Nd-Fe-B(B≤50at.％)三元系相图的研究

本文用X射线衍射、热学分析、磁性测量等手段研究了Nd-Fe-B(B≤50at.％)三元系相图,主要结果如下:1.重新测定了Nd-Fe二元系相图,确证NdFe₂相是不存在的。2.测定了Nd-Fe-B(B≤50at.％)三元系室温横截面。在该三元系中存在三个化合物:Nd₂Fe₁₄B,Nd₈Fe₂₇B₂₄,Nd₂FeB₃。 指出:在未经退火的Nd-Fe-B三元母合金中,存在有过冷液相(非晶)的可能性。实用Nd-Fe-B新型永磁合金,由三相构成,主相为Nd₂Fe₁₄B,次相为Nd和Nd₈Fe₂₇B₂₄。3.测定了Fe₉₄B₆-Nd₁₂Fe₈₂B₆-Nd_33.5Fe_60.5B₆和Nd₂Fe₁₇-Nd₂Fe₁₄B-Nd₈Fe₂₇B₂₄纵截面。指出:在制备Nd-Fe-B三元永磁合金时,最高烧结温度不得高于1100℃,而后热处理的温度在600℃左右为宜。4.研究了Nd₂Fe₁₄B,Nd₈Fe₂₇B₂₄的结构和Nd₂Fe₁₄B的单相区。Nd₂Fe₁₄B为四方晶系,a=8.800,c=12.190,z=4,空间群为P4₂/mnm,X射线密度D_X=7.60g/cm³,测量密度D_O=7.50g/cm³。在测量精度范围内,观测不到Nd₂Fe₁₄B有单相区存在。Nd₈Fe₂₇B₂₄为四方晶系,a=7.12,c=27.40,z=2,D_X=7.01g/cm³,D_O=7.00g/cm³,可能的空间群为P4₂/n。5.在实验的基础上,讨论了Nd₂Fe₁₄B的热稳定性,并对制备Nd-Fe-B永磁合金的粉末冶金工艺提供了解释。     

BaO-Y2O3(La2O3)-CuO三元系相图的研究

本文采用X射线衍射,热学分析、超导电性测量等方法测定了La₂O₃-CuO,BaO-CuO,Y₂O₃-CuO二元系相图,BaO-La₂O₃-CuO,BaO-Y₂O₃-CuO三元系室温截面。在这两个三元系的富CuO区,存在Ba_xLa_2-x CuO₄(x≤0.07),BaLaCu₂O_5+δ,BaLa₄Cu₅O_14+δ,BaLa₂Cu₂O₆和Ba₂YCu₃O_9-y,BaY₂CuO₉化合物。Ba_xLa_2-x,CuO₄(x≤0.07),BaLa₄Cu₅O_14+δ,BaLaCu₂O_5+δ,BaLa₂Cu₂O₆均属四方晶系,点阵常数分别为a=5.356,c=13.20;a=8.660,c=3.863;a=3.917,c=11.75;a=3.992,c=19.96.Ba₂YCu₃O_9-y属正交畸变钙钛矿结构,a=3.892,b=3.824,c=11.64,空间群为Pmmm。BaY₂CuO₅具有正交结构,a=7.123,b=12.163,c=5.649;空间群为Pbnm。研究了组成与超导电性的关系,考查了烧结温度对Ba₂YCu₃O_9-y化合物结构和超导电性的影响,并对超导电性产生的原因进行了讨论。     

BaB2O4-Na2B2O4-K2B2O4三元系的研究

本文用实验测定和理论计算相结合的方法,研究了BaB₂O₄-Na₂B₂O₄-K₂B₂O₄三元系.在对该三元系3个侧边二元系相图热力学分析的基础上,用非对称的Toop模型将二元系热力学数据延拓到三元系,计算了BaB₂O₄-Na₂B₂O₄-K₂B₂O₄三元相图,计算结果与该三元系的一个典型垂直截面的测定结果吻合很好.     

三矩阵乘积的(T,S,2)-逆的反序律

矩阵A的(T,S,2)-逆是指适合XAX=X,R(X)=T和N(X)=S的矩阵X,以矩阵的秩为工具,本文研究了三矩阵乘积的(T,S,2)-逆的反序律,给出了(ABC)_(T4,S4)⁽²⁾=C_(T3,S3)⁽²⁾B_(T2,S2)⁽²⁾A_(T1,S1)⁽²⁾的充要条件。     

有一个实现包含Kr +1的可图序列

设K _{r +1}是一个r +1个顶点的完全图. 一个可图序列π =(d₁, d₂,…, d_n)称为是蕴含K _r+1 -可图的, 如果π有一个实现包含 K _{r +1}作为子图. 该文进一步研究了蕴含K _{r+1 -}可图序列的一些新的条件, 证明了这些条件包含文献[14,10,11]中的一些主要结果和当n≥5r/2 +1时,σ(K _r+1, n)之值(此值在文献[2]中被猜测, 在文献[6,7,8,3]中被证实). 此外, 确定了所有满足n≥5, d₅≥4 且不蕴含K₅ -可图序列π=(d₁, d₂,…, d_n)的集合.     

