Subsolidus phase relations of the SrO–MO2–CuO systems (M = Ti, Zr and Hf) at 900 °C in air

The subsolidus phase relations of the SrO–MO₂–CuO (M = Ti, Zr and Hf) systems were investigated in air. The samples were equilibrated at 900 °C. The SrTi₄Cu₃O₁₂ compound is the only ternary oxide phase stable under these conditions in the investigated systems. This phase is non-stoichiometric, its actual composition being Sr_0.95Ti_4.05Cu_2.95O_x. The SrO–ZrO₂–CuO and SrO–HfO₂–CuO systems have a similar structure. No Zr or Hf equivalents of the SrTi₄Cu₃O₁₂ phase were formed under the present conditions.     

Thermal and conductometric studies of the CeBr3–MBr binary systems (M = Li, Na)

DSC was used to investigate phase equilibrium in the CeBr₃–MBr (M = Li, Na) systems. They represent typical examples of simple eutectic systems. The eutectic composition and eutectic temperature, x(CeBr₃) = 0.249, T_eut = 709 K and x(CeBr₃) = 0.372, T_eut = 692 K, were found for CeBr₃–LiBr and CeBr₃–NaBr systems, respectively.

The electrical conductivity of CeBr₃–MBr liquid mixtures, together with that of pure components was measured down to temperatures below solidification. Results obtained are discussed in term of possible complex formation.     

Syntheses and single-crystal structures of La3AgSnS7, Ln3MxMS7 (Ln = La, Ho, Er; M = Ge, Sn; 1/4 ≤ x ≤ 1/2)

In our investigation of non-centrosymmetric rare earth sulfides in the La₃AgSnS₇/KBr, LaAlGeS₅/NaBr, HoAlGeS₅/KBr, ErAlGeS₅/NaBr, Er₃AgGeS₇/KBr and La₃NaSnS₇/NaBr systems, five compounds belonging to the R₆B₂C₂Q₁₄ family have been obtained. These compounds crystallize in the P6₃ space group, and the crystal data are as follows—La₃AgSnS₇: a = 10.3780(15) Å, c = 5.9900(12) Å, Z = 2; La₃Ge_0.25GeS₇: a = 10.2970(15) Å, c = 5.8120(12) Å, Z = 2; Ho₃Ge_0.272(10)GeS₇: a = 9.6480(14) Å, c = 5.7920(12) Å, Z = 2; Er₃Ge_0.330(10)GeS₇: a = 9.5930(14) Å, c = 5.8490(12) Å, Z = 2; La₃Sn_0.25SnS₇: a = 10.2770(15) Å, c = 6.0030(12) Å, Z = 2. Single-crystal analysis indicated that the crystal structures consist of three types of building block: LnS_n, MS₄, and AgS₃ (for La₃AgSnS₇) or MS₆ units (for Ln₃M_xMS₇, Ln = La, Ho, Er; M = Ge, Sn; 1/4 ≤ x ≤ 1/2), as any other compounds belonging to the R₆B₂C₂Q₁₄ family. Ln₃M_xMS₇ (Ln = La, Ho, Er; M = Ge, Sn; 1/4 ≤ x ≤ 1/2) are deficient compounds with the B sites occupied partly by M(II), and/or M(IV).     

Optical spectroscopy of europium nitrate with 2,2′-bipyridine Eu(NO3)3·Bpy3. One more of compounds with outer-sphere Bpy molecule?

The complex compound Eu(NO₃)₃·Bpy₃ (Bpy, 2,2′-bipyridine) was synthesised and analysed by methods of optical spectroscopy. The spectra and details of the structure were discussed and compared with ones of well-known compounds Eu(NO₃)₃·Bpy₂ and Eu(NO₃)₃·Phen₂ (Phen, 1,10-phenanthroline). The water admixed to the ethanol as solvent promotes Bpy building into the outer sphere of complex [Eu(NO₃)₃·Bpy₂]·Bpy. Both kinds of Bpy molecules in Eu(NO₃)₃·Bpy₃ compound are nearer to coplanar, than Bpy in Eu(NO₃)₃·Bpy₂. The bonds Eu–N are stronger and the bonds Eu–O are weaker in Eu(NO₃)₃·Bpy₃ in comparison with the ones in Eu(NO₃)₃·Bpy₂. The outer-sphere Bpy molecule, effecting as a “steric” factor, changes the nearest surroundings of Eu³⁺ ion in [Eu(NO₃)₃·Bpy₂]·Bpy, making it similar to one of Eu(NO₃)₃·Phen₂.     

