Lithium ion conductive glass–ceramics with Li3Fe2(PO4)3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li₂O–(25 − x)Fe₂O₃–xNb₂O₅–37.5P₂O₅ (mol%) (x = 5,10,15) are prepared, and it is found that the addition of Nb₂O₅ is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li₃Fe₂(PO₄)₃ crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10^− 6 Scm^− 1 at room temperature and the activation energies of 0.48 eV (x = 5) and 0.51 eV (x = 10) for Li⁺ ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li₃Fe₂(PO₄)₃ crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li₃Fe₂(PO₄)₃ crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.     

Electrical conductivity of Ag/Na ion-exchanged titanosilicate glasses

The Ag₂O–TiO₂–SiO₂ glasses were prepared by Ag⁺/Na⁺ ion-exchange method from Na₂O–TiO₂–SiO₂ glasses at 380–450 °C below their glass transition temperatures (T_g), and their electrical conductivities were investigated as functions of TiO₂ content and the ion-exchange ratio (Ag/(Ag+Na)). In a series of glasses 20R₂O·xTiO₂·(80−x)SiO₂ with x=10, 20, 30 and 40 in mol%, the electrical conductivities at 200 °C of the fully ion-exchanged glasses of R=Ag were in the order of 10⁻⁵ or 10⁻⁴ S cm⁻¹ and were 1 or 2 orders of magnitude higher than those of the initial glasses of R=Na. The glass of x=30 exhibited the highest increase of conductivity from 3.8×10⁻⁷ to 1.3×10⁻⁴ S cm⁻¹ at 200 °C by Ag⁺/Na⁺ ion exchange among them. When the ion-exchange ratio was changed in 20R₂O·30TiO₂·50SiO₂ system, the electrical conductivity at 200 °C exhibited a minimum value of 7.6×10⁻⁸ S cm⁻¹ around Ag/(Ag+Na)=0.3 and increased steeply in the region of Ag/(Ag+Na)=0.5–1.0. When the ion-exchange temperature was changed from 450 to 400 °C, the conductivity of the ion-exchanged glass of x=30 decreased. The infrared spectroscopy measurement revealed that the ion-exchange temperature of 450 °C induced a structural change in the glass of x=30. The T_g of the fully ion-exchanged glass of x=30 was 498 °C. It was suggested that the incorporated silver ions changed the average coordination number of titanium ions to form higher ion-conducting pathway and resulted in high conductivity in the titanosilicate glasses.     

Improved quantification of alite and belite in anhydrous Portland cements by Si MAS NMR: Effects of paramagnetic ions

The applicability, reliability, and repeatability of ²⁹Si MAS NMR for determination of the quantities of alite (Ca₃SiO₅) and belite (Ca₂SiO₄) in anhydrous Portland cement was investigated in detail for 11 commercial Portland cements and the results compared with phase quantifications based on powder X-ray diffraction combined with Rietveld analysis and with Taylor–Bogue calculations. The effects from paramagnetic ions (Fe³⁺) on the spinning sideband intensities, originating from dipolar couplings between ²⁹Si and the spins of the paramagnetic electrons, were considered and analyzed in spectra recorded at four magnetic fields (4.7–14.1 T) and this has led to an improved quantification of alite and belite from ²⁹Si MAS NMR spectra recorded at “high” spinning speeds of ν_R=12.0–13.0 kHz using 4 or 5 mm rotors. Furthermore, the impact of Fe³⁺ ions on the spin-lattice relaxation was studied by inversion-recovery experiments and it was found that the relaxation is overwhelmingly dominated by the Fe³⁺ ions incorporated as guest-ions in alite and belite rather than the Fe³⁺ sites present in the intimately mixed ferrite phase (Ca₂Al_xFe_2−xO₅).     

