Nature of the transient species formed in the pulse radiolysis of 4‐hydroxybenzyl alcohol in aqueous solutions: observation of equilibrium in the reaction of OH‐adducts with HPO ions

Reactions of ^. OH/O ^.? radicals, H‐atoms as well as specific oxidants such as N and Cl radicals with 4‐hydroxybenzyl alcohol (4‐HBA) in aqueous solutions have been investigated at various pH values using the pulse radiolysis technique. At pH 6.8, ^. OH radicals were found to react with 4‐HBA (k = 6 × 10⁹ dm³ mol^?1 s^?1) mainly by contributing to the phenyl moiety and to a minor extent by H‐abstraction from the ? CH₂OH group. ^. OH radical adduct species of 4‐HBA, i.e., ^. OH‐(4‐HBA) formed in the addition reaction were found to undergo dehydration to give phenoxyl radicals of 4‐HBA. Decay rate of the adduct species was found to vary with pH. At pH 6.8, decay was very much dependent on phosphate buffer ion concentrations. Formation rate of phenoxyl radicals was found to increase with phosphate buffer ion concentration and reached a plateau value of 1.6 × 10⁵ s^?1 at a concentration of 0.04 mol dm^?3 of each buffering ion. It was also seen that ^. OH‐(4‐HBA) adduct species react with HPO ions with a rate constant of 3.7 × 10⁷ dm³ mol^?1 s^?1 and there was no such reaction with H₂PO ions. However, the rate of reaction of ^. OH‐(4‐HBA) adduct species with HPO ions decreased on adding KH₂PO₄ to the solution containing a fixed concentration of Na₂HPO₄ which indicated an equilibrium in the H⁺ removal from ^. OH‐(4‐HBA) adduct species in the presence of phosphate ions. In the acidic region, the ^. OH‐(4‐HBA) adduct species were found to react with H⁺ ions with a rate constant of 2.5 × 10⁷ dm³ mol^?1 s^?1. At pH 1, in the reaction of ^. OH radicals with 4‐HBA (k = 8.8 × 10⁹ dm³ mol^?1 s^?1), the spectrum of the transient species formed was similar to that of phenoxyl radicals formed in the reaction of Cl radicals with 4‐HBA at pH 1 (k = 2.3 × 10⁸ dm³ mol^?1 s^?1) showing that ^. OH radicals quantitatively bring about one electron oxidation of 4‐HBA. Reaction of ^. OH/O ^.? radicals with 4‐HBA by H‐abstraction mechanism at neutral and alkaline pH values gave reducing radicals and the proportion of the same was determined by following the extent of electron transfer to methyl viologen. H‐atom abstraction is the major pathway in the reaction of O ^.? radicals with 4‐HBA compared to the reaction of ^. OH radicals with 4‐HBA. At pH 1, transient species formed in the reactions of H‐atoms with 4‐HBA (k = 2.1 × 10⁹ dm³ mol^?1 s^?1) were found to transfer electrons to methyl viologen quantitatively. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman microscopy of the mixite mineral BiCu6(AsO4)3(OH)6·3H2O from the Czech Republic

Raman microscopy of the mixite mineral BiCu₆(AsO₄)₃(OH)₆·3H₂O from Jáchymov and from Smrkovec (both Czech Republic) has been used to study their molecular structure. The presence of (AsO₄)³⁻, (AsO₃OH)²⁻, (PO₄)³⁻ and (PO₃OH)²⁻ units, as well as molecular water and hydroxyl ions, was inferred. O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra using Libowitzky's empirical relation. Small differences in the Raman spectra between both samples were observed and attributed to compositional and hydrogen‐bonding network differences. Copyright © 2009 John Wiley & Sons, Ltd.     

A Raman and infrared spectroscopic study of Ca2+ dominant members of the mixite group from the Czech Republic

The minerals of the mixite group—zálesíite CaCu₆[(AsO₄)₂(AsO₃OH)(OH)₆]·3H₂O from abandoned uranium deposit Zálesí, Czech Republic and calciopetersite CaCu₆[(PO₄)₂(PO₃OH)(OH)₆]·3H₂O from a quarry near Domašov na Bystřicí, northern Moravia, Czech Republic—were studied by Raman and infrared spectroscopy. The observed bands were assigned to the stretching and bending vibrations of (AsO₄)³⁻ and (AsO₃OH)²⁻ ions in zálesíite, and (PO₄)³⁻ and (PO₃OH)²⁻ in calciopetersite, and to molecular water, hydroxyl ions, and Cu‐(O,OH) units in both minerals. O H···O hydrogen‐bond lengths in zálesíite and calciopetersite structures were calculated with Libowitzky's empirical relation. Copyright © 2010 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of the antimony mineral klebelsbergite Sb4O4(OH)2(SO4)