A general hydrothermal route to synthesis of nanocrystalline lanthanide stannates: Ln2Sn2O7 (Ln = Y, La–Yb)

A general hydrothermal process with use of lanthanide (III) nitrates and Na₂SnO₃ as precursors has been proposed for synthesizing nanocrystalline lanthanide stannates with general formula: Ln₂Sn₂O₇ (Ln = Y, La–Yb). Stannates of all lanthanides except for the radioactive promethium were successfully synthesized. Characterization by XRD and TEM revealed that all the products were phase-pure nanocrystalline lanthanide stannates with pyrochlore-type structure. Photoluminescent properties of three samples (i.e. Tb₂Sn₂O₇, Dy₂Sn₂O₇ and Yb₂Sn₂O₇) are also presented. The mole ratio of Ln(NO₃)₃:Na₂SnO₃ and hydrothermal temperature were two key factors for this general hydrothermal route.     

Preparation and electrochemical properties of MgNi–MB (M = Co, Ti) composite alloys

Alloys MgNi–MB (M = Co, Ti) were successfully synthesized by means of mechanical alloying (MA). The XRD spectroscopy suggested that the alloys were amorphous. The discharge capacity and cycle life of these alloys were tested, showing that as borides were introduced, the cycling life of the alloys became much better than MgNi alloy. For instance, 10 h composite MgNi–CoB and MgNi–TiB retained 53.2% and 54.1% of the initial capacity after 30 cycles, while the MgNi alloy kept only 23.3%. The exchange impedance spectroscopy and the potentiodynamic polarization curves proved that the electrochemical properties of the composite alloys were improved significantly. MgNi–CoB was used as an example to study the mechanism of electrochemical hydrogen storage.     

The reduction of Eu to Eu in air and luminescence properties of Eu activated ZnO–B2O3–P2O5 glasses

A valence change from Eu³⁺ to Eu²⁺ was observed in the europium ion-doped ZnO–B₂O₃–P₂O₅ glasses prepared at high temperature in air. The fluorescence emission spectrum of the sample consists of a broad emission band ascribed to the 5d–4f transition of Eu²⁺ ion and sharp emission peaks assigned to the transitions of ⁵D_o–⁷F_J (J = 0, 1, 2, 3, and 4) of Eu³⁺ ion, indicating that part of Eu³⁺ can be reduced into Eu²⁺ in the glass. A charge compensation model is proposed. The rigid tetrahedral network structure of glasses plays an important role in stability of Eu²⁺. The fabrication conditions are also studied.     

Spectroscopic properties of Eu(III) complexes with 2,6-lutidine N-oxide and its bromo-methoxy derivative; of Eu(LNO)6, Eu(LNO)5L, EuCl3(BrMLNO)3 and Eu(LNO)8 type

Luminescence, luminescence excitation and electronic absorption spectra of europium salts of isomeric lutidine N-oxide derivatives were studied at 293 and 77 K. The role of radiative and non-radiative processes in emission intensity is discussed. The absorption transitions to the ³F_J, ⁵D_J, ⁵L_J and ⁵G_J levels and emissions from the ⁵D₀ and ⁵D₂ levels were detected. The role of CT transition inside the ligand and its influence on the LMCT transition is analysed. The co-ordinating function of the lutidine N-oxide group is discussed using IR spectroscopy.     

Induced crystallization and physical properties of Li2O–CaF2–P2O5:TiO2 glass system: Part I. Characterization, spectroscopic and elastic properties

Li₂O–CaF₂–P₂O₅ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 0.8 mol%) were crystallized at 500 °C. The samples are characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. Spectroscopic properties (IR and Raman) and elastic properties (viz., Young's modulus E, shear modulus G and micro-hardness H) at room temperature are studied. The X-ray diffraction and the scanning electron microscopic studies revealed the presence of lithium phosphate, lithium titanium phosphate and titanium phosphate crystal phases. The differential thermal analysis traces of these samples exhibit three crystalline temperatures. The IR and Raman spectra of these samples have exhibited bands due to TiO₄ and TiO₆ structural units in addition to the conventional bands due to various phosphate structural groups. The analysis of these results indicated that the sample crystallized with 0.6 mol% of TiO₂ possesses the highest density, high mechanical strength and more compact network.     

