XRD,impedance, and Mössbauer spectroscopy study of the Li<Subscript>3</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> composite for Li ion batteries

The synthesis procedure of the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite is presented. The monoclinic (A type) and hematite phases were detected by X-ray diffraction after the synthesis of the composite. The structural α–β (at a temperature of 460 K) and β–γ (at a temperature of 523 K) phase transitions in the composite were indicated by the anomalies of the electrical conductivity, dielectric permittivity, and changes of activation energies of conductivity. Two phase transitions have been detected in the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite by ⁵⁷Fe Mössbauer spectroscopy: the phase transition in Li₃Fe₂(PO₄)₃ from the paramagnetic to antiferromagnetic phase at temperature T _N?=?29.5 K and the Morin phase transition in Fe₂O₃ at temperature T _M?=?235 K.     

Single-crystalline M-type Sr Hexaferrites studied by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The ⁵⁷Fe Mössbauer spectra of the single crystalline and the finely ground Sr_1?x La _x Fe_12?y Co _y O₁₉ (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe²⁺ ions in the Fe³⁺ ions were not observed in our Sr_1?x La _x Fe_12?y Co _y O₁₉ samples. In SrFe₁₂O₁₉, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr_0.544La_0.456Fe_11.775Co_0.225O₁₉. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co²⁺ ion for the Fe³⁺ ion changes the center shifts of the Fe³⁺ ions near the Co²⁺ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co²⁺ ions occupy the 4f ₁ and the 4f ₂ sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe³⁺ ions.     

Recent developments in the doping of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material for 5 V lithium-ion batteries

LiMn₂O₄ has been considered a promising cathode material for lithium-ion batteries in electric vehicles. However, there are still a number of problems of severe capacity fading before any materials modifications. Among all doped LiMn₂O₄, spinel LiNi_0.5Mn_1.5O₄ material is seen as a potential cathode material for use in electric vehicles and energy storage systems in the future because of its high working potential (4.7 V), high energy density (the energy density of LiNi_0.5Mn_1.5O₄ is 20% higher than that of LiCoO₂), acceptable stability, and good cycling performance. In the presented paper, the structure and electrochemical performance of doped LiNi_0.5Mn_1.5O₄ are reviewed. The rate capability, rate performance and cyclic life of various doped LiNi_0.5Mn_1.5O₄ materials are described. This review also focuses on the present status of doped LiNi_0.5Mn_1.5O₄, then on its near future developments.     

A structural,magnetostrictive and Mössbauer study of Tb<Subscript>0.3</Subscript>Dy<Subscript>0.7</Subscript>(Fe<Subscript>0.9</Subscript><Emphasis Type="Italic">T</Emphasis><Subscript>0.1</Subscript>)<Subscript>1.95</Subscript> alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys is the MgCu₂-type cubic Laves phase structure for different substitution. The magnetostrictionλ _s decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostrictionλ _s . It was also found that the effect of different substitutions on the spontaneous magnetostrictionλ ₁₁₁ is distinct. The analysis of the Mössbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In ³⁺, however the spectra are dominated by spectral lines due to paramagnetic Fe²⁺. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe²⁺ state in In ₂O₃. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In ₂O₃. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.     

Sm valence states and magnetic properties in SmBe<Subscript>13</Subscript> and SmTi<Subscript>2</Subscript>Al<Subscript>20</Subscript> investigated by Sm synchrotron-radiation-based Mössbauer spectroscopy

Synchrotron-Radiation-based \(^{\mathrm {149}}\)Sm Mössbauer spectroscopy was applied to Sm intermetallics, SmBe₁₃ and SmTi₂Al₂₀. Temperature dependence of the Mössbauer parameters in SmBe₁₃ indicate the Sm valence state is purely trivalent. SmBe₁₃ also showed second-order Doppler shift in synchrotron-radiation-based \(^{\mathrm {149}}\)Sm Mössbauer spectroscopy. The Mössbauer parameters obtained in SmTi₂Al₂₀ suggest that the Sm valence is fluctuating and the magnitude of the magnetic moment is reduced by hybridization between 4f and conduction electrons and/or effect of crystal electric field.     

