Solvothermal synthesis and luminescence properties of monodisperse Gd2O3:Eu and Gd2O3:Eu@SiO2 nanospheres

A series of uniform, monodispersed Gd(OH)³:Eu³⁺ nanospheres less than 100 nm were successfully synthesized with iron ions as catalyst and DMF as solvent under the solvothermal condition. Cetyltrimethyl ammonium bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as co-surfactant during this facile procedure should be changed as A series of uniform, monodisperse Gd(OH)³:Eu³⁺ nanospheres less than 100 nm in diameter were successfully synthesized with solvothermal method. Iron ion was used as catalyst and Dimethylformamide (DMF) as solvent, Cetyltrimethyl Ammonium Bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as surfactants. Further calcination process was applied to prepare Gd₂O₃:Eu³⁺ nanoshpheres during this facile procedure.     

Gd5Ni0.96Sb2.04 and Gd5Ni0.71Bi2.29: Crystal structure, magnetic properties and magnetocaloric effect. Structural transformation and magnetic properties of hexagonal Gd5Bi3

Nickel was successfully introduced into the Gd₅Sb₃ and Gd₅Bi₃ binaries to yield the Gd₅Ni_0.96(1)Sb_2.04(1) and Gd₅Ni_0.71(1)Bi_2.29(1) phases. Both Ni-substituted compounds adopt the orthorhombic Yb₅Sb₃-type structure. While the Gd₅Ni_0.71Bi_2.29 phase is thermodynamically stable at 800 °C and decomposes at lower temperatures upon annealing, it can be easily quenched to room temperature by rapid cooling from 800 °C. The Gd₅Ni_0.96Sb_2.04 phase is found to be thermodynamically stable till room temperature. Through annealing at different temperatures, Gd₅Bi₃ was proven to undergo the Mn₅Si₃-type (LT)↔Yb₅Sb₃-type (HT) transformation reversibly, whereas Gd₅Sb₃ was found to adopt only the hexagonal Mn₅Si₃-type structure. Orthorhombic Gd₅Ni_0.96Sb_2.04 and Gd₅Ni_0.71Bi_2.29 and low-temperature hexagonal Gd₅Bi₃ order ferromagnetically at 115, 162 and 112 K, respectively. In Gd₅Bi₃, the ferromagnetic ordering is followed by spin reorientation below 64 K. Magnetocaloric effect in terms of ΔS was evaluated from the magnetization data and found to reach the maximum values of −7.7 J/kgK for Gd₅Ni_0.96Sb_2.04 and −5.6 J/kgK for Gd₅Ni_0.71Bi_2.29 around their Curie temperatures.     

Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd³⁺ in diluted solid solutions of Gd₂O₃ in CeO₂ have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn²⁺:CeO₂ samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd³⁺:CeO₂ samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd₂O₃-CeO₂ diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO₂ solid solutions. It is not clear why clustering effects are present in Mn:CeO₂ solid solutions and not in Gd:CeO₂ solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn²⁺ (81 pm) is about 25% smaller that that of Gd³⁺ (107.8 pm). In any case, the fact that Gd:CeO₂ solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO₂ samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd³⁺ ions in CeO₂ is about 0.89 nm.     

Crystal structure of Ca12Al14O32Cl2 and luminescence properties of Ca12Al14O32Cl2:Eu

The crystal structure of Ca₁₂Al₁₄O₃₂Cl₂ was determined from laboratory X-ray powder diffraction data (CuKα₁) using the Rietveld method, with the anisotropic displacement parameters being assigned for all atoms. The crystal structure is cubic (space group , Z=2) with lattice dimensions a=1.200950(5) nm and V=1.73211(1) nm³. The reliability indices calculated from the Rietveld method were R_wp=8.48% (S=1.21), R_p=6.05%, R_B=1.27% and R_F=1.01%. The validity of the structural model was verified by the three-dimensional electron density distribution, the structural bias of which was reduced as much as possible using the maximum-entropy methods-based pattern fitting (MPF). The reliability indices calculated from the MPF were R_B=0.75% and R_F=0.56%. In the structural model there are one Ca site, two Al sites, two O sites and one Cl site. This compound is isomorphous with Ca₁₂Al_10.6Si_3.4O₃₂Cl_5.4. Europium-doped sample Ca₁₂Al₁₄O₃₂Cl₂:Eu²⁺ was prepared and the photoluminescence properties were presented. The excitation spectrum consisted of two wide bands, which were located at about 268 and 324 nm. The emission spectrum, when excited at 324 nm, resulted in indigo light with a peak at about 442 nm.     

