Site occupancy and mechanisms of thermally stimulated luminescence in Ca9Ln(PO4)7 (Ln = lanthanide)

The structural properties, X-ray-excited radioluminescence and thermally stimulated luminescence (TSL) of Ca₉Ln(PO₄)₇ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were investigated. (La–Nd) occupied mainly the largest M3 site, whereas the smallest lanthanides (Yb, Lu) adopted the smallest octahedral M5 site. The intermediate-sized ions (Sm–Tm) occupied the medium-sized sites M1 and M2. Only the Ln³⁺ ions with the highest Ln^3+/4+ ionization energy (Ln = Pr, Nd, Tb, Dy) were able to trap holes and become luminescent centers for thermally stimulated Ln³⁺ 4f–4f emission. For low Ln^3+/4+ ionization potential (Ln = La, Gd, Yb, Lu), no hole trapping at Ln³⁺ was possible and Mn²⁺ impurities at the M5 sites were the effective hole traps and luminescent centers for thermally stimulated Mn²⁺ 3d–3d red emission. Very broad TSL peaks were attributed to thermally assisted detrapping of electrons from positive traps, possibly Ln³⁺ at Ca²⁺ sites, tunneling back towards the hole trap/luminescent center. Ca₉Ln(PO₄)₇ compounds doped with Ln = Tb or Lu were found to be efficient X-ray-excited long-lasting phosphorescence materials, emitting in the green and in the red, respectively.     

Core–shell nanoscale precipitates in Al–0.06 at.% Sc microalloyed with Tb,Ho, Tm or Lu

The age-hardening response at 300 °C of Al–0.06Sc–0.02RE (at.%, with RE = Tb, Ho, Tm or Lu) is found to be similar to that of binary Al–0.08Sc (at.%), except that a shorter incubation period for hardening is observed, which is associated with nanoscale RE-rich Al₃(RE_1?xSc_x) precipitates. In addition, Al–0.06Sc–0.02Tb (at.%) has a much lower peak microhardness than that of Al–0.08Sc (at.%) due to the small solubility of Tb in α-Al(Sc). Peak-age hardening occurs after 24 h, and is associated with a high number density of nanoscale Sc-rich Al₃(Sc_1?xRE_x) precipitates. Analysis by three-dimensional local-electrode atom-probe tomography shows that x increases with increasing atomic number, and that the REs partition to the core of the precipitates.     

Effect of nonstoichiometry of NbCy and TaCy powders on their high-energy ball milling

Nanocrystalline powders of nonstoichiometric carbides NbC_y and TaC_y are experimentally obtained by high-energy milling of coarse-grained powders. For the first time, the effect of nonstoichiometry of NbC_y and TaC_y carbides on the particle size of produced nanopowders is studied. It is shown that the effect of nonstoichiometry on milling is manifested by the concentration dependences of the main characteristics (crystal structure parameters, energy of interatomic bonds, elastic properties) of milled nonstoichiometric compound. The experimental results on NbC_y (0.77 ≤ y ≤ 0.96) and TaC_y (0.81 ≤ y ≤ 0.96) milling are compared with the theoretical model dependences of the particle size D of nanopowders on the duration of milling t and the composition y of nonstoichiometric cubic carbides NbC_y and TaC_y. It is established that the carbide powders with the average nanoparticle size of 20–30 nm and specific surface area of 25–30 m² g^− 1 are produced by 15 h milling, all other factors being equal.     

Erbium and ytterbium solubilities and diffusivities in aluminum as determined by nanoscale characterization of precipitates

Binary aluminum alloys with 0.03–0.06 at.% RE (RE = Yb or Er) were aged to produce coherent, nanosize Al₃RE precipitates in an α-Al matrix. The temporal evolution of precipitate radii and matrix concentrations at 300 °C were measured by transmission electron microscopy and local-electrode atom-probe tomography, respectively. The temporal dependence of the matrix concentration of each RE was utilized to determine its solubility in Al. The solubility and the coarsening rate constants were used to determine the diffusivity of each RE in α-Al and the α-Al/Al₃RE interfacial free energies at 300 °C. When compared to Sc, both Yb and Er exhibited smaller solubilities but larger diffusivities in α-Al and larger α-Al/Al₃RE interfacial energies.     

