Structural and magnetic properties of Dy2Co17—xMnx compounds

Using x-ray diffraction and magnetic measurements, we have studied the structural and magnetic properties of Dy₂Co_17-xMn_x (x=0∽5) compounds with a rhombohedral Th₂Zn₁₇-type structure. With an increasing Mn concentration x, the unit-cell volume V was found to increase linearly. The Curie temperature T_c decreases linearly, and the saturation magnetization M_s at 5K first increases slightly for x<1, then decreases rapidly for x>1 with a further increase of Mn concentration x. In compounds for x=1～3, a spin reorientation was found. A magnetic diagram of the compounds is given.     

Crystalline and optical properties of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1) films doped with silver

The results from studying Cd _x Zn_1–x S (0.5 ≤ x ≤ 1) films fabricated via pyrolysis from thiourea coordination compounds of cadmium and zinc bromides doped with silver ions having impurity concentrations of 10^–7, 10^–6, 10^–5, 10^–4, and 10^–3 mol L^–1 in sputtered solutions are presented. Films prepared at 400°С have the wurtzite lattice. The bandgap of pure and doped films, determined from absorption spectra near the edge of fundamental absorption, varies linearly from 2.5 to 3.11 eV. An order of magnitude increase in the intensity of luminescence is observed after doping with silver.     

Molecular Dynamics simulation of aqueous ZnC12 solutions

An important medium for ore transport within the Earth is by hydrothermal fluids. To understand ore transportation processes by hydrothermal fluids it is necessary to determine the clustering of dissolved ionic species in aqueous solution. We have chosen sphalerite, an important zinc containing mineral, as an example. We describe the results of Molecular Dynamics simulations to predict which chlorozinc complexes will occur at the pressures and temperatures found in the Earth's crust. Potentials have been derived for zinc-water and zinc-chloride interactions using density functional calculations. Although the DFT calculations provide good gas-phase clusters, the resulting potentials do not work well when modelling aqueous solutions. We therefore describe attempts to modify the potential to compensate for these effects. We show that at low chloride concentrations the dominant species are Zn(H₂O)²⁺ ₆, and ZnC1(H₂O)⁺ ₅. At higher temperatures there are a significant number of clusters which contain more than one zinc with bridging chloride ions. In aqueous solutions with a high chloride concentration the dominant species are Zn(H₂O)²⁺ ₆, ZnC1₂(H₂O)⁰ ₄ and ZnC1₃(H₂O)^? ₃. There are almost no clusters containing more than one zinc.     

Pd☎ Ions In NaCl Single Crystal: EPR and Optical Studies

EPR and optical absorption of Pd centres in as grown NaCl single crystal arc reported. The EPR spectra show that palladium forms the Pd^? centre with d_x2-y2 wave function in the ground state. This centre formation and the accompanying distortion give rise to a superhyperfine interaction of the Pd^? ion with the nuclei of the four Cl^? ligands in the plane perpendicular to the C₄ symmetry axis. The results of the fitting of axial spin Hamiltonian parameters to the experimentally observed spectra give the following values at 12K: g∥ =2.85, g ⊥ ? 2.15, A ∥29.8 × 10^?4cm^?1, A ⊥ = 5.9 7imes; 10^?4cm^?1. When the temperature increases, lines are getting broader, their amplitude decreases and a single line with g-value of g= 2.38 at g = 1/3(g∥ ?2g⊥) appears, which demonstrates the known Jahn-Teller behaviour of d⁹ ions EPR spectra.     

Color tuning of up-conversion emission in ytterbium,erbium, aluminum tri-doped zinc oxide crystal by adjusting aluminum concentration

Ytterbium, erbium, aluminum tri-doped zinc oxide crystal was synthesized, which can turn color from red to green up-conversion luminescence through adjusting aluminum content. When the aluminum concentration reached 4?mol%, the color of up-conversion emission first turn from red to green. Meanwhile, the ratio of red to green emission reduced from 25.32 to 0.26, and the coordinates of chromaticity coordinate calculation changes from (0.5749, 0.3378) to (0.2190, 0.7169) with aluminum concentration range from 0 to 4?mol%. The up-conversion emission peaks at 521, 542, and 660?nm of sample originate from the transitions of ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 of erbium ions, respectively. X-ray diffraction patterns perform the better crystallization degree with increasing aluminum concentration. The scanning electron microscopy images show the porous and lamellar structures with different aluminum concentrations. A convenient but effective design to obtain ytterbium, erbium, aluminum tri-doped zinc oxide up-conversion luminescence is reported, which can turn color from red to green.     