Analogous study in low magnetic field between Cu–Ge and Cu–Si ferrites

Two series of mixed copper ferrites, Cu_1+x Ge_x Fe_2−2x O₄ and Cu_1+x Si_x Fe_2−2x O₄, have been analogously investigated for x=0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3. The two systems were prepared using the standard ceramic techniques. X-ray diffraction analysis indicates that both systems formed in a single phase cubic spinel structure. The lattice parameter has a constant value (0.838 nm±0.001) for the two series. The grain diameter was estimated from the scanning electron microscope micrographs for the two series. Some magnetic properties were measured at room temperature. The magnetization M was measured in the range of magnetizing field up to 5500 Am⁻¹. The relative permeability (μ_r) was calculated from the B–H relation. The B–H loops were measured at constant magnetizing current (I=2.5 A which is equivalent to 900 Am⁻¹). Also, the hystersis area and the magnetic parameters B_r, B_s, m_R (B_r/B_s) and apparent energy loss (E) were estimated from the B–H loops; μ_r, B_r, B_s and E are composition dependent.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

Magnetic and magnetotransport properties of Co-doped manganites with perovskite structure

A systematic study of the doping of the Mn-sites by cobalt in three series of manganites — La_0.76Ba_0.24(Mn_1−xCo_x)O₃ single crystals, La_2/3Ba_1/3(Mn_1−xCo_x)O₃ and La(Mn_1−xCo_x)O₃ ceramics has been performed. It was found that La(Mn_1−xCo_x)O₃ annealed at 800°C in the range 0.4x0.9 is a mixture of ferromagnetic domains with ordered Mn and Co ions and ionically disordered spin-glass domains. In the quenched samples the fraction of spin-glass-type component increases strongly. The La_2/3Ba_1/3(Mn_1−xCo_x)O₃ solid solutions exhibit also an evidence for phase separation in the range 0.5x0.8. All the La(Mn_1−xCo_x)O₃ samples show an insulating behavior, however, magnetoresistance reduces strongly when the cobalt content rises to x=0.5. The La_0.76Ba_0.24(Mn_1−xCo_x)O₃ single crystals show first-order phase transition below their Curie points associated with a change of ground state of the Co²⁺ ions. The magnetic phase diagrams are depicted. The results are discussed in terms of positive Mn³⁺–O–Mn⁴⁺, Mn³⁺–O–Mn³⁺, Mn⁴⁺–O–Co²⁺ and negative Mn⁴⁺–O–Mn⁴⁺, Co²⁺–O–Co²⁺, Co²⁺–O–Mn³⁺ superexchange interactions as well as Co²⁺ and Mn⁴⁺ ionic ordering.     

Effect of ZnO on phase emergence, microstructure and surface modifications of calcium phosphosilicate glass/glass-ceramics having iron oxide

The effect of ZnO on phase emergence and microstructure properties of glass and glass-ceramics with composition 25SiO₂-50CaO-15P₂O₅-(10 − x)Fe₂O₃-xZnO (where x = 0, 2, 5, 7 mol%) has been studied. They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Surface modifications of these glass-ceramics in simulated body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide content. Emergence of crystalline phases in glass-ceramics at different heat treatment temperatures was studied using XRD. When glass is heat treated at 800 °C calcium phosphate, hematite and magnetite are developed as major phases in the glass-ceramics samples with ZnO up to 5 mol%. In addition to these, calcium silicate (Ca₃Si₂O₇) phase is also observed when glass is heat treated at 1000 °C. The microstructure of the glass-ceramics heat treated at 800 °C exhibits the formation of nano-size (40-50 nm) grains. On heat treatment at 1000 °C crystallites grow to above 50 nm size and more than one phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface modifications and formation of Ca-P-rich layer on the glass-ceramics when immersed in simulated body fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content.     

