Optical and photocatalytic properties of nanoparticulate (TiO2)x(ZnO)1−x powders

In this study, we have investigated the optical and photocatalytic properties of nanoparticulate (TiO₂)_x(ZnO)_1?x powders that were synthesised by mechanochemical processing. The objective was to establish the suitability of these powders for use as optically transparent ultraviolet light screening agents. It was found that the photocatalytic activity of single phase ZnO can be substantially reduced through the incorporation of TiO₂ at the cost of a comparatively minor decrease in optical transparency. The composition given by (TiO₂)_0.10(ZnO)_0.90 was characterised by a photocatalytic activity that was approximately 20% of that exhibited by the ZnO powder synthesised using similar processing conditions. These results demonstrate that (TiO₂)_x(ZnO)_1?x powders synthesised by mechanochemical processing are potentially useful as optically transparent ultraviolet light screening agents.     

TiMn2-5x(V4Fe)x(x=0.30, 0.35)贮氢合金结构与性能研究

用XRD、SEM等方法与手段,研究TiMn2-5x(V4Fe)x(x=0.30,0.35)贮氢合金的相结构及电化学性能。结果表明:主相为体心立方(bcc)结构的合金,其晶胞参数随x的增加而增大;SEM显示在基体中存在岛状结构,随着x的增加,岛状结构较基体的比率减少;电化学测试表明,x=0.35合金在常温下难以活化,加热到327K才能活化;而x=0.30合金常温下即可活化,该合金在充电过程中出现钝化,327K温度下钝化消除。比较合金在298K的PCT曲线,发现x=0.30合金的平台氢压约为0.2MPa,平台宽度较大,更有开发价值;同时计算x=0.30合金放氢过程的焓和熵,分别为–36.1kJ/mol,–126.9J/(mol·K)。     

Structure,magnetic properties,and thermal stability of Sm1−x Tm x Co5 compounds

Structure, magnetic properties, and thermal stability of ternary Sm1-xTmxCo5 compounds were studied via X-ray diffraction(XRD), thermal magnetic analysis(TMA), and magnetic measurements. XRD results show that all the compounds have a main phase of hexagonal CaCu5-type crystal structure with small amount of impurity phases; increasing Tm content is associated with contraction of the hexagonal unit cell in the direction of the c axis and expansion of the a and b parameters. TMA results indicate that the Curie temperature(TC) of Sm1-xTmxCo5 compounds gets higher with the increase in Tm content.Magnetic measurements show that both the magnetic anisotropy field(HA) and the magnetization at an applied field of 7 T(M7 T) decrease with the increase of Tm content. However, the thermal stability of both the HAand M7 Tof all the Tm doped compounds is remarkably improved compared with that of the pure SmCo5 compound, leading to the result that both the M7 Tand HAof Sm0.8Tm0.2Co5 .2are higher than those of SmCo5 compound at 473 K, which indicates the good potential of Tm doped compound in the practical applications at elevated temperature.     

Spinodal decomposition in (CaxBa1−x)yFe4Sb12

The thermoelectric and structural properties of a double filled skutterudite solid solution (Ca_xBa_1?x)_yFe₄Sb₁₂ were investigated. Using X-ray powder and X-ray micro analyses (EPMA) an immiscibility gap was established with a critical point at x ≈ 0.45 and a critical temperature that depends on the filling level (T_C = 590 ± 5 °C at y = 0.8 and T_C = 610 ± 5 °C at y = 0.9). The thermoelectric properties were measured for samples prepared in four different states: (i) a single phase solid solution (Ca_xBa_1?x)_yFe₄Sb₁₂; (ii) a two phase microcrystalline mixture of Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂; (iii) a single phase structure obtained after annealing of the latter sample at 600 °C for 200 h; (iv) a spinodally demixed sample after annealing at 400 °C for 672 h. The thermoelectric properties of the phase mixture (ii) are compatible with data reported for the microcrystalline end members (Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂), whilst the single phase (i and iii) and spinodally decomposed (iv) samples show increased thermopower and decreased thermal conductivity, similarly to those observed for nano-structured Ca_yFe₄Sb₁₂ and Ba_yFe₄Sb₁₂.     

