perovskite-like NaTaO3, from room temperature to 933 K. The room temperature orthorhombic structure (Pbnm, a = 5.4768(1), b = 5.5212(1), c = 7.7890(2)) transforms to orthorhombic Cmcm at around 700 K, then to tetragonal P4/mbm at 835 K, and finally to cubic Pmm above 890 K. The structure in orthorhombic Cmcm is characterized by simultaneous tilting of the oxygen atom octahedron about two of its tetrad axes, the tilting of successive octahedra being out of phase along the b-axis, and in phase along the c-axis. The two tilt angles are comparable just above 700 K, but the out-of-phase tilt angle falls smoothly to zero as the transition to tetragonal is approached, in the manner suggestive of a tricritical transition. This results in an unusual variation of lattice parameters with temperature in the orthorhombic Cmcm phase. In the tetragonal phase the lattice parameters vary smoothly; however near the transition to cubic the in-phase tilt angle changes more rapidly with temperature than might be expected in a continuous phase transition.
TL;DR: Two-dimensional transition-metal coordination polymers [MCl2(bpy)] (M = Fe, Co, Ni; Co/Ni, bpy = 4, 4‘-bipyridine) have been synthesized in superheated water solutions as discussed by the authors.
Abstract: Two-dimensional transition-metal coordination polymers [MCl2(bpy)] (M = Fe, Co, Ni; Co/Ni, bpy = 4, 4‘-bipyridine) have been synthesized in superheated water solutions. The hydrothermal routes resulted in four compounds [FeCl2(bpy)](I), [CoCl2(bpy)](II), [NiCl2(bpy)](III), and [(Co/Ni)Cl2(bpy)](IV). Compounds I−IV are isostructural and belong to orthorhombic crystal system, space group Cmmm (No. 65). Crystal data for I: a = 11.929(2) A, b = 11.447(2) A, c = 3.638(1) A, V = 496.77(18) A3, Z = 2. Crystal data for II: a = 11.993(2) A, b = 11.374(2) A, c = 3.611(1) A, V = 492.57(18) A3, Z = 2. The structure is a noninterpenetrating two-dimensional network containing transition-metal centers octahedrally coordinated by four bridging chlorine and two bpy ligands at trans positions. The adjacent bpy ligands within a single layer are parallel to each other at a distance of 3.6 A. Spontaneous antiferromagnetic ordering was found in all compounds from the magnetic susceptibility χ(T) measurements under low fields...
TL;DR: In this paper, the authors discuss the physical mechanism that stabilizes orthorhombic LiMnO 2 and discuss how the latter may be stabilized by a judicious choice of dopants.
Abstract: they are difficult to synthesize in the layered α-NaFeO 2 structure which is common to LiCoO 2 and LiNiO2. When synthesized under equilibrium conditions, LiMnO 2 forms an orthorhombic structure with space group Pmmn.2-4 A tetragonal structure can also be formed by synthesizing an LiMn 2O4 spinel and further lithiating it up to composition Li 2Mn2O4. 5 Recently, metastable layered LiMnO2 with space group C2/m has been made through ion exchange processes starting from the layered α-NaMnO 2 precursor. 6,7 In addition, partial substitution of Mn by Cr8 and Al 9 have been shown to stabilize the layered structure. The orthorhombic form of LiMnO 2 is particularly intriguing. It is found only for LiMnO 2, 3 β-NaMnO2, 3 and a metastable form of LiFeO 2. 10,11 Most other LiMO2 compounds with M close to Mn (except for Fe) in the periodic table form the layered α-NaFeO 2 structure. Besides its scientific interest, understanding the uncommon stability of the orthorhombic structure may be of practical interest in designing layered lithium-manganese oxides which form in different structures. In this paper we discuss the physical mechanism that stabilizes orthorhombic LiMnO 2 over layered LiMnO2 and discuss how the latter may be stabilized by a judicious choice of dopants.
TL;DR: In this paper, the stable intermediate structures were optimized by a molecular mechanic approach, giving rise to new hypothetical 3D crystal structures which progress along the transition in the order of increasing density from 2.22 to 3.30 gcm−3.
TL;DR: In this paper, an extensive investigation of the temperature dependence of Raman spectra has been carried out on WO 3 powders from room temperature to 800°C, in particular the orthorhombic-to-tetragonal phase transition occurring at about 740°C has been studied.
TL;DR: The influence of thermal annealing on cation disorder in ABi============ 2============Nb======€ 2======672€ 1======€ 9======€ 1.1€ 1€ 0.
Abstract: The influence of thermal annealing on cation disorder in ABi
2
Nb
2
O
9
(A=Sr, Ba) has been studied using synchrotron powder X-ray diffraction methods. BaBi
2
Nb
2
O
9
adopts a tetragonal (I4
1
/mmm) structure, whilst SrBi
2
Nb
2
O
9
is orthorhombic, space group A2
1
am, irrespective of the annealing conditions. In both complexes the A-type cations, Sr and Ba, are disordered over the perovskite and Bi
2
O
2
layers. Quenching the samples from high temperature results in a slight increase in both the cell volume and the degree of disorder, the extent of disorder being greater in the Ba complex. Variable temperature diffraction studies are also reported.
TL;DR: In this article, the (0001) surface of α-Mo2C prepared by Ar ion bombardment and annealing was characterized using X-ray photoelectron spectroscopy and low energy electron diffraction.
TL;DR: In this paper, the authors investigated the Fe1+xTi2-xO5, 0 less than or equal to x less than and equal to 1 pseudobrookite series with the D-2h(17) space group.