Y1-xNdxSr2Cu2.7Mo0.3O7-δ体系的声子振动谱和输运性质

研究了Y_1-xNd_xSr₂Cu_2.7Mo_0.3O_7-δ(x =0 ,0 .1 ,0 .2 ,0 .5 ,0 .8和 1 .0 )的Ra-man光谱、红外光谱,指出RSr₂Cu_2.7Mo_0.3 O_7-δ结构上与RBa₂Cu₃O_7-δ有显著的差异,而伴随着Nd的掺入,晶体的微结构发生了变化 .结合电阻率和热电势的测量结果 ,我们讨论了这种微结构变化对载流子分布的影响和NdSr₂Cu_2.7Mo_0.3O_7-δ不超导的原因,进而指出在高温超导体中广泛存在的稀土离子尺寸效应也是大稀土离子替代产生的晶体微结构变化的结果     

重层子模型中的介子质量谱

本文假定层子的裸质量很大,层子和反层子之间的相互作用为:V₀γ₅×γ₅+V₁γ₄×γ₄+V₂γ×γ型。在瞬时相互作用近似下,求解介子的B-S方程,得到了介子波函数和介子质量m的公式m²=(m₁+m₂)²+2(m₁+m₂)E,其中m₁,m₂为层子、反层子的等效质量,E为schrdinger方程的本征值。在V₁和V₂的适当选取下,得到了与实验符合较好的新老介子质量谱。本模型对为什么等效质量很小的u,d,s层子体系在形式上满足非相对论的Schrdinger方程提供了一种解释。     

O′-β′ Sialon在Y-Si-Al-O-N系统中的相关系

本文提出了Si₂N₂O-AlN-Y₂O_3系统的亚固相图,并修正了O’-β’Sialon在Y-Si-Al-O-N系统中的相关系。在Si-Al-O-N系统中,Si₃N₄和O’_ss(x=0.3)之间应有结线,它把O’-β’二相区分割成为两个相容性三角区:Si₃N₄-Si₂N₂O-O’_ss(x=0.3)和Si₃N₄-β’_ss(z=0.8)-O’_ss(x=0.3)。 Si₃N₄-O’_ss(x=0.3)-YAG-H相,在1550℃时形成为一相容性四面体区。如果加热到1700℃,而后于1200—1300℃退火热处理,则H相消失,相容性区变成为Si₃N₄-O’_ss(x=0.3)-YAG-Y₂Si₂O₇。 Si₃N₄-Si₂N₂O-O’_ss(x=0.3)-Y-2Si₂O₇(或H),Si₃N₄-O’_ss(x=0.3)-YAG-Y₂Si₂O₇(或H)和Si₃N₄-β_ss(z=0.8)-O’_ss(x=0.3)-YAG,这三个相容性区的确定,对开发制造O’-β’Sialon二相陶瓷有实用意义。     

凹函数定义的弱Orlicz-Hardy空间之间的鞅变换

本文研究了两个弱Orlicz-Hardy鞅空间中元素之间相互转换关系的问题.利用鞅变换的方法,证明了：设φ₁是凹Young函数,φ₂是凹或者凸Young函数,且q_φ1 > 0,0 < q_φ2≤p_φ2 <+∞,则当φ₁≤φ₂时,wH_φ1中的元素是wH_φ2中元素的鞅变换的结果,所得结果将已有的相关结论由强型空间（赋范空间）推广到弱型空间（赋拟范空间）.     

L2(Rs)中正交尺度函数和正交小波的Fourier变换紧支集的刻画

借助于Fourier变换,在较弱条件下给出了φ(x)是L²(R^s)上正交尺度函数的一个充分必要条件.进一步, 假设 {Ψ_μ } 是正交小波, 且正交小波的Fourier变换紧支集是 ∪_μsupp{ψ_μ} =∏^s_i=1[A_i, D_i] -∏^s_i=1(B_i, C_i),A_i≤B_i≤C_i≤D_i, i =1, 2,… , s. 则在最弱条件“每一个 |ψ_μ| 在ω∈∂(∏^s_i=1[A_i, D_i]) 上连续'下, 该文通过一些不等式和等式给出了正交尺度函数和正交小波的Fourier变换紧支集的刻画.文中的结论全面改进了龙瑞麟和张之华的结果.     

Formation of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy under high pressure

The formation of nanocrystalline Fe_73.5 Cu₁Nb₃Si_13.5 B₉ alloy by annealing an amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at a temperature of 823 K under pressures in the range of 1–5 GPa is investigated by using X-ray diffraction, electron diffraction, and transmission electron microscopy. The high pressure experiments are carried out in belt-type pressure apparatus. Experimental results show that the initial crystalline phase in these annealed alloys is a-Fe solid solution (named a-Fe phase below), and high pressure has a great influence on the crystallization process of the a-Fe phase. The grain size of the a-Fe phase decreases with the increase of pressure (P). The volume fraction of the a-Fe phase increases with increasing the pressure as the pressure is below 2 GPa, and then decreases (Pδ2 GPa). The mechanism for the effects of the high pressure on the crystallization process of amorphous Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy is discussed Project supported by the National Natural Science Foundation of China (Grant No. 19674070) and the Natural Science Foundation of Hebei Province.     