非晶态(Fe1-xVx)84B16合金的磁性和电性

用单辊急冷法制备了非晶态(Fe_1-xV_x)₈₄B₁₆(x=0,0.02,0.04,0.06,0.10)合金的薄带,分别用磁天平和四端引线法测量了饱和磁化强度和高温电阻率的温度关系。得到平均每个磁性原子的磁矩随V含量的增加近似线性下降,计算出每个Fe原子和每个V原子的平均磁矩分别为2.08μ_B和-5.08μ_B。居里温度T_c从x=0时的622K下降到x=0.10时的478K。利用自旋波激发公式:σ(T)=σ(0)(1-BT^* 关键词：     

Mössbauer spectroscopy of laser annealed tellurium implanted silicon (II).129I

Laser annealed^129mTc-implanted silicon has been investigated using¹²⁹I Mössbauer spectroscopy. At least three dopedependent charge states of substitutional iodine are found. For heavily doped p-type Si a single line component S₁, with isomer shift S=0.96(4) mm/s w. r. t. Cu¹²⁹I and an effective Debye temperature ?′=196(3) K is observed. This component is attributed to I⁺⁺. For compensated Si a single line component, S₂, assigned to I⁺, with S=2.39 (4) mm/s and ?′=170 (3) K is found. For n-type Si, a component S₃, characterized at 4.2 K by S=2.15 (4) mm/s and a quadrupole splitting eQV_zz/h=452 (8) MHz (n?0)is observed. At higher temperatures S₃ shows quadrupole relaxation and its recoilless fraction becomes strongly anisotropic. This behaviour is explained on the basis of a transition from a static to a dynamic Jahn-Teller distortion. Component S₃ has been attributed to I⁰. In the spectra of compensated and n-type Si a less well-defined component Q, with parameters resembling those of S₃ but showing no quadrupole relaxation, is observed. This component has tentatively also been assigned to I^o. The results can be understood qualitatively on the basis of a simple MO-model.     

Excitation Transfer Between the Two Sites in the Nanometric Scale X1-Y2SiO5:Eu

We have measured the photoluminescence spectra of nanometric scale X^1-Y₂SiO₅:Eu_x. The spectra were recorded at 15K and room temperature using site selective excitation by a dye laser in addition to conventional UV excitation. We found that at low temperature there is a pronounced excitation transfer from site 2→1. The transfer rate increases rapidly with increasing concentration and for x=0.7 no fluorescence from site 2 can be observed. Decaycurve measurement revealed this transfer process directly. The lifetimes of the ⁵Do levels of the two sites were also measured as a function of Eu³⁺ concentration. The results show that the lifetimes of the ⁵D₀ level of site 2 decreases with increasing concentration. The mechanism of the excitation transfer is discussed. Wavelengths of the ⁵D₀→⁷D_0–4 transitions of the two sites were also tabulated.     

Phonon-assisted luminescence anomalies in Eu2+ doped Ca1-xSrxF2 mixed crystals

Abstract

With increasing X on Ca_1-xSr_xF₂ mixed crystals doped with Eu²⁺ (4f⁶5d) ions, the absorption peak shifted linearly to that of SrF₂:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF₂ in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength.     

