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以高纯钆和Gd5Si2Ge2合金为原料,采用放电等离子烧结技术制备了两组元Gdx(Gd5Si2Ge2)1-x(x=0,0.33,0.5,0.7,1)层状复合磁制冷材料.通过自制的磁热效应测量仪器直接测量了复合材料在外加磁场1.5 T下的磁热效应(ΔTad).随着复合比例的变化,材料的最大绝热温变(ΔTad)从x=0.3时的1.6 K增加到x=0.7时的2.0 K,而最大绝热温变峰的位置从286K变到了293 K.同时,与单组元的Gd5Si2Ge2合金相比,随着钆的含量增加时,复合材料的最大绝热温变峰变宽.当x=0.7时,层状复合磁制冷材料在外加磁场1.5 T下的最大绝热温变(ΔT)在260-310K范围里从1.1 K变到2.0 K,这种材料非常适合作为室温磁制冷材料. 相似文献
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快淬低纯Gd5Si2Ge2合金的结构和磁熵变 总被引:1,自引:0,他引:1
采用纯度为99%的低纯稀土金属Gd经电弧炉熔炼获得Gd5Si2Ge2 母合金,然后通过快淬研究快淬工艺对低纯Gd5Si2Ge2 合金结构与磁熵变的影响。粉末衍射结构分析表明,铸态Gd5Si2Ge2 合金由Gd5Si2Ge2 相、Gd5 (Si、Ge)3 相和Gd(Si、Ge)相所组成;而甩带速度为25、40m/s的合金均为Gd5Si4 型正交相。用最小二乘法计算得两种不同快淬速度合金的晶格常数没有明显差异。甩带速度为40m/s 的Gd5Si2Ge2 合金的居里温度(Tc=305K)在室温区间,等温磁熵变为7.25J/kg·K(0~5T)。 相似文献
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基于磁性材料相变过程中伴随的磁热效应而发展起来的磁制冷技术因其绿色环保和高效节能等优点而被广泛关注.高性能磁制冷工质材料的探索一直是本领域的研究热点也是难点之一.本文中,我们通过实验研究结合第一性原理计算,对Gd Fe2Si2化合物的晶体结构、磁性、磁相变以及低温磁热效应进行了系统研究,结果表明Gd Fe2Si2化合物基态为反铁磁且具有大的低温可逆磁热效应.在0–7 T的磁场变化下,其磁制冷参数包括等温磁熵变最大值和制冷能力分别高达30.01 J kg-1K-1和328.45 J kg-1.这些磁制冷参数优于大多数目前已报道的同温区高性能稀土基磁制冷材料,表明反铁磁Gd Fe2Si2化合物在低温磁制冷领域同样具有潜在的应用前景. 相似文献
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用高频真空悬浮炉在氲气保护下制备了(Gd1-xREx)5Si4(RE:Dy,Tb;x=0、0.1、0.125、0.15)和(Gd1-xREx)5Si4(x=0.1、0.125)合金样品,用直接测量方法测定了在永磁体提供的低磁场(H=1.3T)条件下样品的磁热效应曲线(△Tab-T);结果表明,用稀土金属Dy、Tb分别部分替代Gd5Si4合金中的Gd原子,不能增强合金的磁热效应,但可在333~300K范围改变材料的居里温度,且磁热效应峰值范围变宽. 相似文献
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First-principles cluster calculations are reported of the local electronic structure of the three compounds: La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2. The copper
and the planar oxygen 2p
atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the
atomic orbital lowered significantly in energy for chlorine and fluorine apical positions. 相似文献
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SrLa2Al2O7 and SrGd2Al2O7 belong to the structural type Sr3Ti2O7. In SrGd2Al2O7 strontium and gadolinium occupy respectively the 12 and 9 coordinated sites, whereas in SrLa2Al2O7 the homologous cations are statistically distributed. The fluorescence spectra of both phases activated by Eu3+ ions show that the only possible position of Eu3+ is the 9 coordinated site. 相似文献
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根据硬盘基板用材料的要求,制备了MgO-Al2O3-SiO2-TiO2-Y2O3高弹性模量玻璃(120GPa),玻璃的弹性模量随组成的变化服从Makishima-Mackenzie理论,MgO,Al2O3,TiO2,Y2O3等具有较高单位体积离解能的氧化物有利于提高玻璃的弹性模量,但玻璃弹性模量的理论计算值低于测试值,这是因为Makishima-Mackenzie理论没有考虑玻璃内阳离子的具体配位,对MgO,Y2O3堆积密度因子的堆导存在误差,因此利用Makishima-Mackenzie理论发展高弹性模量玻璃时应对MgO,Y2O3等氧化物的计算进行修正。 相似文献
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Transparent glasses in the system (100−x)Li2B4O7–x(SrO---Bi2O3---Nb2O5) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi2Nb2O9 (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (r) and the loss factor (D) for the lithium borate, Li2B4O7 (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix. 相似文献
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The subsolidus phase equilibria of the Li2O-Ta2O5-B2O3, K2O-Ta2O5-B2O3 and Li2O-WO3-B2O3 systems have been investigated mainly by means of the powder X-ray diffraction method. Two ternary compounds, KTaB2O6 and K3Ta3B2O12 were confirmed in the system K2O-Ta2O5-B2O3. Crystal structure of compound KTaB2O6 has been refined from X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pmn21 (No. 31), with lattice parameters a = 7.3253(4) Å, b = 3.8402(2) Å, c = 9.3040(5) Å, z = 2 and Dcalc = 4.283 g/cm3. The powder second harmonic generation (SHG) coefficients of KTaB2O6 and K3Ta3B2O12 were five times and two times as large as that of KH2PO4 (KDP), respectively. 相似文献
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Marko Hrovat Tadej Rojac Andreja Ben?an Janez Holc Marija Kosec 《Materials Research Bulletin》2004,39(11):1723-1728
The subsolidus phase equilibria in air for the Al2O3-CeO2-PbO and Al2O3-CeO2-RuO2 systems were studied with the aim of obtaining information on possible interactions between a CeO2-based solid electrolyte in solid-oxide fuel cells (SOFCs) and other oxides. No ternary compound was found in either of the systems. The tie line in the Al2O3-PbO-CeO2 system is between Al2Pb2O5 and the CeO2. 相似文献
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A. Nazarenko K. J. E. Vos S. Haas E. Dagotto R. J. Gooding 《Journal of Superconductivity》1995,8(5):671-672
Recent angle resolved photoemission (ARPES) measurements for the insulating cuprate Sr2CuO2Cl2 have provided the first experimental data which can be directly compared to the (theoretically) well-studied problem of a single hole propagating in an antiferromagnet. Some discrepancies withthe familiar 2D t— J model were observed. Here we discuss a comparison between the ARPES results and the quasiparticle dispersion of both (i) the extended t— t— J Hamiltonian and (ii) the three-band Hubbard model. 相似文献
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Arthur W. Sleight 《Materials Research Bulletin》1974,9(11):1437-1442
Substitutions into cadmium niobate of the type Cd2?xAxNb2O7 (x≤0.5) have been carried out at 58 kbars and 1100°C. The substituting A cations were Mg, Mn, Fe, Co, Ni, Cu, and Zn which are all smaller than Cd. Rhombohedral or triclinic distortions derived from cubic Cd2Nb2O7 were achieved at values of x as low as 0.05. All the substituted phases appear to be centric at room temperature. Analogous substitutions into Cd2Ta2O7 were also made. 相似文献