Abstract: The Fe1+xTi2-xO5, 0 less than or equal to x less than or equal to 1, solid solution series has been systematically investigated by means of x-ray diffraction, Mossbauer spectroscopy and neutron diffraction. The results confirm that the Fe1+2Ti2-xO5, 0 less than or equal to x less than or equal to 1 pseudobrookite series has an orthorhombic structure with the D-2h(17) (Cmcm) space group. The unit cell contains four formula units. The site occupancies obtained from both Mossbauer spectra and neutron diffraction data indicate that the cation (Fe2+, Fe3+ and Ti4+) distributions in the available sites, 4c and 8f, are neither random nor perfectly ordered. At x = 0, most of the iron is in the 4c site, and the 8f site fills progressively as x --> 1. The agreement between the Mossbauer and neutron site occupancies indicates that the Fe3+ and Fe2+ site preferences are the same.
TL;DR: Wide-angle X-ray data point to a three-phase structure in isotropic and drawn specimens of a homogeneous poly(ethylene-co-octene) (7.3 mol % 1-Octene) as mentioned in this paper.
Abstract: Wide-angle X-ray data point to a three-phase structure in isotropic and drawn specimens of a homogeneous poly(ethylene-co-octene) (7.3 mol % 1-octene). In addition to the amorphous halo, the unoriented polymer exhibits Bragg reflections characteristic of the orthorhombic crystalline phase and an additional reflection that is assigned to the hexagonal mesophase. On stretching 800%, the degree of crystallinity increases from ∼25% to ∼50%, due mainly to the formation of smaller hexagonal crystallites, while the proportions of the orthorhombic and amorphous phases decline. Small-angle X-ray data reveal a distinct long period, pointing to the existence of lamellae that become oriented perpendicular to the draw direction. On releasing the specimen, there is a considerable permanent set (∼350% extension), and the crystallinity declines to ∼30% as the hexagonal crystallites appear to revert to the amorphous structure. The results suggest that the hexagonal mesophase is formed by chain segments that have octene si...
TL;DR: In this article, a Landau-Ginsburg-Devonshire-type thermodynamic theory is used to describe equilibrium single-domain states and phase transitions in epitaxial ferroelectric thin films.
Abstract: A Landau-Ginsburg-Devonshire-type thermodynamic theory is used to describe equilibrium single-domain states and phase transitions in epitaxial ferroelectric thin films. For BaTiO3 and PbTiO3 films grown on cubic substrates, the paraelectric to ferroelectric phase transition is found to be of the second order, irrespective of the lattice misfit. The temperature-misfit strain phase diagrams are developed for these films. The existence of a “monoclinic gap” separating the stability ranges of low-temperature tetragonal and orthorhombic states is predicted. Anomalies of the dielectric response associated with the phase transitions in epitaxial films are also discussed
TL;DR: The abplane optical properties of the high-temperature superconductor Bi2Sr2CaCu2O8 are anisotropic in both the normal and the superconducting state as mentioned in this paper.
Abstract: The ab-plane optical properties of the high-temperature superconductor Bi2Sr2CaCu2O8 are anisotropic in both the normal and the superconducting state. Consistent with the orthorhombic structure, the principal axes lie along the a and b crystallographic axes, nearly 45 degrees from the Cu-O bond direction. In the normal state, analysis of the temperature-dependent optical conductivity suggests a:scattering rate for the free carriers that shows ab anisotropy in both magnitude and temperature dependence. In;the superconducting state, the anisotropy in the oscillator strength of the superfluid response determined from the far-infrared frequency dependence of sigma(2)(omega) and from a sum-rule analysis leads to a penetration depth lambda(D) that is larger along the b axis than the a axis: (lambda(L)(b)>lambda(L)(a)). [S0163-1829(99)01845-7].
TL;DR: Detailed crystal structure analyses demonstrate that both the intermolecular pi-pi stacking between the diazafluorene planes in different molecules and intermolescular hydrogen bonds between the water molecules and the deprotonated ligands might be the factors that influence the molecules to be packed in the acentric space group P3(1).
Abstract: A cis-configuration bis(4,5-diazafluorene-9-one thiosemicarbazone) palladium trihydrate, which exhibits approximately five times SHG (second harmonic generation) efficiency of urea, has been designed, synthesized, and structurally characterized. The complex, C(24)H(16)N(10)PdS(2).3H(2)O, crystallizes in trigonal space group P3(1) with cell parameters a = 10.749(2) A, c = 19.872(4) A, V = 1988.3(6) A(3), and Z = 3. The coordination geometry about the Pd(II) is surprisingly a cis-configuration square-planar formed by two imino nitrogen atoms N(3) and N(8) and two sulfur atoms S(1) and S(2) from two thiosemicarbazone ligands. Intramolecular contact analyses in the crystals and 1D and 2D (1)H NMR spectra in solution show that the cis-positioning of the two ligands was stabilized by the pi-pi interaction between the two delocalized diazafluorene moieties. Detailed crystal structure analyses demonstrate that both the intermolecular pi-pi stacking between the diazafluorene planes in different molecules and intermolecular hydrogen bonds between the water molecules and the deprotonated ligands might be the factors that influence the molecules to be packed in the acentric space group P3(1). The crystal structure of the free ligand was also reported here for comparison. The ligand, C(12)H(9)N(5)S, crystallizes in orthorhombic space group Pbca with cell parameters a = 8.432(2) A, b = 15.427(3) A, c = 17.387(3) A, V = 2272.7(8) A(3), and Z= 8. The thiosemaicarbazone moiety adopts an E configuration with N(1) cis to N(3).