Electronic structural properties and formation energy of Sn1−xPbxO2 solid solutions electrode

First-principles calculations based on density functional theory within the generalized gradient approximation have been performed for the Sn_1−xPb_xO₂ solid solution. The doped formation energies and electronic structures are also analyzed. Results show that the Sn_0.9375Pb_0.0625O₂ solid solution has the highest stability because of its minimum formation energy value of 0.04589 eV at a doping ratio of 0.0625. The SnO₂ lattice constants expand in a distorted rutile structure after Pb doping. The band structure and density of states calculations indicate that the band gap of SnO₂ narrowed due to the presence of the Pb impurity energy levels in the forbidden band, namely, Pb 6s energy band overlaps with the conductivity band in the F–Q direction. In addition, the number of electrons filled at the bottom of the conduction band increases from 0.13 to 3.96 after doping, resulting in the strengthening of the conductivity of the solid solution after doping of plumbum. The results provide a theoretical basis for the development and application of the Sn_1−xPb_xO₂ solid solution electrode.     

Microstructures and microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm³, a dielectric constant (ε_r) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τ_f) of −86 ppm/°C were obtained for La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75): A first-principles study

The structural, elastic, electronic and optical (x=0) properties of doped Sn_1−xBi_xO₂ and Sn_1−xTa_xO₂ (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants C_ij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO₂ in two polarization directions are compared with both previous calculations and measurements.     

Improving microwave dielectric properties of La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics with CuO additive

The microwave dielectric properties of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were investigated with a view to their application in microwave devices. CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of CuO-doped La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics exhibited no significant variation of phase with sintering temperature. By adding 0.75 wt.% CuO, a dielectric constant of 20.07, a quality factor (Q × f) of 63,000 GHz, and a temperature coefficient of resonant frequency τ_f (−77.0 ppm/°C) were obtained when La_2.98/3Sr_0.01(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1500 °C for 4 h.     

First-principles study of electronic structure and magnetic properties of doped SnO2 (rutile) with single and double impurities

Using the augmented spherical wave method, the electronic structure and magnetic properties of the rutile SnO₂ doped with single and double impurities: Sn_1−xMn_xO₂, Sn_1−xW_xO₂, and Sn_1−2xMn_xW_xO₂ with x=0.0625, have been studied. The scalar-relativistic implementation with a generalized gradient approximation functional has been used for treating the effects of exchange and correlation. The ground state of Mn-, and W-doped SnO₂ systems have a total magnetic moments of 3 and 2 μ_B, respectively. The half-metallic nature appears in Sn_1−2xMn_xW_xO₂, which makes them suitable as spintronic systems with total magnetic moment of 5 μ_B. The advantages of doping SnO₂ with double impurities are investigated in this work. The total moment of the system, the local magnetic moments of the impurities, and their oxidation states are also discussed. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic) for double-impurities-doped SnO₂. Magnetic properties and interatomic exchange have been computed for various distances between Mn and W. The indirect exchange between double impurities has similarities with the Zener mechanism in transition metal oxides. Based on the interaction between localized moments, via hybridization between impurities orbitals with the host oxygen, a double exchange mechanism is proposed to explain the ferromagnetism of our system.     

Room-temperature ferromagnetism in Sn1−xMnxO2 nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Sn_1−xMn_xO₂ (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn_1−xMn_xO₂ thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn³⁺ ions have substituted Sn⁴⁺ ions without changing the tetragonal rutile structure of pure SnO₂. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn_1−xMn_xO₂ (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10⁻⁴ emu saturation magnetization and 92 Oe coercivity in case of Sn_1−xMn_xO₂ (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration.     

