Mössbauer spectroscopic study of photo-sensitive organic–inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)3](dto = C2O2S2, SP = spiropyran)

A photo-sensitive organic–inorganic hybrid system (SP)[Fe^IIFe^III(dto)₃] (SP = spiropyran, dto = C₂O₂S₂), has recently been developed, where the photo-isomerization of the intercalated spiropyran in solid state triggers the change of the magnetic properties, including the ferromagnetic transition temperature from 5 to 22 K. We performed ⁵⁷Fe Mössbauer measurement in order to probe the microscopic states of iron ions in (SP)[Fe^IIFe^III(dto)₃] and have investigated the photo-induced effect on them. The sample without UV-irradiation shows the charge transfer phase transition between 200 and 70 K and the higher and lower temperature phases coexist below 70 K, whereas the UV-irradiated sample does not undergo the charge transfer phase transition and the higher temperature phase is stable between 200 and 6 K.     

Effect of nanoparticles agglomeration on electrical properties of La1−xAxMnO3 (A = Sr,Ba) nanopowder and ceramic solid solutions

Peculiar features of the sol–gel synthesis of substituted manganites La_1−xA_xMnO₃ (A = Sr, Ba) have been investigated. Variation of the gel pH during synthesis was shown to affect the aggregation of particles and their crystal structure. Electrical properties of nanopowder and ceramic La_1−xA_xMnO₃ solid solutions were studied. Additional heat treatment was revealed to affect not only the resistivity, but also the character of its temperature dependence. It was shown that under the synthesis and heat treatment conditions used in the work, the La_1−xBa_xMnO₃ solid solutions with x = 0.15 have the lowest conductivity at 1200 K, which allows using them as thick-film cathodes.     

Characterisation of prehnite by EPMA, Mössbauer, optical absorption and EPR spectroscopic methods

A sample of prehnite from Rayalaseema zone of Andhra Pradesh, India containing about 2.565 wt.% Fe(2)O(3) is used in the present work. The mineral has been characterized by EPMA, optical absorption, EPR, NIR and M?ssbauer techniques. M?ssbauer studies confirm the presence of iron as an impurity in two sites. An EPR study on powder sample confirm the presence of Fe(III) impurity in the mineral. Optical absorption spectrum also indicates that Fe(III) impurity is present in two sites with octahedral structure. NIR results are due to water fundamentals.     

Helical chains of [MO5Cl] octahedra – Three compounds in the new family AEM2Te3O8Cl2 (AE = Ca,Sr and M = Co,Ni)

The compounds CaCo₂Te₃O₈Cl₂, SrCo₂Te₃O₈Cl₂ and SrNi₂Te₃O₈Cl₂ were synthesized via solid–gas reactions and investigated using single-crystal X-ray diffraction. While the compound CaCo₂Te₃O₈Cl₂ formed large enough single crystals to allow for a detailed structural analysis, crystals of the Sr-containing compounds yielded evidence that they are isostructural. CaCo₂Te₃O₈Cl₂ crystallizes in the monoclinic system, space group P2₁/c, a = 6.537(2) Å, b = 9.088(2) Å, c = 19.500(9) Å, β = 113.36(4)°, Z = 4. It exhibits [CoO₅Cl] helical chains along the [010] direction, connected by [CaO₈] polyhedra, [TeO₃E] tetrahedra and [TeO₄E] trigonal bipyramids (the lone pair of electrons on Te^IV is designated as E) to form a layer. The layers are held together only by weak van der Waals forces; the shortest interlayer distance is a Te?Cl contact of 3.432(4) Å.     

Magnetic,Mössbauer and hyperthermia properties of Co1−xMnxFe2O4 nanoparticles

Journal of Radioanalytical and Nuclear Chemistry - Hyperthermia is used to combat and reduce the effects of tumors. This study relates to Co1?xMnxFe2O4 magnetic nanoparticles and their...     