Ca2SiO4:Dy3+材料的制备及其发光特性

采用高温固相法制备了Ca₂SiO₄:Dy³⁺发光材料.在365nm紫外光激发下,测得Ca₂SiO₄:Dy³⁺材料的发射光谱为一多峰宽谱,主峰分别位于486nm,575nm和665nm处;监测575nm发射峰,测得材料的激发光谱为一多峰宽谱,主峰分别位于331nm,361nm,371nm,397nm,435nm,461nm和478nm处.研究了Dy³⁺掺杂浓度对Ca₂SiO₄:Dy³⁺材料发射光谱及发光强度的影响,结果显示,随Dy³⁺浓度的增大,黄、蓝发射峰强度比(Y/B)逐渐增大,利用Judd-Ofelt理论解释了其原因;随Dy³⁺浓度的增大,Ca₂SiO₄:Dy³⁺材料发光强度先增大,在Dy³⁺浓度为4 mol%时到达峰值,而后减小,根据Dexter理论其浓度猝灭机理为电偶极-电偶极相互作用.研究了电荷补偿剂Li⁺,Na⁺和K⁺对Ca₂SiO₄:Dy³⁺材料发射光谱的影响,结果显示,不同电荷补偿剂下,随电荷补偿剂掺杂浓度的增大,Ca₂SiO₄:Dy³⁺材料发射光谱强度的演化趋势相同,即Ca₂SiO₄:Dy³⁺材料发射峰强度先增大后减小,但不同电荷补偿剂下,材料发射峰强度最大处对应的补偿剂浓度不同,对应Li⁺,Na⁺和K⁺时,浓度分别为4mol%,4mol%和3mol%. 关键词： 白光LED 2SiO₄:Dy³⁺')" href="#">Ca₂SiO₄:Dy³⁺ 发光特性 电荷补偿     

从X射线的衍射强度测定晶体的德拜特征温度

本文详尽地讨论了从X射线衍射强度测定均匀的且各向同性的晶体的德拜特征温度的方法。本方法指明:如将所有的计算强度对观察强度之比的自然对数In(I_calc/I_obs)对sin²θ/λ²标绘,则应该得到一条直线,这条直线的斜率为2B。在德拜的比热理论中,B可表示为(6h²T/MkΘ_D²){φ(x)+(x/4)},其中x=Θ_D/T。如使G=BMkT/6h²,则φ(x)+x/4=Gx²,既然已求得了B值,则这个方程式中的G是一个可量度的数。求解这个方程式可用图解法来进行。使y₁=Gx²,而y₂=φ(x)+x/4,则从这两个方程式的标绘可以得到两条曲线,这两条曲线的交点就是所要测定的x值,由x值可确定在测定温度时的特征温度。必须指出,由于Θ_D本身是温度的一个函数,本方法提供了一个在所需要的温度测定德拜特征温度的可能性。 关键词：     

COMBINED EFFECTS OF SUBCOOLING AND SURFACE ORIENTATION ON POOL BOILING OF HFE-7100 FROM A SIMULATED ELECTRONIC CHIP

The effects of orientation and subcooling on pool boiling of the HFE-7100 dielectric liquid near atmospheric pressure (0.085 MPa) from a 10 × 10 mm smooth copper surface are investigated experimentally. Results are obtained for inclination angles θ = 0° (upward-facing), 30°, 60°, 90°, 120°, 150°, and 180° (downward-facing) and liquid subcoolings ΔT_sub = 0, 10, 20, and 30 K. Increasing θ decreases the saturation nucleate boiling heat flux at high surface superheats (ΔT_sat > 20 K), but increases it only slightly at lower surface superheats. The critical heat flux (CHF) decreases slowly with increasing θ from 0° to 90°, and then deceases faster with increasing θ to 180°. CHF increases linearly with increased subcooling, but the rate increases from 0.016 K^?1 at 0° to 0.048 K^?1 at 180°. At θ = 0° and ΔT_sub = 30 K, CHF is ～ 36 W/cm² and 24.45 W/cm² for saturation boiling, while at θ = 180° CHF = 10.85 W/cm² at ΔT_sub = 30 K and only 4.30 W/cm² at saturation. The developed correlation for CHF of HFE-7100, as a function of θ and ΔT_sub, is within ±10% of the present data. The recorded still photographs of the boiling surface in the experiments illustrate the effects of liquid subcooling and surface orientation at different nucleate boiling heat fluxes and surface superheats on vapor bubble accumulation and/or induced mixing at the surface.     

The pressure dependence of the superconducting transition temperature of LaT4P12(T = Fe,Ru, Os)

The superconducting transition temperature, T_c, of the LaT₄P₁₂ compounds with T = Fe, Ru, or Os has been measured under hydrostatic pressure P up to 1.8 GPa. The T = Fe compound exhibits a substantial increase of T_c from T_c (P = 0) = 4.1 K at a rate (dT_c/dP)_P=0= +7.2 x 10^-1 K/GPa. In contrast, the Ru and Os compounds exhibit only weak decreases of T_c from T_c (P = 0) = 7.2 K and 1.8 K with (dT_c/dP)_P=0= -1.6 x 10^-1 K/GPa and -9.5 x 10^-2 K/GPa, respectively. An analysis of this strikingly divergent behavior of T_c(P) in terms of the structural characteristics of the RT₄X₁₂ class of compounds where R = rare earth element, T = Fe, Ru, or Os, and X = P, As, or Sb suggests that T_c(P) for these materials consists of two competing contributions: a depression of T_c due to the compression of the lattice (i.e., decrease in volume), and an enhancement of T_c due to the effect of pressure on La itself.     

