Thermoelectric Properties of TlIn1 – x Yb x Te2 (0.01 ≤ x ≤ 0.09) Crystals

The thermoelectric properties of TlIn_{1 – x} Yb _x Te₂ (0.01 x 0.09) crystals are studied. The results indicate that the crystals possess high thermoelectric figures of merit in the range 500–700 K.     

Photoconductivity in single crystals of (TlGaSe2)1−x(TlInS2)x alloys (0−0.45 ≤ x ≤0.55-1)

The spectral distribution of the photoconductivity in (TlGaSe₂)_1−x(TlInS₂)_x single crystals has been studied at 77 K and 300 K. At O ≤ x ≤ 4, Eg is observed to vary linearly with x. Eg(x) deviates from linearity at x = 0.6. This deviation is attributed to the effect of disorder in the composition. Over the range 0.6 to 2.2 eV pronounced impurity photoconductivity is detected at 77 K and 300 K. Deep impurity levels and their neighbourhood in this alloy are established to preserve their positions with the variation in the composition. The analysis of the obtained results indicates that the impurity centres are mainly connected with the cation neighbourhood.     

Preparation and Structure of Ga2 – x Sc x O3 (0.42 ≤ x ≤ 0.52)

The structure of a scandium gallium oxide single crystal grown by the Czochralski process from a charge of composition Ga_1.5Sc_0.5O₃ is determined by x-ray diffraction. The structure is shown to be a superstructure to -Ga₂O₃. The superstructure parameters are found to vary both along the axis of the crystal and radially, which is due to variations in Ga : Sc ratio. A structural model of the Ga_1.5Sc_0.5O₃ crystal is proposed.     

Phase diagram of the CrxVSe2 system (0 ≤ x ≤ 1.0)

The phase diagram of the pseudo-binary CrVSe₂ (i.e. Cr_xVSe₂) system was determined by means of X-ray and DTA measurements, in the composition range 0≤x≤1.0. As the results, the following 6 phases have been confirmed to be existent in the temperature range 300≤T≤1100 : CdI₂,M₅X₈,M₃X₄,α,NiAs and Cr. Among them, M₅X₈,M₃X₄ and α phases undergo a phase transition to the CdI₂- or NiAs-type structures at high temperatures. The α phase (0.825≤x≤0.875 at 500°C) is a new phase firstly confirmed by this study.     

Conduction in nanostructured La1?x Sr x FeO3 (0 ≤ x ≤ 1)

We investigated electrical properties of nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO₃ with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO₃ from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe⁴⁺ ions in addition to Fe³⁺ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La_0.9Sr_0.1FeO₃.     

Fast ion transport in the new mixed system (CuI)x·[(Ag2O)2·(V2O5)]100−x (40≤x≤80)

The new mixed system (Cul) _x ·[(Ag₂O)₂·V₂O₅)]_100–x where x=40, 45, 50, 55, 60, 65, 70, 75 and 80 mol% was investigated as a possible glassy fast ion conductor by preparing molten mixtures and quenching them to low temperatures. The analysis of their composition was carried out using differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) techniques. These studies have confirmed the formation of new substances. Formation of AgI in some samples was also revealed by XRD analysis and by the occurrence of a characteristic phase transition temperature around 420 K identified through DSC experiments as well. Detailed temperature-dependent a.c. electrical conductivity studies were carried out on the new materials by a.c. impedance analysis in the frequency range 65.5 kHz-1 Hz and over the temperature range 293 to 398 K. It has been found that the highest electrical conductivity of 3.64×10^–3 S cm^–1 at 305 K due to the migration of Ag⁺ ions and the lowest activation energy of 0.1 eV in the above temperature range of investigation could be realized for the composition 40CuI-40Ag₂O-20V₂O₅ in the mixed system.     

LiGdxMn2-xO4(0≤x≤0.1)材料的结构与电化学性能

采用高温固相法合成掺杂Gd3+的锰酸锂LiGdxMn2+O4(x=0、0.01、0.05、0.1)锂离子电池正极材料并研究了其结构与电化学特性.XRD分析表明,随着Gd3+含量的增加,材料的晶格参数、晶胞体积、Mn-Mn、Mn-O键距、Mn3+/Mn4+比值均下降,材料结构稳定性得到改善.当x≥0.05时第二相Gd2O...     

