Novel alkaline-free Er-doped fluorophosphate glasses for broadband optical fiber lasers and amplifiers

Two sets of Er³⁺-doped alkaline-free glass systems, MgF₂–BaF₂–Ba(PO₃)₂–Al(PO₃)₃ (MBBA) and Bi(PO₃)₃–Ba(PO₃)₂–BaF₂–MgF₂ (BBBM), have been prepared and investigated with the aim of using them as active media. Radiative lifetimes (τ_rad) and branching ratios (β) have been obtained for the excited states of Er³⁺. The absorption spectra were recorded to obtain the intensity parameters (Ω_t) which are found to be Ω₂ = 4.47 × 10⁻²⁰ cm², Ω₄ = 1.31 × 10⁻²⁰ cm², Ω₆ = 0.81 × 10⁻²⁰ cm² for the MBBA system and Ω₂ = 4.03 × 10⁻²⁰ cm², Ω₄ = 1.34 × 10⁻²⁰ cm², Ω₆ = 0.53 × 10⁻²⁰ for the BBBM system, respectively. The emission cross-section for the ⁴I_13/2 → ⁴I_15/2 transition is determined by the Fuchtbauer–Ladenburg method and found to be 2.35 × 10⁻²⁰ cm² and 3.54 × 10⁻²⁰ cm² for the MBBA and BBBM system, respectively. Comparison of the measured values to those of Er³⁺ transitions in other glass hosts suggests that our new glass systems are good candidates for broadband compact optical fiber and waveguide amplifier applications.     

Magnetic structure of the CeScSi-type RScGe compounds (R = Pr, Nd, Tb)

Subsequent magnetic transitions were recently reported for the CeScSi-type RScGe (R = rare earth) equiatomic intermetallic compounds. The compounds TbScGe and NdScGe order ferromagnetically at T_C = 216 K and T_C = 200 K, respectively whereas PrScGe orders antiferromagnetically at T_N = 140 K. In addition, PrScGe demonstrates two other magnetic transitions at T_C1 = 88 K and T_C2 = 80 K in an applied field of 5 kOe. An investigation by neutron diffraction has been now carried out on these phases in an attempt to solve the magnetic structures corresponding to each ordering, and in this article the results obtained are reported. Below the Curie point, the magnetic structure of TbScGe and NdScGe is collinear ferromagnetic. The magnetic moment of Tb atoms coincides with the Z-axis of CeScSi-type unit cell (M_Tb = 8.63μ_B at 2 K), whereas the magnetic moment of Nd atoms has the θ = 52(2)° angle with Z-axis (M_Nd = 3.53(2)μ_B at 2 K). Below the Néel temperature, T_N = 140 K the magnetic structure of PrScGe consists of antiferromagnetic (0 0 2) rare-earth double layers with magnetic moments of the rare earth atoms collinearly ordered. The magnetic moments of Pr atoms (M_Pr = 1.72(3)μ_B at 100 K) have the θ = 62(2)° angle with the Z-axis. Between T_C1 = 82 K and T_C2 = 62 K the conversion of the commensurate antiferromagnetic collinear type structure to the ferrimagnetic collinear type structure with propagation vector K = [0, 0, 1/2] was observed: the magnetic moments of Pr double layers became sine modulated along the Z-axis. Below T_C2 = 62 K the magnetic structure of PrScGe compound consists of ferrimagnetic (0 0 1/2) layers (amplitude of Pr magnetic moment M_Pr = 3.31(9)μ_B at 5 K).     

Structure and anelasticity of Fe3Ge alloy

The structure and anelastic properties of Fe-27 at.%Ge alloy are studied. Long-term annealing of the as-cast alloy at 1273 K leads to homogenising and several transformations take place below 873 K. These low temperature transitions are studied by several methods: X-ray diffraction, calorimetry, vibrating-sample magnetometry and internal friction, and are related to magnetic transitions in the different phases. A high stability of the hexagonal (D0₁₉) phase at room temperature is recorded. The hexagonal β (B8₁) phase is also detected in the alloy at room temperature, while the presence of the ′ and phases is doubtful. A broad internal friction relaxation peak with the relaxation strength of Δ = 0.0036, the activation energy of about 1.78 eV and the preexponential relaxation time of τ₀ = 2 × 10⁻¹⁷ s was discovered and classified as the Zener peak in both the and β phases.     