Thermoelectric properties of p-type (Bi2Te3)x(Sb2Te3)1−x prepared by spark plasma sintering

High performance (Bi₂Te₃)_x(Sb₂Te₃)_1?x bulk materials have been prepared by combining fusion technique with spark plasma sintering, and their thermoelectric properties have been investigated. With the increase of Bi₂Te₃ content, the electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases signi?cantly, which lead to a great improvement in the thermoelectric ?gure of merit ZT. The maximum ZT value reaches 1.33 at 398 K for the composition of 20% Bi₂Te₃–80%Sb₂Te₃ with 3 wt% excess Te.     

Infrared spectroscopic and magnetic behaviour of xNd2O3(1−x)Na2B4O7 glasses

Glasses of the xNd₂O₃^·(1−x)Na₂B₄O₇ system with 0=x=0.25 were studied by IR spectroscopy, density and magnetic susceptibility measurements. IR and density measurements show that the neodymium ions play a network modifier role in the host glass matrix. Magnetic susceptibility data show a mictomagnetic type behaviour due to the Nd³⁺ ions present as both isolated and exchange coupled species.     

化合物Gd1-xLaxMn2Ge2(x=0.06, 0.07)中场诱导的反铁磁→铁磁一级磁相变

在脉冲强磁场中测量了Gd1-xLaxMn2 Ge2 (x =0 .0 6 ,0 .0 7)化合物在不同温度下的磁化曲线。结果表明 ,当这些化合物处于反铁磁状态的温度范围内时 ,Mn次晶格中发生了场诱导的从反铁磁状态到铁磁状态的一级磁相变。随着温度的降低 ,相变临界磁场逐渐增大 ,达到最大值后 ,随着温度的进一步降低 ,临界磁场很快减小 ;随La含量的增加 ,相变临界磁场也很快减小。在交换相互作用的分子场模型基础上 ,考虑层面间Mn Mn交换作用随晶格常数a以及温度的变化 ,从理论上计算了这种场诱导的反铁磁→铁磁一级磁相变所对应的临界磁场 ,理论计算结果较好地描述了临界磁场随温度的变化规律。理论模型也较好地解释了在这些化合物中发生的从亚铁磁结构到反铁磁结构再到铁磁结构的一级自发磁相变     

Mg-6Al-5Zn-xCa(x=4,5,6,7)-5Gd合金的显微组织和力学性能

研究了不同高含Ca量的Mg-6Al-5Zn-x Ca(x=4,5,6,7)-5Gd合金铸态以及热处理后的显微组织和力学性能。结果表明,铸态时,随着含Ca量的增加,连续分布于晶界处的第二相β-Mg_(25)(Al,Zn)_(37.5)逐渐变细,呈颗粒状的Al_2Gd相和块状的CaZn_5相部分溶解,以更加圆润的小颗粒状相和小块状相分布在组织中,其抗拉强度和屈服强度先升高后降低,伸长率下降;固溶处理后,大部分β-Mg_(25)(Al,Zn)_(37.5)相逐渐溶入合金基体中,合金的强度和伸长率均显著增加,随着含Ca量的增加,固溶组织中分布更多的颗粒状相和块状相,其抗拉强度和屈服强度先升高后降低,伸长率变化不大;固溶+时效处理后,产生时效强化,时效12 h后合金硬度达到峰值,随时效时间延长,硬度稍有降低,然后趋于平缓,说明合金有较优异的热稳定性。断口分析表明,随着含Ca量的增加和热处理方式的不同,合金的断裂机制有从脆性断裂向韧性断裂转变的趋势。当含Ca质量分数为6%时,合金铸态断口形貌中有明显韧窝存在,热处理后,其断口形貌中韧窝数量增多,大小一致,分布趋于均匀。实验合金以Mg-6Al-5Zn-6Ca-5Gd合金经390℃/8 h固溶+200℃/12 h时效处理后的力学性能最佳。     

Magnetic and magnetocaloric properties of (MnCo)1 − x Ge compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)_{1 ? x} Ge compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni₂In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell’s relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change.     

