Sm Phase Research Articles

A complex of poly(4-vinylpyridine) and tolane based hemi-phasmid benzoic acid: towards luminescent supramolecular side-chain liquid crystalline polymers.

A supramolecular side-chain liquid crystalline (LC) polymer P4VP(1)x was prepared using poly(4-vinylpyridine) and a tolane based hemi-phasmid benzoic acid. P4VP(1)x exhibits good processability, forming smectic and hexagonal columnar LC phases at different compositions. Its photoluminescence properties depend on the LC structures.

Antiferroelectric and ferroelectric SmC* phases in racemic mixture

Antiferroelectric Sm phase can be created at cooling from Iso, SmA* and SmC* phases. When antiferroelectric phase appears from the ferroelectric one, the magnitude of Goldstone mode detected in SmC* is much higher than the amplitude of low frequency PL mode observed in Sm. Due to this fact it is impossible to compare both modes. Such a comparison would be interesting because the mechanism of forming the Goldstone and PL modes seems to be similar. In this article we compare the Goldstone mode with the PL one. It is possible because the new racemic mixture, which shows both SmC* and Sm phases, was prepared. Moreover, the magnitude of the Goldstone mode in the racemate is comparable with the magnitude of PL mode, which makes the comparison possible. The results show that the behavior of PL and Goldstone modes are very similar. The parameters of the Goldstone mode in SmC* and parameters of PL mode in Sm change continuously.

Structure, Photochromism and Liquid Crystal Properties of 1-Alkyl-2-(Arylazo)Imidazoles (Raai-C<sub>n</sub>H<sub>2n+1</sub>, n (Even) = 10 - 22)

Photochromism is the reversible structural change of the molecules upon light irradiation having different spectral pattern before and after irradiation. Liquid crystal (LC) is a long-range orientational order of the molecules in between solid and isotropic liquid phases which share the properties of the crystal and liquid phases. 1-Alkyl-2-(ary-lazo)imidazoles, (Raai-CnH2n+1, R = H, Me and n = 10, 12, 14, 16, 18, 20, 22) exhibits photochromism and two of them (Haai-C18H37 and Haai-C22H45) show Liquid crystal (LC) properties. One of these compounds, Meaai-C16H33 is structurally characterized by single crystal X-ray diffraction study. The compounds upon irradiation with UV light show E-to-Z isomerisation. Quantum yields (φE→Z) of E-to-Z isomerisation vary with the molar mass of the compounds. The reverse transformation, Z-to-E, is recorded in thermal condition. The activation energy (Ea) of isomerisation is determined by the controlled temperature reaction. Liquid crystal property of the molecules is examined by polarizing optical microscopy (POM) and DSC. The carbon chain length n = 18 shows nematic (N)-isotropic (I) phase transition and an unknown Smectic (Sm) phase is observed with n = 22 on heating cycle.

The Samarium Depleted Zone in SmCo<sub>5</sub> Magnets

After sintering, SmCo5magnets may present a surface layer depleted in Samarium. This happens because Samarium is much more susceptible for oxidation than cobalt. Besides, samarium has high vapour pressure. This Sm depleted zone is of the order of ~ 1 mm (in a 10 mm diameter magnet), and present oxygen content 1000 ppm higher than the center of the magnet. This layer is composed by SmCo(5+x), which presents low coercivity (1-2 kOe). The occurrence of the Sm depleted layer is associated with kinks in the 2ndquadrant of the hysteresis curve. After the removal of this layer, the hysteresis kinks disappear. The efficacy of different chemical etchings (Nital and chromic acid) to reveal microstructural constituents was discussed in detail. Nital is recommended for observation of magnetic domains under polarized light (Kerr effect), whereas chromic acid is more suitable to identify Sm2Co7and other high Sm phases.

Photoluminescence and X-ray Absorption Fine Structure Analysis of Sm-Doped TiO2 Thin Films

The local structure of samarium-doped titanium dioxide (TiO2:Sm) thin films fabricated by laser ablation and post annealing has been investigated by Sm L III-edge X-ray absorption fine structure (XAFS) analysis using a synchrotron radiation. The TiO2:Sm samples at annealing temperatures lower than 1000 °C showed an anatase (A-)TiO2:Sm crystal structure and transferred into a rutile (R-)TiO2:Sm phase at annealing temperature of 1100 °C. All the A-TiO2:Sm phase samples showed intense Sm-related photoluminescence (PL) at room temperature. It was shown that the samples which showed intense PL have shorter coordination distance for the first nearest neighbor of Sm than that of the samples which did not show PL after the crystal phase transition.