Diffusion of mercury into for HgxCd(1−x)Te 0≤x≤0.03

Experiments carried out to fabricate Hg_xCd_(1-x)Te by diffusing mercury into CdTe slices from the vapour, resulted in obtaining slices with a maximum value of x=0.004. Measurements on the diffusion of mercury into such slices, where 0≤x≤0.03, under saturated vapour pressure conditions, resulted in two component profiles, each profile giving two values of D. These results were similar to ones obtained earlier, indicating that the diffusion was rate-limiting. In addition, the diffusivities were found to be independent of x. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic Properties and Metamagnetic Transition in SmCo1−x Fe x AsO (0≤x≤0.2)

Polycrystalline SmCo_1?x Fe _x AsO (x=0, 0.05, 0.1, 0.2) materials with single phase have been synthesized by solid-state reaction. According to the X-ray diffraction patterns, the a-lattice parameter shrinks, but the c-lattice parameter expends with the increased amount of Fe doping. Complicated magnetisms consist of antiferromagnetic, ferromagnetic, and paramagnetic have been observed between 5 K and 300 K in the present system. Magnetic measurement shows that with increasing Fe content, antiferromagnetic order of SmCoAsO is suppressed and ferromagnetic order is enhanced. Below their antiferromagnetic transition temperature, metamagnetic transition can be detected in samples with x<0.2, and the transition field decreases with increasing Fe content. When Fe content reaches 0.2, no metamagnetic transition is observed down to 5 K. A canting of the spins plays a crucial role in metamagnetic behavior of the present system.     

Crystal Structures and Magnetic Properties of the Co2Mn1−x V x Sb (0 ≤ x ≤ 1) Heusler Compounds

Crystal structure and magnetic properties of the Co₂Mn_1?x V _x Sb (0 ≤ x ≤ 1) Heusler compounds have been studied by X-ray powder diffraction (XRD), magnetometric measurements, and full-potential linearized augmented plane wave (FP–LAPW) method. All compounds crystallize in a cubic Cu₂MnAl-type crystal structure with the space group Fm–3m. The samples for x<0.8 have the Curie temperatures above room temperature, while the Curie temperature is observed at 68 K for the sample with x = 0.8. The saturation magnetization at 5 K decreases linearly with increasing vanadium concentration x. The values of the saturation magnetization obtained by FP–LAPW–local density approximation (LDA) calculations are in better agreement with the experimental results compared with the results obtained by FP–LAPW–generalized gradient approximation (GGA) calculations.     

(Mg_(1-x)Zn_x)_2SiO_4(0≤x≤1)陶瓷微波介电性能研究

采用固相反应法制备(Mg1-xZnx)2SiO4(0≤x≤1)微波介质陶瓷,研究(Mg1-xZnx)2SiO4陶瓷在0≤x≤1范围内的相演变、微结构与其微波介电性能间相互关系.XRD测试结果表明:橄榄石结构的Mg2SiO4与硅矽矿结构的Zn2SiO4在晶体结构上存在很大差别,(Mg,Zn)2SiO4在0≤x≤1范围内只能部分地实现有限固溶.背散射电子扫描显微镜(BESEM)测试结果显示:随着x的增加,MgSiO3第二相得到抑制;陶瓷出现液相烧结,促进晶粒生长与玻璃相在晶界处沉积.微波介电性能测试结果表明:由于Zn2+离子极化能力大于Mg2+离子,(Mg1-xZnx)2SiO4(0≤x≤1)陶瓷介电常数随x值增加而增大;0≤x≤1范围内,Mg2SiO4陶瓷微波性能由于第二相、气孔率增加与晶粒增大而降低,Zn2SiO4陶瓷由于微结构得到改善,陶瓷微波性能得到优化.当x=0.6时,得到较好的(Mg0.4Zn0.6)2SiO4陶瓷微波性能为:εr=6.6,Qf=95650GHz,τf=-60×10-6/℃.     

