Sealed Ampoules Research Articles

Relaxation Processes in Erbium Monosulfide Thin Films

Thin crystalline ErS films have been grown by flash evaporation in vacuum using a pre-synthesized bulk material on quartz and sapphire substrate. The bulk material was synthesized by direct synthesis in sealed quartz ampoules at a temperature of 800 K. During the film growth process, the vacuum in the deposition chamber was maintained at 6 10  Pa, evaporator temperature was  2750 K and the substrate temperature  900 K. Film thickness was about 0.4-0.6 µm. All prepared films had a stoichiometric composition and a NaCl crystal lattice with a lattice parameter a = 5.48 Å. After deposition of films and cooling to room temperature the dependence of electrical resistivity on time was investigated by the four-probe method at atmospheric pressure. It is shown that the relaxation process on films deposited on a quartz substrate proceeds much more slowly than on films prepared on a sapphire substrate. A possible mechanism for such a difference is given.

Magnesium and barium in two substructures: BaTMg2 (T = Pd, Ag, Pt, Au) and the isotypic cadmium compound BaAuCd2 with MgCuAl2 type structure

Abstract The intermetallic barium compounds BaTMg2 (T = Pd, Ag, Pt, Au) and BaAuCd2 were synthesized by reactions of the elements in sealed tantalum ampoules in muffle furnaces. The five compounds crystallize with the orthorhombic MgCuAl2 type structure, space group Cmcm, with small differences in chemical bonding between the magnesium and cadmium series. All samples were characterized through their Guinier powder diffraction patterns. The structures of BaPdMg2 (a = 444.57(4), b = 1174.67(10), c = 827.58(7) pm, wR2 = 0.0460, 475 F 2 values, 16 variables), BaAuMg2 (a = 450.27(6), b = 1183.94(16), c = 838.76(11) pm, wR2 = 0.0355, 473 F 2 values, 16 variables) and BaAuCd2 (a = 463.31(5), b = 1112.79(12), c = 826.63(8) pm, wR2 = 0.0453, 469 F 2 values, 16 variables) were refined from single crystal X-ray diffraction data. The large barium atoms push the [TMg2] respectively [AuCd2] substructures apart. This allows fast moisture attack and leads to fast hydrolyzes of the samples when they get in contact with water. The influence of the difference in electronegativity between magnesium and cadmium is reflected for the pair of compounds BaAuMg2 and BaAuCd2. The magnesium compound shows the higher auridic character, while the cadmium compound shows a tendency towards a three-dimensional cadmium substructure.

Sc2In-based solid solutions in the Sc-Fe-In and Sc-Au-In systems

Abstract Phase analytical studies in the scandium-rich parts of the Sc-T-In systems (T = Fe, Au) revealed the formation of small areas of solid solutions Sc2−x Fe x In and Sc2Au x In1−x that are derived from the binary Ni2In-type phase Sc2In, space group P63/mmc. The samples were synthesized from the elements in sealed tantalum ampoules in an induction furnace. The structures of Sc1.88Fe0.12In (a = 498.37(6), c = 630.94(8) pm, wR2 = 0.0603, 124 F 2 values, nine variables), Sc2Au0.37In0.63 (a = 494.65(5), c = 632.42(6) pm, wR2 = 0.0639, 123 F 2 values, nine variables) and Sc2Au0.22In0.78 (a = 496.09(3), c = 628.29(4) pm, wR2 = 0.0331, 124 F 2 values, nine variables) were refined from single-crystal diffractometer data. Sc1.88Fe0.12In shows Sc/Fe mixing on Wyckoff position 2a, while gold is substituted for indium on site 2c. Analyses of the reciprocal space gave no hint for superstructure formation, and the three refinements show slightly enhanced U 33 displacement parameters for the 2d scandium sites which react on the mixed occupancies.

Magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr)

Abstract The magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr) were synthesized from the elements in sealed tantalum ampoules through heat treatment in an induction furnace. X-ray powder diffraction studies confirm the hexagonal Gd3Ru4Al12 type structure, space group P63/mmc. Three structures were refined from single crystal X-ray diffractometer data: a = 973.47(5), c = 1037.19(5) pm, wR2 = 0.0296, 660 F 2 values, 30 variables for Gd3Ag3.82(1)Mg12.18(1), a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F 2 values, 29 variables for Yb3Ag3.73(1)Mg12.27(1) and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F 2 values, 28 variables for Ca3Ag3.63(1)Mg12.37(1). Refinements of the occupancy parameters revealed substantial Ag/Mg mixing within the silver-magnesium substructure, a consequence of the Ag@Mg8 coordination. The alkaline earth and rare earth atoms build Kagome networks. Temperature dependent magnetic susceptibility measurements indicate diamagnetism/Pauli paramagnetism for the compounds with Ca, Sr, Y and YbII, while the others with the trivalent rare earth elements are Curie-Weiss paramagnets. Most compounds order antiferromagnetically at T N = 4.4(1) K (RE = Pr), 34.6(1) K (RE = Gd) and 23.5(1) K (RE = Tb) while Eu3Ag4Mg12 is a ferromagnet (T C = 19.1(1) K). 151Eu Mössbauer spectra confirm divalent europium (δ = −9.88(1) mm s−1). Full magnetic hyperfine field splitting (18.4(1) T) is observed at 6 K. Yb3Ag4Mg12 shows a single resonance in its 171Yb solid state NMR spectrum at 6991 ppm at 300 K indicating a strong, positive Knight shift.

Influence of the conservation mode of seawater for dissolved organic carbon analysis

Marine dissolved organic matter (DOM) is one of the largest exchangeable organic carbon reservoir on the planet. The main proxy to track the distribution of DOM in the aquatic environments remains dissolved organic carbon (DOC). Thereby the optimal protocol for long-term DOC preservation in seawater samples must be defined. In this context, we monitored bulk DOC concentrations and its size class distribution in filtered seawater samples during yearlong experiments. With different conservation mode, we tested two types of commonly used materials (borosilicate brown glass and high-density polyethylene, HDPE) and three conditioning protocols (untreated, acidified at pH 2 and frozen at −20 °C). Offshore samples collected along the entire water column of the Pacific Ocean and stored in HDPE bottles were also analysed after 2 years of storage at pH of 2 and compared to frozen samples. Results demonstrated that bulk DOC concentrations can be accurately determined in untreated samples for one month and for years in frozen samples as well as in acidified samples, when samples are stored in acid cleaned HDPE bottles or flame sealed glass ampoules. Storage in brown glass vials with Bakelite caps seems more uncertain. The study of the size class distribution of DOC reveals the possibility to study DOM for 1 month in filtered samples with no additional treatment and for years in frozen samples when stored in acid cleaned HDPE bottles. Significant changes in DOC size fractionation were observed when samples were acidified. The high molecular weight (HMW) compounds and the humic substances from the upper 1000 m were significantly degraded at pH 2, incorporating DOC in the low molecular weight (LMW) fractions. These experiments provide preservation guidelines for future studies that aim either to study bulk DOC or the chemical properties marine DOM. It is recommended to store seawater in HDPE vials at −20 °C for DOM study, or at pH 2 for bulk DOC measurements.

Lu26 T 17–x In x (T = Rh, Ir, Pt) – first indium intermetallics with Sm26Co11Ga6-type structure

Abstract Several Lu26 T 17−x In x (T = Rh, Ir, Pt) phases with varying x values were obtained by induction-melting reactions of the elements in sealed tantalum ampoules. All samples were characterized through their X-ray powder diffraction patterns. These compounds crystallize with the tetragonal Sm26Co11Ga6-type structure, space group P4/mbm and Z = 2. The structure of Lu26Pt7.55In9.45 has been refined from single-crystal X-ray diffractometer data: a = 1165.32(5), c = 1547.46(6) pm, wR2 = 0.0895, 2173 F 2 values and 70 variables. The Lu26 T 17−x In x phases are the first indium representatives of the Sm26Co11Ga6 type. They belong to the n = 4 members of Parthé’s A 5n+6 B 3n+5 series, which show different stacking sequences of square prisms and antiprisms. Lu26Pt7.55In9.45 as a lutetium-rich intermetallic compound exhibits a broader range of shorter Lu–Lu distances (341–375 pm). Temperature dependent magnetic susceptibility measurements show Pauli paramagnetism for Lu26Ir8.5In8.5 and Lu26Rh7In10 with room temperature values of the magnetic susceptibility of χ = 1.53 × 10−3 emu mol−1 for Lu26Rh7In10 and χ = 6.54 × 10−4 emu mol−1 for Lu26Ir8.5In8.5.