Synthesis and magnetic structure of the YbMn2Sb2 compound

A neutron diffraction investigation has been carried out on the trigonal La₂O₃-type (hP5, space group , No. 164; also CaAl₂Si₂-type) YbMn₂Sb₂ intermetallic. A two-step synthesis route has been tried in this work, and successfully utilised to prepare single phase samples of this compound. This study shows that YbMn₂Sb₂ presents antiferromagnetic ordering below 120 K. The magnetic structure of this intermetallic consists of antiferromagnetically coupled magnetic moments of the manganese atoms, in the Mn1 (1/3, 2/3, Z_Mn) and Mn2 (2/3, 1/3, 1 − Z_Mn) sites; the direction of magnetic moments of manganese atoms forming a φ and a θ angle, respectively with the X- and the Z-axis. At 4 K the magnetic moment of the Mn1 atom is μ_Mn = 3.6(1) μ_B, with φ = 0° and θ = 62(4)°, whilst the Mn2 atom has a magnetic moment μ_Mn = 3.6(1) μ_B, with φ = 0° and θ = 242(4)°. On the other hand, in this compound no local moment was detected on the Yb site.     

On the crystal structure of new series of compounds, RPt2+xSb2−y (x = 0.125, y = 0.25; R = La, Ce, Pr)

A new compound CePt_2+xSb_2−y (x = 0.125, y = 0.25) was synthesized by arc-melting of the elements. The chemical and structural characterizations were carried out at room temperature on as-cast samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. According to the results of X-ray single crystal diffraction this antimonide crystallizes in I4cm space group (no. 108), Z = 32, ρ = 12.19 Mg/m³, μ = 89.05 mm⁻¹ (a = 12.5386(3) Å, c = 21.4692(6) Å (crystal I) and a = 12.5455(2) Å, c = 21.4791(5) Å (crystal II)). The structure and composition were confirmed by powder X-ray diffraction (a = 12.4901(2) Å, c = 21.3620(4) Å) and EDS-microanalysis respectively. Isotypic compounds were observed with La and Pr from X-ray powder diffraction of as-cast alloys at room temperature (a = 12.6266(4) Å, c = 21.4589(6) Å for LaPt_2+xSb_2−y and a = 12.5184(5) Å, c = 21.4178(7) Å for PrPt_2+xSb_2−y). The CePt_2+xSb_2−y structure is derived from CaBe₂Ge₂ (a = 2a₀ − 2b₀, b = 2a₀ + 2b₀, c = 2c₀) and comprises a new atomic arrangement with both vacancy on 4(b) pyramidal site and substitution of antimony atoms (X) by platinum (B) in the B–XX–B layers (referring to the subcell structure) forming two B––1/2B1/2XX–3/4B and two X–BB–X layers per cell. The structure of CePt_2+xSb_2−y is compared with those reported before for URh_1.6As_1.9 and CeNi_1.91As_1.94.     

The brittle compressive failure of fresh-water columnar ice loaded biaxially

New experiments have been performed on the brittle compressive failure of columnar-grained, S2 fresh-water ice, proportionally loaded biaxially across the columns at −10 °C at 4.5 × 10⁻³ s⁻¹. The results and analysis show that under higher confinement (σ₂₂/σ₁₁ > 0.2) where terminal failure occurs via across-column cleavage and spalling out of the loading plane, a combination of wing crack growth and Euler buckling of deformation-induced thin plates underlies the process.     

Ce(Au,Sb)2 with UHg2 structure type, a new member of the AlB2 family

A new ternary compound Ce(Au,Sb)₂, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au_1−xSb_x)₂ (x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/mmm space group, V = 70.997(17) Å³, Z = 1, ρ = 10.732 Mg/m³, μ = 76.369 mm⁻¹, R₁ = 0.0415, wR₂ = 0.0793 for 99 reflections with I > 2σ(I₀). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe₆X₃X₂]. Ce atom is coordinated by 14 atoms: [CeX₁₂Ce₂]. The compound is isotypic with UHg₂ structure, a deformation derivative of AlB₂ structure type. It forms isostructural compounds with La and Pr.     