Substituted transition metal phospho olivines LiMM′PO4 (M = Mn,M′ = Fe,Co, Mg): Optimisation routes for LiMnPO4

Since transition metal phospho olivines gain increasing interest as cathode materials for lithium ion batteries in the last decades lots of publications appeared. Various synthesis methods were in the focus of interest as well as structural investigations of the pure LiMPO₄ and mixed Li (MM′)PO₄ phases (M, M′ = Fe, Mn, Co, Ni, Mg, Zn, Al) and their structural changes during electrochemical conversion. Lithium insertion and exsertion mechanisms have been studied with the help of e.g. structural, optical and electronic, and electrochemical characterisation methods. Likewise many efforts have been done for material optimisation concerning synthesis procedure or substitution.We tend to give an overview about Li (MM′Mn)PO₄ (M, M′ = Mg, Fe, Co) on the basis of our results. For the greater topic of enhancement of performance and energy density of LiMnPO₄ we discuss different solution approaches concerning the raise of specific capacity, redox potential and optimisation of material characteristics. Thus we consider effects due to the intrinsic conductivity, structural stability of the charged phase as well as its chemical stability against the electrolyte and the dynamic stability of the interface between charged phase and discharged phase during electrochemical conversion.For this purpose in our experimental part we focus on three different approaches: substitution with an electrochemically active transition metal, substitution with an electrochemically inactive metal in case for the manipulation of unit cell volume alternation and the substitution with electrochemically inactive metals for the purpose of providing a “lithium reservoir”. This generated “lithium reservoir” is expected to be accessible for the utilisation of a new redox step. Phase transition in mixed transition metal phospho olivines Li(MnCo)PO₄ has been investigated as example for the effect of substitution with an electrochemically active transition metal. Substitution with an electrochemically inactive metal leading to binary Li(MgMn)PO₄ has been structurally and electrochemically investigated. Promising new electrochemical characteristics of binary Li(MgMn)PO₄ phospho olivines are introduced for the first time. When charged to high potentials (>4.9 V) the activation of the Mn³⁺/Mn⁴⁺ step is reported.     

On the physical properties of Sr1−xNaxRuO3 (x = 0–0.19)

The metallic ferromagnetic perovskite-type SrRuO₃ (T_C ～ 160 K) belongs to the “class” of materials with strongly correlated electrons. Nonetheless a simple ferromagnetism associated with isotropic interactions of low spin Ru⁴⁺ ions local moments is far too simple to explain the complex interplay between charge carriers and magnetic interactions. In that sense the suppression of ferromagnetism in isoelectronic Sr_1?xCa_xRuO₃ was tentatively associated to the increased lattice distortion influencing primarily the 4d Ru bandwidths and, hence, the itinerancy and respective populations of the spin-up and spin-down electrons.In order to probe the robustness of the metallic ferromagnetism against electron occupation of 4d Ru orbital we prepared and characterized polycrystalline Sr_1?xNa_xRuO₃ (x = 0.0–0.19) ceramics. The substitution of Sr²⁺ by Na¹⁺, leading to formally mixed valence Ru⁴⁺/Ru⁵⁺, induces the decrease of the Curie temperature and spin-wave stiffness, which was determined independently from magnetic and specific heat data. On the other hand the effective paramagnetic moment remains essentially unchanged. All compounds are metallic in a sense of electrical resistivity and thermopower temperature dependence; the low temperature upturn of the electrical resistivity was explained on a base of the weak localization. The metallic nature of the samples is corroborated by Pauli paramagnetism and high Sommerfeld coefficient γ, extracted from the low temperature specific heat, which increases from 30.9 mJ mol^?1 K^?2 (x = 0.0) to 43.0 mJ mol^?1 K^?2 (x = 0.19).     

Magnetic properties of RE5Ir2X (RE = Y,Gd–Ho,X = Sn,Sb, Pb,Bi) and magnetocaloric characterization of Gd5Ir2X