LiNi_(0.5)Mn_(0.5-x)Co_xO_2(0≤x≤0.12)正极材料的制备及其电化学性能

将简单共沉淀与高温固相法相结合制备了LiNi_(0.5)Mn_(0.5-x)Co_xO_2(0x≤0.12)正极材料,使用XRD、SEM、EDS和XPS等手段表征其物相结构、形貌、各元素的含量和价态,根据恒电流充放电和电化学交流阻抗谱表征其电化学性能。结果表明,LiNi_(0.5)Mn_(0.5-x)Co_xO_2正极材料具有a-NaFeO_2型层状结构;成功地将Co引入到材料的晶格内部分替代了Mn;Ni和Mn的价态分别为+2和+4,Co的价态为+3,引入Co使材料出现氧缺失。引入Co可明显改善材料的倍率性能、循环稳定性和低温性能。在2.75~4.35 V和0.2C条件下x=0.12的电极材料其首次放电比容量为180.8 m Ah·g-1,100次循环后容量保持率为92.3%,-20℃的放电比容量为25℃放电比容量的66.3%。     

Preparation of the single phase γ′-(Fe1−x Ni x )4N compounds (0 ≤x ≤ 0.6)

Single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds (0 x 0.6 have been synthesized for the first time by controlled heat treatment of iron-nickel oxalates in a gaseous flow of NH₃ xand H₂. The preparation processes were investigated using differential scanning calorimetry (DSC), X-ray diffraction and Mössbauer spectroscopy. The results confirmed that annealing of oxalates in the NH₃ and H₂ atmosphere included the processes of dehydration, decomposition and reduction, nitrogenation and thermal decomposition of the nitrides. The decomposition and reduction occur simultaneously. The final products depend on the flow rate ratio of NH₃ H₂ and the annealing temperature. The formation conditions for the single phase -Fe₄N type (Fe_1–xNi_x)₄N compounds are related to the nickel concentration, with increasing nickel content, the nitrogenation temperature decreased, in contrast the flow rate ratio of NH₃ H₂ increased.     

Cu_(2-x)S(0≤x≤1)化合物:制备技术、物理特性及应用

铜硫化合物由于具有优异的性质一直是研究人员的重点研究对象,其优点在于:(1)铜、硫两种元素储量丰富、价格低廉,对环境的影响很小,生物相容性好;(2)铜硫化合物有合适的直接带隙、等离子激元特性、高的载流子浓度及迁移率;(3)铜硫化合物结构多样、化学计量比丰富。因此,铜硫化合物在很多领域(如光电转换、传感器、电子和光电芯片、医疗等)都发挥着重要的作用。目前,对于铜硫化合物的研究主要集中在通过对结构和形貌的控制实现单一性质的调控,从而优化其特定性能。但是大多数情况下这种调控是随机的,无法根据需要实现较为精确的制备。此外,绝大多数既有的研究都围绕在三维纳米晶,缺乏低维度下对铜硫化合物的研究,这限制了研究者对铜硫化合物性能的探索(因为在低维度下材料可能会展现出更为优异的特性)。与此同时,通过将铜硫化合物与其他材料复合实现性能优异的复合材料也是一大研究热点,但其机理尚有许多不明确的地方。另外,人们对众多非化学计量比铜硫化合物的认识还甚少,如何实现这些非化学计量比铜硫化合物的大面积、高质量可控制备,并探索其结构和性质也是目前需解决的问题。对几种稳定相的形貌控制是目前研究铜硫化合物最成功之处,通过对实验技术的改善及实验参数的探索,实现了各种形貌的可控制备,如纳米棒、纳米颗粒、纳米线、纳米空心球、纳米片、纳米盘、纳米管、纳米薄膜以及其他一些奇特的形状。铜硫化合物基复合材料的研究主要体现在光伏电池、对电极材料和储能材料上,通过将铜硫化合物与其他硫化物、氧化物、氧化石墨烯、二氧化钛、碳材料等复合提高综合性能。近年来,计算材料学也逐渐揭示了一些铜硫化合物独特的能带结构,预测了与能带结构相关的众多性能,使得铜硫化合物显示出更为独特的魅力,但是实验上的验证和探索还需制备高质量的铜硫化合物样品。本文结合了前人研究,对铜硫化合物的结构组成、制备技术、物理特性及实际应用进行系统详尽的归纳,对当前的研究热点进行分析总结及展望,以期为铜硫化合物的研究提供参考和指导。     