Electronic structure and thermoelectric power of CeNi4Si

The studies of the thermoelectric power and band structure calculations for CeNi₄Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi₄Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μ_eff = 0.52μ_B/f.u. and the paramagnetic Curie temperature θ_P = −2 K. This effective paramagnetic moment is lower than the free Ce³⁺ value. The obtained values for the f occupancy n_f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi₄Si is characterized by γ = 16 mJ mol⁻¹ K⁻² and θ_D = 335 K.     

Theoretical investigation of local lattice structure of the tetragonal FeF5O cluster in KMgF3:Fe crystal

The relationship between the electronic and molecular structure has been established based on the complete energy matrices for a 3d⁵ configuration ion in a tetragonal ligand-field. By diagonalizing the complete energy matrices, the zero-field splitting parameters and the local lattice structure of the tetragonal FeF₅O cluster in KMgF₃:Fe³⁺ crystal have been studied. The distortion of local lattice distortion structure parameters ΔR₁ = 0.10464 Å and ΔR₂ = 0.10094 Å are determined. Simultaneously, the local lattice structure parameters R₁ = 1.88936 Å and R₂ = 1.89306 Å, which reflect the interactions between impurity and crystal lattice, are determined from our calculation.     

Magnetic ordering in Th3P4-type Tb4Sb3 compound

The nature of the magnetic ordering of Tb₄Sb₃ compound (Th₃P₄-type, cubic; cI28, space group , No. 220, a = 0.91518(7) nm) has been investigated by using the techniques of magnetization and neutron diffraction. AC and DC magnetisation measurements indicate antiferromagnetic ordering at 108 K in zero magnetic field that is accompanied by a field-induced metamagnetic transition to a ferromagnetic state, in fields above 0.3 T. Neutron diffraction experiment in zero applied magnetic field shows that below T_N = 112(4) K Tb₄Sb₃ exhibits an antiferromagnetic flat spiral-type ordering with propagation vector K₁ = [±1/8, ±1/8, ±1/8]. The magnetic moment of Tb atoms is found to be M_Tb = 6.7(3) μ_B at 80 K. The magnetic moment of Tb atoms lie in the (1 1 1) plane of Tb₄Sb₃ unit cell (the cone axis arranges along [1 1 1] direction with cone angle β = 90°). Below T_N2  50 K, Tb₄Sb₃ shows second antiferromagnetic transition with K₂ = [1/2, 1/2, 1/2] with possible re-orientation of Tb magnetic moments.     

Structural investigation of the alluaudite-like mixed-valence iron phosphate: Na1.25Mg1.10Fe1.90(PO4)3

A new mixed-valence iron phosphate Na_1.25Mg_1.10Fe_1.90(PO₄)₃ has been synthesized as single crystals by a flux technique and its structure has been refined from X-ray data to a residual R₁ = 0.032. The compound crystallizes in the monoclinic space group C2/c with the parameters: a = 11.7831(3) Å, b = 12.4740(3) Å, c = 6.3761(2) Å, β = 113.643(2)° and Z = 4. The structure belongs to the alluaudite structural type, and thus it obeys to the X(2)X(1)M(1)M(2)₂(PO₄)₃ general formula. The X(2) and X(1) sites are occupied by sodium while the M(1) and M(2) sites feature a statistical distribution of iron and magnesium.

Additional information about the cation distribution has been extracted from a Mössbauer spectroscopy study which confirmed the mixed valency of the compound. A magnetic susceptibility study has also been undertaken and has shown the compound to be antiferromagnetic with a Neel temperature of about 35 K.     

Investigation of cation-deficient quaternary thiospinels: single crystal study of Ag1.4Cr1.47Sn2.53S8

Single crystals of the quaternary thiospinel Ag_1.41(1)Cr_1.47(5)Sn_2.52(5)S₈ have been obtained by heating stoichiometric mixtures of elemental metals and sulfur at 750 °C. Structural analysis by single crystal X-ray diffraction shows that the above phase crystallizes in the space group with a = 10.4142(3) Å (R₁ = 0.0156 and wR₂ = 0.0416). The Ag-deficiency has been confirmed by solving the structures of crystals prepared in different batches and was observed to vary slightly between crystals. Magnetic studies on a monophasic powder sample with a nominal composition of Ag_1.63CrSn₃S₈ indicates anti-ferromagnetic ordering at low temperature. The high temperature susceptibility leads to a magnetic moment of 3.45 B.M. suggesting that chromium exists predominantly in a trivalent state.     