Neutron diffraction studies of Gd2Zr2O7 pyrochlore

The structure of Gd₂Zr₂O₇ pyrochlore over the temperature range 4-300 K has been refined from powder neutron diffraction data. The sample was enriched in ¹⁶⁰Gd to avoid the high neutron absorption of naturally occurring Gd. The diffraction pattern showed well resolved superlattice reflections indicative of the pyrochlore structure and no evidence is found for anion-disorder from the structural refinements.     

Thermodynamic studies on SrFe12O19(s), SrFe2O4(s), Sr2Fe2O5(s) and Sr3Fe2O6(s)

The citrate-nitrate gel combustion route was used to prepare SrFe₂O₄(s), Sr₂Fe₂O₅(s) and Sr₃Fe₂O₆(s) powders and the compounds were characterized by X-ray diffraction analysis. Different solid-state electrochemical cells were used for the measurement of emf as a function of temperature from 970 to 1151 K. The standard molar Gibbs energies of formation of these ternary oxides were calculated as a function of temperature from the emf data and are represented as (SrFe₂O₄, s, T)/kJ mol⁻¹ (±1.7)=−1494.8+0.3754 (T/K) (970?T/K?1151). (Sr₂Fe₂O₅, s, T)/kJ mol⁻¹ (±3.0)=−2119.3+0.4461 (T/K) (970?T/K?1149). (Sr₃Fe₂O₆, s, T)/kJ mol⁻¹ (±7.3)=−2719.8+0.4974 (T/K) (969?T/K?1150).Standard molar heat capacities of these ternary oxides were determined from 310 to 820 K using a heat flux type differential scanning calorimeter (DSC). Based on second law analysis and using the thermodynamic database FactSage software, thermodynamic functions such as Δ_fH°(298.15 K), S°(298.15 K) S°(T), C_p°(T), H°(T), {H°(T)-H°(298.15 K)}, G°(T), free energy function (fef), Δ_fH°(T) and Δ_fG°(T) for these ternary oxides were also calculated from 298 to 1000 K.     

Effect of carbon nanotubes addition on electrochemical performance and thermal stability of Li4Ti5O12 anode in commercial LiMn2O4/Li4Ti5O12 full-cell

Li₄Ti₅O₁₂ (LTO)/carbon nanotubes (CNTs) composite material is synthesized based on a solid-state method by sand-milling, spray-drying and calcining at 850 ℃ under N₂ flow. The LTO/CNTs samples with 1 wt% and 3 wt% weight ratio of CNTs addition and the pristine LTO sample are prepared. The rate performance and the thermal stability of these samples are investigated based on LiMn₂O₄ (LMO)/LTO full-cell. The results show that theweight ratio of CNTs addition has distinct effect on LTO performances. The composite materials of LTO composited CNTs have better performance at high-rate due to the intercalation enhancement by conductive network of CNTs. At second, the overcharging temperature response of the cell's surface with 1 wt% CNTs addition is the lowest. The particle size distribution is measured and the most uniform particles are obtained with 1 wt% CNTs addition. This trend could explain that the mediumquantity of CNTs is optimal to improve the heat and mass transfer and prevent the problems of crystallite growing interference and aggregation during the calcination process.     

X-ray powder diffraction studies and thermal behaviour of NaK2B9O15, Na(Na.17K.83)2B9O15, and (Na.80K.20)K2B9O15

