Modulation of the ferromagnetic insulating phase in Pr0.8Ca0.2MnO3 by Co substitution

Ferromagnetic insulator Pr_0.8Ca_0.2Mn_1–yCo_y O₃ (0 ≤ y ≤ 0.7) thin films were epitaxially grown by pulsed laser deposition on substrates of (LaAlO₃)_0.3(SrAl_0.5Ta_0.5O₃)_0.7 (100). To probe the ferromagnetic insulator state, the Co content dependences of the structural, magnetic, and transport properties were studied. Variation of lattice constant by the Co substitution is well reproduced considering that divalent and trivalent Co ions substitute for Mn ions at the perovskite B‐sites. For 0 ≤ y ≤ 0.3, the Curie temperature, saturation magnetization, and magnetoresistance increase with increasing Co content, retaining the insulating properties. Detailed analyses of transport and magnetic properties indicate the contribution of both double exchange and superexchange interactions to the appearance of the ferromagnetic insulating phase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase diagram and transport properties of Sb-doped Ca0.88La0.12Fe2As2 single crystals

The effects of isovalent Sb substitution on the superconducting properties of the Ca_0.88La_0.12Fe₂(As_1-ySb_y)₂ system have been studied through electrical resistivity measurements. It is seen that the antiferromagnetic or structural transition is suppressed with Sb content, and a high-T_c superconducting phase, accompanied by a low-T_c phase, emerges at 0.02 ≤ y ≤ 0.06. In this intermediate-doping regime, normal-state transport shows non-Fermi-liquid-like behaviors with nearly T-linear resistivity above the high-T_c phase. With further Sb doping, this high-T_c phase abruptly vanishes for y > 0.06 and the conventional Fermi liquid is restored, while the low-T_c phase remains robust against Sb impurities. The coincidence of the high-T_c phase and non-Fermi liquid transport behaviors in the intermediate Sb-doping regime suggests that AFM fluctuations play an important role in the observed non-Fermi liquid behaviors, which may be intimately related to the unusual nonbulk high-T_c phase in this system.     

Phase transition and high temperature thermoelectric properties of copper selenide Cu2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu_2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu_2-xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu_2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu_2-xSe compounds possess a cubic structure with a space group of Fm3m (#225) when 0.15 < x le 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu₂Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.     

Enhancement of thermoelectric performance with pressure in Ce0.8Fe3CoSb12.1

Transport properties (resistivity, thermal conductivity, and Seebeck coefficient) and sound velocities have been determined for the skutterudite Ce_0.8Fe₃CoSb_12.1 with pressure up to 14 GPa. From these measurements, high pressure anomalous features were found in all transport properties. By correlating these with results from previous x-ray work, it has been determined that there is likely an electronic topological transition in this material induced by pressure. This is possibly due to the known pressure variation of valence in the void-filling Ce atom and has been found to induce an improved figure of merit at higher pressures, which shows a nearly two-fold increase with applied pressure. At higher pressures, it was determined that this anomalous behavior is suppressed and is possibly induced by insertion of Sb from the cage into the remaining central voids of the structure, similar to that seen in the CoSb₃ parent compound.     

Nanoscale order in GaAs:(B, Sb)

Nanoscale order caused by self-assembling of 1B4Sb and 4B10Sb clusters in GaAs:(B, Sb) is described. Self-assembling occurs in wide ranges of temperature and impurity concentration. Co-doping with boron and Sb isoelectronic impurities transforms GaAs into GaAs-rich B_xGa_1−xSb_yAs_1−y quaternary alloy. The self-assembling conditions are obtained from 0 to 800 °C with boron and Sb concentrations from x=1×10^–5 to x=2×10^–4 and from y=5×10^–4 to y=0.01, respectively. If Sb content is much larger than that of boron almost all boron atoms are in 1B4Sb clusters up to 800 °C and other boron impurities are isolated. If boron content is nearly equal or larger than that of Sb the formation of 4B10Sb clusters is preferential.     

