Study of Crystal Structure of Polypropylene/Mg2B2O5 Whisker Composite

The effects of whisker content, sample holding time, and differential scanning calorimetry (DSC) analysis of the crystal structure of polypropylene/Mg ₂ B ₂ O ₅ whisker composites were investigated. DSC shows a double melting peak, T ₁ at about 151°C and T ₂ at about 166°C. Detailed analysis of wide angle X-ray diffraction (WAXD) shows that a γ phase may exist in the polypropylene/Mg ₂ B ₂ O ₅ composite. The experimental results also show that the crystal structure according to MPLT (melting peak at low temperature) was more perfect and the crystallinity according to MPLT increased with increasing whisker content. The sample holding time at room temperature following injection molding had a significant effect on the number of γ -crystal nuclei.     

Microstructure and properties of Pb(Mg1/3Nb2/3)O3–Portland cement composites

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), ceramics particles was mixed with Portland Cement (PC) using a water to cement ratio of 0.50 and PMN content at 40% and 60% by weight to produce 0–3 Pb(Mg_1/3Nb_2/3)O₃–Portland cement (PMN–PC) composites. Microstructure and hydration of the composites were investigated. Calcium silicate hydrate gel can be seen surrounding the PMN particles. Dielectric constant of the composites was found to increase with PMN content. Successful poling of the composites was achieved. Interestingly, SEM micrographs of the PMN40 composite clearly showed calcium silicate hydrate gel (an essential hydration product of Portland cement) surrounding the PMN particles. In PMN60 composite, the gel can also still be seen but of less quantity. This is thought to be due to the increase in the volume ratio of the ceramics where the amount of calcium silicate hydrate gel was reduced in relation to the overall volume.     

蓝色荧光粉Sr2B5O9Cl:Eu2+发光特性的研究

采用高温固相法合成了近紫外光激发的蓝色荧光粉Sr₂B₅O₉Cl:Eu²⁺,研究了SrCl₂ ·6H₂O用量和Eu²⁺浓度对其结构和发光性能的影响.随着Eu²⁺浓度的增加,其结构无明显变化,发光强度先增强后减弱,当其浓度为8mol%时,荧光粉的发光强度最大;当用Ca取代Sr时,荧光粉的发射峰从425 nm红移到453 nm. 适当过量 关键词： 氯硼酸盐 蓝色荧光粉 LED     

Vibration Spectra and Structural Characteristics of Ba[(Zn1-x Mg x )1/3Nb2/3]O3 Solid Solutions

Abstract

The Ba[(Zn_1-x Mg _x )_1/3Nb_2/3]O₃ (BZMN, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solution ceramics were synthesized by the conventional solid-state reaction method. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection [FTIR] spectroscopy) and X-ray diffraction (XRD) were employed to evaluate the correlation between crystal structures and vibration modes of these solid solutions as a function of Zn²⁺ ions replaced by Mg²⁺ ions. Spectroscopic and structural data show sensitivity to the sample structural evolution with Mg²⁺ concentration, and a 1:2 ordered structure appears for Mg-rich samples where x ≥ 0.6. The Ba[(Zn_0.4Mg_0.6)_1/3Nb_2/3]O₃ has a 1:2 ordered monoclinic unit cell, which is distorted by the antiphase tilting of the oxygen octahedra. The phonon modes were assigned, and a correlation of phonon vibrations with the microstructure was found. The position and width of the phonon modes were determined and correlated to the ionic radii, mass, and tolerance factors for the different atoms substituted in the B′-site.     

High-temperature specific heat of Cu5Bi2B4O14

Cu₅Bi₂B₄O₁₄ single crystals are grown by spontaneous crystallization from a melt of a CuO, Bi₂O₃, and B₂O₃ mixture. The specific heat of the crystals in the temperature range 396–633 K is measured by differential scanning calorimetry. Using the experimental data, the thermodynamic properties of the Cu₅Bi₂B₄O₁₄ solid compound are calculated.     

First-principles study of the difference in permittivity between Ba(Mg1 / 3Ta2 / 3)O3 and Ba(Mg1 / 3Nb2 / 3)O3

This paper discusses the difference in permittivity at infrared frequencies between Ba(Mg_1/3Ta_2/3)O₃ (BMT) and Ba(Mg_1/3Nb_2/3)O₃ (BMN) based on a first-principles calculation. The permittivity, far-infrared and Raman spectra are successfully computed. Analysis of these results shows that the smaller amplitude of O in the low frequency mode E_u² (BMT), which is caused by the larger polarizability of Ta⁵⁺, is the origin of the smaller permittivity of BMT.     