The crystal structures of NaK₂B₉O₁₅ (, , , β=94.080(1)°, R_p=0.047, R_wp=0.059, R_B=0.026), Na(Na_.17K_.83)₂B₉O₁₅ (, , , β=94.228(2)°, R_p=0.053, R_wp=0.068, R_B=0.026), and (Na_.80K_.20)K₂B₉O₁₅ (, , , β=94.071(1)°, Z=4, R_p=0.041, R_wp=0.052, R_B=0.023) were refined in the monoclinic space groups P2₁/c(Z=4) using X-ray powder diffraction data and the Rietveld method. These nonaborates are isostructural to K₃B₉O₁₅. Their crystal structure consists of a three-dimensional open framework built up from three crystallographically independent triborate groups. The alkali metal cations are located on three different sites in the voids of the framework. High-temperature X-ray diffraction studies show that NaK₂B₉O₁₅ decomposes at about 700 °C in accordance with the peritectic reaction NaK₂B₉O₁₅↔K₅B₁₉O₃₁+liquid. The thermal expansion of NaK₂B₉O₁₅ and Na(Na_.17K_.83)₂B₉O₁₅ is highly anisotropic. A similarity of the thermal and compositional (Na-K substitution) deformations of NaK₂B₉O₁₅ is revealed: heating of NaK₂B₉O₁₅ by 1 °C leads to the same deformations of the crystal structure as increasing the amount of K atoms in (Na_1−xK_x)₃B₉O₁₅ by 0.04 at% K.     

Structural disorder in Ba0.6Sr0.4Al2O4

The structural disorder in Ba_0.6Sr_0.4Al₂O₄ (space group P6₃22) was investigated by X-ray powder diffraction and selected-area electron diffraction (SAED). The initial structural model was determined using direct methods, and it was further modified by the combined use of Rietveld method and maximum-entropy method (MEM). MEM-based pattern fitting method was subsequently applied, resulting in the final reliability indices of R_wp=9.61%, R_p=6.96%, R_B=1.40% and S=1.25. The electron density distribution was satisfactorily expressed by the split-atom model in which the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites. The diffuse scattering in SAED was mainly attributable to the positional disorder of oxygen atoms.     

Synthesis and crystal structures of (C8h8)Nd(C5H9C5H4) (THF)2 and [(C8H8)Gd(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)2]

LnCl₃ (Ln=Nd, Gd) reacts with C₅H₉C₅H₄Na (or K₂C₈H₈) in THF (C₅H₉C₅H₄ = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C₅H₉C₅H₄)LnCl₂(THF)_n (orC₈H₈)LnCl₂(THF)_n], which further reacts with K₂C₈H₈ (or C₅H₉C₅H₄Na) in THF to form the litle complexes. If Ln=Nd the complex (C₈H₈)Nd(C₅H₉C₅H₄)(THF)₂ (a) was obtained: when Ln=Gd the 1 : 1 complex [(C₈H₈)Gd(C_%H₉)(THF)][(C₈H₈)Gd(C₅H₉H₄)(THF)₂] (b) was obtained in crystalline form.

The crystal structure analysis shows that in (C₈H₈)Ln(C₅H₉C₅H₄)(THF)₂ (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η⁵), cyclooctatetraenyl (η⁸) and two oxygen atoms from THF are coordinated to Nd³⁺ (or Gd³⁺) with coordination number 10.

The centroid of the cyclopentadienyl ring (Cp′) in C₅H₉C₅H₄ group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd³⁺ (or Gd³⁺). In (C₈H₈)Gd(C₅H₉C₅H₄)(THF), the cyclopentyl-cyclopentadienyl (η⁵), cyclooctatetraenyl (η⁸) and one oxygen atom are coordinated to Gd³⁺ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd³⁺, which is almost in the plane (dev. -0.0144 Å).     

用3种方法合成Y3Al5O12：RE^3＋（RE=Eu,Dy）发光粉的对比研究

以金属硝酸盐为反应原料,分别采用柠檬酸－凝胶法、共沉淀法和固相法制备了YAG和YAG：RE^3 (RE=Eu,Dy)（1％,摩尔分数）发光粉,并通过XRD,TG－DTA和发光光谱对样品进行了表征。柠檬酸－凝胶法、共沉淀法和固相法制备的YAG和YAG：Eu的晶相形成温度分别是800和900℃。Eu^3 在非晶态和晶态YAG中其激发和发射光谱有明显差异,在一定温度范围内,发光强度随烧结温度的升高而增强。由于碳杂质的存在,900和1000℃下柠檬酸－凝胶法制备样品的发射强度较其他两种方法低。     

Syntheses, structures, and properties of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2(MoO3)3SeO3

Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) has been synthesized by reacting AgNO₃, MoO₃, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO₂²⁺ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C₂ distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C₂ distortion. Upon heating Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) looses SeO₂ in two distinct steps to yield Ag₂MoO₄. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) Å, V=1419.41(12), Z=4, R(F)=2.72% for 121 parameters with 1829 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ was synthesized by reacting AgNO₃ with MoO₃, SeO₂, and HF under hydrothermal conditions. The structure of Ag₂(MoO₃)₃SeO₃ consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO₆ units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [bc] plane. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): monoclinic, space group P2₁/n, a=7.7034(5), b=11.1485(8), c=12.7500(9) Å, β=105.018(1) V=1002.7(2), Z=4, R(F)=3.45% for 164 parameters with 2454 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ decomposes to Ag₂Mo₃O₁₀ on heating above 550 °C.     