Intermetallic compounds RE 2Ga2Mg (RE = Tb–Tm, Lu) with Mo2B2Fe-type structure

Abstract The rare earth intermetallic compounds RE 2Ga2Mg with RE = Tb–Tm and Lu were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. These rare earth-rich phases crystallize with the tetragonal Mo2B2Fe-type structure, space group P4/mbm and Z = 2. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of Er2Ga2.092(1)Mg0.908(1), Tm2Ga2.037(1)Mg0.963(1) and Lu2Ga2.176(1)Mg0.824(1) have been refined from single crystal X-ray diffractometer data. The refinements revealed small homogeneity ranges (small degrees of Mg/Ga mixing on the 2a sites). The magnesium atoms show square planar coordination by Ga2 dumbbells (282 pm Mg–Ga and 257 pm Ga–Ga in the lutetium compound). Geometrically one can describe the RE 2Ga2Mg phases as 1:1 intergrowth structures of CsCl and AlB2-related slabs of compositions REMg and REGa2. From DFT based calculations, charge transfer from the rare earth and magnesium atoms towards gallium can be illustrated in electron localization function ELF slice planes showing strong localization around gallium in the basal plane as well as along the tetragonal c axis signaling Ga–Ga pair interactions. The site-projected density of states DOS and COOP data further quantify this observation. Temperature dependent magnetic susceptibility measurements show Pauli paramagnetism for Sc2Ga2Mg and Lu2Ga2Mg with low room temperature susceptibility values of 2.1(1) × 10−4 and 1.1(1) × 10−4 emu mol−1, respectively. Ho2Ga2Mg, Er2Ga2Mg and Tm2Ga2Mg are Curie-Weiss paramagnets with stable trivalent rare earth ground states. Antiferromagnetic ordering was detected below the Néel temperatures of T N = 18.6(1) (RE = Ho), 11.9(1) (RE = Er) and 6.4(1) K (RE = Tm). The three compounds show metamagnetic transitions in their 3 K magnetization isotherms. Tm2Ga2Mg exhibits a square loop behavior with small hysteresis.

Intermediate ytterbium valence in YbRhSn2

Abstract The stannide YbRhSn2 has been synthesized. An arc-melted Rh25Sn48 precursor sample was reacted with ytterbium in a sealed tantalum ampoule in an induction furnace. The structure of YbRhSn2 was refined from single-crystal X-ray diffractometer data: MgCuAl2 type, Cmcm, a = 433.10(3), b = 1076.63(8), c = 739.36(5) pm, wR2 = 0.0676, 444 F 2 values and 16 variables. The rhodium and tin atoms form a three-dimensional [RhSn2] δ− polyanionic network with short Rh–Sn (271–273 pm) and Sn–Sn (301–324 pm) distances. The tin substructure is an orthorhombically distorted lonsdaleite network. YbRhSn2 shows paramagnetic behavior with a reduced magnetic moment of 2.2(1) µB per ytterbium atom, classifying it as an intermediate-valent compound.

Stabilizing the Homopolycation (I4 )2+ with a Hexasulfate in (I4 )[S6 O19 ] and a Borosulfate in (I4 )[B(S2 O7 )2 ]2.

The reaction of elemental iodine and SO3 in a sealed glass ampoule yielded a turquoise-colored solution. At temperatures below 7 °C, deep red crystals of (I4 )[S6 O19 ] grow. With the addition of B2 O3 and pyridine-SO3 complex red crystals of (I4 )[B(S2 O7 )2 ]2 can be obtained after heating the mixture to 120 °C. The combination of an (I4 )2+ cation with oxoanions has previously not been observed. Both anions have a significant but different influence on the structural properties of the (I4 )2+ cation.

Lu37Ru16.4In4 – coloring and vacancy formation in a new structure type closely related to a 8 × 8 × 8 bcc superstructure

Abstract The lutetium-rich intermetallic compound Lu37Ru16.4In4 was synthesized by induction melting of the elements in a sealed tantalum ampoule and subsequent annealing. The Lu37Ru16.4In4 structure was refined from single crystal X-ray diffractometer data: new type, I a 3 ‾ d $Ia\overline{3}d$ , a = 2756.21(11) pm, wR2 = 0.0579, 3056 F 2 values and 92 variables. The superstructure formation of Lu37Ru16.4In4 is discussed on the basis of a group–subgroup scheme starting from the bcc structure as the aristotype.