トリフェニレンに結合した液晶性アゾベンゼンユニットの光異性化によるカラムナー相―スメクチック相―等方性液体間の相転移制御

トリフェニレンに結合した液晶性アゾベンゼンユニットの光異性化によるカラムナー相―スメクチック相―等方性液体間の相転移制御

Effects of Eu doping on SmB6single crystals

The various phases in Sm${}_{1\ensuremath{-}x}$Eu${}_{x}$B${}_{6}$ are investigated based on magnetic susceptibility, resistivity, and Hall effect measurements. The end compounds are a Kondo insulator (SmB${}_{6}$) and a polaronic ferromagnet (EuB${}_{6}$). For $x$ \ensuremath{\approx} 0.2, the ground state undergoes a transition from a Kondo insulator to an antiferromagnetic (AF) insulator phase. Further doping induces a transition to an AF metal at $x$ \ensuremath{\approx} 0.4. The spin gap is reduced rapidly with the Eu substitution, while there is a charge gap up to $x$ \ensuremath{\approx} 0.4. The Hall effect indicates a dramatic decrease in the carrier density at low temperatures ($T$) for the Kondo insulator regime, whereas, the carrier density is almost independent of $T$ in the AF metallic phase.

Lyotropic Smectic B Phase Formed in Suspensions of Charged Colloidal Platelets

Here, we present the first observation of a smectic B (Sm(B)) phase in a system of charged colloidal gibbsite platelets suspended in dimethyl sulfoxide (DMSO). The use of DMSO, a polar aprotic solvent, leads to a long range of the electrostatic Coulomb repulsion between platelets. We believe this to be responsible for the formation of the layered liquid crystalline phase consisting of hexagonally ordered particles, that is, the Sm(B) phase. We support our finding by high-resolution X-ray scattering experiments, which additionally indicate a high degree of ordering in the Sm(B) phase.

A new anhydrous bismuth potassium nitrate, K 3Bi 2(NO 3) 9: Synthesis, structure characterization and thermal decomposition

Abstract A new K 3 Bi 2 (NO 3 ) 9 phase was discovered at a synthesis of Bi-containing photocatalysts. K 3 Bi 2 (NO 3 ) 9 has cubic structure with unit cell parameter a = 13.5354(20) A, and belongs to P4 3 32 (No. 212) space group. New phase is isostructural with the K 3 Ln 2 (NO 3 ) 9 ( Ln = La, Ce, Pr, Nd, and Sm) phases. The crystal structure was refined from powder X-ray diffraction (XRD) data. The R wp factor at Rietveld refinement was equal to 8.62%. The morphology of K 3 Bi 2 (NO 3 ) 9 was characterized using scanning electron microscopy. The value of ionic radius of Bi 3+ in 12-fold coordination calculated from the unit cell parameter was found to be 1.314(5) A. K 3 Bi 2 (NO 3 ) 9 phase and products of its thermal decomposition were studied using XRD, Fourier transform infrared spectroscopy (FTIR) methods and thermal gravimetric analysis (TGA). At 350 °C, K 3 Bi 2 (NO 3 ) 9 phase was transformed to new unknown intermediate bismuth potassium nitrate that most likely belongs to Sillen type of structure. Geometrical solution for unit cell of this phase was proposed.

Microstructure investigation of SiC films synthesized from liquid phase in Sm–Co melts

Abstract Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure of 10 5 Pa. The synthesis was carried out in a tube furnace through cyclic heating process using methane as a carbon source and Sm–Co mixed powder as a solvent. The growth of SiC from rare earth Sm-based solvent is an innovative approach, and Co can promote the formation of solvent during the growth process. The structural and compositional analyses were carried out using X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and transmission electron microscopy. Results indicated that β-SiC was successfully fabricated on Si (1 1 1) substrate. The heterogeneous nucleation of β-SiC was found to be observed initially at the edge of triangle-shaped sites on Si (1 1 1) surface that formed due to the existence of Co, and then grew and expanded to form β-SiC film. The growth process of SiC via vapour–liquid–solid mechanism was also discussed in this study.

Comment on “Feshbach-Einstein Condensates”

In a recent paper (Phys. Rev. Lett. 102, 015301 (2009), arXiv:0810.3763) Rousseau and Denteneer claim that an unconventional "super-Mott" (SM) phase is realized by bosons trapped in an optical lattice close to a Feshbach resonance with a molecular state. The supposed SM phase, observed via quantum Monte Carlo (QMC) simulations of an atom-molecule Bose-Hubbard model, is an incompressible phase developing spontaneous atomic/molecular supercurrents which are perfectly anticorrelated. Here we show that the identification of this phase is based on a misinterpretation of the estimators of superfluidity in QMC, which break down in the presence of coherent atom/molecule conversion. Our conclusion is that the supposed SM phase is in fact a fully normal insulator.