Influence of A-site cation size-disorder on structural, magnetic and magnetocaloric properties of La0.7Ca0.3−xKxMnO3 compounds

The structural and magnetic properties of perovskite oxides La_0.7Ca_0.3−xK_xMnO₃ (0 ≤ x ≤ 0.15) have been investigated to explore the influence of the A-site cation size-disorder (σ²). The materials were prepared by the solid-state method and then characterized by X-ray diffraction (XRD). The XRD data have been analyzed by Rietveld refinement technique. For K doping concentration x ≤ 0.075, the samples crystallize in the orthorhombic structure, while for x ≥ 0.1, the structure becomes rhombohedral. The variation of the magnetization M as a function of the applied magnetic field μ₀H reveals the presence of a structural distortion leading to a reduction of the magnetization at low μ₀H values. When increasing μ₀H, the structural distortion decreases and for a high applied magnetic field, the M (μ₀H) curves saturate indicating the disappearance of the structural distortion. The influence of K doping concentration and the applied magnetic field on the magnetocaloric properties has been considered. A large magnetic-entropy change (|ΔS_M|  5 J/kg K) is obtained in all samples at Curie temperatures between 270 and 280 K for an applied magnetic field of 3 T. These results show that these materials can be used as candidates for magnetic refrigerants near room temperature.     

Magnetic structures of Zr6CoAs2-type Ho6−xErxMnBi2 solid solutions

Investigations were made by neutron diffraction on Zr₆CoAs₂-type (space group no. 189) Ho_6−xEr_xMnBi₂ solid solutions. The ferromagnetic ordering temperature decreases from Ho₆MnBi₂ (T_C = 200(6) K) to Er₆MnBi₂ (T_C = 100(4) K), whereas temperatures of ferrimagnetic (or antiferrimagnetic) ordering (T_Ferri and T_AFerri) are found to have non-monotonic dependences on the content of Er: T_Ferri = 58(4) K for Ho₆MnBi₂, T_Ferri = 162(4) K for Ho_4.5Er_1.5MnBi₂, T_Ferri = 150(4) K for Ho₃Er₃MnBi₂, T_AFerri = 78(4) K for Ho_1.5Er_4.5MnBi₂ and T_AFerri = 52(4) K for Er₆MnBi₂.

In these compounds, no local moment was detected on the manganese ion site, except for Ho_1.5Er_4.5MnBi₂ and Er₆MnBi₂ compounds. The manganese magnetic moments (μ_Mn) is 1.5μ_B and these are antiferromagnetically coupled with that of rare earth moments.     

The effect of Hf substitution for Zr on glass forming ability and magnetic property of FeCoZrMoBAlY bulk metallic glasses

Bulk metallic glasses (BMGs) Fe₆₁Co₆Zr_8−xHf_xMo₇B₁₅Al₁Y₂ (x = 0–8) have been produced by copper mold casting technique using industrial raw materials. The effect of substitution of Hf for Zr on the glass forming ability (GFA) and the magnetic property has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). It was found that the substitution of an appropriate amount of Hf for Zr can improve the GFA of the base alloy Fe₆₁Co₆Zr₈Mo₇B₁₅Al₁Y₂, as demonstrated by the increase in reduced glass transition temperature T_rg (=T_g/T_l) and GFA parameters of γ (=T_x/T_g + T_l) and δ (=T_x/T_l − T_g). The Fe₆₁Co₆Zr₅Hf₃Mo₇B₁₅Al₁Y₂ alloy exhibits the highest GFA with the largest T_rg (0.612) and δ (1.633), and can cast a fully amorphous rod in 3 mm diameter. The substitution of Hf for Zr also enhances the magnetic properties, as verified by the increase in saturation magnetization (M_s) in the alloy of Fe₆₁Co₆Zr₃Hf₅Mo₇B₁₅Al₁Y₂, whose M_s is approximately 1.5 times higher than that of the base alloy (x = 0) at room temperature. Finally, the effect of the substitution of Hf for Zr on glass forming ability and magnetic properties is discussed.     

