Thermal property of binary tetrahedral semiconductors

In this paper we present an expression relating the lattice thermal expansion coefficient α_L (10⁻⁶ K⁻¹) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂), melting temperature (T_m) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (T_m), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for A^IIIB^V and A^IIB^VI semiconductors.     

Mössbauer study of fluorides: Ba2MFeF9 and NaBaFe2F9

The Mössbauer spectra of the compounds Ba₂NiFeF₉, Ba₂FeCrF₉ and NaBaFe₂F₉ have been studied as a function of temperature. Values of the Néel temperature are obtained and the effects of cationic inversion between the two sites of M^II and M^III in compounds Ni^IIFe^III and Fe^IICr^III are observed. In the latter compound, we observe broad lines at all temperatures and a smearing of the magnetic ordering temperature. However, the Fe^IIFe^III compound shows strict structural order. The two sites of Fe^III in NaBaFe₂F₉ have not been resolved.     

Analysis of low power spatial light modulation characteristics of bacteriorhodopsin

We present a detailed and accurate analysis of low power spatial light modulation characteristics of bacteriorhodopsin (bR) based on nonlinear intensity induced absorption. Amplitude modulation of probe laser read beam transmissions at 410 nm and 640 nm, corresponding to the peak absorption of M^II and O states of D96N bR and WT bR respectively, by the modulation laser write beam intensity-induced population changes at 570 nm has been analyzed, considering all intermediate states with both forward and backward transitions in the respective bR photocycles, using the rate equation approach. The SLM characteristics are shown to be sensitive to the normalized small signal absorption coefficient β, rate constants of M^II and O intermediate states and the absorption cross-section of the initial B state at the probe wavelength (σ_Bp). There exists an optimum value of β for which maximum percentage modulation can be achieved. It is shown that for extended M^II state lifetime of 250 s in D96N bR and O state lifetime of 2.2 s in WT bR, with σ_Bp= 0, 100% modulation of read beam transmissions can be achieved, leading to high dynamic range and sensitivity for low laser write beam intensities of 50 μW/cm² and 4 mW/cm² at 570 nm, respectively.     

Magnetic and Mössbauer spectra observed for mixed-metal magnets NBu4 {\bf Fe}^{\bf II}_{\bf n}MA II 1 − n [FeIII(OX)3] (MA=Mn, Fe)

Mixed-metal molecular-based magnets NBu₄ ${\rm Fe}^{\rm II}_{\rm n}$ M_A ^II _1???n[Fe^III(OX)₃] (M_A=Mn, Fe) were investigated by magnetic and Mössbauer measurements. The magnetic susceptibility of NBu₄ ${\rm Fe}^{\rm II}_{0.07}{\rm Mn}^{\rm II}_{0.93}$ [Fe^III(OX)₃] can be fitted to a Curie-Weiss law with a Weiss paramagnetic Curie temperature of θ?=??114.76 K. The negative Weiss constant indicates an intramolecular antiferromagnetic coupling interaction between the adjacent Fe(II) and Fe(III) ions through the oxalate bridge. In the complex NBu₄Fe^II[Fe^III(OX)₃], the Mössbauer results indicate that the Fe^II and Fe^III sublattices experience spontaneous magnetizations. The compound contains two different spin carriers; i.e. Fe^II(S = 2), Fe^III(S = 5/2). Two magnetic sublattices are defined. The appearance of nuclear Zeeman splittings suggests that long range magnetic ordering takes place below 50 K.     

Relative internal conversion electron intensities of the 113 keV transition in177Hf

The intensities of the internal conversion lines of the 113 keVM1 +E2 transition in¹⁷⁷Hf have been measured. From comparison with theoretical conversion coefficients the transition has been found to be (95.2 ± 0.5)%E2 corresponding to ¦δ¦=4.5 ± 0.3. The theoreticalL _I andM _I conversion coefficients used in the comparison have been increased by 5% according to the result that for pureE2 transitions in the deformed region theL _I/L _II,L _I/L _III,M _I/M _II, andM _I/M _III theoretical ratios are too low (～5%). Moreover, the present result indicates that theL _II/L _III andM _II/M _III ratios obtained from the tabulations by Hager and Seltzer and from the computer program by Pauli are too high (1–2%).     