Thermoelectric properties of solution-combustion-processed Na(Co1−xNix)2O4

We synthesize nano-sized Na(Co_1?xNi_x)₂O₄ (0 ≦ x ≦ 0.12) powders by the solution combustion method using aspartic acid as combustion fuel. The influence of Ni²⁺ on the thermoelectric properties for the Na(Co_1?xNi_x)₂O₄ is investigated. When the Ni²⁺ content is increased, the electrical conductivity (σ) is lowered mainly because of an increase in the porosity. In addition, the Ni²⁺ substitution leads to a significant increase in the Seebeck coefficient (α) up to x=0.06, and then a decrease with further increasing its content. The power factor (σα²) is thus improved by the Ni²⁺ substitution. We obtain the highest power factor (5.55×10^?4 Wm^?1K^?2 at 800 °C) for Na(Co_0.94Ni_0.06)₂O₄. This value is over five times higher than that of NaCo₂O₄ (1.08×10^?4 Wm^?1K^?2) at 800 °C.     

Ni-Cu-x(x=Si,Cr)合金时效初期调幅组织的TEM研究

调幅组织(modulated structure)可以通过调幅分解(spinodal Decomposition)而产生,使合金获得成分不同的呈周期规则排列的两相结构;它也可通过形核-长大机制,即在长大(或粗化)过程中由于各向异性的共格应变能的作用,形成有取向的规则排列的两相组织。因此相分解的两种机制:调幅分解和形核-长大,在相变后期都可获得几乎相同的调幅组织,难以区分。有人认为电子衍射中出现卫星反射(Satellite)(或X衍射中出现边带)和TEM     

Magnetocaloric properties of a novel ferromagnet Gd3Co4+xAl12−x (x = 0.50)

A novel gadolinium and cobalt based aluminide, namely Gd₃Co_4+xAl_12−x (x = 0.50(3)) is shown to crystallize in the hexagonal Gd₃Ru₄Al₁₂ structure-type (space-group P6₃/mmc, a = 8.6830(1) Å, c = 9.3164(2) Å at room temperature). The investigation of its magnetic properties revealed a reversible ferromagnetic ordering at T_C ≈ 40 K but expanding in a wide temperature range, potentially due to the geometrical magnetic frustrations expected in this structure-type. The magnetocaloric properties of this intermetallic, determined from both magnetization and specific heat data, are dominated by a maximum entropy variation of −3.28 J kg⁻¹ K⁻¹ at 39(1) K and an adiabatic temperature change of about 1.5 K extending from 20 to 40 K, highlighting some interest for low temperature applications.     

Effect of La-Substitution on the Electrical Conductivity of Sr1−x La x MoO4+δ (x = 0-0.3) Compounds

Various compositions of Sr_1?x La _x MoO_4+δ (x = 0.05, 0.1, 0.2, and 0.3) compounds were prepared by solid state reaction route. The samples were characterized by powder-XRD, TG-DTA, and SEM-EDAX techniques. Formation of single crystalline phases of Sr_1?x La _x MoO_4+δ was confirmed from powder-XRD patterns. The thermal stability of La-doped SrMoO₄ compounds was investigated by TG-DTA. Uniform grain distribution was observed in the SEM image of 10-20 mol.% La-substituted compositions. Needle-shaped structures were observed in the SEM image of Sr_0.3La_0.1MoO_4+δ and were confirmed to be La₂Mo₂O₉ by XRD examination. The electrical conductivity of these compounds was measured by AC-impedance technique in the temperature range of 373-1073 K in air ambience and compared with that of pristine SrMoO₄. The electrical conductivity was found to decrease for La-substituted SrMoO₄ compared to pristine SrMoO₄. The diffusion coefficient calculated from the electrical conductivity was found to be in the range of 1.94 ± 0.02 × 10^?13 to 1.15 ± 0.01 × 10^?11 cm²/S at 873-1173 K for substituted composition and 3.47 ± 0.02 × 10^?13 to 2.48 ± 0.01 × 10^?10 cm²/S for pristine SrMoO₄ at 673-1073 K temperature range.     