Investigation of structural and electrical properties of (1 − x) Bi0.5Mg0.5TiO3–(x) PbTiO3 ceramic system

A 3 V cathode material for lithium ion batteries, Li_0.33MnO₂, was synthesized by solid-state reaction. Two Mn crystallographic positions, Mn₍₁₎ and Mn₍₂₎, were determined by X-ray diffraction analysis. The [Mn₍₂₎O₆] octahedron had a lower symmetrical degree than that of [Mn₍₁₎O₆], which was attributed to the geometrical effects of the non-symmetrical environment around Mn₍₂₎. Li_0.33MnO₂ delivered a reversible discharge capacity 140 mA h g⁻¹. In situ synchrotron diffraction clearly showed a reversible phase transition of Li_0.33MnO₂ during electrochemical process. The analysis of X-ray absorption near edge spectroscopy observed the conversion of Mn⁴⁺ to Mn³⁺ with Li⁺ intercalation into Li_0.33MnO₂, accompanied by the formation of more severely distorted [MnO₆] octahedron.     

Fluorescence and Judd–Ofelt analysis of Nd doped P2O5–Na2O–K2O glass

Sodium potassium phosphate glass consisting different Nd₂O₃ concentrations have been prepared to study the effect of Nd³⁺ concentration on optical absorption and fluorescence properties. From the absorption spectra, Racah (E¹, E², E³), spin-orbit (ξ_4f) and configuration interaction (α) parameters are calculated and reported for all the Nd³⁺ doped glasses. Judd–Ofelt intensity parameters (Ω₂, Ω₄, Ω₆) are evaluated and these parameters are used to study the covalency as a function of Nd³⁺ concentration. Results show that covalency decreases with the increase of Nd³⁺ concentration. By using these three intensity parameters, total radiative transition probabilities (A_T), radiative lifetimes (τ_R), branching ratios (β) and integrated absorption cross-sections (Σ) have been computed for certain excited states of Nd³⁺ in these mixed alkali phosphate glasses for all the concentrations. From the fluorescence spectra, peak stimulated emission cross-sections (σ_p) have been calculated for the two transitions, ⁴G_7/2 → ⁴I_13/2 and ⁴G_7/2 → ⁴I_11/2 of Nd³⁺ in all these glass matrices. From the absorption spectra, the optical band gaps (E_opt) for both direct and indirect transitions have been obtained. All these spectroscopic parameters are compared for different Nd³⁺ concentrations. From these studies, a few transitions are identified for laser excitation among various transitions.     

Spectroscopic studies of KGd(WO4)2:Ho single crystals

Single crystals of KGd(WO₄)₂ doped with Ho³⁺ ions were grown by the top seeded solution growth method. Polarized room temperature absorption spectra were analyzed by means of the conventional Judd-Ofelt theory taking into account strong dependence of the host refractive index on the wavelength. In addition to the intensity parameters Ω₂, Ω₄, Ω₆, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. The transitions predicted by the phenomenological model as potential transitions for laser applications are discussed. Emission spectra in the green, red, and near-infrared spectral regions were recorded for different excitation wavelengths. Comparison with spectroscopic properties of Ho³⁺ ion in other crystals is discussed.     

Structural, optical and electromagnetic properties of Bi1−xHoxFeO3 multiferroic materials

Bi_1−xHo_xFeO₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) polycrystalline ceramics were synthesized by a solid-state reaction and their structural, absorption, Raman scattering, impedance and magnetic properties were investigated. The substitution of rare earth Ho for Bi was found to decrease the impurity phase in BiFeO₃ ceramics. There appears an anomalous change in the lattice constants, optical band gap as well as the impedance spectroscopy and magnetization of samples at x = 0.10, suggesting a limit of dissolubility of Ho doped ions in BiFeO₃. Additionally, the Raman measurement performed for the lattice dynamics study of Bi_1−xHo_xFeO₃ samples reveals a band centered at around 1000-1300 cm⁻¹ which is associated with the resonant enhancement of two-phonon Raman scattering in the multiferroic Bi_1−xHo_xFeO₃ samples. Ho-doped BiFeO₃ also showed a ferromagnetic-like behavior with M_r = 1070 × 10⁻⁴ and M_s = 1.60 emu/g for optimum content x = 0.10, which is similar to the solid solution system of BiFeO₃.     