Raman scattering in monocrystal Bi3B5O12

Raman spectra of a Bi₃B₅O₁₂ monocrystal are investigated for the first time and compared with the Raman spectra of crystals α-Bi₂O₃ and Bi₁₂SiO₂₀. The most intensive lines observed in the Raman spectrum of Bi₃B₅O₁₂ are identified. Promising prospects of use of Bi₃B₅O₁₂ crystals as SRS converters of radiation are shown.     

Nonlinear optical properties of (B3O7)5- and (B3O6)3- groups

3 O₅ (LBO) crystal has been studied by using the bond valence theory of complex crystals. Chemical bond parameters and linear and nonlinear optical (NLO) properties of each type of constituent chemical bonds are quantitatively determined. Because of the different crystal structure characteristics of LBO from those of β-BaB₂O₄ (BBO), the two anionic groups, (B₃O₇)^5- in LBO and (B₃O₆)^3- in BBO, play different roles in contributions to their own total NLO tensor coefficients of LBO and BBO, respectively. By comparison, we find that planar (B₃O₆)^3- groups are the ideal structure model, leading to little cancellation of contributions of each kind of bond in these groups, and this gives us a useful guide to design new NLO materials in the future. Received: 24 January 1997/Accepted: 27 March 1997     

Properties of LiZn x V2−x O4 and LiMg x V2−x O4 mixed oxides

The phase composition of the mixed oxides, series LiMe _x V_2–x O₄, where Me=Zn, Mg, was studied using X-ray analysis. The minor phases present in the investigated samples together with the basic spinel phase were determined as Li₃VO₄ and Zn₂V₂O₇ or Mg₂V₂O₇ respectively. Their presence is caused by the tendency of tetravalent vanadium ions to the disproportionation. For the compositionsx=0·375 were determined the quantitative phase compositions. The lattice constant of the spinel phase is linearly changing according to Vegard's rule, for the zinc series in the range 0x0·375 and for the magnesium series in the range 0xs0·25. Further substitution in magnesium series caused tetragonal deformation of the cubic spinel lattice.The author is indebted to Dr. A.Bergstein for helpful discussions and to Mrs. E.Hrubá for technical assistance.     

Frequency domain measurements on Na2B4O7−V2O5 semiconducting glass

Summary Dielectric measurements on Na₂B₄O₇(99.5%)−V₂O₅(0.5%) glass system, in the frequency range 10⁻³ to 10⁴ Hz and temperature range 300 to 500 K, have been carried out. The normalized plots of complex capacitance have shown a single mechanism responsible for conduction for both volume and surface measurements with their close values of activation energies (0.67±0.03) eV and (0.64±0.03) eV, respectively. The low-frequency dispersion (LFD) behaviour has been observed to be perturbed by the presence of more than one competing process. The impedance plots have shown a parallel combination of a capacitor (C) and a resistor (R), with some contribution of a dispersive element due to charge accumulation in the vicinity of the electrodes. The values ofR andC were found to be of the same order of magnitude, for both surface and volume measurements. The observedR has shown a decrease with an increase in temperature due to an increase in mobility of Na⁺ ions, whereasC remains practicaly constant. The complex capacitance surface behaviour is dominated by volume, due to hygroscopy of this glass system.     

Synthesis,Structural and Magnetic Resonance Studies of YxEr2-xCu2O5 Compounds

Polycrystalline samples of Y_xEr_2—xCu₂O₅ compound, where x = 2.0, 1.75, 1.5, 1.25. 1.0,0.75.0.25, and 0.0, have been synthesized by the solid state reaction technique. The XRD measurements have shown that the obtained samples were single-phase and belong to the orthorhombic space group Pna2₁. The measured lattice constants of Y_xEr_2-xCu₂O₅ compounds scaled linearly with the itrium index x. The TGA/DSC measurements allowed to establish the temperature range of stability for the samples and enabled the observation of their decomposition. EPR studies at room temperature showed that the integral intensity of the resonance line decreases nonlinearly with the increasing erbium content and that the Er₂Cu₂O₅ compound is EPR inactive. A broad copper EPR line has been analyzed in order to establish the contributions of different spin—spin relaxation mechanism. The observed resonance linewidth has been explained by the action of the dipole—dipole, anisotropic exchange, and Dzialoshinky—Moriya (DM) interactions.     