Spin polarization and Gilbert damping of Co2Fe(GaxGe1−x) Heusler alloys

The spin polarization (P) of ferromagnetic Heusler alloys, Co₂Fe(Ga_xGe_1?x) (x = 0, 0.25, 0.5, 0.75, and 1), is investigated by point contact Andreev reflection (PCAR) measurements. While the P values of the ternary Co₂FeGe and Co₂FeGa alloys are 0.58 and 0.59, respectively, the corresponding value for Co₂Fe(Ge_0.5Ga_0.25) is as high as 0.69. Co₂Fe(Ge_0.5Ga_0.5) alloy shows a strong tendency for L2₁ ordering and a high Curie temperature of 807 °C. Ab initio calculations indicate that the band structures of the Co₂FeGe and Co₂Fe(Ge_0.5Ga_0.5) alloys with L2₁ or B2 structures are half-metallic. Thin films of the quaternary Co₂Fe(Ge_0.5Ga_0.5) alloy grown on MgO(0 0 1) substrates order to the L2₁ structure upon annealing at 500 °C, giving rise to a high P of 0.75. This is the highest P value reported for Heusler alloy thin films using the PCAR technique. Ferromagnetic resonance measurements show that the Gilbert damping constant of the film is ～0.008. All these indicate that the Co₂Fe(Ge_0.5Ga_0.5) alloy is promising as a spin polarized current source for spintronics devices.     

Structure and magnetic properties of intermetallic compounds Gd5Si2-xGe2-xM2x

1 Introduction Nowadays, there is much interest in magnetic refrigeration materials, as they offer the prospect of an energy-efficient and environment friendly alternative for the traditional vapour cycle refrigeration technique. Magnetic refrigeration is…     

Corrosion and discharge behavior of Mg−xLa alloys (x=0.0−0.8) as anode materials

The corrosion and discharge performances of binary Mg−xLa (x=0.2−0.8, wt.%) alloys as anode materials for Mg-based batteries were evaluated. Microstructure, hydrogen evolution, mass loss, electrochemical behavior, and half-cell discharge capabilities were characterized. The results show that the corrosion rate of the Mg matrix was decreased by alloying with La, and this could be attributed to the formation of a protective La₂O₃-containing film on the surface of the alloy. The Mg−0.2La alloy displayed the lowest corrosion rate, i.e., 2.4 mm/a in a 3.5 wt.% NaCl solution, Furthermore, the discharge performance of Mg−0.4La alloy was superior to that of pure Mg and other Mg−La alloys; this could be associated with the modified microstructure of the Mg−0.4La alloy, which decreased the self-corrosion and accelerated the detachment of the discharge products.     

固相反应合成Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)磷酸盐粉体

以SrCO_3、SiO_2、ZrO_2和(NH_4)H_2PO_4为实验原料,采用固相反应法制备出磷酸盐Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体.XRD和SEM分析表明:在1100 ℃,4 h温度下煅烧能够合成单相Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体,1100 ℃,4 h条件下制备的Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体成球状,平均粒径在300～500 nm之间.在1100 ℃煅烧温度下适当延长保温时间,有利于Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)单相粉体的形成.     

Structural state of metastable cubic compounds Ni1 − x Zn x O (0.6 ≤ x ≤ 0.99)

The fine crystalline structure of metastable cubic oxide compounds Ni_{1 ? x} Zn _x O (0.6 ≤ x ≤ 0.99) has been examined using X-ray diffraction. The compounds have been synthesized from the original hexagonal phase by quenching specimens from an elevated temperature under an external hydrostatic pressure. It has been found that the diffraction patterns of the compounds include a system of superlattice diffuse maxima, the number and intensity of which depend greatly on their composition. The origin of this superstructure is discussed.     

n–p transformation in TlBi(1−x)SbxTe2 system

TlBi_(1?x)Sb_xTe₂ quaternary crystals that crystallize in a rhombohedral structure and according to their properties are classified between semimetals and narrow energy gap semiconductors, are studied. The study of their optical and electrical behavior reveal that they are quite sensitive to the Sb content x, and it is found that the substitution of Bi- with Sb-atoms in TlBiTe₂ crystals leads initially to a decrease in the plasma frequency. However, for higher Sb contents, the plasma frequency increases. At room temperature, samples with x < 0.8 are n-type semiconductors, becoming p-type ones for x > 0.8.A model suggesting a suppression of the free electron concentration induced by the incorporation of Sb atoms into the crystal lattice of TlBiTe₂ is used to explain this transition in the conductivity type.