Structural changes and valence-mixing transition in EuBaCo2O5

High-intensity high-resolution synchrotron powder diffraction (SXPD) and differential scanning calorimetry (DSC) are used to investigate the valence-mixing transition in EuBaCo2O4.999(3) sample of composition homogenized by annealing with zirconium-metal oxygen getter in a sealed ampoule. The crystal structures are refined between 100 and 400 ​K. Fine scans by SXPD as well as DSC reveal two continuous transitions with no hysteresis: At 233 ​K, disappearance of the long-range charge-ordered Co2+/Co3+ superstructure from SXPD patterns, at 360 ​K, transition into paramagnetic state. The smooth evolution of lattice parameters as well as the DSC results suggest no spin-state change.

Crystal structure and magnetic properties of some compounds with GdNi2Ga3In type structure

Abstract The GdNi2Ga3In type crystal structures (Pnma) of the quaternary intermetallic compounds TbNi2Ga3.03(1)In0.97(1) (a = 2.41554(2), b = 0.41614(4), c = 0.92220(10) nm, wR2 = 0.0512, 2006 F 2 values, 90 parameters) and HoNi2Ga3.03(2)In0.97(2) (a = 2.41822(7), b = 0.41400(15), c = 0.9199(3) nm, wR2 = 0.0588, 1980 F 2 values, 89 parameters) were refined from the single crystal X-ray diffraction data. Single crystals were obtained by high-frequency annealing of the samples in sealed tantalum ampoules. The compounds with RE = Y, Dy and Ho are isotypic and were characterized by powder X-ray diffraction. The magnetic behaviour of the compounds RENi2Ga3In (RE = Y, Dy, Ho) was characterized by means of magnetization and dc magnetic susceptibility measurements, carried out in the temperature range 1.72–400 K in external magnetic fields up to 5 T. YNi2Ga3In was found to be a Pauli paramagnet with a molar magnetic susceptibility of about 4⋅10−5 emu mol−1 at room temperature. DyNi2Ga3In and HoNi2Ga3In are Curie-Weiss paramagnets which order antiferromagnetically below T N = 10.5 K (DyNi2Ga3In) and 4.4 K (HoNi2Ga3In).

Ordered CaCu5-type phases REPd2Zn3 (RE = Y, La–Nd, Sm, Gd–Dy)

Abstract The ternary intermetallic phases REPd2Zn3 (RE = Y, La–Nd, Sm, Gd–Dy) were synthesized from the elements by induction melting in sealed niobium ampoules followed by annealing. The CaCu5-type samples (space group P6/mmm) were characterized through Guinier powder patterns. The structures of YPd2Zn3 (a = 523.91(4), c = 430.88(3) pm, wR2 = 0.0570, 96 F 2 values, 9 variables) and NdPd2Zn3 (a = 535.08(7), c = 427.81(6) pm, wR2 = 0.0217, 123 F 2 values, 9 variables) were refined from single-crystal X-ray diffractometer data. The zinc atoms form Kagome layers in AA stacking which leave trigonal prismatic voids for the palladium and hexagonal prismatic voids for the rare earth atoms. The Zn–Zn distances within the Kagome network of YPd2Zn3 are 262 pm and the Pd–Zn distances in the Pd@Zn6 trigonal prisms are 263 pm.

Synthesis and study of the properties of synthetic analogues of the mineral naffildite with the participation of rare earth elements

In recent years, there has been a significant increase in interest in ternary and quaternary compounds with the participation of rare earth elements (REE), as well as copper, antimony, and bismuth, which have a wider range of physical properties. Due to their valuable physical properties, they have become promising targets of research for modern materials science. Therefore, the purpose of this work is to study the properties of synthetic analogues of naffildite with the participation of rare earth elements. The samples were synthesised from ternary sulphides (in the case of obtaining Cu2LaSb3S7, Cu2CeSb3S7, Cu2PrSb3S7 and Cu2NdSb3S7) by fusion in sealed quartz ampoules, preliminarily evacuated to a residual pressure of 10-3 mmHg at 950–1100 K for 8 hours. The remaining antimony and bismuth-containing analogues, due to the peritectic nature of formation, were synthesised through batches (2Cu + Ln + 3Sb(Bi) + 7S) from especially pure elements. After completion of the reaction, homogenizing annealing was carried out for a month at 600–700 K, depending on the composition. The obtained samples were investigated by differential thermal (DTA), X-ray phase (XRD) and microstructural (MSA) analyzes, as well as bymeasuring the microhardness and determining the density. Compounds of the Cu2LnSb3S7 or Cu2LnBi3S7 (Ln – REE) type have been synthesised by direct synthesis from elements or from the ligature CuSbS2(CuBiS2) and LnSbS3(LnBiS3). It was found that they are sostructural and crystallize in the orthorhombic system (Cu2LnSb3S7 – a = 14.490÷14.264, b = 21.422÷21.206, c = 3.902–3.804 Å; Cu2LnBi3S7 – a = 14.722÷14.506, b = 21.864÷21.564, c = 4.142÷3.464 Å; Z = 4, simple group Pbnm or Pbn21) and belong to the structure type of naffildite Pb2Cu (Pb, Bi) Bi2S7. Cu2LaSb3S7, Cu2PrSb3S7 and Cu2NdSb3S7 melt congruently at 975, 985, and 1015 K, respectively, and other compounds are formed by a peritectic reaction.