The magnetocaloric effect of Gd-Tb-Dy-Al-M (M = Fe,Co and Ni) high-entropy bulk metallic glasses

In this article, we report the formation of the high-entropy Gd₂₀Tb₂₀Dy₂₀Al₂₀M₂₀ (M = Fe, Co and Ni) bulk metallic glasses with good magnetocaloric properties. Compared with most of the rare earth based metallic glasses, these alloys are found to have the comparably large maximum magnetic entropy changes (ΔS_M), but much broader widths of the ΔS_M peaks, and hence larger refrigerant capacity (RC). This can be attributed to the combination of the spin glass behaviors and the complicated compositions in these alloys. Our work show that the high entropy bulk metallic glasses is a promising candidate material as the magnetic refrigerant.     

Microstructural, Raman and dielectric properties of (1−x)NaNbO3–xBiCrO3 biphase ceramics

The phase, microstructural and dielectric properties of (1−x)NaNbO₃–xBiCrO₃ (x = 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics with perovskite–pyrochlore mixed-phase were investigated. A single-phase solid solution in the sintered specimens was identified as observed perovskite phase for x = 0.1 and pyrochlore for x = 0.5. The results indicate that the microstructure has mixed large and small grains. Dielectric constants and dielectric loss were measured as functions of temperatures (−15 to 200 °C) at 1 kHz. Complex impedance spectroscopy shows the presence of barrier layers in biphase ceramics. The Raman spectra and porosity percentage in the biphase system were also measured.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

Crystallization properties of RE-doped (RE = Eu, Er, Tm) Zn2TiO4 prepared by the sol-gel method

Samples of pure and rare earth (RE)-doped nanocrystalline Zn₂TiO₄ (RE = Eu, Er, Tm) have successfully been prepared by the single batch sol-gel method in a form of powders. The powders were annealed up to 1200 °C and analyzed by DTA and XRD methods. Sizes of formed nanocrystals were calculated from the Scherer equation and verified by the SEM analysis. Activation energies of crystallization were calculated using the Kissinger, Ozawa and Augis-Bennett approximations and reaction mechanisms were proposed evaluating the Avrami exponents from the Johnson-Mehl-Avrami equation. It has been found that RE elements particularly substitute zinc ions in the crystal lattice and are fully soluble up to 0.5 at.% related to the some of cations. Furthermore, the results have shown that the presence of RE elements blocks the crystallite growth and supports the nucleation process leading to the formation of smaller and more uniform nanocrystals compared to the undoped Zn₂TiO₄.     

Spectroscopic and 1.06 μm laser properties of Nd-doped K–Sr–Al phosphate and fluorophosphate glasses

Optical absorption, fluorescence and decay curves for the ⁴F_3/2 level of Nd³⁺ ions in phosphate (P₂O₅–K₂O–SrO–Al₂O₃) and fluorophosphate (P₂O₅–K₂O–SrO–Al₂O₃–AlF₃ and P₂O₅–K₂O–SrO–Al₂O₃–BaF₂) glasses doped with three concentrations (0.1, 1.0 and 2.0 mol%) of Nd³⁺ ions have been investigated. The Judd–Ofelt (JO) theory has been applied to the absorption spectra of 1.0 mol% Nd³⁺-doped glasses to derive JO intensity parameters which are in turn used to calculate the radiative properties of the Nd³⁺ ion fluorescent levels. The assigned energy level data of Nd³⁺ (4f³) ions are analysed in terms of a parametrized free-ion Hamiltonian model that consists of 20 interaction parameters of atomic nature. The stimulated emission cross section and branching ratios have been calculated using the emission spectra. The relatively higher branching ratio for ⁴F_3/2 → ⁴I_11/2 transition shows the suitability of these glasses for laser application. It is interesting to note that the measured decay curves of the ⁴F_3/2 level remain nearly single exponential even for higher Nd³⁺ ion concentration but with shortening of lifetime.