Systematic phase analytical studies of the systems RE-Ir-X (X = Sn, Pb, Sb, Bi) led to 15 new stannides, plumbides, antimonides and bismuthides with the composition RE₅Ir₂X. The compounds have been synthesized and characterized by X-ray powder diffraction. The structures of Gd₅Ir₂Sb and Dy₅Ir₂Bi have been refined from single crystal X-ray diffractometer data: Mo₅SiB₂ type, I4/mcm, a = 775.2(2), c = 1361.3(5) pm, wR2 = 0.0933, 404 F² values, 16 variables for Gd₅Ir₂Sb and a = 767.5(1), c = 1368.9(3) pm, wR2 = 0.0694, 571 F² values, 16 variables for Dy₅Ir₂Bi. Magnetic measurements of Gd₅Ir₂X (X = Sn, Pb, Sb, Bi), Tb₅Ir₂X (X = Sn, Pb, Sb, Bi), Dy₅Ir₂Pb, Dy₅Ir₂Bi and Ho₅Ir₂Pb indicate ferromagnetic transitions at T_C = 154.3, 159.3, 124.4, 119.3, 99.2, 98.2, 65.5, 68.6, 45.1, 35.6 and 23.5 K, respectively. Gd₅Ir₂Bi and Gd₅Ir₂Sb show an additional antiferromagnetic transition at T_N = 118.5 and 91.0 K. The magnetocaloric effect of Gd₅Ir₂X (X = Sn, Pb, Sb, Bi) in terms of the isothermal entropy change ΔS_m is −7.3(3), –6.5(3), –8.7(3) and −9.0(3) J kg⁻¹ K⁻¹ at temperatures of 153, 157, 120 and 126 K for a 5 T field change. ¹¹⁹Sn Mössbauer spectra of Gd₅Ir₂Sn at 78 K show a huge transferred hyperfine field of 21.9(1) T and an isomer shift of 1.94(1) mm s⁻¹, typical for stannides. ¹²¹Sb Mössbauer spectra of Gd₅Ir₂Sb at 78 K show a transferred hyperfine field of 14.2(3) T and an isomer shift of −7.45(8) mm s⁻¹ reflecting the antimonide character.     

Thermal behaviour,surface properties and vibrational spectroscopic studies of the synthesized Co3xNi3−3x(PO4)2·8H2O (0 ≤ x ≤ 1)

Co_3xNi_3−3x(PO₄)₂·8H₂O (x = 1, 0.8, 0.6, 0.4, 0.2, and 0) were synthesized via simple wet chemical reaction and energy saving route method. The final decomposition products of hydrates are corresponding anhydrous tri(cobalt nickel) diphosphates. The metal and water contents of the synthesized hydrates were confirmed by AAS and TG/DTG/DTA techniques, respectively. The observed metal and water contents agree well with the formula of the title compounds. The crystal structures and lattice parameters as well as crystallite sizes of the studied compounds were determined using XRD data. The results from XRD and TG/DTG/DTA techniques confirmed that Co_3xNi_3−3x(PO₄)₂·8H₂O at all ratios were the single phase. The FTIR spectra of studied compounds were recorded and assigned. The thermal behaviours of single and binary tri(cobalt nickel) diphosphate octahydrates were studied for the first time. The morphologies of the studied compounds were investigated by using the SEM technique. The micrographs of all studied compounds exhibited the thin plated morphology. The surface area and the pore size data of anhydrous forms were measured by N₂ adsorption at −190 °C according to the BET method. The anhydrous forms of binary metal phosphate at x = 0.8, Co_2.4Ni_0.6(PO₄)₂, exhibits the highest surface area and expects to improve the catalytic activity.     

Synthesis and structural mechanisms of the 2201-type ferrites and polytypes: Fe2(Sr2 − xAx)FeO6.5 − δ/2 (A = Ba,La, Tl,Pb and Bi)

The Fe₂(Sr_2 ? xA_x)FeO_6.5 ? δ/2 systems have been investigated, by doping the iron rich 2201-type parent structure with Ba²⁺, La³⁺ and 5d¹⁰ post-transition cations. The syntheses have been carried out up to the limit of the 2201-type solid solutions, in order to test the role of the double iron layer Fe₂O_2.5 ? δ/2. The localisation of the charge carriers in these compounds is consistent with their strong antiferro-magnetism. The investigation was then carried out in the transition part of the diagram up to the formation of stable phases. The study of structural mechanisms was carried using high resolution electron microscopy (transmission and scanning transmission), electron diffraction and energy dispersive spectroscopy. Different non-stoichiometry mechanisms are observed, depending on the electronic structure and chemical properties of the doping elements. The specific behavior of the modulated double iron layer is discussed.     

Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.     