Effects of ZSM-5 Treatment on the Properties of Gd2Ti2O7-nHZSM-5 Composites for RBR-X3B Degradation

Gd₂Ti₂O₇-nHZSM-5 (GTO-nZ) composites are prepared using HZSM-5 zeolite via a sol–gel route. The hydrochloric acid concentration in zeolite treatment can affect the properties of GTO-nZ composites. GTO has a typical pyrochlore phase Gd₂Ti₂O₇, and HZSM-5 zeolite does not have noticeable influences on GTO crystal formation. The bandgap energies are 3.77, 3.73, 3.67, 3.65, and 3.64 eV for GTO-nZ composites when hydrochloric acid concentration is 0, 0.2, 0.3, 0.5, and 1 mol L⁻¹, respectively. The isotherms of GTO-nZ composites are classified as IUPAC type IV of mesoporous material, while the adsorbed nitrogen quantities on GTO-nZ composites are much larger than the nitrogen quantity on GTO. The small amount of HZSM-5 zeolite can improve the porosity of GTO in the composites, and the surface area of GTO in the composites is significantly enlarged. The hydrochloric acid concentration has an apparent influence on the photocatalytic degradation efficiency of GTO-nZ composites. RBR-X3B (Reactive Brilliant Red-X3B) degradation efficiency is enhanced with increasing hydrochloric acid concentration to the maximum value at 0.3 mol L⁻¹. The reaction rate constants are 2.03 × 10⁻², 9.1 × 10⁻³, and 3.1 × 10⁻³ min⁻¹ for GTO-0.3Z, GTO-0Z, and GTO, respectively.     

Synthesis and magnetic properties of Cu3B2O6 single crystals

The temperature dependence of the magnetic susceptibility of Cu₃B₂O₆ single crystals grown by spontaneous crystallization from a melt consisting of a mixture of CuO and B₂O₃ and the behavior of their magnetization are investigated in magnetic fields up to 55 kOe. A broad susceptibility maximum is observed near 39 K, and a sharp drop in susceptibility is observed at T<10 K. The paramagnetic Néel temperatures for all orientations of the magnetic field in the crystal investigated are negative, attesting to the predominantly antiferromagnetic character of the exchange interactions. The effective magnetic moment of the Cu²⁺ ion is anisotropic and lies in the range from 1.054μ _B to 1.545μ _B. The magnetization depends linearly on magnetic field at T>10 K, whereas at temperatures below 10 K a discontinuity is observed at fields of the order of 40 kOe. At room temperature, electron magnetic resonance characterized by an almost isotropic g factor (g=2.165) is detected at 36.22 GHz. The exchange interactions in Cu₃B₂O₆ are analyzed on the basis of the Goodenough-Kanamori rules. The possibility of the establishment of a singlet magnetic state in the crystal is analyzed. Fiz. Tverd. Tela (St. Petersburg) 41, 677–679 (April 1999)     

Ab‐initio thermodynamic calculations of Mg2BIV (BIV = Si,Ge, Sn) solid solutions

The thermodynamic properties of ternary Mg₂B^IV (B^IV = Si, Ge, Sn) solid solutions were first calculated by the ab‐initio density functional method. The results showed that there exist composition regions with d²G /dx² < 0 in Mg₂Si_1–x Sn_x and Mg₂Ge_1–x Sn_x systems, implying the possibility of spinodal decomposition of the pseudobinary solid solutions. It is suggested that the spinodal decomposition would be a potential way to obtain Mg₂B^IV based bulk in‐situ nanocomposites with reduced grain sizes and enhanced phonon scattering, and hence an improved thermoelectric figure of merit. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Group theoretical aspects ofU B(6) ⊗U F(20) symmetry limits of IBFM related to theU B(5) andO B(6) limits of IBM