Study of dielectric and ac impedance properties of Ti doped Mn ferrites

We have reported dielectric and ac impedance properties of Ti doped Mn_1+xFe_2−2xO₄ (0x0.5) ferrites prepared by solid-state reaction method, using dielectric and impedance spectroscopy in the frequency range of 42 Hz–5 MHz, between the temperatures (300K–473K). The dielectric constant and dielectric loss (tan δ) decreases with increasing frequency but these parameters increase with increasing temperature. The dielectric loss tangent curves exhibit dielectric relaxation peaks at high frequencies (3.6 kHz–5 MHz), which are attributed to the coincidence of the frequency of charge hopping between the localized charge states and the external field. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell–Wagner’s two-layer model and the hopping of charge between Fe²⁺ and Fe³⁺ as well as between Mn³⁺ and Mn²⁺ ions at B-sites. The complex impedance analysis has been used to separate grain and grain boundary in studied samples. Two semicircles corresponding to grain and grain boundary have been observed at low temperature, while only one semicircle has been seen at high temperatures. The resistance of grain and grain boundary both increase with Ti⁴⁺ doping.     

Cationic behavior and the related magnetic and magnetotransport properties of manganese ferrite thin films

Manganese ferrite (Mn_xFe_3−xO₄) thin films have been prepared by a sol–gel method. The samples (x≤1.25) are polycrystalline containing well-defined grains and maintain cubic spinel structure with increasing lattice constant with x. The substituting Mn ions were found to have multi-valence, +2 and +3, by X-ray photoelectron spectroscopy. The saturation magnetization of the Mn-substituted films measured by vibrating sample magnetometry was found to increase from that of Fe₃O₄ at low x and then gradually decreases as x increases further. Such magnetic behavior can be explained in terms of the dominance of Mn²⁺ species over Mn³⁺ at low x and the gradual decrease in the population ratio Mn²⁺/Mn³⁺ as x increases. The observed decrease in the coercivity with increasing x implies the increase in octahedral Mn²⁺ population. The Mn-substituted samples exhibit magnetoresistance (MR) effect the maximum intensity of which is gradually reduced with x from that of Fe₃O₄. All samples show increasing MR with increasing external field (H), while their magnetization curves start to saturate near H=2 kOe. Such increasing MR with H can be explained in terms of the tunneling of spin-polarized carriers across grain boundaries. The reduction in the MR intensity with x can be partly explained in terms of the decrease in spin-polarized carrier density associated with octahedral occupation of Mn²⁺ ions.     

Structural characteristics and morphology of SmxCe1−xO2−x/2 thin films

Effect of the deposition temperature (200 and 500 °C) and composition of Sm_xCe_1−xO_2−x/2 (x = 0, 10.9–15.9 mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar⁺ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce⁴⁺ oxidation state, suggesting the presence of CeO₂ phase, which was confirmed by X-ray diffraction (XRD). The Ce³⁺ oxidation states corresponding to Ce₂O₃ phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.     

Concentration-dependent luminescence of Tb ions in high calcium aluminosilicate glasses

This study deals with the results on the concentration-dependent fluorescence properties of Tb³⁺-doped calcium aluminosilicate (CAS) glasses of composition (100−x)(58SiO₂–23CaO–5Al₂O₃–4MgO–10NaF in mol%)-x Tb₂O₃ (x=0, 0.25, 0.5, 1, 2, 4, 8, 16, 24, 32, 40 in wt%). The FTIR reflectance spectra suggested the role of dopant ions as network modifiers in the glass network. The fluorescence spectra of low Tb³⁺-doped glasses have revealed prominent blue and green emissions from ⁵D₃ and ⁵D₄ excited levels to ⁷F_j ground state multiplet, respectively. The glass with 2 wt% of Tb₂O₃ has exhibited maximum intensity of blue emission from ⁵D₃ level, while green emission from ⁵D₄ level has increased linearly up to 24 wt% and showed reduction in the rate of increase for higher Tb₂O₃ concentrations. The concentration quenching of blue emission (⁵D₃→⁷F_j) is attributed mainly to the resonant energy transfer (RET) assisted cross-relaxation (CR) among the excited and nearest neighbour unexcited Tb³⁺ ions in the glass matrix. The decline in rate of increase of green emission (⁵D₄→⁷F_j) at higher concentrations has been explained due to a possible occurrence of cooperative energy transfers leading to 4f⁸→4f⁷5d transition interactions. The blue and green emission decay kinetics have been recorded to compute the excited level (⁵D₃ and ⁵D₄) lifetimes, which confirmed the Tb³⁺ concentration quenching of the blue emission in these glasses.     

