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.     

Phase equilibria of Co−Mo−Zn ternary system

To experimentally determine the isothermal sections of Co−Mo−Zn ternary system at 600 and 450 °C, the equilibrated alloy and diffusion couple methods were adopted by using scanning electron microscopy coupled with energy-dispersive spectrometry, X-ray diffractometry and electron probe microanalysis. Experimental results show that there are six three-phase regions on the Co−Mo−Zn isothermal section at 600 °C and nine three-phase regions on the Co−Mo−Zn isothermal section at 450 °C. No ternary compound is found in these two isothermal sections. Both the maximum solubilities of Mo in the Co−Zn compounds (γ-Co₅Zn₂₁, γ₁-CoZn₇, γ₂-CoZn₁₃ and β₁-CoZn) and that of Zn in ε-Co₃Mo are no more than 1.5 at.%. The maximum solubilities of Zn in μ-Co₇Mo₆ are determined to be 2.1 at.% and 2.7 at.% at 600 and 450 °C, respectively. In addition, the maximum solubilities of Co in MoZn₇ and MoZn₂₂ are 0.5 at.% and 4.7 at.% at 450 °C, respectively.     

On the formation of WC1−x in nanocrystalline cemented carbides

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Plasma Spray Physical Vapor Deposition of La1−x Sr x Co y Fe1−y O3−δ Thin-Film Oxygen Transport Membrane on Porous Metallic Supports

Plasma spray physical vapor deposition (PS-PVD) is a very promising route to manufacture ceramic coatings, combining the efficiency of thermal spray processes and characteristic features of thin PVD coatings. Recently, this technique has been investigated to effectively deposit dense thin films of perovskites particularly with the composition of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) for application in gas separation membranes. Furthermore, asymmetric type of membranes with porous metallic supports has also attracted research attention due to the advantage of good mechanical properties suitable for use at high temperatures and high permeation rates. In this work, both approaches are combined to manufacture oxygen transport membranes made of gastight LSCF thin film by PS-PVD on porous NiCoCrAlY metallic supports. The deposition of homogenous dense thin film is challenged by the tendency of LSCF to decompose during thermal spray processes, irregular surface profile of the porous metallic substrate and crack and pore-formation in typical ceramic thermal spray coatings. Microstructure formation and coating build-up during PS-PVD as well as the annealing behavior at different temperatures of LSCF thin films were investigated. Finally, measurements of leak rates and oxygen permeation rates at elevated temperatures show promising results for the optimized membranes.     

A microscopic study of the effect of γ-radiation on Pb1 − x Mn x Se epitaxial films

The surface morphology of n- and p-type epitaxial films of lead manganese selenide (Pb_1?x Mn _x Se (x = 0.01)) on barium fluoride substrates of the (111) orientation in the initial state and after exposure to gamma-radiation is studied by atomic force microscopy. It is shown that the surface relief undergoes modification in the absorbed dose region of 5 ≤ D _γ ≤ 35 kGy. The p?n conductivity inversion at 10 ≤ D _γ ≤ 25 kGy is found from the characteristics of the surface structures and confirmed by the electrophysical measurements. It is revealed that the radiation resistance of these films is violated at a dose above 35 kGy.     

Magnetic properties of the Mn1.9 − x Co x Ge compounds with a hexagonal crystal structure

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn_{1.9 ? x} Co _x Ge (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the Ni₂In type have been studied. As the Co content (x) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.     

Dependency of the thermal and electrical conductivity on temperatures and compositions of Zn in the Al−Zn alloys

The variations of thermal conductivity (K) with temperature for Al–xZn (x = 5, 10, 20, 30, 50 and 60 wt. %) alloys were measured by using a radial heat flow furnace. The variations of electrical conductivity (σ) of solid phases with temperature for the studied alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of K from the plots of K. The thermal temperature coefficient (α_TTC) and the electrical temperature coefficient (α_ETC) were obtained. Dependency of the α_TTC and α_ETC on the composition of Zn in the Al?Zn alloys was also investigated. According to the present experimental results, K of Al–Zn alloys linearly decrease with increasing temperatures up to the melting temperature for each composition and exponentially decrease with the increasing Zn content. On the other hand, the σ of Al based Al-Zn alloys exponentially decrease with increasing temperature and Zn content.     

Magnetic structure and double exchange in the La1 − x Ca x MnO3

This paper considers from a theoretical viewpoint the problem of the appearance of different magnetic structures in the series of compounds La_{1 ? x} Ca _x MnO₃, 0 ≤ x ≤ 1. It is assumed that the entire series possesses the structure of the GdFeO₃ type. The problem is analyzed in the nearest-neighbor approximation with allowance for direct exchange, double exchange, and anisotropy energy (ten interaction parameters on the whole). The spin operator of double exchange interaction in the crystal between the different-valence ions of manganese Mn³⁺ and Mn⁴⁺ is the direct generalization of two-spin operator in the well-known problem of the Anderson-Hasegawa molecule. The minimization of the energy along the direction angles of magnetic sublattices leads to a set of transcendental equations, whose solutions give eleven types of magnetic configurations: two ferromagnetic, three collinear antiferromagnetic, and six noncollinear antiferromagnetic. As the concentration of calcium ions x changes, one spin configuration changes another as the ground state. The appearance of angular configurations in the system occurs only due to the simultaneous presence of direct Heisenberg interaction and substantially non-Heisenberg double exchange.     