Magnetic and electronic properties of nanocrystalline Gd3Fe5O12 garnet

The Gd₃Fe₅O₁₂ nanocrystalline Gadolinium Iron Garnet (GdIG) obtained from a sintered block was milled in a high energy ball mill. We measured the magnetization at 5 K under applied fields up to 12 T. We report here our study of approach to saturation magnetization. The results have been interpreted within the framework of random anisotropy model. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. We have determined the anisotropy field H_r and the local magnetic anisotropy constant K_L. In addition, first-principles spin-density functional calculations, using the Full potential Linear Augmented Plane Waves (FLAPW) method are performed to investigate electronic and magnetic structures. All computed parameters are discussed and compared to available experimental data.     

Metamagnetic transition in the 75 K antiferromagnet Gd4Co2Mg3

Gd₄Co₂Mg₃ (Nd₄Co₂Mg₃ type; space group P2/m; a=754.0(4), b=374.1(1), c=822.5(3) pm and β=109.65(4)° as unit cell parameters) was synthesized from the elements by induction melting in a sealed tantalum tube. Its investigation by electrical resistivity, magnetization and specific heat measurements reveals an antiferromagnetic ordering at T_N=75(1) K. Moreover, this ternary compound presents a metamagnetic transition at low critical magnetic field (H_cr=0.93(2) T at 6 K) and exhibits a magnetic moment of 6.3(1) μ_B per Gd-atom at 6 K and H=4.6 T. Due to this transition the compound shows a moderate magnetocaloric effect; at 77 K the maximum of the magnetic entropy change is ΔS_M=−10.3(2) J/kg K for a field change of 0-4.6 T. This effect is compared to that reported previously for compounds exhibiting a magnetic transition in the same temperature range.     

Neutron diffraction, specific heat and magnetic susceptibility of Ni3(PO4)2

The Ni₃(PO₄)₂ phosphate was synthesized by the ceramic method in air atmosphere. The crystal structure consists of a three-dimensional skeleton constructed from Ni₃O₁₄ edge-sharing octahedra, which are interconnected by (PO₄)³⁻ oxoanions with tetrahedral geometry. The magnetic behavior was studied on powdered sample by using susceptibility, specific heat and neutron diffraction data. The nickel(II) orthophosphate exhibits a three-dimensional magnetic ordering at approximately 17.1 K. However, its complex crystal structure hampers any parametrization of the J-exchange parameter. The specific heat measurements of Ni₃(PO₄)₂ exhibit a three-dimensional magnetic ordering (λ-type) peak at 17.1 K. Measurements above T_N suggest the presence of a small short-range order in this phase. The total magnetic entropy was found to be 28.1 KJ/mol at 50 K. The magnetic structure of the nickel(II) phosphate exhibits ferromagnetic interactions inside the Ni₃O₁₄ trimers which are antiferromagnetically coupled between them, giving rise to a purely antiferromagnetic structure.     

Quantum efficiency of double activated Tb3Al5O12:Ce, Eu

The quantum efficiency and luminescence properties of double activated terbium aluminum garnet samples were investigated in the present study. A mathematical procedure and PL measurement system are developed for express analysis of quantum efficiency of luminescent materials. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce,Eu with improved CIE and CRI in LED device is demonstrated.     

Synthesis and thermochemistry of SrB2O4·4H2O and SrB2O4

Two pure strontium borates SrB₂O₄·4H₂O and SrB₂O₄ have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB₂O₄·4H₂O and SrB₂O₄ in 1 mol dm⁻³ HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol⁻¹ and −(81.27 ± 0.30) kJ mol⁻¹, respectively. The molar enthalpy of solution of Sr(OH)₂·8H₂O in (HCl + H₃BO₃)(aq) were determined to be −(51.69 ± 0.15) kJ mol⁻¹. With the use of the enthalpy of solution of H₃BO₃ in 1 mol dm⁻³ HCl(aq), and the standard molar enthalpies of formation for Sr(OH)₂·8H₂O(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol⁻¹ for SrB₂O₄·4H₂O, and of −(2038.4 ± 1.7) kJ mol⁻¹ for SrB₂O₄ were obtained.     