Mössbauer studies of mixed-valence spin-crossover iron complexes with a hexadentate tripod ligand

The spin-crossover behaviors of mixed-valence iron compounds [Fe^IIH₃L][Fe^IIIL](NO₃)₂ (1) and [Fe^IIH₃L^Me][Fe^IIIL^Me](NO₃)₂ (2) have been investigated by ⁵⁷Fe Mössbauer spectroscopy, where H₃L is a hexadentate N₆ tripod ligand containing three imidazole groups and H₃L^Me is its 2-methylimidazole derivative. Deconvolution analyses of the Mössbauer spectra revealed that a two-step SCO (LS Fe^II–LS Fe^III→HS Fe^II–LS Fe^III→HS Fe^II–HS Fe^III) proceeds in each compound on elevating the temperature. Compound 2 exhibited lower spin-transition temperatures than 1. “Frozen-in effect” was observed below 120 and 50 K for 1 and 2, respectively.     

Synthesis and Spectroscopic Properties of Iron(H) Complex with Sterically Encumbered Thiolate Ligand: 2,4,6-Triphenylbenzenethiolate

Abstract

Novel iron(II) complex of 2,4,6-triphenylbenzenethiolate (tpbt) was synthesized by ligand exchange reaction of (Et₄N)2[Fe^II(S-t-Bu)₄] with tpbt-H. The complex shows absorption maxima at 277 nm (36500 M^?1cm^?1) and 367 nm (22800 M^?1 cm^?1), and Fe²⁺/Fe³⁺ redox potential at-0.78 V vs SCE in acetonitrile. While in tetrahydrofuran solution, the complex is found to be unstable and form a Fe(II) complex with low coordination number.     

Crystal structure and ferromagnetism of (n-C3H7)4N[CoFe(dto)3] (dto=C2O2S2)

Recently, we have discovered a new type of first order phase transition around 120 K for (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] (dto=C₂O₂S₂), where the charge transfer transition between Fe^II and Fe^III occurs reversibly. In order to elucidate the origin of this peculiar first order phase transition. Detailed information about the crystal structure is indispensable. We have synthesized the single crystal of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃] whose crystal structure is isomorphous to that of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃], and determined its detailed crystal structure. Crystal data: space group P6₃, a=b=10.044(2) Å, c=15.960(6) Å, α=β=90°, γ=120°, Z=2 (C₁₈H₂₈NS₆O₆FeCo). In this complex, we found a ferromagnetic transition at T_c=3.5 K. Moreover, on the basis of the crystal data of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃], we determined the crystal structure of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] by simulation of powder X-ray diffraction results.     

Mössbauer and infrared spectroscopic studies of novel mixed valence states in cobaltous ferrocyanides and ferricyanides

Novel mixed valence states have been obtained by the treatment of cobaltous ferrocyanides (Co⁺²Fe^II) and ferricyanides (Co⁺²Fe^III) in an ozone flow. The CN stretching bands occur at 2085 cm^–1 for Co⁺²Fe^II and at 2160 cm^–1 for Co⁺²Fe^III. After the ozonization process of Co⁺²Fe^II, an intense band approximately at 2125 cm^–1 is detected. This intermediate band must correspond to a mixed valence state of the type: Fe^II–CN–Co²⁺–NC–Fe^III Mössbauer spectra recorded in situ during the ozonization of Co⁺²Fe^II show the presence of two components: a doublet with isomer shift and quadrupole splitting values close to the cobalti ferricyanide and a very broad line for the mixed valence state. From the Mössbauer and infrared spectra of the aged samples of the Co⁺²Fe^II after ozonization, a relaxation process to the initial state of the samples is observed but the mixed valence state is stable.     

Synthesis by Coprecipitation of Al-Substituted Hydroxysulphate Green Rust FeII 4FeIII (2−y)AlIII y (OH)12SO4,nH2O

Al-substituted hydroxysulphate green rust (Al-GR{SO₄}) were synthesised by the coprecipitation of Fe^II, Fe^III and Al^III cations. The Al-GR{SO₄} crystals (～50 nm) are significantly smaller than the hydroxysulphate green rust GR{SO₄} crystals (～500 nm). The Mössbauer spectrum of Al-GR{SO₄} was adjusted with two ferrous doublets D₁ and D₃ and one ferric doublet D₂. Doublet D₃ is attributed to Fe^II ions that have Al^III ions as a first neighbour.

