新化合物Al_(14)Gd_5Si的晶体结构及其Rietveld精修

利用X射线粉末衍射技术和R ietve ld结构修正方法对A l14G d5S i进行了研究,新三元化合物A l14G d5S i具有N i3Sn结构类型,空间群为P 63/mm c(N o.194)。点阵参数为a=0.63022(1)nm,c=0.45856(1)nm,指标化的可靠性因子F30=218.1(33)。用R ietve ld方法对该化合物的晶体结构成功地进行了精化修正,精修得到的R因子为Rp=0.119,Rwp=0.157。

New ternary compound La_8Al_(13)Sn_3

A new ternary compound La8Al13Sn3 was synthesized and studied by means of X-ray powder diffraction technique. The compound La8Al13Sn3 crystallizes in a hexagonal AlB2-type structure with space group P6/mmm （No. 191） and the lattice parameters a = 0.44919（1） nm and c = 0.43835（1） nm. The Smith and Snyder figure of merit for index, FN, is F30 = 197.3（30）. The Rietveld refinement for the crystal structure of the compound was carried out successfully. The liability R-factors of Rietveld refinement are Rp = 0.114 and Rwp = 0.148. The compound La8Al13Sn3 decomposes into LaAl2 with cubic structure and space group Fd 3m （227）, LaAl3 with hexagonal structure and space group P63/mmc （194）, and Sn at 720°C.

Crystal structure and Rietveld refinement of the new ternary compound Al_(14)Nd_5Si

The new ternary compound Al14NdsSi has been studied by means of the X-ray powder diffraction technique and the Rietveld method. The ternary compound Al14Nd5Si has a hexagonal Ni3Sn-type structure with space group P63/mmc （No.194）, the lattice parameters are a = 0.64470 （2） nm and c = 0.45926 （1） nm. The Smith and Snyder figure of merit for the index, FN, is F30 = 97.8 （30）. The X-ray diffraction data indicated that the crystal structure of the compound Al14Nd5Si has been successfully refined by the Rietveld method. The R-factors of Rietveld refinement are Rp = 0.088 and Rwp = 0.120, respectively. The thermal dependence of magnetization for the compound was measured by a vibrating sample magnetometer. The experimentally determined magnetic effective paramagnetic moment is μeff= 3.60 μB per Nd atom. The paramagnetic Currie temperature θp = -33.7 K was also obtained from the Currie-Weiss law.

风格派在现代建筑中的应用与发展

流行于20世纪前期的风格派,对建筑和艺术设计都产生过深远的影响。杜斯伯格致力于风格派理念的研究与推广,里德维尔特把风格派的定义诠释到了建筑上,柯布西埃在空间关系和色彩构成上深受风格派艺术的影响,密斯则强调空间的统一性与流动性。风格派艺术在当今社会得到了传承和创新,设计者们更强调人与自然的统一、和谐关系。

镱掺杂的Ca1-xYbxMnO3(x=0～0.2)化合物的Rietveld结构精修和热电性能

采用溶胶-凝胶和无压烧结的方法制备了Yb掺杂的钙钛矿型Ca1-xYbxMnO3（x=0~0.2）系列固溶体,并结合X射线R ietveld精修、扫描电子显微镜及热电性能测试,系统研究了Yb掺杂量对产物相组成、晶体结构、显微结构和热电性能的影响。结果表明,Yb的掺杂引起了CaMnO3的晶格畸变,导致Mn-O2-Mn键角（氧八面体在水平方向的扭转）随着Yb的增加而减小;Yb的掺杂大幅度降低了样品的电阻率,并改变了电传输特性：Seebeck系数绝对值显著降低,同时随着掺杂量的增加,进一步减小。Yb的掺杂明显抑制了晶粒长大,此外,其重原子特性和少量第二相的生成显著降低了材料的热导率。其中x=0.1的样品Ca0.9Yb0.1MnO3在T=700℃时,ZT值达到0.093,较单相的CaMnO3提高了120%。