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11.
Abdessalem Badri María Luisa López Alain Wattiaux 《Journal of solid state chemistry》2011,184(4):937-944
Single crystals of a new phosphate KCuFe(PO4)2 have been prepared by the flux method and its structural and physical properties have been investigated. This compound crystallizes in the monoclinic system with the space group P21/n and its parameters are: a=7.958(3) Å, b=9.931(2) Å, c=9.039(2) Å, β=115.59(3)° and Z=4. Its structure consists of FeO6 octahedra sharing corners with Cu2O8 units of edge-sharing CuO5 polyhedra to form undulating chains extending infinitely along the b-axis. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the K+ ions are located. The Mössbauer spectroscopy results confirm the exclusive presence of octahedral Fe3+ ions. The magnetic measurements show the compound to be antiferromagnetic with Cm=5.71 emu K/mol and θ=−156.5 K. The derived experimental effective moment μex=6.76μB is somewhat higher than the theoretical one of μth=6.16μB, calculated taking only into account the spin contribution for Fe3+ and Cu2+ cations. Electrical measurements allow us to obtain the activation energy (1.22 eV) and the conductivity measurements suggest that the charge carriers through the structure are the potassium cations. 相似文献
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The influence of the potassium (K+) doping on the structure of multiferroic BiFeO3 and its relation with ferroelectric and magnetic properties was investigated for perovskites with composition Bi1−xKxFeO3 in the range 0?x?0.07. All the studied samples are described in R3c space group (No. 161). Typical cell parameters (BiFeO3) in hexagonal setting are ahex=5.5769(2) Å and chex=13.8531(2) Å with Z=6 formula units. The structure determination shows that as the K+ content increases, the average cations displacements decrease reducing the polar character of doped samples with respect to pure BiFeO3 and leading to a change from rhombohedral to a pseudo-cubic symmetry. A structural disorder is related to the substitution of K+, which results in strong diffuse scattering (DS) located at the bottom of the Bragg peaks. Magnetic measurements reveal that all the compounds remain antiferromagnetic at room temperature (RT) with almost no change in the transition temperature (Néel temperature TN). 相似文献
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The purpose of this work was to investigate numerically the drying of saturated deformable porous media. The considered sample is a rectangular porous plate which assumed to be both hydro-dynamically and thermally anisotropic, while the mechanical behavior of the sample is supposed to be isotropic. All walls of the plate are subjected to a convective heat flux. Moreover, the top and bottom walls are allowed the mass transfer. The Darcy–Brinkman extended model was used as the momentum balance equation for the liquid and solid phases. The energy balance equation is based on the local thermodynamic equilibrium assumption between the both phases. The lattice Boltzmann method is used to solve the governing differential equation system. A comprehensive analysis of the effect of anisotropy and the drying air parameters on macroscopic fields is investigated throughout this work. 相似文献
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This research work involves the dyeing of acrylic fabric with natural dye extracted from date pits powders using Soxhlet extraction process. The effect of dye bath pH, salt concentration, dyeing time and temperature were studied. The optimal dyeing conditions where pH 4, 0 g/L salt, 60 min, and 80 °C. The COD and the BOD5 of the residual dye bath were measured and it was shown from the registered values that the residual dye bath presents an acceptable rate of organic discharge. 相似文献
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Critical behavior in La0.7Pb0.05Na0.25MnO3 has been investigated by dc magnetization measurements. Magnetic data indicate that the compound exhibits a continuous (second-order) paramagnetic (PM) to ferromagnetic (FM) phase transition. Estimates of critical exponents yield δ=4.80±0.01, γ=1.296±0.002 and β=0.344±0.007 (consistent with both the predictions for the three-dimensional-Heisenberg model and with those reported for materials when the FM transition is ascribed to the double exchange (DE) mechanism as a major origin) with TC=334.54±0.08. The critical exponent γ is slightly inferior than predicted from the 3D Heisenberg model. Such a difference may be due, within the context of the quenched disorder, to the presence of some alterations of short-range magnetic order of FM clusters in the PM phase. The temperature variation in the effective exponent (γeff) is similar to those for disordered ferromagnets. 相似文献
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Anowar Tozri Moez Bejar Essebti Dhahri EL Kébir Hlil 《Central European Journal of Physics》2009,7(1):89-95
X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na+ ion substitution for Ca2+ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La0.7Ca0.3−x
Na
x
MnO3 manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter
σ
2. The temperature dependence of magnetization of all samples obeys the Bloch T
3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na+ ions causes a decrease in total exchange integral Aof the samples.
相似文献
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J. Khelifi A. Tozri E. Dhahri 《Applied Physics A: Materials Science & Processing》2014,116(3):1041-1051
Magnetocaloric effect and order of transition in (La1?x Nd x )2/3(Ca1?y Sr y )1/3MnO3, prepared by conventional solid-state reaction, have been investigated. Using Banerjee criterion, we demonstrate first-order transition for (J1) and (J2 ) as well as second-order transition for (J3 ), (J4 ), and (J5 ) samples. The ΔS M max is ranging between 9.18 Jkg?1 K?1 and 4.87 when Nd and Sr content changes leading to relative cooling power (RCP) varying between 330 and 229.35 J/kg. Both ΔS M max and the RCP are found sensitive to the disorder σ 2. The universal behavior obtained from ΔS variation curves confirmed the first-order transition for (J1) and (J2 ) samples and second-order transition for (J3), (J4), and (J5 ) samples obtained by Banerjee criterion. All samples with second-order phase transition exhibit inhomogeneous character estimated from local exponent n. 相似文献
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