Many minerals based upon antimonite and antimonate anions remain to be studied. Most of the bands occur in the low wavenumber region, making the use of infrared spectroscopy difficult. This problem can be overcome by using Raman spectroscopy. The Raman spectra of the mineral klebelsbergite Sb₄O₄(OH)₂(SO₄) were studied and related to the structure of the mineral. The Raman band observed at 971 cm⁻¹ and a series of overlapping bands are observed at 1029, 1074, 1089, 1139 and 1142 cm⁻¹ are assigned to the SO₄²⁻ν₁ symmetric and ν₃ antisymmetric stretching modes, respectively. Two Raman bands are observed at 662 and 723 cm⁻¹, which are assigned to the Sb O ν₃ antisymmetric and ν₁ symmetric stretching modes, respectively. The intense Raman bands at 581, 604 and 611 cm⁻¹ are assigned to the ν₄ SO₄²⁻ bending modes. Two overlapping bands at 481 and 489 cm⁻¹ are assigned to the ν₂ SO₄²⁻ bending mode. Low‐intensity bands at 410, 435 and 446 cm⁻¹ may be attributed to O Sb O bending modes. The Raman band at 3435 cm⁻¹ is attributed to the O H stretching vibration of the OH units. Multiple Raman bands for both SO₄²⁻ and Sb O stretching vibrations support the concept of the non‐equivalence of these units in the klebelsbergite structure. It is proposed that the two sulfate anions are distorted to different extents in the klebelsbergite structure. Copyright © 2010 John Wiley & Sons, Ltd.     

Pulse radiolysis studies of 2‐ and 3‐hydroxybenzyl alcohols: inhibition of dehydration of ·OH‐(hydroxybenzyl alcohols) adducts by H2PO4− ions

Reactions of ·OH/O ^.? radicals and H‐atoms as well as specific oxidants such as Cl₂^.? and N₃· radicals have been studied with 2‐ and 3‐hydroxybenzyl alcohols (2‐ and 3‐HBA) at various pH using pulse radiolysis technique. At pH 6.8, ·OH radicals were found to react quite fast with both the HBAs (k = 7.8 × 10⁹ dm³ mol^?1 s^?1 with 2‐HBA and 2 × 10⁹ dm³ mol^?1 s^?1 with 3‐HBA) mainly by adduct formation and to a minor extent by H‐abstraction from ? CH₂OH groups. ·OH‐(HBA) adduct were found to undergo decay to give phenoxyl type radicals in a pH dependent way and it was also very much dependent on buffer‐ion concentrations. It was seen that ·OH‐(2‐HBA) and ·OH‐(3‐HBA) adducts react with HPO₄^2? ions (k = 2.1 × 10⁷ and 2.8 × 10⁷ dm³ mol^?1 s^?1 at pH 6.8, respectively) giving the phenoxyl type radicals of HBAs. At the same time, this reaction is very much hindered in the presence of H₂PO ions indicating the role of phosphate ion concentration in determining the reaction pathway of ·OH adduct decay to final stable product. In the acidic region adducts were found to react with H⁺ ions. At pH 1, reaction of ·OH radicals with HBAs gave exclusively phenoxyl type radicals. Proportion of the reducing radicals formed by H‐abstraction pathway in ·OH/O ^.? reactions with HBAs was determined following electron transfer to methyl viologen. H‐atom abstraction is the major pathway in O ^.? reaction with HBAs compared to ·OH radical reaction. H‐atom reaction with 2‐ and 3‐HBA gave transient species which were found to transfer electron to methyl viologen quantitatively. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of the joaquinite minerals

Selected joaquinite minerals have been studied by Raman spectroscopy. The minerals are categorised into two groups depending upon whether bands occur in the 3250 to 3450 cm⁻¹ region and in the 3450 to 3600 cm⁻¹ region, or in the latter region only. The first set of bands is attributed to water stretching vibrations and the second set to OH stretching bands. In the literature, X‐ray diffraction could not identify the presence of OH units in the structure of joaquinite. Raman spectroscopy proves that the joaquinite mineral group contains OH units in their structure, and in some cases both water and OH units. A series of bands at 1123, 1062, 1031, 971, 912 and 892 cm⁻¹ are assigned to SiO stretching vibrations. Bands above 1000 cm⁻¹ are attributable to the ν_as modes of the (SiO₄)⁴⁻ and (Si₂O₇)⁶⁻ units. Bands that are observed at 738, around 700, 682 and around 668, 621 and 602 cm⁻¹ are attributed to O Si O bending modes. The patterns do not appear to match the published infrared spectral patterns of either (SiO₄)⁴⁻ or (Si₂O₇)⁶⁻ units. The reason is attributed to the actual formulation of the joaquinite mineral, in which significant amounts of Ti or Nb and Fe are found. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl mineral pseudojohannite Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O