Control of magnetic ordering by altering Co–Co distances in La0.9R0.1Co2P2 (R=Ce, Pr, Nd, and Sm) phases with ThCr2Si2-type structures

To clarify the origins of different magnetic behavior in ferromagnetic LaCo2P2 and antiferromagnetic RCo2P2 (R=Ce, Pr, Nd, and Sm), quaternary phases La0.9R0.1Co2P2 have been investigated. While LaCo2P2 orders ferromagnetically at 132 K, the introduction of the small amount of R into the La sublattice increases the ferromagnetic ordering temperature, which correlates with the size of the R3+ ion (TC=144 K, 150 K, 161 K, and 165 K for Ce, Pr, Nd, and Sm, respectively). This change is attributed to the increasing Co–Co separation within the [Co2P2] layer, which results in higher spin polarization of the Co 3d subband. The low-temperature magnetism of La0.9R0.1Co2P2 strongly depends on the nature of the rare-earth metal.

Structure and thermal stability of the RMgPb rare earth compounds, and the anomalous melting behaviour of SmMgPb

Abstract The synthesis, crystal structure and melting behaviour of the new family of ternary rare earth RMgPb compounds is reported in this work. All the rare earth elements (including Y and Sc) form the equiatomic phase 1:1:1 with Mg and Pb, similar to the recently investigated RMgSn compounds series. Unlike RMgSn, all the RMgPb phases (the lighter, as well as the heavier, trivalent lanthanides) crystallize with the same crystal structure: the tetragonal CeScSi-type (an ordered derivative of the La 2 Sb-type structure, tI 12, space group I 4 /mmm ). Both the observed unit cell volume ( V obs ) and the mean atomic volume ( V obs / n , where n is the number of atoms in a unit cell) decrease linearly from LaMgPb [ a = 4.598(1) A, c = 16.512(2) A] to LuMgPb [ a = 4.356(1) A, c = 15.783(2) A] confirming the lanthanide contraction in the RMgPb series. On the other hand, the volume of formation (Δ V %) becomes more negative by a non-linear trend on going from La to Lu. A high temperature polymorph phase, orthorhombic TiNiSi-type, has been found for both YbMgSn and YbMgPb. Further work concerning the existence of the phase “ScMgSn” has been also performed. The relationships between the structural properties and formation thermodynamics of both the RMgSn and the RMgPb series of compounds have been examined in the present work. All the RMgPb phases form congruently (including YMgPb and ScMgPb) and their melting temperatures decrease non-linearly from LaMgPb to ScMgPb. YbMgSn and YbMgPb also form congruently with anomalously high melting points. A particular and interesting anomaly has been observed for SmMgPb and Sm containing pseudo-ternary compounds [Nd 1− x Sm x MgPb ( x = 0.4, 0.6, 0.8) and Sm 1− y Gd y MgPb ( y = 0.6, 0.4, 0.2)]; their melting temperature are lower than the ones expected from the trend established by the other RMgPb phases by as much as 70 °C. This anomalous behaviour led to an examination of the melting points of selected Sm-bearing materials, including Sm metal. The low melting points are thought to be due to a decrease in the valence of trivalent Sm phases at 25 °C as the materials are heated and thus a lower bonding strength.

Structural, magnetic properties and magnetostriction studies of Sm 1− xNd xFe 1.55 alloys

Structural, magnetic properties and magnetostriction studies of Sm(1-x)Nd(x)Fe(1.55) (0 <= x <= 0.56) alloys have been performed. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm(1-x)Nd(x)Fe(1.55) alloys with 0 <= x <= 0.48. The lattice parameter of alloys increases linearly with increase in Nd content while the Curie temperature behaves in the opposite way. The alloy x=0.08 exhibits a giant magnetostriction value(lambda(parallel to)-lambda(perpendicular to)) of -2187 ppm at a magnetic field of 12 kOe due to the anisotropy compensation between Sm(3+) and Nd(3+) ions. (C) 2010 Elsevier B.V. All rights reserved.

Structure, magnetic and magnetostrictive properties of Sm 0.7Pr 0.3Fe x alloys

The structure, magnetic and inagnetostrictive properties of Sm(0.7)Pr(0.3)Fe(x) (1.45 <= x <= 1.95) alloys is investigated. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm(0.7)Pr(0.3)Fe(x) alloys with 1.45 <= x <= 1.85. The saturation magnetization of the alloys tends to increase with increasing Fe content. Sm(0.7)Pr(0.3)Fe(1.55) has the highest magnetostriction among all the Sm(0.7)Pr(0.3)Fe(x) alloys at low fields and shows a large magnetostriction lambda(parallel to)-lambda(perpendicular to) = 1008 ppm at a magnetic field of 12 kOe. (C) 2009 Elsevier B.V. All rights reserved.