Magnetocaloric effect in Pr6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Pr₆Co_1.67Si₃ compound have been investigated by magnetization measurements. The saturation moment at 5 K is found to be 10.7μ_B. The compound undergoes two magnetic transitions below Curie temperature T_C = 48 K and shows a reversible second-order magnetic transition around T_C. A magnetic entropy change ΔS = 6.9 J/(kg K) is observed for a magnetic field change from 0 to 5 T. The full width at half maximum of the ΔS peak is found to be about 38 K.     

The Minor Precipitation at the Final Stage of U720Li Solidification

The minor precipitations caused by B and Zr which are the normal constituents of U720 Li alloy have been studied by analyzing the solidification process and the composition evolution. The present study aims to supply the elementary information about the existing form of B and Zr in the as-cast microstructure, which is helpful for the subsequent processing, such as homogenization treatment. The M_3B_2 and Ni_5Zr phases were observed in the U720 Li alloy in as-cast state, which were usually accompanying with each other together with g-Ni_3 Ti phase at the edge of eutectic(γ+γ'). Combining the DTA analysis and heating and quenching tests, the solidification sequence was determined to be the following: c matrix, eutectic(γ+γ'), g-Ni_3Ti, M_3B_2 and Ni_5Zr. The in situ composition analysis by EDS and EPMA revealed that the precipitation and microstructure were governed by the composition evolution in the liquids. The solidification of c matrix increased the Ti concentration in the residual liquids and resulted in the eutectic(γ+γ') formation; the(γ+γ') formation increased the Ti/Al radio in the liquids and the g-Ni_3Ti was formed in front of the eutectic(γ+γ'); the g-Ni_3Ti precipitation consumed up Al and Ti and increased the concentration of B, Mo and Cr, and M_3B_2 boride is formed;the previous precipitation of the phases consumed up most of the elements other than Ni and Zr, and Ni_5Zr is formed finally. The melting points are in the ranges of 1130–1140 °C for Ni_5Zr phase, 1180–1190 °C for M_3B_2 boride and1190–1200 °C for g-Ni_3Ti phase.     

FEM numerical simulation of tube axial drawing process

Tube inversion by the axial drawing is an advanced forming process for manufacturing double-walled tubes with high quality, high efficiency, and low consumption. However, to realize forming process depends on producing the tearing in deforming zone, which has a close relationship with forming load. So in this paper, the influence of forming condition parameters on the deforming force and the process is investigated by rigid-plastic FEM numerical simulation. The results show that: (1) during the whole forming process, the shape of the tube remains unchanged when the radius of the core die is larger than a certain value, so a precision forming can be easily realized; (2) for a given r/d₀ or t₀/d₀, the deforming force depends mainly on the value of r/t₀, and there is a critical parameter k, when r/t₀ < k, the steady forming force decreases with an increase of r/t₀; on the contrary, when r/t₀ > k, the steady forming force increases with an increase of r/t₀; (3) the material hardening exponent n of the tube and the friction coefficient μ have a remarkable influence on the deforming force. The smaller the value of n and the larger the value of μ the larger the forming force.     

Elastic–plastic transition during nanoindentation in bulk GaN crystal

Mechanical properties of a defect-free bulk GaN single crystal has been studied by nanoindentation in the C (0001) surface. Our experiments provide consistent evaluations of Young's modulus (E = 320 GPa) measured with both Berkovich and spherical indenters. Additionally, Berkovich hardness (H = 17 GPa) and true hardness (H_t = 25 GPa) were determined. Pop-in events are confirmed to indicate the elastic–plastic transition of the material, and give also consistent yield (maximum) shear stress, τ_max = 19 GPa, for both the indenters. To achieve these precise analyses, the effective curvature of the indenter was determined by the Hertz analysis of the contact between the indenter and a diamond crystal, in addition to the Oliver–Pharr method with a standard fused quartz.