Precipitation evolution in Al–0.1Sc,Al–0.1Zr and Al–0.1Sc–0.1Zr (at.%) alloys during isochronal aging

Precipitation strengthening is investigated in binary Al–0.1Sc, Al–0.1Zr and ternary Al–0.1Sc–0.1Zr (at.%) alloys aged isochronally between 200 and 600 °C. Precipitation of Al₃Sc (L1₂) commences between 200 and 250 °C in Al–0.1Sc, reaching a 670 MPa peak microhardness at 325 °C. For Al–0.1Zr, precipitation of Al₃Zr (L1₂) initiates between 350 and 375 °C, resulting in a 420 MPa peak microhardness at 425–450 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, Zr additions provide a secondary strength increase from the precipitation of Zr-enriched outer shells onto the Al₃Sc precipitates, leading to a peak microhardness of 780 MPa at 400 °C for Al–0.1Sc–0.1Zr. Compositions, radii, volume fractions and number densities of the Al₃(Sc_1?xZr_x) precipitates are measured directly using atom-probe tomography. This information is used to quantify the observed strengthening increments, attributed to dislocation shearing of the Al₃(Sc_1?xZr_x) precipitates.     

High strength nanocrystalline L12-Al3(Ti,Zr) intermetallic synthesized by mechanical alloying

Nanocrystalline L1₂-Al₃(Ti,Zr) intermetallic has been synthesized directly by mechanical alloying of elemental blends of the nominal composition Al₇₅(Ti_25−xZr_x) for x = 0, 5, 10, 15, 20 and 25. The long range order parameter is found to increase with the Zr content. The lattice parameter difference between the L1₂-Al₃(Ti,Zr) and Al was minimum for the alloy with 10% Zr. A very high hardness of 3.23 GPa was achieved for the L1₂ phase in the Al₇₅Ti₁₅Zr₁₀ composition in the green compact condition with a relative density of 77.6%.     

Role of silicon in accelerating the nucleation of Al3(Sc,Zr) precipitates in dilute Al–Sc–Zr alloys

The effects of adding 0.02 or 0.06 at.% Si to Al–0.06Sc–0.06Zr (at.%) are studied to determine the impact of Si on accelerating Al₃(Sc,Zr) precipitation kinetics in dilute Al–Sc-based alloys. Precipitation in the 0.06 at.% Si alloy, measured by microhardness and atom-probe tomography (APT), is accelerated for aging times <4 h at 275 and 300 °C, compared with the 0.02 at.% Si alloy. Experimental partial radial distribution functions of the α-Al matrix of the high-Si alloy reveal considerable Si–Sc clustering, which is attributed to attractive Si–Sc binding energies at the first and second nearest-neighbor distances, as confirmed by first-principles calculations. Calculations also indicate that Si–Sc binding decreases both the vacancy formation energy near Sc and the Sc migration energy in Al. APT further demonstrates that Si partitions preferentially to the Sc-enriched core rather than the Zr-enriched shell in the core/shell Al₃(Sc,Zr) (L1₂) precipitates in the high-Si alloy subjected to double aging (8 h/300 °C for Sc precipitation and 32 days/400 °C for Zr precipitation). Calculations of the driving force for Si partitioning confirm that: (i) Si partitions preferentially to the Al₃(Sc,Zr) (L1₂) precipitates, occupying the Al sublattice site; (ii) Si increases the driving force for the precipitation of Al₃Sc; and (iii) Si partitions preferentially to Al₃Sc (L1₂) rather than Al₃Zr (L1₂).     

Nanoscaled grain boundaries and pores,microstructure and mechanical properties of translucent Yb:[LuxY(1−x)O3] ceramics

Translucent ceramics of Yb:[Lu_xY_(1?x)O₃] system doped by ZrO₂ was sintered from nanopowder synthesized by laser evaporation. The relative density of the ceramics was 99.97%, residual pores had sizes from 8 nm to 20 nm, Young modulus was 200 GPa at the applied load of 2000 mN, the microhardness was 12.8 GPa. The grains of ceramics had sizes 1–10 μm, but the thickness of grain boundaries was about 1 nm. The transcrystalline type of the crack propagation was detected in the specially broken ceramics. The results indicated high strength of grain bonds and good perfection of grain boundaries in the studied ceramics but an increased content of pores (higher than 10^?3 vol.%) and stoichiometry deviation (Lu:Y:O = 0.21:0.79:3) from the required one (Lu:Y:O = 0.25:0.75:3).     

The new series of RZnGe compounds (R = rare earth element) with the YPtAs structure type

The synthesis and crystal structure of the new family of rare earth ternary equiatomic RZnGe phases are reported. The compounds are found to form for R = La to Nd, Sm, Gd to Tm, Y, all crystallizing with the hexagonal hP12-P6₃/mmc YPtAs structure type, a four-layers superstructure derivative of the AlB₂ type. No formation of the equiatomic phase has been observed for R = Lu and Sc. The unit cell parameters, as obtained by the Guinier method on polycrystalline samples, vary regularly from the La [a = 4.333(1), c = 17.017(2) Å] to the Tm homologous [a = 4.192(1), c = 15.314(2) Å]. The crystal structure has been refined for the Ce, Gd and Y compounds by single crystal data.     