Raman spectra of pseudojohannite were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (SO₄)²⁻ units and of water molecules. The published formula of pseudojohannite is Cu_6.5(UO₂)₈[O₈](OH)₅[(SO₄)₄]·25H₂O. Raman bands at 805 and 810 cm⁻¹ are assigned to (UO₂)²⁺ stretching modes. The Raman bands at 1017 and 1100 cm⁻¹ are assigned to the (SO₄)²⁻ symmetric and antisymmetric stretching vibrations. The three Raman bands at 423, 465 and 496 cm⁻¹ are assigned to the (SO₄)²⁻ν₂ bending modes. The bands at 210 and 279 cm⁻¹ are assigned to the doubly degenerate ν₂ bending vibration of the (UO₂)²⁺ units. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrical and Thermal Transport Properties of n-type Bi6Cu2Se4O6 (2BiCuSeO + 2Bi2O2Se)

New thermoelectric materials, n-type Bi₆Cu₂Se₄O₆ oxyselenides, composed of well-known BiCuSeO and Bi₂O₂Se oxyselenides, are synthesized with a simple solid-state reaction. Electrical transport properties, microstructures, and elastic properties are investigated with an emphasis on thermal transport properties. Similar to Bi₂O₂Se, it is found that the halogen-doped Bi₆Cu₂Se₄O₆ possesses n-type conducting transports, which can be improved via Br/Cl doping. Compared with BiCuSeO and Bi₂O₂Se, an extremely low thermal conductivity can be observed in Bi₆Cu₂Se₄O₆. To reveal the origin of low thermal conductivity, elastic properties, sound velocity, Grüneisen parameter, and Debye temperature are evaluated. Importantly, the calculated phonon mean free path of Bi₆Cu₂Se₄O₆ is comparable to the interlayer distance for BiO─CuSe and BiO─Se layers, which is ascribed to the strong interlayer phonon scattering. Contributing from the outstanding low thermal conductivity and improved electrical transport properties, the maximum ZT ≈0.15 at 823 K and ≈0.11 at 873K are realized in n-type Bi₆Cu₂Se_3.2Br_0.8O₆ and Bi₆Cu₂Se_3.6Cl_0.4O₆, respectively, indicating the promising thermoelectric performance in n-type Bi₆Cu₂Se₄O₆ oxyselenides.     

Observation of stimulated Raman scattering in polar tetragonal crystals of barium antimony tartrate trihydrate,Ba[Sb2((+)C4H2O6)2]·3H2O

The non‐centrosymmetric polar tetragonal (P 4₁) barium antimony tartrate trihydrate, Ba[Sb₂((+)C₄H₂O₆)₂]·3H₂O, was found to be an attractive novel semi‐organic crystal manifesting numerous χ ⁽²⁾‐ and χ ⁽³⁾‐nonlinear optical interactions. In particular, with picosecond single‐ and dual‐wavelength pumping SHG and THG via cascaded parametric four‐wave processes were observed. High‐order Stokes and anti‐Stokes lasing related to two SRS‐promoting vibration modes of the crystal, with ω_SRS1 ≈ 575 cm^?1 and ω_SRS2 ≈ 2940 cm^?1, takes place. Basing on a spontaneous Raman investigation an assignment of the two SRS‐active vibration modes is discussed.

     

Raman spectroscopic study of the uranyl sulphate mineral jáchymovite (UO2)8(SO4)(OH)14· 13H2O

Raman spectra of jáchymovite, (UO₂)₈(SO₄)(OH)₁₄·13H₂O, were studied, complemented with infrared spectra, and compared with published Raman and infrared spectra of uranopilite, [(UO₂)₆(SO₄)O₂(OH)₆(H₂O)₆]·6H₂O. Bands related to the stretching and bending vibrations of (UO₂)²⁺, (SO₄)²⁻, (OH)⁻ and water molecules were assigned. U O bond lengths in uranyl and O H· · ·O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Interface perpendicular magnetic anisotropy in Fe/MgAl2O4 layered structures

The recently reported MgAl₂O₄ tunnel barrier for the magnetic tunnel junctions (MTJs) is considered to be an alternative to the conventional MgO barrier, since a large tunnel magnetoresistance (TMR) ratio was obtained for the MgAl₂O₄‐based MTJs. In this study, we demonstrated large perpendicular magnetic anisotropy (PMA) arising from the interfaces of Fe(001)/MgAl₂O₄ layered structures, which can be useful for developing perpendicularly magnetized MgAl₂O₄‐based MTJs. A PMA energy density of 0.4 MJ/m³ was achieved for an epitaxially grown 0.7 nm thick Fe/MgAl₂O₄(001). Interestingly, the interface PMA was also obtained for the Fe/non‐epitaxially grown MgAl₂O₄ structures, which indicates that the crystallographic structure of MgAl₂O₄ layer has no critical influence on the obtained PMA.