Mossbauer, infrared and magnetic susceptibility studies of iron sodium borate glasses doped by sulphur

The affect of sulphur on the structural properties of iron sodium diborate glasses having the composition {(100−x)Na₂B₄O₇+xFe₂O₃}+yS, where x=0.05, 0.15 and 0.25 mol% and Y=0, 2.5 and 5 wt% was studied by infrared, Mossbauer spectroscopy and magnetic susceptibility measurements. It was found that, for samples having 5 mol% Fe₂O₃ and free from sulphur, the iron ions are present in both Fe²⁺ and Fe³⁺ states and also 92% of the total iron enters the glass network as a glass former. The ratio of Fe³⁺/Fe²⁺ increases with increasing the iron content for sulphur-free samples and others containing sulphur. This ratio also decreases with increasing the sulphur content. The magnetic susceptibility was found to decrease with increasing the sulphur content. Also, the increase of Fe₂O₃ content led to a less symmetrical environment of Fe³⁺ ions and vice versa for the Fe²⁺ environment.     

The relationship between magnetic behaviour and local structure around Fe ions in Fe-doped TiO2 rutile

The magnetic and structural characterization of Ti_1−xFe_xO₂ (x=0.025, 0.05, 0.07, 0.125, and 0.15) samples prepared by mechano-synthesis using TiO₂ and Fe₂O₃ as starting materials are reported. XANES measurements performed at the Fe K-edge show that Fe ions are in 3+ oxidation state in the 7 at% Fe-doped sample and in a mixture of 2+ and 3+ oxidation states in the other samples. EXAFS results show the incorporation of Fe ions substituting Ti ones in the rutile TiO₂ structure. They also reveal a strong correlation between the number of oxygen nearest neighbours and the Fe²⁺ fraction, i.e the number of oxygen near neighbours decreases when the Fe²⁺ fraction increases. All samples present ferromagnetic-like behaviour at room temperature. We found a clear dependence between saturation magnetization and coercivity with the fraction of Fe²⁺ and/or the number of Fe near neighbour oxygen vacancies.     

EPR investigations of calcium phosphate glasses containing manganese ions

Glasses of the xMnO·(100−x)[yP₂O₅·CaO] systems, with y=1, 2, 3 and 0≤x≤50 mol% MnO were prepared and investigated by means of electron paramagnetic resonance (EPR). The local order in diamagnetic vitreous matrices could be revealed by the Mn²⁺ paramagnetic ions used in EPR experiments. In each systems corresponding to a particular value of y, the effect of increasing the MnO content in the samples was investigated. The structure of our glasses shows an evolution depending of MnO content from structural units involving Mn²⁺ ions in well defined vicinities, to structural units containing clustered manganese ions. The changes of the linewidth and the intensity of the resonance line centered at g_eff≈2.0 when the content of manganese ions are increasing revealed this evolution.     

Structural and electrical properties of iron molybdenum phosphate glasses

Summary  Iron molybdenum phosphate glasses [xMoO₃ · (0.6 -x)P₂O₅ · 0.4Li₂O] :yFe₂O₃ with 0 ≤x ≤ 0.6 andy = 0.03 (mol%) prepared in ambient atmosphere using the melt quenching technique were studied by using DC electrical conductivity,⁵⁷Fe M?ssbauer and infrared spectroscopies. The DC conductivity depends on the MoO₃ concentrationx. It was observed that, with increasingx, the ratio Fe²⁺ /(Fe³⁺ + Fe²⁺) and the DC conductivity increase. Infrared spectroscopy and X-ray powder diffraction indicate that a Li₂ MoO₄ crystalline phase is present for high MoO₃ content samples (x = 0.5, 0.6). This work was partly sponsored by FINEP, CNPq (Brazilian agencies) and UECE (Universidade Estadual do Cearà).     