The new ternary silicide Gd5CoSi2: Structural, magnetic and magnetocaloric properties

Gd₅CoSi₂ was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffraction shows that the ternary silicide crystallizes in a tetragonal structure deriving from the Cr₅B₃-type (I4/mcm space group; a=7.5799(4) and c=13.5091(12) Å as unit cell parameters). The Rietveld refinement shows a mixed occupancy on the (8h) site between Si and Co atoms. Magnetization and specific heat measurements performed on Gd₅CoSi₂ reveal a ferromagnetic behaviour below T_C=168 K. This magnetic ordering is associated to an interesting magnetocaloric effect; the adiabatic temperature change ΔT_ad is about 3.1 and 5.9 K, respectively, for a magnetic field change of 2 and 4.6 T.     

New manganites NdM3Sr3Mn4O12 and NdM3Ba3Mn4O12 (M = Li, Na, K): Synthesis and X-ray diffraction characteristics

Manganites NdM₃Sr₃Mn₄O₁₂ and NdM₃Ba₃Mn₄O₁₂ (M = Li, Na, K) were synthesized by a ceramic method from the corresponding oxides and carbonates. The X-ray diffraction analysis showed that all the compounds crystallized in the tetragonal crystal system with the following lattice parameters: NdLi₃Sr₃Mn₄O₁₂: a = 10.88 ?, c = 9.52 ?, V ^o = 1126.9 ?³, Z = 4, ρ_X = 4.95 g/cm³, ρ_pycn = 4.87 ± 0.05 g/cm³; NdNa₃Sr₃Mn₄O₁₂: a = 10.73 ?, c = 10.66 ?, V ^o = 1227.3 ?³, Z = 4, ρ_X = 4.80 g/cm³, ρ_pycn = 4.73 ± 0.07 g/cm³; NdK₃Sr₃Mn₄O₁₂: a = 10.87 ?, c = 11.71 ?, V ^o = 1382.6 ?³, Z = 4, ρ_X = 4.50 g/cm³, ρ_pycn = 4.43 ± 0.09 g/cm³; NdLi₃Ba₃Mn₄O₁₂: a = 10.97 ?, c = 10.34 ?, V ^o = 1244.3 ?³, Z = 4, ρ_X = 5.33 g/cm³, ρ_pycn = 5.23 ± 0.09 g/cm³; NdNa₃Ba₃Mn₄O₁₂: a = 10.99 ?, c = 11.15 ?, V ^o = 1346.7 ?³, Z = 4; ρ_X = 5.11 g/cm³, ρ_pycn = 5.05 ± 0.06 g/cm³; NdK₃Ba₃Mn₄O₁₂: a = 10.997 ?; c = 13.80 ?, V ^o = 1668.9 ?³, Z = 4, ρ_X = 4.32 g/cm³, ρ_pycn = 4.26 ± 0.07 g/cm³. Original Russian Text ? B.K. Kasenov, E.S. Mustafin, M.A. Akubaeva, S.T. Edil’baeva, Sh.B. Kasenova, Zh.I. Sagintaeva, S.Zh. Davrenbekov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 424–427.     

Thermoluminescence and synchrotron radiation studies on the persistent luminescence of BaAl2O4:Eu,Dy

The persistent luminescence materials, barium aluminates doped with Eu²⁺ and Dy³⁺ (BaAl₂O₄:Eu²⁺,Dy³⁺), were prepared with the combustion synthesis at temperatures between 400 and 600 °C as well as with the solid state reaction at 1500 °C. The concentrations of Eu²⁺/Dy³⁺ (in mol% of the Ba amount) ranged from 0.1/0.1 to 1.0/3.0. The electronic and defect energy level structures were studied with thermoluminescence (TL) and synchrotron radiation (SR) spectroscopies: UV-VUV excitation and emission, as well as with X-ray absorption near-edge structure (XANES) methods. Theoretical calculations using the density functional theory (DFT) were carried out in order to compare with the experimental data.