Low temperature molten-salt synthesis of nanocrystalline cubic Sr 2SbMnO 6

Sr2SbMnO6 (SSM) powders were successfully synthesized at reasonably low temperatures via molten-salt synthesis (MSS) method using eutectic composition of 0.635 Li2SO4-0.365 Na2SO4 (flux). High-temperature cubic phase SSM was stabilized at room temperature by calcining the as-synthesized powders at 900 degrees C/10 h. The phase formation and morphology of these powders were characterized via X-ray powder diffraction and scanning electron microscopy, respectively. The SSM phase formation associated with similar to 60 nm sized crystallites was also confirmed by transmission electron microscopy. The activation energy associated with the particle growth was found to be 95 +/- 5 kJ mol(-1). The dielectric constant of the tetragonal phase of the ceramic (fabricated using this cubic phase powder) with and without the flux (sulphates) has been monitored as a function of frequency (100 Hz-1 MHz) at room temperature. Internal barrier layer capacitance (IBLC) model was invoked to rationalize the dielectric properties.

Molecular Alignment Structure of Dimeric Liquid Crystal Having INACA Phase Sequence

Antiferroelectric liquid crystals (AFLCs) composed of low-mass mesogens do not show the nematic (N) phase. Recently, it has been reported that an AFLC containig dimeric molecules may show the N phase. However, it is not obvious why the antiferroelectric SmC (SmCA) and N phases may coexist in the phase sequence of the dimeric LCS. In this study, the molecular alignment structure has been researched with an X-ray diffractometer. It is found that a dimeric LC 8PY11OCB has a bookshelf structure in the SmA phase and a chevron structure in the SmCA phase. Moreover, the molecular alignment is an intercalated structure in both Sm phases. The bent molecular structure is stable even in the SmA phase, in which the phenylpyrimidine moieties of 8PY11OCB freely rotates due to a high thermal motion with the axis being another mesogenic part including cyano group.

Thermodynamic study on phase stability in nanocrystalline Sm–Co alloy system

To study the phase stability and the phase transformation behavior in the nanocrystalline (NC) stoichiometric alloys, a thermodynamic model has been developed in the present paper. Using the NC Sm–Co alloy as an example, the thermodynamic properties of various phases in the alloy system were evaluated systematically. In particular, the grain-size-dependence of the Gibbs free energy of each alloy phase at different temperatures was provided. Based on the model calculations, the stabilities of different phases in the NC Sm–Co system were analyzed. As distinctly different from the phase stability in the conventional polycrystalline alloys, the Gibbs free energies of some NC phases become positive at the room temperature when the nanograin size is reduced to below a certain critical value, which implies that these phases cannot stably exist at the room temperature. In order to verify the thermodynamic model, the stoichiometric Sm–Co alloy was prepared, and the grain structure and the phase constitution of the alloy were characterized by combining x-ray diffraction and transmission electron microscopy analyses. The experimental findings have confirmed the thermodynamic model predictions for the NC alloy system.

Molecular Shapes of Monosubstituted Polyacetylenes in their Liquid Crystalline Phases

AbstractIn this short review, we discuss the molecular shapes of monosubstituted polyacetylenes (MSPAs) in their liquid crystalline (LC) phases. Their rigid backbone with high stereoregularity can endow MSPAs with significant shape persistency, which largely determines their LC structures. Helical cis‐cisoidal and cis‐transoidal MSPAs render rod‐like shapes and can form columnar LC (Φ) phases. In the smectic LC (Sm) phases of MSPAs with mesogenic side‐chains, the main chain, with trans‐cisoidal, trans‐transoidal or extended cis‐transoidal conformation, is in fact largely coplanar with the side‐chains, resulting in a sheet‐like molecular shape. From a simple geometric point of view, the rod‐ or sheet‐like MSPA molecules serve as the building block of their LC phases.magnified image

Samarium-atom adsorption and desorption on iridium

The adsorption and condensation of samarium on Ir(111) are investigated by thermionic emission spectroscopy and thermal desorption spectroscopy (TDS). During Sm deposition, the work function is found to fall monotonically from 5.8 to 2.7 eV and then to rise slowly to a plateau at 2.9 eV, for any substrate temperature from the range 700–1200 K. The optimal Sm coverage is estimated at 0.51 ± 0.03. The activation energy E+ and the preexponential factor C for Sm-ion desorption and those for Sm-atom desorption, E0 and D, respectively, are determined in the temperature range 1800–2050 K and at a coverage small enough not to alter the work function of the iridium. Their values are as follows: E+ = 5.72 ± 0.10 eV, E+ = 5.72 ± 0.10 eV, D ∼ 1 × 1013s−1, and C ∼ 1.3 × 1013 s−1. Several Sm phases are detected in each TDS peak.