Preparation and characterization of Cd1−x Zn x S buffer layers for thin film solar cells

Cd1-xZnxS(x = 0, 0.1, 0.2, 0.3, 1.0) thin films have been grown successfully on soda-lime glass substrates by chemical bath deposition technique as a very promising buffer layer material for optoelectronic device applications. The composition, structural properties, surface morphology, and optical properties of Cd1-xZnxS thin films were characterized by energy dispersive analysis of X-ray technique (EDAX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectrophotometer techniques, respectively. The annealed films were observed to possess the deficient sulfur composition. The results of XRD show that the Cd1-xZnxS (x = 0.1) thin film annealed at 450 ℃ forms hexagonal (wurtzite) structure with lattice parameters a = 0.408814 nm, c = 0.666059 nm, and its average grain size is 24.9902 nm. The diffraction peaks become strong with the increasing annealing temperatures. The surface of Cd1-xZnxS (x = 0.1) thin film annealed at 450℃ is uninterrupted and homogenous as compared to other temperatures. From optical properties, it is observed that the presence of small amount of Zn results in marked changes in the optical band gap of CdS. The band gaps of the Cd1-xZnxS thin films vary from 2.42 to 3.51 eV as composition varies from x = 0.0 to 1.0.     

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.     

Stacking faults in quaternary InxAlyGa1−x−yN layers

Quaternary In_0.12Al_0.29Ga_0.59N and In_0.10Al_0.02Ga_0.88N layers ∼200 nm thick were grown on (0 0 0 1) GaN/sapphire composites using metalorganic chemical vapor deposition. The layers were studied using transmission electron microscopy (TEM). TEM results indicate that the quaternary layers contain high-density stacking faults (SFs). Weak-beam dark-field analysis coupled with high-resolution electron microscopy reveal that SFs have zinc-blende structures bounded by Shockley partials. Compared with In_0.10Ga_0.90N layers, SF density increases substantially in the In_0.10Al_0.02Ga_0.88N layer with only 2% additional Al. Z-contrast annular dark-field images showed that SFs are Al-rich in the In_0.12Al_0.29Ga_0.59N layer, but not in the In_0.10Al_0.02Ga_0.88N layer. Two reference Al_xGa_1−xN layers were grown using identical conditions except the carrier gases. Using H₂ carrier gas resulted in a ∼400 nm thick Al_0.45Ga_0.55N layer with no SFs, while using N₂ carrier gas resulted in a ∼250 nm thick Al_0.25Ga_0.75N layer with SFs. It is suggested that the low surface mobility of (CH₃)₂Al:NH₂ species in the N₂ environment led to SF formation in the quaternary layers.     

Study of the martensitic transformation in the Co–9 at % Al alloy

Phase transformations in the Co–9 at % Al have been investigated after slow furnace cooling. It has been shown that the structure and phase composition of the alloy after slow cooling do not correspond to the equilibrium phase diagram of the alloy of this chemical composition. It has been established that the α → ε martensitic transformation does not require overcooling and occurs even during a slow cooling of the alloy. It has been found that the formation of 4H modulated martensite is a specific feature of the binary alloys of cobalt and is not connected with the rate of their cooling. The Curie temperatures for the B2, α, and ε phases have been determined.     

Mn3−xZnxO4 spinel phases in the Zn–Mn–O system

The thermal evolution of the Zn–Mn–O system in air was studied by X-ray diffraction, transmission electron microscopy–energy dispersive spectroscopy and electron energy loss spectroscopy. The obtained results suggest that this evolution involves the formation of different Mn_3−xZn_xO₄ spinel-type phases. With increasing temperature these spinels experience phase transformations which are found to be induced by the Mn(IV) to Mn(III) reduction process. This last cation is an active Jahn–Teller ion which leads to an appreciable distortion of the Mn_3−xZn_xO₄ spinel structure, from a cubic symmetry at low temperatures to highly distorted tetragonal symmetries at high temperatures.     

Crystal structure and properties of the new ternary YbZnxGa4−x and Yb3Zn11−xGax phases

Crystal structures of three new ternary YbZn_xGa_4?x (0.25 ≤ x ≤ 0.5 and 0.75 ≤ x ≤ 2) and Yb₃Zn_11?xGa_x (3.5 ≤ x ≤ 4.2) phases have been determined by means of single crystal X-ray as well as powder diffraction. They crystallize in known structure types, namely: CaCu_0.15Ga_3.75, BaAl₄ and La₃Al₁₁. Magnetic and transport properties were investigated for the new YbZn_xGa_4?x compounds. All phases studied show metallic-like and diamagnetic behavior.     

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.