NEUTRON-POWDER-DIFFRACTION STUDY OF THE STRUCTURE AND MAGNETIC PROPERTIES OF Nd2Fe14Si3

The crystal and magnetic structures of Nd₂Fe₁₄Si₃ at room temperature were refined by Rietveld analysis of neutron-powder-diffraction data. It was found that silicon atoms occupy preferentially both 18h and 18f of Th₂Zn₁₇-type structure with occupancies 0.36 and 0.14, respectively, The Fe-Fe bond-lengths computed with the refined crystallographic parameters have optimum values, as compared with those of Nd₂Fe₁₇ compounds, which can explain well why the Curie temperature rises strongly when the unit cell volume reduces with the substitution of silicon for iron in Nd₂Fe₁₇.     

NEUTRON-POWDER-DIFFRACTION STUDY OF THE STRUCTURE AND MAGNETIC PROPERTIES OF Nd2Fe14Si3

The crystal and magnetic structures of Nd₂Fe₁₄Si₃ at room temperature were refined by Rietveld analysis of neutron-powder-diffraction data. It was found that silicon atoms occupy preferentially both 18h and 18f of Th₂Zn₁₇-type structure with occupancies 0.36 and 0.14, respectively, The Fe-Fe bond-lengths computed with the refined crystallographic parameters have optimum values, as compared with those of Nd₂Fe₁₇ compounds, which can explain well why the Curie temperature rises strongly when the unit cell volume reduces with the substitution of silicon for iron in Nd₂Fe₁₇.     

离子色谱非梯度洗脱法同时测定7种稀土元素的研究

研究了离子色谱非梯度洗脱法同时测定7种稀土元素的方法，用草酸一元淋洗液，采用非梯度洗脱方式，以PAR为显色荆，在520nm处对7种稀土元素同时进行检测。考察了淋洗液的组成、浓度、pH及流量等因素对被测组分分离和测定的影响，选择了显色剂的浓度、流量和检测波长，并进行了干扰实验，在选定的最佳分离测定条件下，测定了7种稀土元素的线性回归方程、检出限0．04～0．20mg／L，回收率在94．3％～101．5％之间。本方法已用于稀土氧化物的高温氯化产物中稀土元素的测定。     

EFFECT OF MANGANESE SUBSTITUTION IN R2AlFe16-x Mnx(R=Y,Ho,Nd AND Pr)COMPOUNDS ON STRUCTURAL AND MAGNETIC PROPERTIES

The structural and magnetic properties of R₂AlFe_16-xMn_x(0≤x≤8 for Y,Ho,0≤x≤10 for Pr, 0≤x≤16 for Nd)compounds have been investigated by means of X-ray diffraction and magnetization measurements.The R₂AlFe_16-xMn_x compounds have a hexagonal Th₂Ni₁₇-type structure for R=Y and Ho, and a rhombohedral Th₂Zn₁₇-type structure for Nd and Pr.With increasing x,the unit-cell volumes have a small increase initially,followed by a greater linear increase.The Curie temperature and the saturation magnetizati on of these compounds show marvelous drop with increasing x.Compensation point was observed in the temperature dependence of the magnetization for Ho₂AlFe₁₂Mn₄ compound.     

α-蒎烯和间戊二烯共聚工艺

研究了共聚反应条件对α-蒎烯（α-P）和间戊二烯(PD)共聚产物的影响,确定最佳反应条件为：反应时间2 h,原料比例n(α-P)∶n(PD)=1∶2,反应温度15 ℃,溶剂甲苯,催化剂AlCl3用量为单体总质量1%,获得产物树脂的收率为72.3%,软化点为121.3 ℃,色度为4,相对分子质量为1549,相对分子质量分布为1.92。 其热稳定性和粘结相容性好。     

NEUTRON-POWDER-DIFFRACTION STUDY OF ErFe11.35Nb0.65 AND ErFe11.35Nb0.65Ny

ErFe_11.35Nb_0.65 AND ErFe_11.35Nb_0.65N_y have been synthesized and neutron-powder-diffraction experiments at room temperature performed. The ErFe_11.35Nb_0.65N_y nitride, obtained by gas-solid reaction, retains the ThMn₁₂-type structure of its parent compound. The Nb atoms occupy 8i sites and the nitrogen atoms are located at 2b sites. The atomic magnetic moments of the Er ions are antiparallel to those of the Fe atoms. Upon nitrogenation, the lattice cell expands mainly along the a-axis and the atomic magnetic moments of Fe are enhanced.     

MAGNETIC PROPERTIES OF Dy2Fe17-xCrx AND Er2Fe17-xCrx(x=0-3)COMPOUNDS

The crystal structure and magnetic properties of R₂Fe_17-xCr_x(R=Dy,Er,0≤x≤3) compounds have been investigated by me ans of X-ray diffraction and magnetization measurements. These compounds have hexagonal Th₂Ni₁₇-type structure. The unit-cell volumes decrease with the increase of Cr concentration x. The Curie temperature T_c of the Er₂Fe_17-xCr_x compounds increases from 320 K for x=0 to 403 K for x=1.0 and then decreases with further increase of x. The Cur ie temperat ure T_c of Dy₂Fe_17-xCr_x compounds increases from 364 K for x=0 to 435 K for x=1.0 and then decreases with further increase of x. The saturation magnetization of these compounds shows an approximately linear decrease with the increase of x. Spin reorientation transitions occur s in Er₂Fe_17-xCr_x(x=2.0 and 3.0).     

A NEUTRON POWDER DIFFRACTION STUDY OF THE STRUCTURE IN Nd2Fe17Nx(x = 2.5, 3.0, 5.5)

The crystallographic and magnetic structures of Nd₂Fe₁₇N_x(x = 2.5, 3.0, 5.5) at room temperature were refined by Rietveld analysis of neutron powder diffraction data. We found that Nd₂Fe₁₇N_x has a Th₂Zn₁₇ type structure (S.G. R3m) and the nitrogen atoms occupy both 9e and 18g sites simultaneously and at different rates.     

NEUTRON-POWDER-DIFFRACTION STUDY OF ErFe11.35Nb0.65 AND ErFe11.35Nb0.65Ny

ErFe_11.35Nb_0.65 AND ErFe_11.35Nb_0.65N_y have been synthesized and neutron-powder-diffraction experiments at room temperature performed. The ErFe_11.35Nb_0.65N_y nitride, obtained by gas-solid reaction, retains the ThMn₁₂-type structure of its parent compound. The Nb atoms occupy 8i sites and the nitrogen atoms are located at 2b sites. The atomic magnetic moments of the Er ions are antiparallel to those of the Fe atoms. Upon nitrogenation, the lattice cell expands mainly along the a-axis and the atomic magnetic moments of Fe are enhanced.     

中子散射与1994年诺贝尔物理奖

中子以它特有的性质，使它成为继Ｘ射线和电子衍射子之后的又一研究微观物质结构的有效广阔，于中子散射技术的发展，人们才得以在声子色散曲线和同位素效应的研究等方面有所收获。中子散射可以说是对Ｘ射线衍射和电子衍射的一个重要的不同缺少的补充，Ｓｈｕｌｌ和Ｂｒｏｃｋｈｏｕｓｅ由于在这一领域中的杰出贡献而获得１９９４年诺尔物理奖。