Electrical and optical properties of high-purity p-type single crystals of GeFe2O4

Single crystals of the spinel GeFe₂O₄, grown by the chemical vapor transport technique, are p-type semiconductors with an acceptor ionization energy of 0.39 eV. The material is a heavily compensated band-type semiconductor, with a typical hole concentration of 10¹⁴ cm^?3 near room temperature, and a temperature-independent Hall mobility of 2 cm²/V·sec. Optical absorption measurements show the optical band gap to be ?2.3 eV; the octahedral field splitting of the Fe²⁺d-levels is 10 200 cm^?1. Magnetic measurements show that n_eff is 5.26, from which a trigonal field splitting of 950 cm^?1 is derived.     

Oxygen evolution on SrFeO3 electrode

Oxygen evolution reactions on SrFeO₃ were investigated in alkaline and acidic solutions. It was found that the catalytic activity for the oxygen evolution reaction in the alkaline solution is high. The following reaction steps (V)+Fe+2H₂O→(O)+FeOH₂+2H⁺+2e^? in acidic solution and FeOH+OH^?→FeO^?+H₂O in alkaline solution are presumed to be rate-controlling in the anodic evolution of oxygen on SrFeO₃ electrode, where (V) denotes oxygen vacancy on the electrode surface. The reaction mechanism and the catalytic property are discussed in connection to the band structure of the oxide.     

Über Ordnungs-Unordnungsphänomene bei Sauerstoff perowskiten vom Typ A2+3B2+M5+2O9

Perovskites of the type A²⁺₃B²⁺M⁵⁺₂O₉, where A²⁺ = Ba, Sr; B²⁺ = Mn, Co, Ni, Zn; M⁵⁺ = Nb, Ta, show order-disorder phenomena. At lower temperatures a thermodynamically unstable disordered cubic perovskite is formed ($\text{1}\text{3}$ formula unit—$\text{AB}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{M}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$—in the cell), which transforms irreversibly into a 1: 2 ordered high-temperature form with 3L structure (sequence (c)₃). For A²⁺ = Ba this lattice is hexagonal (space group $\text{P}\text{3}\text{m1}$; one formula unit in the cell); with A²⁺ = Sr a triclinic distortion is observed. For Ba₃CoNb₂O₉ a second transformation into a cubic disordered perovskite takes place at 1500°C. This transition is reversible and of the order-disorder type. The vibrational and diffuse reflectance spectra are discussed.     

X-ray and mössbauer studies of tricyclohexyltin(IV) halides. The crystal structures of (cyclo-C6H11)3SnX (X = F,Br and I)

The structures of tricyclohexyltin fluoride (I), bromide (II) and iodide (III) have been determined by X-ray analysis. Compound I crystallizes in the space group P2₁/m with a = 10.422(6), b = 17.238(9), c = 5.769(3) Å, β = 104.6(1)° and Z = 2. Compounds II and III crystallize in the space group Pcmn with a = 10.427(6), b = 16.914(9), c = 11.366(6) Å, Z = 4; and a = 10.400(6), b = 16.900(10), c = 11.400(4) Å, Z = 4, respectively. All three structures consist of discrete tetrahedral (cyclo-C₆H₁₁)₃SnX units.The temperature dependence of the Mössbauer resonance areas has been examined in order to obtain information about the relationship between chemical structure and lattice dynamics.     

Photoelectronic properties of Cu3PS4 and Cu3PS3Se single crystals

Single crystals of Cu₃PS₄ and Cu₃PS₃Se grown by chemical vapor transport were shown to be diamagnetic p-type semiconductors. Electrical measurements showed room temperature resistivities ranging from 1 to 5 ohm-cm and carrier concentrations of 10¹⁷ cm^?3. Both materials were shown to be active as cathodes for the photoelectrolysis of water. Spectral response measurements show that substitution of selenium for sulfur lowers the optical band gap from 2.38(5) eV for Cu₃PS₄ to 2.06(4) eV for Cu₃PS₃Se.     

Allylbutyltin halides (CH2CHCH2)SnBu3−nCln (n = 0, 1, 2, 3). Preparation,carbon-13 NMR characterization and allylstannylation ability towards ketones and aldehydes

Mixed allylbutyltin halides (CH₂CHCH₂)SnBu_3-nCl_n (n = 0–3) have been prepared, and characterized by carbon-13 NMR spectroscopy. Their ability to bring about allylstannylation of ketones and aldehydes, to form organostannoxy compounds, Bu_3-nSnCl_nOC(R′)(R″)CH₂CHCH₂, has been shown to increase on increasing the value of n, that is on increasing the acceptor ability of the tin centre.     