Thermal conductivity of GexSb(As)ySe100‐x‐y glasses measured by Raman scattering spectra

We systematically measured thermal conductivity of Ge_xSb(As)₁₀Se_90−x, Ge_xSb₁₅Se_85−x, and Ge_xSb(As)₂₀Se_80−x chalcogenide glasses by measuring their Stokes and anti‐Stokes Raman scattering spectra and estimating the temperature raised by laser irradiation via the ratio of Stoke and anti‐Stokes scattering cross‐section. We aimed at demonstrating the viability of Raman scattering method for thermal conductivity measurements, and understanding the role of chemical composition in determining thermal conductivity of the chalcogenide glasses. We found that, while the values of the thermal conductivity measured in the paper are in a range from ~0.078 to 1.120 Wm^‐1K^‐1 that are in agreement with those reported data in the literatures, thermal conductivity increases before it reaches a maximum at the glass with chemically stoichiometric composition, and then decreases with increasing Ge content. We ascribed the threshold behavior of the thermal conductivity to the demixing of the structural units like GeSe₂, As₂Se₃ and Sb₂Se₃ from the main glass network. The present study demonstrated that Raman scattering method is simple and easy to measure thermal conductivity of the material. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of Ga alloying on thermoelectric properties of InSb

As a potential thermoelectric (TE) material, the high lattice thermal conductivity and relatively low weighted mobility severely limit TE property optimization of InSb binary compound. In this paper, we substituted In of InSb with Ga and systematically investigated the effect of Ga alloying on the Seebeck coefficient, electrical conductivity and lattice thermal conductivity of InSb between 300 K and 770 K. We found that Ga alloying simultaneously reduced the lattice thermal conductivity and optimized the weighted mobility of InSb. The lattice thermal conductivity has been analyzed using Abeles model to gain more insight on the roles of Ga in In_1-xGa_xSb(x = 0, 0.1, 0.15, 0.2) solid solution. The synergetic effect of Ga alloying on the electron and phonon transport leads to a marked enhancement in TE potential of InSb. The dimensionless figures of merit of InSb and In_0.8Ga_0.2Sb reach, respectively, 0.54 and 0.52 at 770 K.     

Study on phase stabilization and electrical performance of BICO0.20−xNIxVOX solid electrolyte

BICO_0.20?xNI_xVOX solid electrolyte in the composition range 0 ≤ x ≤ 0.20 was synthesized by standard solid-state reactions. The influence of Ni substitution for Co on the relationship between the phase stabilization and electrical performance was investigated by means of X-ray powder diffraction (XRPD), differential thermal analysis (DTA) and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.13 whose thermal stability increases with Ni content. On the other hand, complex plane plots of impedance suggested a major contribution of polycrystalline grain interiors to the overall electrical conductivity and the fastest oxygen-vacancy diffusion in the perovskite vanadate layers at x = 0.13. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. However, a maximum ionic conductivity at lower temperatures (～2.56 × 10^?4 S cm^?1 at 300 °C) was observed for the composition with x = 0.13.     

Electrical and thermal properties of chalcogenide glass system Se75Ge25−x Sb x

The dc and thermal conductivities of five different compositions of the chalcogenide glass system Se₇₅Ge_25–x Sb _x have been studied in a temperature range below T _g. The dc conductivity results indicate that each composition has a single activation energy in the considered temperature range. The coefficient of thermal conductivity increased linearly with temperature below T _g for the compositions investigated. The increase of Sb content in the chalcogenide glass system leads to an increased coefficient of electrical conductivity , an increased coefficient of thermal conductivity , and to a decreased activation energy E and pre-exponential factor ₀. The observed compositional dependencies of and E have been correlated with the increase of weak bond density and the decrease of covalent bond density in the structure of the compositions investigated with increasing Sb content at the expense of Ge content. The decrease in ₀ and the increase in has been, respectively, correlated with the decrease in mobility and the increase in phonon velocity.     

Order–disorder transition and thermal conductivity of (Yb x Nd1− x )2Zr2O7 solid solutions

X-ray diffraction, transmission electron microscopy and a laser-flash method were used to investigate the order–disorder transition and thermal conductivity of (Yb _x Nd_{1? x} )₂Zr₂O₇ (0 ≤ x ≤ 1.00) solid solutions. The structures were found to be pyrochlore-type for 0 ≤ x ≤ 0.25, defect fluorite for 0.45 ≤ x ≤ 1.00 and a mixture of these at 0.30 ≤ x ≤ 0.40. The thermal conductivities of (Yb _x Nd_{1? x} )₂Zr₂O₇ first gradually decrease with increasing temperature, and then increase slightly above 800°C due to the increased radiation contribution. YbNdZr₂O₇ has the lowest thermal conductivity due to the reduced cation mean free path at the compositional combination of equal molar Yb³⁺ and Nd³⁺ cations.     