Structural properties of composite cathode material LiFePO<Subscript>4</Subscript>–Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Composite cathode material LiFePO₄–Li₃V₂(PO₄)₃ is synthesized through a chemical reduction and lithiation using FeVO₄·xH₂O as both iron and vanadium sources. The structural properties of LiFePO₄–Li₃V₂(PO₄)₃ are investigated. X-ray diffraction results show the composite material containing olivine type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. High-resolution transmission electron microscopy and energy-dispersive X-ray spectrometry results indicate that mutual doping effects take place between the LiFePO₄ and Li₃V₂(PO₄)₃ particles with V³⁺ doping the LiFePO₄ while Fe²⁺ dopes the Li₃V₂(PO₄)₃. LiFePO₄–Li₃V₂(PO₄)₃ nanocomposites are formed in the carbon webs. There is no structural compatibility between monoclinic (Li₃V₂(PO₄)₃) and olivine (LiFePO₄) domains in composite material LiFePO₄–Li₃V₂(PO₄)₃.     

Er,Yb:YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>—efficient 1.5 μm laser crystal

This article summarizes the latest achievements in the growth and characterization of Er,Yb:YAl₃(BO₃)₄ laser crystal emitting in the 1.5–1.6 μm spectral range. Fundamental spectroscopic parameters relevant to laser performance of Er,Yb:YAB derived from absorption and emission spectra and from excited state dynamics are presented. The laser performance of Er,Yb:YAB in the cw and mode-locked regimes is reported.     

Dynamics of iron in Fe-porphyrin aggregates studied by X-ray absorption and Mössbauer spectroscopy

The iron-porphyrin aggregates were studied by optical absorption and fluorescence method, infrared spectroscopy, X-ray absorption and Mössbauer spectroscopy. The aggregation of porphyrin molecules strengthens the Fe-ligands bonds and accelerates the spin-spin relaxations. A significant speeding-up of relaxation was observed with lowering the temperature down to 25 K. The comparison of the EXAFS (Extended X-ray Absorption Fine Structure) and Mössbauer spectroscopy results enabled some separation of the individual Fe vibration from its collective movement with ligands.     

Single-crystalline α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanohexahedron as outstanding anode material for lithium-ion batteries

In this paper, single-crystalline hexahedron hematite is successfully obtained by a simple hydrothermal approach with assistance of PVP as surfactant. SEM and XRD results show that the as-obtained α-Fe₂O₃ has a nanohexahedron shape with high uniformity and high crystallinity. The effects of a few factors influencing the morphology of α-Fe₂O₃, such as PVP amount, reaction temperature, etc., are investigated carefully. More importantly, time-dependent experiments are carried out to have in-depth insight into the formation of the single-crystalline α-Fe₂O₃ nanohexahedron. Based on the full characterization of as-obtained α-Fe₂O₃, it is concluded that PVP as surfactant plays an important role in the formation of the hexahedron shape of α-Fe₂O₃. Besides, the proposed formation mechanism of α-Fe₂O₃ nanohexahedron is that the shape of α-Fe₂O₃ evolves from the nuclei, needle-like shapes, and urchin-like aggregates to the hexahedron shape, driven by minimization of surface energy and Ostwald ripening. When used as an anode material for lithium-ion batteries, nanohexahedron α-Fe₂O₃ shows a high rate capability. Moreover, after 150 cycles, the storage capacity of α-Fe₂O₃ is still up to 680 mAh g^?1 and almost remains unchanged, suggesting high cyclability.

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Mössbauer investigations of Fe and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles for hyperthermia applications

Magnetic nanoparticles of magnetite Fe₃O₄ and Fe synthesized by physical vapor deposition with a fast highly effective method using a solar energy have been studied. Targets have been prepared from tablets pressed from Fe₃O₄ or Fe powders. Relationships between the structure of nanoparticles and their magnetic properties have been investigated in order to understand principles of the control of the parameters of magnetic nanoparticles. Mössbauer investigations have revealed that the nanoparticles synthesized from tablets of both pure iron and Fe₃O₄ consist of two phases: pure iron and iron oxides (γ-Fe₂O₃ and Fe₃O₄). The high iron oxidability suggests that the synthesized nanoparticles have a core/shell structure, where the core is pure iron and the shell is an oxidized iron layer. Magnetite nanoparticles synthesized at a pressure of 80 Torr have the best parameters for hyperthermia due to their core/shell structure and core-to-shell volume ratio.     