RE 3Rh2Sn4 (RE = Y, Gd–Tm, Lu) – first stannides with Lu3Co2In4 type structure

Abstract The stannides RE 3Rh2Sn4 (RE = Y, Gd–Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing (1220 K for RE = Y, Gd–Tm and 1170 K for RE = Lu) in sealed silica ampoules for 11 days. X-ray powder diffraction studies confirm the hexagonal Lu3Co2In4 type structure, space group P 6 ‾ $P\overline{6}$ . The structure of Gd3Rh2Sn4 was refined from single crystal X-ray diffractometer data for a twinned crystal: a = 744.04(6), c = 409.23(4) pm, wR2 = 0.0288, 567 F 2 values and 21 variables. The RE 3Rh2Sn4 stannides derive from the well-known equiatomic stannides RERhSn (≍RE 3Rh3Sn3) by Rh/Sn ordering within the RE 6 trigonal prisms. The striking structural motif is the trigonal planar tin coordination of the Sn2 atoms with 288 pm Sn2–Sn1 distances. The Sn2 atoms carry substantially more negative charge than the Sn1 atoms. This is underlined by 119Sn isomer shifts of δ = 1.86(1) mm s−1 for Sn1 and δ = 2.26(1) mm s−1 for Sn2 detected in the Mössbauer spectrum of Lu3Rh2Sn4. From atoms in molecules (AIM) analysis of the charge density obtained with calculation based on density functional theory (DFT) for Y3Rh2Sn4, the charge transfer proceeds from yttrium towards more electronegative rhodium. Little departure from neutrality is observed for tin whose itinerant s-like states are little involved with the bonding. The site projected density of states (DOS) and the crystal orbital overlap population (COOP) plots further illustrate these observations and reveal major Y–Rh and Rh–Sn bonding, while Y–Sn bonding is weaker.

Bcc superstructures: RE2RuIn with RE = Sc, Y, Dy-Tm and Lu.

The rare earth-rich intermetallic phases RE2RuIn with RE = Sc, Y, Dy-Tm and Lu were synthesized by reactions of the elements in sealed tantalum ampoules in an induction furnace. The samples were characterized through Guinier powder patterns and the structures of Sc2RuIn and Er2RuIn were refined from single crystal X-ray diffraction data. The indides crystallize with the Pt2ZnCd type space group P4/mmm. The RE2RuIn phases are superstructures of the bcc packing and can be explained as intergrowth variants of tetragonally distorted, CsCl derived slabs of compositions RERu and REIn. Chemical bonding is discussed for Sc2RuIn and Sc2RuMg in comparison with the binaries ScRu, ScMg and ScIn. The Ru/Mg respectively Ru/In ordering leads to an increase of Sc-Sc bonding for the slab with the shorter Sc-Sc distances, while the Sc-Ru bond strength values remain similar. The strongest bonding interactions occur within the magnesium and indium square nets. Magnetic susceptibility measurements reveal Pauli paramagnetism for Lu2RuIn while Dy2RuIn, Ho2RuIn, Er2RuIn and Tm2RuIn are Curie-Weiss paramagnets. Antiferromagnetic ordering occurs at 13.1, 5.3 and 2.9 K for Dy2RuIn, Er2RuIn and Tm2RuIn, respectively. Dy2RuIn and Er2RuIn show metamagnetic transitions at critical fields of 4.6 and 3.2 T.