     

Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L‐proline phosphonodipeptides

A comparative study of molecular structures of five L ‐proline (L ‐Pro) phosphonodipeptides: L ‐Pro‐NH‐C(Me,Me)‐PO₃H₂ (P1), L ‐Pro‐NH‐C(Me,iPr)‐PO₃H₂ (P2), L ‐Pro‐L ‐NH‐CH(iBu)‐PO₃H₂ (P3), L ‐Pro‐L ‐NH‐CH(PA)‐PO₃H₂ (P4) and L ‐Pro‐L ‐NH‐CH(BA)‐PO₃H₂ (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6–31 + + G** level using Gaussian 2003 software. The surface‐enhanced Raman scattering (SERS) on Ag‐sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so‐called spacer (−R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (∼1630, ∼1533, ∼1248, ∼800 and ∼565 cm⁻¹), Pro ring (∼956, ∼907 and ∼876 cm⁻¹) and carboxylate group (∼1395 and ∼909 cm⁻¹). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm⁻¹. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the  C CH₃,  NH and  CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm⁻¹) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194–1208 cm⁻¹). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the C_s P bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd.     

Paramagnetic resonance of the (Cr5+O4)H2 Halperin-Varma center in NH4H2AsO4 and KH2AsO4

The electron paramagnetic resonance (EPR) spectrum of Cr⁵⁺(3d ¹,S=1/2) in undeuterated and 58%-deuterated NH₄H₂AsO₄ was investigated. The EPRg-value tensors in the paraelectric and antiferroelectric phases are almost the same as those observed at high and low temperatures in KH₂PO₄ and KH₂AsO₄. This shows that the (Cr⁵⁺O₄)H₂ complex is the same in all crystals, i.e., a wave function ofd _x ²–y ² character coupled to two lateral protons which reorient among the four possible Slater configurations in the paraelectric phase. The remarkable isotope shift of the local dynamic reorientational slowing-down observed in KH₂PO₄ and KH₂AsO₄ in approximate proportion to the shift of the bulk ferroelectric transition temperaturesT _c ^F , and the antiferroelectricT _c ^AF of NH₄H₂AsO₄, is analyzed qualitatively. It is shown to result mainly from the isotope effect of the short-range interactionJ _sr via protons and deuterons for the impurity and for the bulk. Q-band data of the (Cr⁵⁺O₄)H₂ center in 75%-deuterated KH₂AsO₄ are also reported. An averaged high- and nonaveraged low-temperature EPR spectrum is observed in a temperature range of 250 to 290 K. The intensity ratio of the two follows an exp 2(T—T)/ law over four orders of magnitude atT=266 to 273 K and=5.3 to 6.1 K depending on the orientation of the external magnetic field. This novel result in motional narrowing is analyzed analytically to be compatible with a distributionP _A of ₀(T, T, ) of half width, in reorientation times withE=0.23 ±0.02 eV, , probably resulting from the statistical occupation of deuterium atoms among the O—–H–O bridges. Comparison with a theory of Binder definitely proves the extrinsic slowing-down and thus Halperin-Varma type character. In the range of temperatures investigated no local freeze-out has been detected.     

Raman and infrared spectra of doped La8+xSr2−y(SiO4)6O2+δ compounds compared to the ab initio‐obtained spectroscopic characteristics of fully stoichiometric La8Sr2(SiO4)6O2

Vibrational spectroscopy data were used to gain insight into the possible locations of extra oxygen ions introduced into La_8+xSr_2−y(SiO₄)₆O_2+δ compounds to raise their ionic conductivity. Perturbations observed in the Raman and infrared spectra of these compounds with increasing δ were explained by using the ab initio calculation results for the fully stoichiometric (x = y = δ = 0) lattice. This allowed the inference that the extra oxygen ions are incorporated into La O tunnel‐like fragments inherent in the studied structures. Copyright © 2010 John Wiley & Sons, Ltd.     