A PEG-assisted rheological phase reaction synthesis of 5LiFePO<Subscript>4</Subscript>⋅Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as cathode material for lithium ion cells

5LiFePO₄⋅Li₃V₂(PO₄)₃/C composite cathode material is synthesized by a polyethylene glycol (PEG)-assisted rheological phase method. As a surfactant and dispersing agent, PEG can effectively inhabit the aggregation of colloidal particles during the formation of the gel. Meanwhile, PEG will coat on the particles to play the role of carbon source during the sintering. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical methods. XRD results indicate that the 5LiFePO₄⋅Li₃V₂(PO₄)₃/C composites are well crystallized and contain olivine-type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. The composite synthesized at 650 °C exhibits the initial discharge capacities of 134.8 and 129.9 mAh g⁻¹ and the capacity retentions of 96.2 and 97.1 % after 50 cycles at 1C and 2C rates, respectively.     

Mössbauer effect study of Bi<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>FeO<Subscript>3</Subscript> multiferroic on <Superscript>57</Superscript>Fe nuclei

The parameters of hyperfine interactions in the Bi_0.8La_0.2FeO₃ multiferroic have been measured by Mössbauer spectroscopy in the temperature range of 87–850 K. It has been found that the spatial spin-modulated structure that exists in BiFeO3 is destroyed in the substitution of La for 0.2 mol % of Bi and the homogeneous antiferromagnetic structure appears. The temperatures of the magnetic (Néel temperature, T _N = 677 ± 3 K) and ferroelectric (Curie temperature, T _C = 773 ± 3 K) transitions and the Debye temperature (Θ = 431 ± 12) have been measured.     

Mössbauer study of 1% <Superscript>57</Superscript>Fe doped ferromagnetic insulator La<Subscript>0.825</Subscript>Ca<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript>

We have employed magnetization measurements, M?ssbauer and ESR spectroscopic techniques, in order to study the ferromagnetic insulating (FMI) compound La_1-xCa_xMnO₃ (x=0.175) doped with 1% ⁵⁷Fe. We have used two samples; one prepared in air which has cation vacancies and a second in inert atmosphere, which is stoichiometric. An abrupt change of the experimental results is obtained, by all techniques, in the ferromagnetic insulating regime, in the temperature region of T_O/O//≈60 K, where an orbital rearrangement is suggested to occur. An analysis of these findings points to an orbital rearrangement transformation. Ferromagnetic resonance reveals considerable differences between stoichiometric and cation deficient samples, indicating anisotropy of the exchange interactions in the former sample with significant temperature dependence, most pronounced in the vicinity of T_O/O//     

Evolution of the negative electrode (tin/silicate) for Li-ion batteries studied by 119 Sn Mössbauer spectroscopy

A novel tin composite Sn/CaSiO₃ for the anode of Li-ion batteries was prepared by solid-state reaction. The CaSiO₃ matrix was synthesized by a sol-gel route. The crystalline structures and morphology were determined by X-ray diffraction (XRD) and ¹¹⁹Sn Mössbauer spectroscopy; the electrochemical properties were evaluated by galvanostatic charge and discharge. The results obtained show that the Sn/CaSiO₃ composite presents very interesting electrochemical performances in terms of specific capacity in the first discharge (591 mAh/g) and a good reversibility due to both the formation of an interface between active and inactive materials and the reversible formation of Li _x Sn alloys. We have also highlighted, by ¹¹⁹Sn Mössbauer spectroscopy, the various tin species constituting the material of the starting electrode, as well as the chemical evolutions occurring during the discharge and the charge of the electrode.     