Growth and characterization of n-WS2 and niobium-doped p-WS2 single crystals

Single crystals of n- and p-WS₂ were obtained by chemical vapor transport using chlorine and bromine as transporting agents. The best niobium-doped WS₂ crystals were obtained when the concentration of the charge (formulated (1 ? x)WS₂ · (x)NbS₂) was ? 37 mg charge/ml of tube, and x = 0.01 to 0.03. A thermodynamic analysis of the crystal growth process is consistent with the observed doping concentration and other properties of the crystals obtained by this process. The crystals grown are characterized by electrical transport and surface photovoltage measured capacitance techniques.     

Normal modes of the MoO2−4 ion in Tb1.8Eu0.2(MoO4)3 single crystal

Polarized Raman spectra (single crystal) at 300 K and infrared spectra (powder) at 300 and 77 K in the region 250–1000 cm^?1 of a binary molybdate of terbium and europium have been recorded. Based on C_2v symmetry, group theoretical analysis has been carried out and a vibrational assignment is proposed.     

Electrical properties of the CuCr2O4 spinel catalyst

Electrical resistivity of CuCr₂O₄ spinel obtained by a coprecipitation method was measured at various temperatures from 350 to 923K in air. Oxidation of its surface chromium ions at various temperatures was determined by an iodometric method. The temperature dependence of resistivity and the presence of higher-valent chromium ions at higher temperatures indicated CuCr₂O₄ to be an extrinsic semiconductor. Log ? vs $\text{1}\text{T}$ plots yielded straight lines in the whole temperature range with two breaks, one around 550K and the other around 730K. The first break was attributed to the saturation of the surface with higher-valent chromium, while the second break was attributed to tetragonal-to-cubic phase transition in CuCr₂O₄. Log ? vs $\text{1}\text{T}$ plots obtained while cooling exhibited hysteresis near the second break, confirming this break to be due to a first-order diffusionless transition.     

Solid state studies on substituted CuCr2O4 spinel

Changes in crystallographic, electrical, and thermal properties of CuCr₂O₄ spinel were investigated by replacing Cu with Mg, i.e., Cu_1?xMg_xCr₂O₄, and Cr with Al, i.e., CuCr_2?xAl_xO₄. The tetragonal distortion in CuCr₂O₄ disappeared with 60% replacement of Cu by Mg (x = 0.6) or 50% replacement of Cr by Al (x = 1.0). The temperature variation of electrical resistivity for all the tetragonal samples was similar to that of CuCr₂O₄. The first order, diffusionless phase transition was manifest in the hysteresis loops of log ? vs $\text{1}\text{T}$ plots. The resistivity and activation energy for conduction changed sharply near the phase transition composition. With the replacement of Cr by Al, the conduction in CuCr₂O₄ was found to change from p type to n type. The low thermal stability of the spinel was found to be due to a high concentration of tetrahedral Cu²⁺ ions (>80%) and compressed tetragonal distortion which strains the spinel lattice. This strain is removed by replacing either Cu with Mg or Cr with Al, whereby the spinel becomes stable.     

Disorder in the crystal structure of NaNi4(PO4)3

NaNi₄(PO₄)₃ crystallizes in the space group Amam, a = 9.892(1), B = 14.842(2), and c = 6.3576(2) Å. For Z = 4, the calculated density is 3.862 g/cm³ (V = 933.3ų). The presence of several weak reflections (of the class 2k0 and 6k0) which should be systematically absent in this space group has been attributed to a partial disorder of one of the phosphate tetrahedra. Two half-occupied P(2) sites related by a mirror normal to the a axis result in a column of phosphate tetrahedra pointing either up or down in this direction. Nickel atoms occupy five- and six-coordinated sites while sodium is six-coordinated.     

Platinumolefin bond strength in Pt(PPh3)2(CH2CH2) and Pt(PPh3)2 {C(CN)2C(CN)2}

The enthalpy of the reaction: Pt(PPh₃)₂ (CH₂CH₂)(cryst.) + C(CN)₂C(CN)₂ (g) → Pt(PPh₃)₂ {C(CN)₂C(CN)₂}(cryst.) + CH₂ CH₂ (g) has been determined as ΔH₂₉₈=?155.8±8.0 kJ·mol^?1, from solution calorimetry. The interpretation, that the platinumethylene bond is much weaker than the platinumtetracyanoethylene bond, is contrary to conclusions drawn recently from electron emission spectroscopic studies, but in agreement with available structural data.     

Preparation and electronic properties of MoS2 and WS2 single crystals grown in the presence of cobalt

Single crystals of MoS₂ and WS₂ were grown by chemical vapor transport in both the presence and absence of cobalt. Hall measurements indicate that cobalt cannot diffuse appreciably into the bulk of MoS₂ or WS₂ and, therefore, can be present only on the surface. Similar results were obtained for as-grown crystals annealed or sulfided in contact with Co₉S₈ or sulfided after being dipped in a 0.1M CoSO₄/methanol solution.     