A series of water soluble RE(III) complexes: Synthesis,characterization, photophysical property and sensing activity towards Cr(III)

In this paper, four water soluble rare-earth(III) fluorescent chemosensors, Na₃RE(PDA)₃ (PDA = pyridine-2,6-dicarboxylic acid, and RE = Sm, Eu, Tb, Dy), are synthesized and characterized. Their excitation and emission spectra, fluorescence responses towards Cr(III), quenching mechanism, oxygen and thermal sensitivity of the complexes are systemically studied. The emission intensity and the excited state lifetimes of the four complexes decrease with increasing concentration of trivalent chromium (Cr(III)). Their sensing behavior towards Cr(III) is investigated by fluorescence spectroscopy. Results suggest that Na₃Dy(PDA)₃ exhibits highest sensitivity and linear spectral response towards Cr(III) (Stern–Volmer constant = 0.461 × 10⁷ L/mol, linearity = 0.996). It is note worthy that oxygen has little effect on the emission of Na₃RE(PDA)₃ complexes. These important advantages make themselves promising candidates to be utilized in actual applications.     

Effects of quenching speeds on microstructure and magnetic properties of novel SmCo6.9Hf0.1(CNTs)0.05 melt-spun ribbons

By adding carbon nanotubes (CNTs) to SmCo_6.9Hf_0.1, novel SmCo_6.9Hf_0.1(CNTs)_0.05 as-cast alloy has been prepared, which consists of Sm(Co,Hf)₇ as the main phase, a small amount of SmCo₅ and a particle-like grain boundary phase Hf(CNTs). SmCo_6.9Hf_0.1(CNTs)_0.05 ribbons melt-spun at speeds of 10–50 m s^?1 have a single TbCu₇-type structure. Increasing the quenching speed can result in a decrease in ribbon thickness and grain boundary width. Meanwhile, the grain size tends to be smaller and the grain boundary phase tends to be more dispersed. A new Sm(Co,Hf)₇(CNTs)_x boundary phase may be formed in SmCo_6.9Hf_0.1(CNTs)_0.05 ribbons. Increasing the quenching speed can also enhance coercivity, remanence and remanence ratio. The ribbons melt-spun at a speed of 50 m s^?1 display the best magnetic properties: H_ci = 18.781 kOe, M_s2T = 76.87 emu g^?1, M_r = 66.79 emu g^?1 and M_r/M_s2T  = 0.87.     

Synthesis and thermoelectric properties of double-filled skutterudites CeyYb0.5−yFe1.5Co2.5Sb12

Ce–Yb double-filled skutterudites Ce_0.5?yYb_yFe_1.5Co_2.5Sb₁₂ (y = 0.1, 0.2, 0.4 and 0.5) were synthesized by a melting method with subsequent annealing. The thermal conductivity, electrical conductivity and Seebeck coefficient were measured from room temperature up to 773 K. The thermal conductivities of all the double-filled skutterudites were found to be lower than the Yb single-filled skutterudites. An enhancement in the dimensionless thermoelectric figure of merit ZT was also observed in all the double-filled skutterudites as compared to the Yb single-filled skutterudite. Ce_0.3Yb_0.2Fe_1.5Co_2.5Sb₁₂ has the highest dimensionless figure of merit ZT of 0.32 at 723 K, which is 55% higher than the Yb single-filled skutterudite at the same temperature.     

Texture and orientation characteristics of α-Al2O3 films prepared by laser chemical vapor deposition using Nd:YAG laser

α-Al₂O₃ films were prepared by laser chemical vapor deposition (LCVD) and the effects of precursor vaporization temperature (T_vap), total chamber pressure (P_tot), laser power (P_L) and deposition temperature (T_dep) on the phase, orientation and texture of Al₂O₃ film were investigated. At P_tot = 0.93 kPa, α-Al₂O₃ films were obtained in the region of T_vap > 423 K and T_dep > 1100 K. The orientation of α-Al₂O₃ film changed from (1 1 0) to (0 1 2) to (1 0 4) to (0 0 6) with increasing P_tot. Porous α-Al₂O₃ films were formed at high T_vap (443 K) and low P_tot (0.47 kPa). At T_vap = 413 K, α-Al₂O₃ film had hexagonal and rectangular plate-like grains with finely faceted edges. With increasing P_tot = 0.93–1.4 kPa, (0 0 6)-oriented α-Al₂O₃ film with a hexagonal terrace texture was obtained.     