Flexible InGaZnO thin film transistors using stacked Y2O3/TiO2/Y2O3 gate dielectrics grown at room temperature

In this Letter, we report a low operation voltage and high mobility flexible InGaZnO thin‐film transistor (TFT) using room‐temperature processed Y₂O₃/TiO₂/Y₂O₃ gate dielectric. The flexible IGZO TFT showed a low threshold voltage of 0.75 V, a small sub‐threshold swing of 137 mV/decade, a good field effect mobility of 32.7 cm²/V s, and a large I_on/I_off ratio of 1.7 × 10⁶. The low operation voltage, small sub‐threshold swing and high mobility could be ascribed to the combination of high‐κ TiO₂ and large band gap Y₂O₃, which provide the potential to meet the requirements of low‐temperature and low‐power portable electronics.

     

A Raman spectroscopic study of bukovskýite Fe2(AsO4)(SO4)(OH)· 7H2O,a mineral phase with a significant role in arsenic migration

The Raman spectrum of bukovskýite [Fe³⁺₂(OH)(SO₄)(AsO₄)· 7H₂O] has been studied and compared with that of an amorphous gel containing specifically Fe, As and S, which is understood to be an intermediate product in the formation of bukovskýite. The observed bands are assigned to the stretching and bending vibrations of (SO₄)²⁻ and (AsO₄)³⁻ units, stretching and bending vibrations and vibrational modes of hydrogen‐bonded water molecules, stretching and bending vibrations of hydrogen‐bonded (OH)⁻ ions and Fe³⁺ (O,OH) units. The approximate range of O H···O hydrogen bond lengths was inferred from the Raman spectra. Raman spectra of crystalline bukovskýite and of the amorphous gel differ in that the bukovskýite spectrum is more complex, the observed bands are sharp and the degenerate bands of (SO₄)²⁻ and (AsO₄)³⁻ are split and more intense. Lower wavenumbers of δ H₂O bending vibrations in the spectrum of the amorphous gel may indicate the presence of weaker hydrogen bonds compared to those in bukovskýite. Copyright © 2011 John Wiley & Sons, Ltd.     

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C₃O₃NH₇]₂H₃PO₄H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH₂(OH)CH(NH₃)⁺COOH and the zwitterion CH₂(OH)CH(NH₃)⁺COO^?, which are linked with each other and with the H₂PO ^?₄ ion through a hydrogen-bond system involving water molecules.

     

Na‐site energy of P2‐type NaxM O2 (M = Mn and Co)

P2‐type Na_xM O₂ (M = Mn and Co) is a promising cathode material for low‐cost sodium ion secondary batteries. In this structure, there are two different crystallographic Nai (i = 1 and 2) sites with different Coulomb potential $ (\varphi _i)$ provided by M^4–x and O^2–. Here, we experimentally determine a difference ${(\rm \Delta }\varepsilon \equiv \varepsilon _1 - \varepsilon _2)$ of Na‐site energies ${(}\varepsilon _i \equiv e\varphi {\kern 1pt} _i)$ based on the temperature dependence of the site occupancies. We find that ${\rm \Delta }\varepsilon \;{=}\;56\;{K}$ for Na_0.52MnO₂ is significantly smaller than 190 K for Na_0.59CoO₂. We interpret the suppressed ${\rm \Delta }\varepsilon $ in Na_0.52MnO₂ in terms of the screening effect of the Na⁺ charge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman spectroscopic study of the phosphate mineral churchite‐(Y) YPO4·2H2O

Raman spectroscopy has been used to study the rare‐earth mineral churchite‐(Y) of formula (Y,REE)(PO₄) ·2H₂O, where rare‐earth element (REE) is a rare‐earth element. The mineral contains yttrium and, depending on the locality, a range of rare‐earth metals. The Raman spectra of two churchite‐(Y) mineral samples from Jáchymov and Medvědín in the Czech Republic were compared with the Raman spectra of churchite‐(Y) downloaded from the RRUFF data base. The Raman spectra of churchite‐(Y) are characterized by an intense sharp band at 975 cm⁻¹ assigned to the ν₁ (PO₄³⁻) symmetric stretching mode. A lower intensity band observed at around 1065 cm⁻¹ is attributed to the ν₃ (PO₄³⁻) antisymmetric stretching mode. The (PO₄³⁻) bending modes are observed at 497 cm⁻¹ (ν₂) and 563 cm⁻¹ (ν₄). Some small differences in the band positions between the four churchite‐(Y) samples from four different localities were found. These differences may be ascribed to the different compositions of the churchite‐(Y) minerals. Copyright © 2009 John Wiley & Sons, Ltd.