The influence of imperfection of the crystal lattice on the electrokinetic and magnetic properties of disordered titanium monoxide

The conductivity and magnetic susceptibility of disordered titanium monoxide TiO_y (0.920≤y≤1.262) containing vacancies in titanium and oxygen sublattices are investigated. For TiO_y monoxides with an oxygen content y≤1.069, the temperature dependences of the conductivity are described by the Bloch-Grüneisen function at a Debye temperature ranging from 400 to 480 K and the temperature dependences of the magnetic susceptibility are characterized by the contribution from the Pauli paramagnetism due to conduction electrons. The behavior of the conductivity and magnetic susceptibility of TiO_y monoxides with an oxygen content y≥1.087 is characteristic of narrow-gap semiconductors with nondegenerate charge carriers governed by the Boltzmann statistics. The band gap ΔE between the valence and conduction bands of TiO_y monoxides with y≥1.087 falls in the range 0.06–0.17 eV.     

Effect of Cu–Al double substitution on the electrical properties of Bi4V2O11

Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ, 0.02 ≤ x ≤ 0.08, were synthesized by standard solid-state reaction route. Structural and electrical properties of samples are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) and alternating current (AC) impedance spectroscopy. The tetragonal γ′ phase structure is preserved to room temperature with compound x = 0.02. The stabilization of β orthorhombic phase is observed for compositions 0.04 ≤ x ≤ 0.05. As the Al content increases, the monoclinic α phase is evidenced for materials 0.06 ≤ x ≤ 0.08. The electrical investigation of Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ system has been performed in the frequency range from 20 Hz to 1 MHz using AC impedance spectroscopy. The impedance spectra indicate the two semicircle arcs associated with the bulk and grain boundary resistances at temperature below ～450 ^○C. The conductivity generally changes when Al is substituted. The highest conductivity at 300 ^○C (σ = 2.55 × 10^?4 S cm^?1) is shown for x = 0.02.     

Co1-xNixSb3-ySey热电输运中晶界和点缺陷的耦合散射效应

结合机械合金化与放电等离子烧结工艺制备了Ni和Se共掺的细晶方钴矿化合物Co_1-xNi_xSb_3-ySe_y,研究了晶界和点缺陷的耦合散射效应对CoSb₃热电输运特性的影响.通过Ni掺杂优化载流子浓度提高功率因子.在x=0.1时,功率因子达到最大值1750μWm^-1K^-2(450℃),是没有掺Ni试样的两倍.晶界和点缺陷的耦合散射机理使晶格热导率急剧下降,其中Co_0.9Ni_0.1Sb_2.85Se_0.15的室温晶格热导率降低至1.67Wm^-1K^-1,接近目前单填充效应所能达到的最低值1.6Wm^-1K^-1,其热电优值ZT在450℃时达到最大值0.53.将Callaway-Von Baeyer点缺陷散射模型嵌入到Nan-Birringer有效介质理论模型,对晶界散射和点缺陷散射的耦合效应对热导率的影响进行了定量分析,模型计算与实验结果符合.理论模型计算表明,当晶粒尺寸下降到50nm同时掺杂引入点缺陷散射后,Co_0.9Ni_0.1Sb_2.85Se_0.15的晶格热导率下降到0.8Wm^-1K^-1. 关键词： 3')" href="#">CoSb₃ Ni和Se掺杂 热电性能 耦合散射效应     

Effect of chromium and tellurium impurities on the thermoelectric parameters of galena

Concentration dependences of the Seebeck coefficient, resistivity, and thermal conductivity of thermoelectric PbS crystals with chromium (0 < x ≤ 0.01) and tellurium (0 < y ≤ 0.03) impurities are examined in the temperature region of 300–800 K. It is shown that the introduction of chromium increases the number of free electrons in PbCr _x S _1–x crystals and reduces the Seebeck coefficient. However, an increase in the concentration of tellurium in PbCr _x S _1–x–y Te _y alloys raises the Seebeck coefficient while simultaneously reducing the thermal conductivity. As a result, the thermoelectric efficiency of PbCr _x S _1–x–y Te _y crystals increases. The reasons for the observed effects are discussed.     

Ga填充n型方钴矿化合物的结构及热电性能

用熔融退火结合放电等离子烧结(SPS)技术制备了具有不同Ga填充含量的Ga_xCo₄Sb₁₂方钴矿化合物,研究了不同Ga含量对其热电传输特性的影响规律. Rietveld结构解析表明,Ga占据晶体学2a空洞位置,Ga填充上限约为0.22,当Ga的名义组成x≤0.25时,样品的电导率、室温载流子浓度N_p随Ga含量的增加而增加,Seebeck系数随Ga含量的增加而减小. 室温下霍尔测试表明,每一个Ga授予框架0.9个电子,比Ga的氧化价态Ga³⁺小得多. 由于Ga离子半径相对较小,致使Ga填充方钴矿化合物的热导率κ及晶格热导率κ_L较其他元素填充的方钴矿化合物低. 当x＝0.22时对应的样品在300K时的热导率和晶格热导率分别为3.05Wm^-1·K^-1和 2.86Wm^-1·K^-1.在600K下Ga_0.22Co_4.0Sb_12.0样品晶格热导率达到最小,为1.83Wm^-1·K^-1,最大热电优值Z,在560K处达1.31×10^-3K^-1. 关键词： skutterudite化合物 Ga原子填充 结构 热电性能     