NbTi0.5Ni0.5O4 as anode compound material for SOFCs

NbTi_0.5Ni_0.5O₄ (NTNO) has been prepared using solid state synthesis and investigated as a potential anode material. The oxide form of NTNO has single phase rutile-type structure with tetragonal (P42/mnm) space group. The reduced form is a composite of nano-scaled particles of metallic Ni and Nb_1.33Ti_0.67O₄ phase. Reduced NTNO showed high electronic conductivity up to 280 S.cm^− 1 at 900 °C in reducing atmosphere, but suffers from low CTE equal to 3.78 10^− 6 K^− 1. Studies of NTNO as anode material were carried out in a three electrode - electrochemical half cell configuration under pure humidified H₂ at 900 °C using a 2 mm thick zirconia electrolyte and without any additional current collector material. The results show a reasonable series resistance (R_s) equal to 2.7 Ωcm² (about 50% higher than for metallic gold layers) indicating a good current collection performance for a 10 μm layer of material. The polarization resistance (R_p) was equal to 33 Ωcm² and is attributed to a poor density of three phase boundaries (TPB) and shortage of oxide ion conduction in the anode layer. The results show the potential of NTNO as an anode material, especially after optimization of the microstructure towards the increase of TPB length.     

The magnetic properties of oxide spinel Li0.5Fe2.5−2xAlxCrxO4 solid solutions

The exchange interactions (J_BB and J_AB are the intra and the inter-sublattice exchange interactions between neighbouring spins, respectively) are obtained by using the general expressions of canting angle and critical temperature obtained by mean field theory of Li_0.5Fe_2.5−2xAl_xCr_xO₄. The expression of magnetic energy of Li_0.5Fe_2.5−2xAl_xCr_xO₄ is obtained for different spin configurations and dilution x. The saturation magnetisation of Li_0.5Fe_2.5-2xAl_xCr_xO₄ is obtained with different values of dilution x. The magnetic phase diagram of Li_0.5Fe_2.5-2xAl_xCr_xO₄ materials is obtained by high temperature series expansions (HTSEs). The critical exponent associated with the magnetic susceptibility of Li_0.5Fe_2.5−2xAl_xCr_xO₄ is deduced.     

Magnetic and electronic properties of Cr- and Mn-doped SnO2: ab initio calculations

The ab initio calculations, based on the Korringa–Kohn–Rostoker (KKR) approximation method combined with the coherent potential approximation (CPA), indicated as KKR–CPA, have been used to study the stability of ferromagnetic and ferrimagnetic states, for systems that are SnO₂ doped and co-doped with two transition metals, that is, chromium and manganese. Our results indicate that the ferromagnetic state is more stable than the spin-glass state for the (Sn_1−xCr_xO₂; x = 0.07, 0.09, 0.12 and 0.15)-doped system, while the spin-glass state is more stable than the ferromagnetic state for the (Sn_1−xMn_xO₂; x = 0.02 and 0.05)-doped system. However, the ferromagnetic and/or the ferrimagnetic states are stable for the (Sn_0.98−xMn_0.02Cr_xO₂; x = 0.05, 0.09 and 0.13)-doped system depending on the Cr concentration. Moreover, we estimated the Curie temperature (T_c) for the Cr-doped tin dioxide (SnO₂), and we explained the origin of magnetic behaviour through the total density of states for different doped and co-doped SnO₂ systems.     

Photocatalytic O2 evolution performances of Cd1+xIn2−2xSnxO4 (x=0.1, 0.3, 0.5, 0.7, 1.0) conducting oxides

The conducting oxides solid solutions of Cd_1+xIn_2−2xSn_xO₄ (x=0.1, 0.3, 0.5, 0.7, 1.0) were prepared via a solid state reaction method. The band gaps were estimated to be 2.4 eV for x=1.0, 2.5 eV for x=0.7, 2.6 eV for x=0.5, 2.7 eV for x=0.3 and 2.8 eV for x=0.1. Oxygen could be evolved over Cd₂SnO₄ under the irradiation of Xe-lamp or even visible light (λ>420 nm), while the others could only work in the UV-light range. Raman showed the cation distribution in Cd₂SnO₄ is ordered, while that in the others is disordered. The cations distribution was proposed to be the cause of the difference in photocatalytic O₂-evolution activities.     