Formation of bulk metallic glasses in Cu45Zr48−xAl7REx (RE = La,Ce, Nd,Gd and 0 ≤ x ≤ 5 at.%)

We report a series of bulk metallic glass-forming alloys of compositions (Cu₄₅Zr_48−xAl₇RE_x, RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%). By using a conventional copper mold sucking method, alloys with diameters ranging from 5 to 10 mm can be readily solidified into an amorphous structure without detectable crystallites. The best glass-forming ability is obtained for the alloys Cu₄₅Zr₄₆Al₇RE₂. Possible effects of RE addition on the glass-forming ability are discussed. In addition, the compositional effect on mechanical properties of Zr–Cu–Al–Gd alloys is presented.     

Correlation between microhardness and electronic charge density of hafnium hydrides

Quantitative Vickers microhardnesses for α + δ′-, δ′-, δ-, δ + ?- and ?-phase hafnium hydrides (HfH_x; 1.46 ≤ x ≤ 2.02) and deuterides (HfD_x; 1.55 ≤ x ≤ 1.94) at room temperature have been measured using a Vickers hardness tester. The Vickers microhardnesses of the HfH_x and HfD_x gradually decreased with an increase of the hydrogen concentration, and those for 1.46 ≤ x ≤ 1.70 were higher than that of α-phase metallic Hf. It was revealed by a first-principles calculation as well as an X-ray photoelectron spectroscopy (XPS) measurement that the hydrogen concentration dependence of the microhardnesses for HfH_x and HfD_x was ascribed mainly in terms of its influence on charge transfer from Hf 5d to H 1s and reduction of cohesive energy.     

RE-X二元合金相图的热力学数据库

利用CALPHAD方法,采用亚正规溶体模型、亚点阵模型以及理想气体模型来描述RE-X(Ag,Bi,Cr,Mn,Mo,V,Zn)中二元系各相的Gibbs自由能,并结合相平衡及热力学性质的实验结果,对Ag-RE(RE:Sc,Y Nd,Sm,Gd,.Tb,Ho,Er)、Bi-RE(RE:Nd,Tm,Er,Ho,Pr,Gd)、...     

The z value dependence of photoluminescence in Eu2+-doped β-SiAlON (Si6−zAlzOzN8−z) with 1 ≤ z ≤ 4

Eu²⁺-doped β-SiAlON (Si_6?zAl_zO_zN_8?z) phosphors with 1 ≤ z ≤ 4 were synthesized by gas pressure sintering. The emission spectra exhibit two broad bands with maxima at about 415 nm (violet) and 540 nm (green) under ultraviolet excitation. The green emission is dominant at z ≤ 2, while the violet emission becomes dominant at z > 2. The combination of two emission bands in a compound could lead to a white emission in Eu²⁺-doped β-SiAlON with 2 < z ≤ 3.     

Isothermal section of the Er–Fe–Al ternary system at 800 °C

Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe_12?xAl_x with 5 ≤ x ≤ 8 (ThMn₁₂-type), ErFe_1+xAl_1?x with ?0.2 ≤ x ≤ 0.75 (MgZn₂-type), ErFe_3?xAl_x with 0.5 < x ≤ 1 (DyFe₂Al-type), Er₂Fe_17?xAl_x with 4.74 ≤ x ≤ 5.7 (TbCu₇-type) and Er₂Fe_17?xAl_x with 5.7 < x ≤ 9.5 (Th₂Zn₁₇-type), seven extensions of binaries into the ternary system; ErFe_xAl_3?x with x < 0.5 (Au₃Cu-type), ErFe_xAl_2?x with x ≤ 0.68 (MgCu₂-type), Er₂Fe_xAl_1?x with x ≤ 0.25 (Co₂Si-type), ErFe_2?xAl_x with x ≤ 0.5 (MgCu₂-type), ErFe_3?xAl_x with x ≤ 0.5 (Be₃Nb-type), Er₆Fe_23?xAl_x with x ≤ 8 (Th₆Mn₂₃-type), and Er₂Fe_17?xAl_x with x ≤ 4.75 (Th₂Ni₁₇-type) and one intermetallic compound; the ErFe₂Al₁₀ (YbFe₂Al₁₀-type).     

Creep- and coarsening properties of Al–0.06 at.% Sc–0.06 at.% Ti at 300–450 °C

Upon aging at 300–450 °C, nanosize, coherent Al₃(Sc_1−xTi_x) precipitates are formed in pure aluminum micro-alloyed with 0.06 at.% Sc and 0.06 at.% Ti. The outstanding coarsening resistance of these precipitates at these elevated temperatures (61–77% of the melting temperature of aluminum) is explained by the significantly smaller diffusivity of Ti in Al when compared to that of Sc in Al. Furthermore, this coarse-grained alloy exhibits good compressive creep resistance for a castable, heat-treatable aluminum alloy: the creep threshold stress varies from 17 MPa at 300 °C to 7 MPa at 425 °C, as expected if the climb bypass by dislocations of the mismatching precipitates is hindered by their elastic stress fields.