     

Simultaneous Registration of Contraction and Cytosolic Calcium ([Ca2+]i) of Smooth Muscle Strips Using Front-Surface Fluorimetry

Using front-surface fluorimetry with fura-2-loaded smooth muscle strips, simultaneous registration of the cytosolic calcium concentration ([Ca²⁺]_i) changes and tension development was done under the action of 40 mM KCl and the myotropic peptide 10^–6 M angiotensin II. The strips were mounted vertically, connected to a force transducer that keeps a basal isometric tension of 0.5 g, and maintained in a bathing solution oxygenated at 37°C. The fiber-optic platform FluoroMax-2 accessory 1950F was used to do the remote sensing for the samples. Light from the excitation spectrometer (FluoroMax-2), alternating between 340 and 380 nm, was focused onto the fiber-optic bundle and directed to the smooth muscle strip. The fluorescence (505 nm) was collected and redirected to the emission port of the fluorimeter FluoroMax-2. The ratiometric method (R340/380) was used as an index of [Ca²⁺]_i change during smooth muscle contraction. All data, R340/380 and tension, were recorded using a computerized data acquisition system: Soft & Solution and GRAMS/386 of Galatic Industries Corporation.     

Magnetic properties of substitutional solid solutions of nickel and iron hexacyanoferrate–hexacyanochromate

In order to evaluate the influence of substitution at the central metal ion position in transition hexacyanometallates in some detail, the magnetic studies were carried out on a series of solid solutions of metal hexacyanometallates of the composition M[Fe^II(CN)₆]_{1? x} [Cr^III(CN)₆] _x , where M?=?Ni^II and Fe^III. The temperature and field dependences of magnetization were studied using a superconducting quantum interference device magnetometer. The field dependence of the samples at 5?K shows a hysteresis behaviour. For M?=?Ni^II, the transition temperature increases with increase in the substitution of low-spin Fe(III) by Cr(III) in the hexacyanometallate unit. The saturation magnetization was found to decrease with increase in the iron concentration. The observed variation in the magnetic properties, such as the value of T _C and the nature of magnetic ordering, is attributed to the variation in the composition of the transition-metal ion in the coordination sphere of carbon. On the other hand, for M?=?Fe^III, the transition temperature and saturation magnetization remained almost unchanged, indicating that substitution at the carbon coordination site did not produce any change in the magnetic interaction among the transition-metal ions through the cyanide ions.     

Luminescent crystals of MIIGa2S4:Er3+ (MII = Eu, Yb, Ca)

We have studied the photoluminescent properties of M^IIGa₂S₄:Er³⁺ polycrystals (M^II = Eu, Yb, Ca) for excitation by radiation with λ = 976 nm as a function of temperature. The samples were obtained by solid-state reaction. We have studied the comparative characteristics of the anti-Stokes and IR luminescence of these luminophores. We have determined the mechanisms for anti-Stokes emission of M^IIGa₂S₄:Er³⁺ crystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 332–335, May–June, 2007.     

Mn3<Emphasis Type="Italic">s</Emphasis> X-ray photoelectron spectra of polynuclear trimethylacetate complexes of manganese

The Mn3s X-ray photoelectron spectra of manganese at oms in mono-, bi-, tri-, and hexanuclear trimethylacetate Mn complexes and Mn^IICl₂, Mn^IIIOOH, Mn^IVO₂. ionic compounds were measured. The 3s spectra of the manganese atoms in Mn^II, Mn^III, and Mn^IV valent states were calculated within the isolatedion approximation. The relationship between the characteristics of the Mn3s spectra and the magnetic moments of the manganese ions in the complexes is discussed.     