Gd-doped SnO2 nanoparticles: Structure and magnetism

Gd-doped SnO₂ nanoparticles were chemically prepared doping 0-12.5% Gd into SnO₂ and calcined at 600 °C. X-ray diffraction and Fourier transformed infrared spectroscopy measurements show the formation of single phase of Sn_1−xGd_xO₂ up to x=0.0625 while at x=0.125, an additional secondary phase of tetragonal GdO₂ (not cubic Gd₂O₃) is detected. The transmission electron microscopy studies show that the individual particles are single crystalline with an average size in the range of 10-12 nm. Magnetization measurements show the absence of ferromagnetic and antiferromagnetic ordering in all samples; however surface spin effects and enhanced Gd-O-Gd interactions are proposed to account for the observed magnetic properties of the samples.     

Ce4+离子在Ca2SnO4一维结构基质中的电荷迁移光谱研究

利用高温固相反应法制备了Ca₂Sn_1-xCe_xO₄和Ca_2-ySr_ySn_1-xCe_xO₄一维结构发光体. XPS结果显示 Ca₂SnO₄拥有两种结合能分别为5277 eV和5293 关键词： 2Sn_1-xCe_xO₄')" href="#">Ca₂Sn_1-xCe_xO₄ 2-ySr_ySn_1-xCe_xO₄')" href="#">Ca_2-ySr_ySn_1-xCe_xO₄ 一维结构 电荷迁移光谱     

Structural and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films deposited on LaNiO3 and Pt bottom electrodes

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ thin films were deposited on LaNiO₃(LNO)/SiO₂/Si(1 0 0) and Pt/Ti/SiO₂/Si(1 0 0) substrates by metal-organic decomposition, and the effects of bottom electrodes LNO and Pt on the ferroelectric, dielectric and piezoelectric properties were investigated by ferroelectric tester, impedance analyzer and scanning probe microscopy, respectively. For the thin films deposited on LNO and Pt electrodes, the remnant polarization 2P_r are about 22.6 and 8.8 μC/cm² under 375 kV/cm, the dielectric constants 238 and 579 at 10 kHz, the dielectric losses 0.06 and 0.30 at 10 kHz, the statistic d_33eff values 95 and 81 pm/V. The improved piezoelectric properties could make (Na_1−xK_x)_0.5Bi_0.5TiO₃ thin film as a promising candidate for piezoelectric thin film devices.     

Microwave dielectric properties of high quality factor La(Mg0.5−xCaxSn0.5)O3 ceramics

The microwave dielectric properties of La(Mg_0.5−xCa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5−xCa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5−xCa_xSn_0.5)O₃ ceramics contained Ca₂SnO_4, CaSnO₃, and La₂O₃. The amount of Ca₂SnO₄ increased with increasing sintering temperature. However, the relative amount of CaSnO₃ decreased with increasing sintering temperature. An apparent density of 6.52 g/cm³, a dielectric constant (ε_r) of 20.2, a quality factor (Q×f) of 80,500 GHz, and a temperature coefficient of resonant frequency (τ_f) of −79 ppm/°C were obtained for La(Mg_0.4Ca_0.1Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

DC and AC conductivities of (As2S3)100−x(AsSe0.5Te0.5I)x chalcogenide glasses

The DC and AC conductivities of samples from the system (As₂S₃)_100−x(AsSe_0.5Te_0.5I)_x, where x=0, 5, 10, 15, 20, 25, 30, 35, 50, 70 and 90 mol%, were measured as a function of temperature. Besides, the AC conductivities of the samples with x=10 and 30 were measured as a function of frequency from room temperature to the glass transition temperature. The DC conductivity dependence on temperature is of the Arrhenius type, whereas the value of the pre-exponential factor suggests the electrical conduction by localized states in the band tails and by localized states near the Fermi level. The small values of the conduction activation energy (10⁻²-10⁻¹ eV) obtained at higher frequencies suggest that the conduction in these materials is due to hopping of charge carriers between close defect states near the Fermi level.     

0.5NdAlO3-0.5CaTiO3电子结构及光学性质的第一性原理计算

采用基于第一性原理密度泛函理论的平面波赝势方法,对0.5NdAlO₃-0.5CaTiO₃晶体进行结构优化,并对其能带结构,态密度和光学性质进行了理论计算.结构优化后晶格参数与实验数据相符合,误差小于1%;能带计算结果表明0.5NdAlO₃-0.5CaTiO₃为间接带隙,带隙值为0.52eV;费米面附近的能带由Nd-4f,O-2p,Nd-4p,Al-3p,Ti-4d层的电子态密度确定.同时也计算了该结构的介电函数,反射率和复折射率等光学性质.     