TheU ^B(6)⊗U ^F(20) Bose-Fermi dynamical symmetry of interacting boson-fermion model arises when the odd nucleon occupies single particle orbits withj=1/2, 3/2, 5/2, and 7/2. The subgroup structures ofU ^B(6)⊗U ^F(20) related to theU ^B(5) andO ^B(6) limits of sdIBM (U ^B(6)) are analysed. Broadly speaking,U ^B(6)⊗U ^F(20) admitsU ^BF(5)⊗U _s ^F (4), Spin^BF(5)⊗U _k ^F (5) andU ^BF(5)⊗U _s ^F (2) limits withU ^B(5) core and Spin^BF(6),O ^BF(5)⊗U _s ^F (4), Spin^BF(6)⊗U _k ^F (5) andO ^BF(6)⊗U _s ^F (2) limits withO ^B(6) core respectively. For each of these seven symmetry limits, group chains, quantum numbers labelling the basis states, generators and Casimir operators for the various subgroups and energy formulas are given. Recoupling coefficients (reduced Wigner coefficients) for constructing wavefunctions of low-lying states are tabulated and these will allow (together with sdIBMU ^B(5) andO ^B(6) limit results) one to calculateB(E2)’s,B(M1)’s, one and two nucleon transfer strengths etc. in the seven symmetry limits. Experimental examples for theU ^B(6)⊗U ^F(20) symmetry limits are briefly discussed.     

Piezoelectric properties of PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics

(1 – x)Pb(Hf_1–yTi_y)O₃–x Pb(Mg_1/3Nb_2/3)O₃ (x = 0.1 ～ 0.25, y = 0.555) ternary piezoelectric ceramics were prepared using the two‐step precursor method. Morphotropic phase boundary (MPB) compositions, located at x = 0.18 ～ 0.22, were confirmed using X‐ray diffraction and by their dielectric, piezoelectric and ferroelectric properties. The optimum dielectric and piezoelectric properties were achieved for the MPB composition 0.8Pb(Hf_0.445Ti_0.555)O₃–0.2Pb(Mg_1/3Nb_2/3)O₃, with dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p and Curie temperature T_C being on the order of 2800, 680 pC/N, 70% and 276 °C, respectively. Of particular significance is that the new ternary ceramics exhibit comparable piezoelectric and electromechanical properties to commercial PZT5H ceramics, but with much improved T_C, showing a potential for applications at elevated temperature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Predictions of mechanical and thermodynamic properties of Mg17Al12 and Mg2Sn from first-principles calculations

Using first-principles calculations, we predict mechanical and thermodynamic properties of both Mg₁₇Al₁₂ and Mg₂Sn precipitates in Mg–Al–Sn alloys. The elastic properties including the polycrystalline bulk modulus, shear modulus, Young’s modulus, Lame’s coefficients and Poisson’s ratio of both Mg₁₇Al₁₂ and Mg₂Sn phases are determined with the Voigt–Reuss–Hill approximation. Our results of equilibrium lattice constants agree closely with previous experimental and other theoretical results. The ductility and brittleness of the two phases are characterized with the estimation from Cauchy pressure and the value of B/G. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young’s modulus. The higher Debye temperature of Mg₁₇Al₁₂ phase means that it has a higher thermal conductivity and strength of chemical bonding relative to Mg₂Sn. The anisotropic sound velocities also indicate the elastic anisotropies of both phase structures. Additionally, density of states and Mulliken population analysis are performed to reveal the bonding nature of both phases. The calculations associated with phonon properties indicate the dynamical stability of both phase structures. The temperature dependences of thermodynamic properties of the two phases are predicted via the quasi-harmonic approximation.     

SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.     

Magnetic properties of amorphous Bi2DyFe5O12

Amorphous Bi₂DyFe₅O₁₂ films have been prepared by rf sputtering technique. The magnetic properties, structure and effect of annealing have been investigated. The magnetization increases with increasing magnetic field and is not saturated at a high magnetic field of 65 kOe. In the temperature range 20 K<T<200 K the susceptibility can be described by a Curie-Weiss law with a Weiss constant of =–15 K. The effective paramagnetic moment for the iron ion (4.1 _B ) is much smaller than the theoretical moment (5.9 _B ). Above 200 K the slope in ^–1 vsT curve changes. The Weiss constant and effective paramagnetic moment for the iron ion increase. After annealing above 600°C the amorphous samples crystallize to a single garnet phase with the magnetization of 21 emu/g at 1.5 K and 7.2 emu/g at 300 K, which are the same as those of the bulk Bi₂DyFe₅O₁₂ garnet ferrites.     

Interfacial barrier contribution in Na2B4O7 glass system

Summary Frequency domain measurements on Na₂B₄O₇ and Na₂B₄O₇(95%)-V₂O₅(5%) glass systems have been carried out in the frequency range 10⁻² to 10⁴ Hz and temperature range 300 to 450 K. The complex capacitance has shown fractional power law dependences on frequency which obey the generalized Maxwell-Wagner relationships. The activation energy is found to increase with an increase in V₂O₅ composition.