Magnetic properties of double perovskite Ca2FeMoO6 by neutron diffraction and Mössbauer spectral studies

Journal of Radioanalytical and Nuclear Chemistry - Crystallographic and magnetic properties of the double perovskite oxide Ca2FeMoO6 were studied. The single phase polycrystalline Ca2FeMoO6 powder...     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Mössbauer spectroscopic studies of thermal decomposition of substituted pentacyanoferrate(II) complexes

The thermal behaviour of substituted pentacyanoferrates(II) of the type Na₃[Fe(CN₅)L]·xH₂O, whereL=n-, sec-, tert- oriso-butylamine,di-iso-butylamine ortri-n-butylamine, was investigated with the aid of Mössbauer spectroscopy, XRD and TG-DTG-DTA. The Mössbauer spectra of these complexes exhibit a quadrupole doublet with E _Q=0.70–0.83 mm s^–1 at room temperature. The isomer shift, =0.00±0.03 mm s^–1 suggests that the iron atom is in the +2 low-spin state. The complexes start to decompose at 50°C, yielding a residual mass of 5.8 –21.3% in the temperature range 900–950°C. The Mössbauer spectra recorded after heating at 150 and 300°C exhibit an asymmetric doublet, suggesting partial decomposition. The Mössbauer spectra at higher temperature are complex. At different stages of the thermal process, the presence of -Fe₂O₃, -Fe₂O₃, -Fe, Fe₃C and Fe₃O₄ was demonstrated.On leave from A. N. College, Anandwan-442 914, IndiaWe are grateful to the Monbusho (Ministry of Education, Science, Sports and Culture) for the award of a fellowship to RBL and for financial assistance for the research work. Thanks are also due to Dr. T. Nakamoto for valuable cooperation.     

Study on the cesium Tutton compounds,Cs2M(XO4)2∙6H2O (M = Mg,Co, Zn; X = S,Se): Preparation,X-ray powder diffraction and infrared spectra

The crystallization processes in the three-component systems Cs₂SO₄–MSO₄–H₂O (M = Mg, Co, Zn) have been studied at 25 °C. It has been established that cesium Tutton compounds, Cs₂M(SO₄)₂·6H₂O (M = Mg, Co, Zn; X = S, Se), crystallize from the ternary solutions within large concentration ranges. The double salts were identified by means of X-ray powder diffraction and infrared spectroscopy. Infrared spectra of the cesium compounds are presented and discussed with respect to both the normal modes of the tetrahedral ions and the water molecules. The water librations are also discussed. The strength of the hydrogen bonds formed in the cesium salts as deduced from the frequencies of ν_OH is commented. The analysis of the spectra reveals that stronger hydrogen bonds are formed in the cesium selenates as compared to those in the respective sulfates due to the stronger proton acceptor ability of the selenate ions.     

Sr induced modification of structural,optical and magnetic properties in Bi1−xSrxFeO3 (x = 0, 0.01, 0.03, 0.05 and 0.07) multiferroic nanoparticles

Multiferroic nanoparticles of Bi_1?xSr_xFeO₃ (x = 0, 0.01, 0.03, 0.05 and 0.07) were prepared by a facile sol–gel route and the variation of their structural, optical, dielectric and magnetic properties on strontium concentration has been studied. XRD and TEM results confirm the phase purity of the samples having high degree of crystallinity and monodispersity. The average particle size shows an exponential decline with increase in Sr concentration. A shape transformation from a multifaceted polygon to a spherical one has been observed as Sr concentration in the sample increases to 5%. In the second derivative FTIR spectra, the intensity of vibration peak at ～593 cm^?1 that is characteristic of rhombohedral BiFeO₃ is seen to decrease after Sr doping. All the samples showed typical M–H behavior of a ferromagnet with saturation magnetization achieved within an applied magnetic field of 10 kOe. The sample with 3% Sr substitution displayed saturation and remanent magnetization values 1.37 emu/g and 0.32 emu/g respectively that are highest among all the samples studied. Presence of exchange coupling produced due to interaction between the antiferromagnetic core and ferromagnetic shell is also observed in all Bi_1?xSr_xFeO₃ nanoparticles.     

Electroconductivity of Solid Solutions Cs3–2x M x PO4 (M = Ba, Sr, Ca, Mg)

Solid solutions Cs_{3 – 2x} M _x PO₄ (M = Ba, Sr, Ca, Mg) are synthesized and their thermal behavior and electroconductivity are examined. Adding elements of Subgroup IIA of the periodic table into cesium orthophosphate shifts the phase transition, which occurs in pure Cs₃PO₄ at 450–620°, towards lower temperatures and raises the cesium cation conductivity at low temperatures. The electroconductivity of a high-temperature modification of Cs₃PO₄ is weakly dependent on the presence and concentration of such additives, which points to structural disordering of the cesium sublattice.