Effects of double filling of Pb and Ba on thermoelectric properties of PbxBayCo4Sb11.5Te0.5 compounds by HPHT

Skutterudite compounds Pb_xBa_yCo₄Sb_11.5Te_0.5 (x≤0.23,y≤0.27) with bcc crystal structure have been prepared by the high pressure and high temperature (HPHT) method. The study explored a chemical method for filling Pb and Ba atoms into the voids of CoSb₃ to optimize the thermoelectric figure of merit ZT in the system of Pb_yBa_xCo₄Sb_11.5Te_0.5. The structure of Pb_xBa_yCo₄Sb_11.5Te_0.5 skutterudites was evaluated by means of X-ray diffraction. The Seebeck coefficient, electrical resistivity and power factor were performed from room temperature to 710 K. Compared with Co₄Sb_11.5Te_0.5, the thermal conductivity of Pb and Ba double-filled samples was reduced evidently. Among all filled samples, Pb_0.03Ba_0.27Co₄Sb_11.5Te_0.5 showed the highest power factor of 31.64 μW cm⁻¹ K⁻² at 663 K. Pb_0.05Ba_0.25Co₄Sb_11.5Te_0.5 showed the lowest thermal conductivity of 2.73 W m⁻¹ K⁻¹ at 663 K, and its maximum ZT value reached 0.63 at 673 K.     

非线性光学晶体HgGa2S4 和 Hg0.5Cd0.5Ga2S4的能带结构、化学键及光学性质研究

用密度泛函理论和非谐振子模型计算了晶体HgGa₂S₄和Hg_0.5Cd_0.5Ga₂S₄的能带结构、态密度、化学成键及线性、非线性光学性质。结果表明：HgGa₂S₄的价带顶部主要是Ga-S成键态的贡献，导带底部主要是Ga-S反键态的贡献; Hg_0.5Cd_0.5Ga₂S₄的价带顶部主要由S-3p轨道组成，导带底部主要是Ga-S反键态的贡献。布居分析表明Ga-S键主要是共价成分，而Hg-S和Cd-S键主要是离子成分。HgGa₂S₄的折射率计算值与实验值在低能量区很好吻合。另外，HgGa₂S₄的能隙计算值比Hg_0.5Cd_0.5Ga₂S₄小，而二阶非线性极化率比Hg_0.5Cd_0.5Ga₂S₄大。     

First-principle study on the electronic and optical properties of Mn-doped SnO2

Using the full-potential linearized augmented plane wave method (FP-LAPW), we have investigated the electronic and optical properties of Sn_1−xMn_xO₂ (x=0, 0.0625, 0.125, 0.1875, 0.25). The doped Mn results in reduction of the band gap, which can be attributed to a series of impurity bands at the bottom of the conduction band caused by the strong hybridization between Mn 3d and O 2p. The results also show that the Mn-doped systems tend to convert into p-type semiconductor with direct band gaps. With the increase of Mn concentration, both the imaginary part of dielectric function and the absorption spectrum show red-shift corresponding to the change of band gaps.     

Structure and magnetic properties of Sn1−xMnxO2

The microstructure and magnetic properties have been investigated systematically for Sn_1−xMn_xO₂ polycrystalline powder samples with x=0.02-0.08 synthesized by a solid-state reaction method. X-ray diffraction revealed that all samples are pure rutile-type tetragonal phase and the cell parameters a and c decrease monotonously with the increase in Mn content, which indicated that Mn ions substitute into the lattice of SnO₂. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism. Furthermore, magnetic investigations demonstrate that magnetic properties strongly depend on doping content, x. The average magnetic moment per Mn atom decreases with increase in the Mn content, because antiferromagnetic super-exchange interaction takes place within the neighbor Mn³⁺ ions through O²⁻ ions for the samples with higher Mn doping. Our results indicate that the ferromagnetic property is intrinsic to the SnO₂ system and is not a result of any secondary magnetic phase or cluster formation.