A study of thermodynamic properties of dilute Fe-Ru alloys by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for Fe_1?x Ru _x solid solutions with x in the range 0.01 ≤ x ≤ 0.08. The obtained data were analysed in terms of short-range order parameter (SRO) and the binding energy E _b between two ruthenium atoms in the studied materials using the extended Hrynkiewicz-Królas idea. The extrapolated value of E _b for x = 0 was used to compute the enthalpy of solution H _FeRu of Ru in Fe matrix. The result was compared with corresponding values given in the literature which were derived from experimental calorimetric data as well as with the value resulting from the cellular atomic model of alloys by Miedema. It was found that all the H _FeRu values are negative or Ru atoms interact repulsively. At the same time, the Mössbauer data were used to determine values of the short-range order parameter α ₁. For the as-obtained samples in which atoms are frozen-in high temperature state, close to the melting point, the negative α ₁ values were found. The findings indicates ordering tendencies in such specimens. On the other hand, in the case of the annealed samples where the observed distributions of atoms should be frozen-in state corresponding to the temperature 700 K, the Fe_1?x Ru _x alloys with x ≥ 0.05 exhibit clustering tendencies (a predominance of Fe-Fe and Ru-Ru bonds), which manifest themselves by positive values of the calculated SRO parameter. The clustering process leads to a local increase in ruthenium concentration and nucleation of a new ruthenium-rich phase with the hcp structure.     

<Superscript>151</Superscript>Eu Mössbauer study of multiferroic Eu<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript>

We are herewith reporting the ¹⁵¹Eu Mössbauer spectra collected on a polycrystalline powder sample of Eu_0.75Y_0.25MnO₃ from 15 K to room temperature. All the spectra consist of a single line, whose shape and related sample thickness are dependent on the temperature T. The thermal trend of the mean square displacement of Eu ion, obtained from the spectra analysis, clearly reveals a large low-temperature anharmonicity and in concomitance with the onset of the magnetic ordering consists in a linear strong decrease interrupted by two narrow wells at 29.5 K and 40 K. This behavior is interpreted in connection with the transfer of spectral weight from the 120 cm^-1 optical phonon to the electromagnonic modes. The T-trend of the central shift shows that Eu³⁺ electronic ground state in the magnetically ordered phase differs from the one in the paramagnetic state. Finally, the temperature dependence of the hyperfine field under T _N gives a contribution to interpret some controversial features regarding the phase-diagram.     

Synthetic versiliaite and apuanite: investigation by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The minerals versiliaite and apuanite have been synthesised for the first time. The ⁵⁷Fe Mössbauer spectra recorded at 298 and 4 K are reported. The results are indicative of a formulation for versiliaite as \(\left (\text {Fe}_{4}^{2+}\text {Fe}_{4}^{3+}\right )^{\text {oct}}\left [\text {Fe}_{4}^{3+}\text {Sb}_{12}^{3+}\right ]^{\text {tet}}\textit {O}_{32}\textit {S}_{2}\) and of apuanite as \(\left (\text {Fe}_{4}^{2+}\text {Fe}_{8}^{3+}\right )^{\text {oct}}\left [\text {Fe}_{8}^{3+}\text {Sb}_{16}^{3+}\right ]^{\text {tet}}\textit {O}_{48}\textit {S}_{\mathrm {4.}}\) The spectra recorded at low temperature are indicative of complex magnetic interactions. The results indicate the potential for the synthesis of further new structurally-related materials with different compositions and new low dimensional physical properties.     

Synthesis of high performance Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C cathode material by ultrasonic-assisted sol–gel method

A novel ultrasonic-assisted sol–gel method is proposed to prepare Li₃V₂(PO₄)₃/C cathode material. X-ray diffraction analyses show that both Li₃V₂(PO₄)₃/C(A) synthesized by the ultrasonic-assisted sol–gel method and Li₃V₂(PO₄)₃/C(B) synthesized by a traditional sol–gel method have monoclinic structure. Scanning electron microscopy images indicate that the Li₃V₂(PO₄)₃/C(A) composite has a more uniform morphology than that of the Li₃V₂(PO₄)₃/C(B) composite. In the voltage range of 3.0–4.3 V (vs. Li/Li⁺), the initial specific discharge capacities of the Li₃V₂(PO₄)₃/C(A) and Li₃V₂(PO₄)₃/C(B) samples are 129.8 and 125.9 mAh g⁻¹ at 1C rate (1C = 133 mA g⁻¹), respectively. Furthermore, at 2-C charge/10-C discharge rate, the specific discharge capacity of the Li₃V₂(PO₄)₃/C(A) composite retains 113.2 mAh g⁻¹ after 50 cycles, but the Li₃V₂(PO₄)₃/C(B) composite only presents a capacity of 94.8 mAh g⁻¹.