Microstructure and Thermoelectric Properties of Bi- and Cu-Substituted Ca_3Co_4O_9 Oxides

Bi- and Cu-substituted Ca3Co4O9 samples were prepared by conventional solid-state reaction method and the effect of element substitution on the microstructures and thermoelectric properties was investigated. Partial substitution of Cu for Co leads to an increase in electrical conductivity and a decrease in Seebeck coefficient due to the rise of hole concentration. The microstructure of Cu-substituted sample is almost unchanged compared with undoped Ca3Co4O9. On the other hand, partial substitution of Bi for Ca gives rise to a significant increase in the grain size, and c-axis-oriented structure can be formed in Ca2.7Bi0.3Co4O9, resulting in an obvious increase in electrical conductivity. Cu and Bi co-substitution further increases the grain growth and the electrical conductivity of Ca2.7Bi0.3Co3.7Cu0.3O9. Thus, Cu and Bi co-substitution samples possess the optimal thermoelectric performance at high temperature and the highest value of power factor can reach 3.1×10^-4 Wm^-1.K^-2 at 1000 K.

First principle study on the possibilities of magnetism in one-dimensional In and Tl atomic wires with the full-potential linearized augmented plane wave method

Using ab initio total energy calculations with the full-potential linearized augmented plane wave method, the possibilities of magnetism in one-dimensional In and Tl wires were explored and their properties as the function of geometric structures were studied. The results suggest that the linear In and Tl wires show magnetization at the equilibrium bond distance with magnetic moments of 0.71 and 0.67 μB/atom, respectively. Allowing ions to relax, the wires were deformed as zigzag structures, but no dimerization occurs. The zigzag wires also exhibit spontaneous magnetization, although the magnetic moments are lower than those of straight wires.

The Observation of Martensite and Magnetic Domain Structures in Ni_(53)Mn_(24)Ga_(23) Shape Memory Alloys by Scanning Electron Acoustic Microscopy and Scanning Thermal Microscopy

We present observations of martensite variants and ferromagnetic domain structures of Ni_(53)Mn_(24)Ga_(23) ferromagnetic shape memory alloys with a pure tetragonal martensitic phase by using scanning electron aconstic microscopy (SEAM) and scanning thermal microscopy (SThM).Electron acoustic images show a polycrystalline morphology with martensite variants.Direct coincidence between crystallographic martensitic twin variants and magnetic domains is found.A domain-like structure,obtained by SThM,is firstly reported,and then confirmed by magnetic force microscopy (MFM).The experimental results will be helpful for investigating the local thermal properties of ferromagnets and understanding the relationship between martensite variants and magnetic domains.

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo_2O_(5+δ)(RE= Pr,Gd,Y)

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5＋δ,GdBaCo2O5＋δ,and YBaCo2O5＋δ were investigated by the thermogravimetry（TG）method in the temperature range of 400~900 ℃.The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides,such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ,whereas,the oxygen permeation flux was comparable to that of the latter,which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere（Δδ/Vmol）in these double perovskite structure oxides.The large oxygen adsorption/desorption rate constants of GdBaCo2O5＋δ and PrBaCo2O5＋δ made them nice catalyst coating materials,on other membrane surfaces,to improve the oxygen permeability.

Clarification of the oxygen adsorption properties of YBaCo_4O_7 at high temperature by thermogravimetry

The oxygen adsorption/desorption properties of YBaCo4O7 at high temperature were investigated by thermogravimetry(TG) method,in which two types of oxygen adsorption were combined.The first type adsorbed oxygen at about 700 °C and released the adsorbed oxygen at 880 °C.After the first type oxygen desorption,even the temperature and oxygen flow were kept the same,a second type oxygen adsorption at about 880 °C occurred and the adsorbed oxygen were released at above 980 °C.The combination of these two types of...

Deposition pressure effect on the surface roughness scaling of microcrystalline silicon films

The scaling behaviour of surface roughness evolution of microcrystalline silicon （/zc-Si：H） films prepared by very- high frequency plasma-enhanced chemical vapour deposition （VHF-PECVD） has been investigated by using a spectroscopic eHipsometry （SE） technique. The growth exponent β was analysed for the films deposited under different pressures Pg. The results suggest that films deposited at Pg = 70 Pa have a growth exponent β about 0.22, which corresponds to the definite diffusion growth. However, abnormal scaling behaviour occurs in the films deposited at Pg = 300 Pa. The exponent β is about 0.81 that is much larger than 0.5 of zero diffusion limit in the scaling theory. The growth mode ofμc-Si：H deposited at Pg = 300 Pa is clearly different from that of μc-Si：H at Pg = 70 Pa. Monte Carlo simulations indicate that the sticking process and the surface diffusion of the radicals are two key factors to affect the growth mode under different pressures. Under Pg = 300 Pa, β〉 0.5 is correlated with the strong shadowing effect resulting from the larger sticking coefficient.

Ab initio STUDIES ON MAGNETISM OF 3d TRANSITION METAL DIMERS

Ab initio calculations with the self-consistent full-potential linearized augmented-plane-wave method （FLAPW）, under generalized gradient approximation, have been carried out to describe the electronic and magnetic properties of 3d transition metal dimers. It predicted the antiferromagneticity of Cr2 and ferromagneticity of other species. The Mn2 dimer was shown to be ferromagnetic coupling with a local magnetic moment of 5μB. retaining the value of its free atom state. The V2 and Ni2 exhibited low spin-polarization with local magnetic moment of only 1μB per atom. On the other hand, Fe2 and Co2 were highly spin-polarized with local magnetic moments of 3 and 2μB.

From atom to monatomic wire:an ab initio study of magnetism in 3d transition metals

A systematic ab initio study on magnetism of the 3d transition metals（TM） from atom to monoatomic wire within density functional theory with generalized gradient approximation（GGA） was performed.The results show that the spin coupling has strong intraatomic exchange strengths about 1 eV for isolated 3d TM atoms.The magnetic moments are distinctly lower than those of free atoms for all dimers except Mn 2 .All the 3d TM elements exhibit magnetic ground states in the linear wire structure.