Exchange fields in Gd–Fe intermetallics studied by inelastic neutron scattering

Inelastic neutron scattering (INS) was used to study the magnetic excitations in the compounds Gd_1−xY_xFe₂ and Gd_2−xY_xFe₁₄B. Three inelastic magnetic lines were observed in the INS spectra of these compounds, the two smaller lines appearing as shoulders to the main line. From the concentration-dependent shift of the dominant magnetic line we have obtained experimental information of the strength of the Gd–Gd interaction in these materials and showed that the Gd–Gd contribution to the total molecular field experienced by the Gd moments is roughly an order of magnitude smaller than the contribution of the Gd–Fe interaction. Our results are compared with several earlier published results, including results of electronic band structure calculations.     

High permeability and low power loss of Ti and Zn substitution lithium ferrite in high frequency range

The effect of Zn and Ti on the magnetic, power loss and structural properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in step of 0.05)+0.5 wt% Bi₂O_3, prepared by standard ceramic technique, has been investigated. Complex permeability (μ*=μ′−jμ″) has been analyzed at room temperature in frequency range from 1 to 10³ MHz. It was found an enhancement in permeability with Ti and Zn concentration in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ and exhibits the maximum value 106 for x=0.20 sample. Complex permeability of these ferrites exhibits stable frequency response up to 7 MHz beyond which the real part decreases sharply and imaginary part increases to have a peak at the relaxation frequency. Power loss measurements have been carried out in induction condition (B=10 mT) in frequency range of 50 kHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti and Zn in lithium ferrite.     

Magnetic properties of xCoO.(1-x)[2B2O3.K2O] glasses

The results of magnetic investigations onxCoO.(1-x)[2B₂O₃.K₂O] glasses are reported. The magnetic properties of these glasses are dependent on the CoO content. For glasses withx > > 10 mol% CoO, the Co²⁺ ions are coupled antiferromagnetically.     

Magnetic properties of bioactive glass-ceramics containing nanocrystalline zinc ferrite

Glass-ceramics with finely dispersed zinc ferrite (ZnFe₂O₄) nanocrystallites were obtained by heat treatment of x(ZnO,Fe₂O₃)(65?x)SiO₂20(CaO,P₂O₅)15Na₂O (6≤x≤21 mole%) glasses. X-ray diffraction patterns of the glass-ceramic samples revealed the presence of calcium sodium phosphate [NaCaPO₄] and zinc ferrite [ZnFe₂O₄] as major crystalline phases. Zinc ferrite present in nanocrystalline form contributes to the magnetic properties of the glass-ceramic samples. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with applied magnetic field sweeps of ±20 kOe and ±500 Oe, in order to evaluate the potential of these glass-ceramics for hyperthermia treatment of cancer. The evolution of magnetic properties in these samples, viz., from a partially paramagnetic to fully ferrimagnetic nature has been explored using magnetometry and X-ray diffraction studies.     

Effect of Zn substitution on the magnetic properties of Mg1−xZnxFe2O4 ferrites

Polycrystalline Mg_1−xZn_xFe₂O₄ (x=0.0–0.6) ferrites have been prepared using solid-state reaction technique. The X-ray diffraction analysis revealed that the samples crystallize in a single-phase cubic spinel structure. The lattice parameter increases linearly with increase in zinc content obeying Vegard's law. The continuous decrease in Curie temperature (T_c) with an increase in Zn content is attributed to the weakening of A–B exchange interaction. Saturation magnetization (M_s) and magnetic moment are observed to increase up to x=0.4, and thereafter decrease due to the spin canting in B-sites. The initial permeability is found to increase with the addition of Zn²⁺ ions but the resonance frequency shifts towards the lower frequency.