On the Plasma Chemistry of an RF Discharge Containing Aluminium Tri‐Isopropoxide Studied by FTIR Spectroscopy

In Ar and Ar/N₂ radio frequency (RF) discharges with admixtures of aluminium tri‐isopropoxide (ATI) the fragmentation of this metal‐organic precursor was studied by means of Fourier Transform Infrared (FTIR) spectroscopy using an optical long path cell providing an optical length of l = 17.2 m. The experiments were performed in an asymmetric capacitively coupled process plasma at a frequency of f = 13.56 MHz and at pres‐sure values in the range of p = 1–10.5 Pa. The discharge power was chosen between P = 10–100 W. Using FTIR spectroscopy the evolution of the concentrations of ATI and of six stable molecules, CH₄, C₂H₂, C₂H₄, C₂H₆, CO and HCN, was monitored under flowing conditions at gas flows of Φ_total = 0.5–14.5 sccm in the discharge. The concentrations of the reaction products were measured tobe between 2 x 10¹² molecules cm^–3 as e.g. found for C₂H₄and C₂H₆, and 5 x 10¹³ molecules cm^–3, as e.g. in the case of CO. In the plasma a complete dissociation of the precursor ATI was found at a power value of about P = 80 W independent on the admixture of Ar or N₂. The fragmentation efficiency (F_E) of the reaction products which originate from the ATI molecules ranges between 0.2 and 4 x 10¹⁶ molecules J^–1 while the fragmentation rate (F_R) reached up to 2.5 x 10¹⁸ molecules s^–1. The multi component detection ability of the spectrometer served to analyse the carbon balance of the by‐product formation. For all experiments, the carbon balance never exceeded 25%. Therefore, in the plasmas the majority of the provided carbon is most likely deposited at the reactor walls or forms dust particles or higher molecular C_xH_y. The conversion efficiencies (C_E) of the produced molecular species ranges between 0.1 x 10¹⁵ molecules J^–1 for C₂H₄ and 5 x 10¹⁵ molecules J^–1 for C₂H₆ depending on the discharge conditions of the RF plasma. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

EPR, luminescence and IR studies of Mn activated ZnGa2O4 phosphor

Electron paramagnetic resonance (EPR), luminescence and infrared spectra of Mn²⁺ ions doped in zinc gallate (ZnGa₂O₄) powder phosphor have been studied. The EPR spectra have been recorded for zinc gallate phosphor doped with different concentrations of Mn²⁺ ions. The EPR spectra exhibit characteristic spectrum of Mn²⁺ ions (S=I=5/2) with a sextet hyperfine pattern, centered at g_eff=2.00. At higher concentrations of Mn²⁺ ions, the intensity of the resonance signals decreases. The number of spins participating in the resonance has been measured as a function of temperature and the activation energy (E_a) is calculated. The EPR spectra of ZnGa₂O₄: Mn²⁺ have been recorded at various temperatures. From the EPR data, the paramagnetic susceptibility (χ) at various temperatures, the Curie constant (C) and the Curie temperature (θ) have been evaluated. The emission spectrum of ZnGa₂O₄: Mn²⁺ (0.08 mol%) exhibits two bands centered at 468 and 502 nm. The band observed at 502 nm is attributed to ⁴T₁→⁶A₁ transition of Mn²⁺ ions. The band observed at 468 nm is attributed to the trap-state transitions. The excitation spectrum exhibits two bands centered at 228 and 280 nm. The strong band at 228 nm is attributed to host-lattice absorption and the weak band at 280 nm is attributed to the charge-transfer absorption or d⁵→d⁴s transition band. The observed bands in the FT-IR spectrum are assigned to the stretching vibrations of M-O groups at octahedral and tetrahedral sites.     