Neutron investigation of Nd2-x-yCexLayCuO4 (0≤x≤0.2; y=0.5,1)

Samples of the electron-doped superconductor precursor Nd_2-x-yCe_xLa_yCuO₄ with 0x0.2 and y=0.5, I have been synthesized with a sol-gel method. While the as-prepared samples are in the normal state, oxygen reduction results in superconducting samples. The dependence of T_c upon Ce-doping x and oxygen content (4-) was determined in detail. It turned out that the internal pressure exerted by the La ions results in an extended superconducting range in x and compared to Nd_2-xCe_xCuO_4- Elastic neutron scattering was used to investigate the dependence of structural features upon doping. Upon oxygen reduction a non-isotropic shrinking of the unit cell (lattice parameter a increases, c decreases) and indications for interstitial oxygen were found. The local electronic surrounding of the Nd ions was observed via the crystal-field splitting by inelastic neutron scattering and turned out to be inhomogeneous. Such electronic inhomogeneities were previously measured for other high-T_c superconductors.     

Effect of reducing atmosphere on the magnetism of Zn(1-x)Co(x)O (0≤x≤0.10) nanoparticles

We report the crystal structure and magnetic properties of Zn(1-x)Co(x)O?(0≤x≤0.10) nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in the wurtzite ZnO structure after annealing in air and in a forming gas (Ar95%?+?H5%). The x-ray diffraction and x-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co(2+) ions in tetrahedral symmetry, indicating the substitution of Co(2+) in the ZnO lattice. However, samples with x = 0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77?K. The essential ingredient in achieving room temperature ferromagnetism in these Zn(1-x)Co(x)O nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.     

Appearance of Griffiths Phase in La0.7−x Pr x Ba0.3MnO3 (0 ≤x≤ 0.2)

Polycrystalline La_0.7?x Pr _x Ba_0.3MnO₃ (0 ≤x≤ 0.2) samples were prepared using solid-state reaction and checked by X-ray diffraction. Magnetization measurements versus temperature and applied magnetic field were used to investigate their magnetic properties. For samples with x= 0.2, the Griffiths phase is observed when the inverse of susceptibility (1/ χ vs. T) is analyzed.     

Phase Formation in the Course of Oxidation of In x Se1 − x Alloys (0.47 ≤ x ≤ 0.53)

We have determined the characteristic temperature ranges of heating of In _x Se_{1 – x} (0.50 x 0.52) alloys in air. We have established that the annealing of InSe powder in selenium vapors leads to the stabilization of the rhombohedral structure.     

Magnetocaloric Effects in Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) Manganese Oxides

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr_0.6?x Er _x Sr_0.4MnO₃ (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T _C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS _M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr_0.45Er_0.15Sr_0.4MnO₃ sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.     

Structural, Raman Spectroscopy, and Magnetic Ordering in New Delafossite-Type Oxide CuCr1−x Ti x O2 (0≤x≤0.1)

We investigated in this paper a new mixture +3/+2 B cations delafossites by the doping at Cr³⁺ sites in CuCrO₂ by nonmagnetic cation Ti²⁺. Ceramics of CuCr_1?x Ti _x O₂ (0≤x≤0.1) were prepared via solid state synthesis techniques in a controlled atmosphere of O₂. The compound crystallized into the 3R delafossite phase with hexagonal structure. The slightly different size in B cations induced a slightly variation in unit cell parameters. We modulate the spin chirality by the effect of spin dilution for Ti²⁺ on the structural and magnetic properties of delafossite CuCrO₂ having a S=3/2 antiferromagnetic triangular lattice (ATL).