Photoluminescence of Ag8SnSe6 argyrodite

A basic study of the low-temperature photoluminescence of an Ag8SnSe6 argyrodite compound is reported. Measurements were performed on wafers grown by the direct melting of a high-purity stoichiometric mixture of elementary Ag, Sn, and Se in a sealed silica ampoule. Two peaks with maxima located at 0.85 and 0.95 eV were visible in the photoluminescence spectra of an Ag8SnSe6 argyrodite. The temperature and excitation dependences of the dominant peak at 0.85 eV suggest that this transition can be associated with donor-acceptor recombination. The activation energies of the defects involved in this transition were calculated based on temperature-dependent photoluminescence and transmission measurements. We found the ionization energies to be at 44 and 72 meV for the shallower and deeper defects, respectively. The second peak in the spectra at 0.95 eV was assigned to a band-to-band transition or a transition between band tails.

Growth and scintillation properties of Eu doped Li2SrCl4/LiSr2Cl5 eutectic

In this study, a Eu-doped Li2SrCl4/LiSr2Cl5 eutectic with a high 6Li concentration was developed as a novel thermal neutron scintillator. The doped Eu served as an activator in the Li2SrCl4 and LiSr2Cl5 phases. The Eu-doped Li2SrCl4/LiSr2Cl5 eutectic was grown using the vertical Bridgman method in a sealed quartz ampoule. The eutectic exhibited a lamellar eutectic structure elongated along the pulling direction, and was optically transparent. The emissions at 401 and 412 nm were attributed to the Eu2+ 4f-5d transition in the Li2SrCl4 and LiSr2Cl5 phases, respectively. The light yield under 5.5 MeV α -rays was estimated to be 5,600 photons/5.5 MeV α -rays. The scintillation decay time was 312 ns. In the eutectic, the Li2SrCl4 and LiSr2Cl5 phases contributed to scintillation and neutron capture by the 6Li (n, a) 3H reaction.

Sodium-Vanadium Bronze Na9V14O35: An Electrode Material for Na-Ion Batteries.

Na9V14O35 (η-NaxV2O5) has been synthesized via solid-state reaction in an evacuated sealed silica ampoule and tested as electroactive material for Na-ion batteries. According to powder X-ray diffraction, electron diffraction and atomic resolution scanning transmission electron microscopy, Na9V14O35 adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO5 tetragonal pyramids and VO4 tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate Na9V104.1+O19(V5+O4)4. Behavior of Na9V14O35 as a positive and negative electrode in Na half-cells was investigated by galvanostatic cycling against metallic Na, synchrotron powder X-ray diffraction and electron energy loss spectroscopy. Being charged to 4.6 V vs. Na+/Na, almost 3 Na can be extracted per Na9V14O35 formula, resulting in electrochemical capacity of ~60 mAh g−1. Upon discharge below 1 V, Na9V14O35 uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO4 tetrahedra and VO5 tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered Na9V14O35 structure transforms into a rock-salt type disordered structure and ultimately into amorphous products of a conversion reaction at 0.1 V. The discharge capacity of 490 mAh g−1 delivered at first cycle due to the conversion reaction fades with the number of charge-discharge cycles.

Characterization and photocatalytic activity of titanium dioxide powder treated with PH3 gas

NH3 treatment for nitrogen doping to metal oxides is widely used as a method of band gap narrowing. However, PH3 treatment of titanium dioxide(TiO2) powders has not yet been established. In the present study, PH3 treatment of TiO2 was attempted by heating TiO2 powders and solid-state sodium hypophosphite in a sealed ampoule. The color of the powders changed from colorless for untreated TiO2 to beige for TiO2 treated at 250, 290, 350 °C, or to gray for TiO2 treated at 450 °C. X-ray photoelectron spectroscopy (XPS) analysis of the treated TiO2 revealed that the phosphorus was in a phosphate form and that a part of Ti4+ in TiO2 was reduced to Ti3+. The absorption spectra and the XPS data suggested the generation of oxygen vacancies. Adsorption experiments of methylene blue and Eosin Y onto the treated TiO2 indicated the presence of phosphate on the surface of TiO2. X-ray diffraction (XRD) analysis indicated that the crystallite sizes of the treated TiO2 increased with increasing in temperature. Photodegradation rates of the pigments by the treated TiO2 under UV light depended on phosphate, oxygen vacancy and crystallinity. PH3 treatment of crystalline TiO2 were found to give priority to phosphate formation in contrast to NH3 treatment for nitrogen doping.