Absolute intensities and pressure broadening coefficients measured at different temperatures for the 201II ← 000 band of 12C16O2 at 4978cm-1

Absolute line intensities and self-broadening coefficients have been measured at 197° and 294°K for the 201_II ← 000 band of ¹²C¹⁶O₂ at about 4978cm^-1. The vibration-rotation factor (F_VR), the purely vibrational transition moment (∣R(O)∣), and the integrated band intensity (S_band) are deduced from the measurements. The results are: F_VR(m)=1+(0.24±0.08)x10^-4m+(0.55+0.21)x10^-4m², ∣R(O)∣= (4.340±0.008x10^-3 debye, S_band=96372±190cm^-1km^-1atm^-1_STP. The results for self-broadening coefficients, as well as for individual vibration-rotation lines, are presented in the text.     

Lithium ion conductivity of the B-site substitution in Li3xLa0.67−xRE y III Ti1−2yPyO3 system (REIII=Sc3+, Y3+, Nd3+, Sm3+, Eu3+, Yb3+)

The B-site substituted perovskite solid solution systems Li_3xLa_0.67−xRE_yTi_1−2yP_yO₃ (RE=Sc, Y, Nd, Sm, Eu, Yb) have been investigated. Perovskite solid solutions formed in the range of x=0.10, y<0.10 for RE=Sc³⁺, Y³⁺, Yb³⁺, x=0.10, y≤0.05 for RE=Nd³⁺, Sm³⁺, Eu³⁺. Li_0.3La_0.57Nd_0.05Ti_0.9P_0.05O₃ has the highest bulk conductivity of 4.31×10⁻⁴ S·cm⁻¹ and the highest total conductivity of 2.52×10⁻⁴ S·cm⁻¹ at room temperature in all prepared compositions. The compositions have low activation energies of about 24–30 kJ/mol in the temperature ranges of 298–523 K. SEM studies showed that the sample made by solid-state reaction has a sphere-like morphology and a rough particle with particle size of about 50 μm. The research results also indicated that the reaction temperature decreases and the electrochemical stabilities of the titanate-based perovskite-type solid solutions are improved by using RE³⁺ and P⁵⁺ replaced Ti⁴⁺ on B-site in the Li_3xLa_0.67−xTiO₃ parent.     

Origin of the electron spin resonance signal in the manganites: from polarons to phase separation

In the manganites L_1?xM_xMnO₃ (L = La, Nd, Pr, …; M = Sr, Ba, Ca, …), the doping concentration introduces a mixed valence (Mn³⁺, Mn⁴⁺) which governs the magnetic and electric properties of the compound. Mn³⁺ (S = 2) is scarcely observed in electron spin resonance (ESR). In contrast, Mn⁴⁺ (S = 3/2), is a good ESR probe. However, X-band measurements show an enhanced Mn⁴⁺ susceptibility, which is the signature of some kind of coupling of the Mn⁴⁺ ions with the Mn³⁺ ions, but its exact nature is still controversial. We present multifrequency ESR experiments (9–385 GHz) obtained on different systems (La_1?δMnO₃, La_1?xMnO₃, La_1?xCa_xMnO₃, and Nd_1?xCa_xMnO₃) in the low-concentration range (0 <x< 0.33). In the paramagnetic regime, the Mn³⁺ spectrum cannot be observed because of fast relaxation. The signal arises from polarons, whose size, temperature and magnetic field dependences vary with M andx. The single line observed in the metallic compound evolves towards a double-peak structure visible at high frequency in La_0.97MnO₃. Its evolution with temperature below the magnetic transition reveals the presence of manganese ions in a different magnetic environment, i.e., phase separation. The magnetic order of the separated phase is not ferromagnetic. It is a more complex order, which depends substantially on the nature of the cation M.     

Mössbauer study of magnetic hyperfine interactions in Tb(1−x)Co x intermetallic compounds

Sign and magnitude of the average magnetic hyperfine field H_hf of⁵⁷Fe in Tb_(1?x)Co_x intermetallic compounds have been investigated by Mössbauer spectroscopy. For x>0.5, H_hf decreases linearly with increasing Tb concentration. The sign changes from positive for x<0.8 to negative for x>0.8. These trends are discussed in terms of a simple rigid-band model of the Tb_(1?x)Co_x intermetallics.     

Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.