Electrical transport properties of a nonstoichiometric rare earth sulfide,EuGd2S4

The electrical transport properties of nonstoichiometric EuGd₂S₄ prepared by heating under a high vacuum have been investigated. The samples heated were classified into two groups on the basis of their electrical transport behavior. One group comprised semiconducting materials heated at 1500 and 1600°C, for which the transport mechanism was found to be via electron hopping with activation energies ranging from 0.013 to 0.027 eV. Another group comprised metallic materials heated at 1700 and 1800°C. Their electrical transport was carried out through ordinary band conduction over the measured temperature range except at temperatures lower than 120°K, where hopping with a very small activation energy (～0.0035 eV) occurred predominantly.     

Infrared spectra of KNaSO4 and K3Na(SO4)2

The infrared spectra, transmittance and polarized reflectance, of KNaSO₄ and K₃Na(SO₄)₂ are reported. Group theoretical analysis was carried out and a vibrational assignment proposed on basis of C_3v and D_3d symmetries. Factor group and site effects are discussed.     

Electrical conductivity—differential thermal analysis measurements on some MnHgI4 complexes

The electrical conductivity (EC) and differential thermal analysis (DTA) curves of M_nHgI₄ complexes (M = Ag¹⁺, Cu¹⁺, Hg₂²⁺, Tl¹⁺ and Pb²⁺) and HgI₂ and AgI are reported. The EC—DTA curves were obtained for each of the following heating—cooling modes: (a) initial heating; (b) cooling; and (c) reheating. Each set of curves is discussed. The effect of sample history was also studied.     

X-ray crystal analysis of tricyclohexyltin trifluoroacetate and Mössbauer data for (cyclo-C6H11)3SnO2CR′ (R′ = CH3, CH2CL,CHCL2, CCl3 and CF3)

The halogenocarboxylates (cyclo-C₆H₁₁)₃SnO₂CR′, (R′ = CH₃, CH₂Cl, CHCl₂, CCl₃ and CF₃) have been prepared, and characterized by Mössbauer and IR spectroscopy. The crystal structure of (cyclo-C₆H₁₁)₃SnO₂CCF₃ has been determined by X-ray analysis. The crystals are orthorhombic, space group Pcmn, with unit cell parameters a 14.390 ± 0.004, b, 13.427 ± 0.004, c 11.516 ± 0.003 Å. The structure was resolved by Patterson methods and refined to an R value of 0.147. The coordination about the tin atom can be considered distorted trigonal-pyramidal or distorted tetrahedral. Mössbauer data are explained in terms of distortions of bond angles about the tin atom.     

Different oxidation pathways with various MnO2 types: Anomalous reaction with gibberellic acid

The oxidation of gibberellic acid (1) with neutral manganese dioxide prepared according to Mancera et al., involves the free carboxylic group and gives rise to three anomalous products which correspond to oxidative decarboxylation (3,4) or lactonization (5). Optimal conditions for a normal allylic oxidation of 1 have been found using alkaline MnO₂ prepared according to Attenburrow et al. in acetone which gives yields of keto acid (2) up to 56%.     

Synthese et etude des complexes [C5H4(CH2)3C5H4]Ti(C5H5)2 presentant un pont entre deux ligands cyclopentadienyles

The complex (di-η⁵-C₅H₄CH₂CH₂CH₂C₅H₄)Ti(η¹-C₅H₅)₂ (I) can be obtained unambiguously starting from the corresponding bridged titanocene dichloride. Attempts to synthesize the isomeric compounds (η⁵-C₅H₅)₂ Ti(di-η¹-C₅H₄-CH₂CH₂CH₂C₅H₄) (I′) by the action of a convenient bridged dianion on (C₅H₅)₂ TiCl₂ afford several compounds, one of them is the complex I. The possibility of interconversion of these complexes by a fluctional process is discussed.     

The crystal structure of Cu4(PO4)2O

Cu₄(PO₄)₂O crystallizes in the space group $\text{P}\text{1}$ with a = 7.5393(8) Å, b = 8.1021(9) Å, c = 6.2764(8) Å, α = 113.65(1)°, β = 98.42(1)° and γ = 74.19(1)°. The structure was refined by full-matrix least-squares techniques using automatic diffractometer data to R = 0.046 (R_w = 0.056). Four unique copper atoms are in six, five-, and four-coordinated polyhedra which are linked together to form a three-dimensional network. The structure is best described in terms of a cubic close-packed array of oxygen atoms with one-tenth of the possible anion sites vacant.