Structural, magnetic and redox properties of a new cathode material for Li-ion batteries: the iron-based metal organic framework

The iron-based metal organic framework (MOF) presently studied is the first example of MOF showing a reversible electrochemical Li insertion with a very good cycling life. Its potential application as a cathode material in Li-ion battery is nevertheless curbed by a rather poor capacity of 70 mAh/g. To figure out the origin of this limited insertion, first-principles density functional theory (DFT)+U calculations were performed. The results show that Fe^III{OH(BDC)} is a weak anti-ferromagnetic charge transfer insulator at T = 0 K with iron in the high-spin S = 5/2 state. In agreement with the absence of electronic de-localisation along the inorganic chains, lithium insertion leads to the stabilisation of a Fe^II/Fe^III mixed-valence state of class I or II in the Robin–Day classification, whatever the Li sites considered in the calculations. Among these Li sites, the most probable site I (OH-Li) and site II (O=CO-Li) are shown to induce incompatible structural changes on the reduced Li_0.5Fe{OH(BDC)} form that could be at the origin of the small capacity measured for this compound. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Low-temperature magnetic properties of the 2D molecular ferrimagnet N(n-C5H11)4 [FeIIFeIII(C2O4)3]

⁵⁷Fe Mössbauer and magnetometric studies of the molecular ferrimagnet N(n-C₅H₁₁)₄ [ Fe^IIFe^III(C₂O₄)₃] are indicative of a 2D magnetic character with strong uniaxial anisotropy in the basal plane of the crystal. It is established that the change in the sign of the net magnetization of this compound is related to a compensation between Fe^III and Fe^II sublattice magnetizations at T _comp=31.2 K. The form and parameters of the magnetic Hamiltonian describing the temperature dependence of the Fe^III sublattice and the net magnetizations are determined.     

A neutron-diffraction study on the structural relationships of RCo5 hydrides

The hexagonal RCo₅ compounds form several orthorhombic hydrides which are structurally closely related. A neutron-diffraction study of β^I, β^II and β^III types, as found for e.g. PrCo₅D_3·6, PrCo₅D_2·9 and CeCo₅D_2·55 respectively, revealed that the deuterium atoms occupy both octahedral and tetrahedral interstices. In the simplest of these, β^I, the occupancy of the interstices is equal; its space group is Cmmm. In both β^II and β^III the c-axis is doubled compared with β_I. In β^II, space group Im2m, the octahedral positions have a uniformly reduced occupancy, which leads to appreciable ordered shifts of the metal atoms. In β^III (Cccm) half of the octahedral positions are vacant, giving a limiting stoichiometric composition CeCo₅H₃.The magnetizations of the (ferromagnetic) hydrides decrease with increasing hydrogen content. Results of neutron-diffraction analysis are in fair agreement with the magnetization measurements.     

Ferromagnetic order and spin-glass behavior in multi-metallic compound Ni1.125Co0.375[Fe(CN)6] · 6.8H2O

Multi-metallic Prussian blue compound Ni_1.125Co_0.375[Fe(CN)₆] · 6.8H₂O has been synthesized. The Mössbauer spectroscopy at room temperature and IR spectra study revealed that the metal ions are bonded through cyanide ligand and the presence of low spin Fe^III(S = 1/2) and high spin Fe^III(S = 5/2) ions, as showed in these structure: Fe^III(S = 1/2)-CN-(Co^II/Ni^II)(96%) and Fe^III(S = 5/2)-NC-(Co^II/Ni^II) (4%). The Curie constant of C = 3.00 cm³ K mol⁻¹ and Weiss paramagnetic Curie temperature of θ = 16.43 K were observed in fitting according to Curie–Weiss law. These results indicate that there existed a ferromagnetic exchange interaction in the complexes. The observed value of coercive field (H_c) and remanent magnetization (M_r) at 4 K for the compound are 497 Oe and 1.03 Nβ. The presence of spin-glass behaviours in the compound is ascribed mainly to domain mobility or domain growth under different cooling conditions.     

Study on the ferromagnetic state in iron mixed-valence complexes, A[FeIIFeIII(dto)3] (A = (n-CnH2n + 1)4N; dto = C2S2O2) by means of Mössbauer spectroscopy

We have investigated the ferromagnetic states for (n-C_nH_2n?+?1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂) by means of ⁵⁷Fe Mössbauer spectroscopy. The major component of the spin configuration in the ferromagnetic states for n = 3 and 4 is the low-temperature phase (LTP) with the Fe^III (S = 5/2) and Fe^II (S = 0) states. The high-temperature phase (HTP) of n = 4 remains by more than 20%, which is consistent with two ferromagnetic transitions (T_C = 7 & 13 K). Moreover, it was revealed that the Mössbauer spectra in the ferromagnetic states for n = 5 and 6 correspond to the HTP consisting of the Fe^II (S = 2) and Fe^III (S = 1/2) states.