Thermal conductivity of C60 and C70 crystals

We have performed thermal conductivity measurements on C₆₀ and C₇₀ crystals grown by sublimation. For single crystal C₆₀, the thermal conductivity k is 0.4 W/m K at room temperature and is nearly temperature independent down to 260K. We observed a sharp orientational phase transition at 260K, indicated by a 25% jump in k. Below 90K, k is time dependent, which manifests itself as a shoulder-like structure at 85K. The temperature and time dependence of k below 260K can be described by a simple model which accounts for the thermally activated hopping of C₆₀ molecules between two nearly degenerate orientations, separated by an energy barrier of 240 meV. It is found that solvents have a strong influence on the physical properties of C₇₀ crystals. For solvent-free C₇₀ crystal, k is about constant above 300K. There is a broad first-order phase transition in k at 300K with a 25% jump. We associate this transition with the aligning of the fivefold axes of the C₇₀ molecules along the c-axis of the hexagonal lattice. Upon further cooling, k increases and is time independent.     

Effect of hydrogen doping on the magnetic properties of Gd2CuO4

We report the results of ac-susceptibility and dc-magnetization measurements for H_yGd₂CuO₄ (0y0.54). It is shown thatH doping lowers the weak ferromagnetic component in the material. The distinct hysteresis loops observed atT=77 K for both non- and hydrogenated samples change its shape withy. The magnetic ordering temperatures T _N ^Cu and T _N ^Gd , as determined from the temperature dependencies of ac-susceptibility, remain unchanged with sample's hydrogenation. This result seems to indicate that extra electrons are not doped onto the Cu-O planes of Gd₂CuO₄. The frequency dependencies ofx(, T) andx(, T) for bothy=0 andy=0.15 samples are analysed., The maximums ofx andx found at about 200K are considered in terms of susceptibility dependence on the spin-lattice relaxation time (). The anomalies in ac-susceptibility found recently in Gd₂CuO₄ atT _a=8 K andT _b=9.5 K decrease significantly withy. Results are discussed in the context of available data on 214T-type compounds.     

Fe对CeyFexCo4-xSb12化合物结 构和热电传输性质的影响

用熔融法合成了单相填充式skutterudite化合物Ce_yFe_xCo_4-x Sb₁₂(x=0—3.0,y=0—0.74).对Ce的填充范围,置换Fe原子对化合物的结 构及热电传输特性的影响进行了研究,Ce的填充分数随Fe含量的增加而线性增加,当Fe含量 大约为3时,Ce的填充分数达到0.74.晶格常量a随Fe含量的增加而增加,Ce的填充使晶格常 量进一步增加.当Ce填充分数达到饱和状态时,Ce_y 关键词： 填充式skutterudite化合物 晶体结构 热电传输性质     

Growth and properties of ferromagnetic In1−xMnxSb alloys

We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy, In_1−xMn_xSb, and its growth by low-temperature molecular-beam epitaxy. The magnetic properties were investigated by direct magnetization measurements, electrical transport, magnetic circular dichroism, and the magneto-optical Kerr effect. These data clearly indicate that In_1−xMn_xSb possesses all the attributes of a system with carrier-mediated FM interactions, including well-defined hysteresis loops, a cusp in the temperature dependence of the resistivity, strong negative magnetoresistance, and a large anomalous Hall effect. The Curie temperatures in samples investigated thus far range up to 8.5 K, which are consistent with a mean-field-theory simulation of the carrier-induced ferromagnetism based on the 8-band effective band-orbital method.     

Magnetic cluster developement in In1−x Mn x Sb semiconductor alloys

X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and magnetic measurements as a function of applied magnetic field and temperature for In_1?x Mn _x Sb (0.05≤x≤0.2) system are reported. Magnetic measurements performed at high and small magnetic field in ZFC and FC indicate the coexistence of ferromagnetic In_1?x Mn _x Sb solid solution and two types of magnetic cluster: ferromagnetic MnSb and ferrimagnetic Mn₂Sb. XPS valence band and Mn 2p core level spectra have confirmed the presence of MnSb and Mn₂Sb phases. TEM images show some manganese antimonide phase microinclusions with dimension between (30–40) nm.