M?ssbauer study on Sn-doped (Lal1-x,Srx)2Cu1-x,Snx,O4 superconductors under a new concept

¹¹⁹Sn M?ssbauer research is carried out on (La_1-xSr_x),Cu_1-xSn_xO₄(x = 0.075 and 0.110) superconductors which are designed under a new concept. The M?ssbauer spectra results show that Sn occupies Cu position in Sn⁴⁺ state, and there is no Sn²⁺ ion occupying La position. The local lattice deformation near Sn⁴⁺ site is small, but displays an increasing tendency with Sn doping. For La₂CuO₄ matrix, the simultaneous dopings of Sr/Sn induce holes and electrons on CuO₂ layer in a new mechanism which influences superconductivity. Under a new mechanism of extra oxygen, the extra oxygen effect of Sn-doping on superconductivity is discussed     

Synthesis of C3N4 crystals under high pressure and high temperature

C₃N₄ crystals with the size of several micrometers have been synthesized from C₃N₄H₄ in the presence of nickel-based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400°C for 10 min. Scanning electron microscopy, energy-disperse X-ray analysis, and X-ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested.     

Phase transition in layered perovskite-like manganate Ca3Mn2O7 under high pressure

In situ high pressure energy dispersive X-ray diffraction measurements on the layered perovskite-like manganate Ca₃Mn₂O₇ powder under pressures were performed by using the diamond anvil cell with synchrotron radiation. The results show that the structure of layered perovskite-like manganate Ca₃Mn₂O₇ is unstable under pressure due to the easy compression of NaCl-type blocks. The structure of Ca₃Mn₂O₇ underwent two phase transitions under pressures in the range of 0–35 GPa. One was at about 1.3 GPa with the crystal structure changing from tetragonal to orthorhombic. The other was at about 9.5 GPa with the crystal structure changing from orthorhombic back to another tetragonal.     

Fibrous Filler-Matrix Interaction in Oxide Composites

The interaction between a fibrous alumina filler and a hydrated zirconia matrix during the fabrication of ceramic composites is studied. The influence of the crystal structure and porosity of the filler on the properties of the ZrO₂-Al₂O₃ composite material is investigated. It is found that, as a result of addition of alumina fibers of cubic and monoclinic structures (- and -phases), the ZrO₂ hydrogel interacts with fibers and solid ZrO₂ solutions of tetragonal structure are formed. These solutions exist over the range of 600 to 1200°C and, at annealing above 1200°C, due to crystallographic transitions the of - and -phases, they break down, namely Al₂O₃ transforms into -corundum and ZrO₂ into a monoclinic modification. However, the material does not fail and a stable porous ceramic composite is formed. To manufacture a composite with improved mechanical characteristics, fibrous alumina fillers with the structure of -corundum must be used.     

Preparation, structure, magnetic properties and special magnetoresistance effect of Lao.67Sr0.33Mn03+δ/Pr0.7Cao.3 Mn03+δ/Lao.67Sro.33Mn03+δ trilayered thin films

The La_0,67Sr_0.33Mn0_{3 +δ}/Pr_0.7Ca_o.3Mn0_3+δ/La_0.67Sr_0.33Mn0_3+δ(LPL) trilayered films on (100)LaA-1O₃ substrates are prepared by using direct current (DC) magnetron sputtering method. The results obtained by means of X-ray powder diffractometer show that all films are the high quality epitaxial films. The results gained by SQUID magnetometer indicate that there is a magnetic coupling in the LPL trilayered films. The resistivities of LSMO, PC-MO and LPL films are measured using standard four-probe method and analyzed log_p-1/T curve. From the results it is concluded that the middle-layered PCMO which is ferromagnetic may play a role of intra-magnetic field, which weakens the paramagnetism of LSMO film, lowersp _max and enlargesT _p which is the transition temperature from metal to insulator, just as the applied magnetic field does. And the middle-layered PCMO may induce the change of the density of states in the LSMO’s gap. The two reasons above make the resistivity andT _p of the samples in zero field change with the thickness of PCMO layers. Project supported by the Chinese Academy of Sciences and the Foundation of State Science and Technology Commission of China.     

Differences in microstructure of Pd77.5Au6Si16.5 alloy solidified under microgravity and gravity conditions

The microstructure of Pd_77.5Au₆Si_16.5alloy solidified both on board a Chinese Retrievable Satellite and on the earth is studied. Postmortem analyses of microstructure presented that the same types of phases, primary phase (Pd₃Si) and eutectics (Pd₃Si + Pd solid solution) were formed in both cases. But the phase morphologies were quite different. It was dendritic for the primary phase and lamellar for the eutectics under normal gravity condition. However, under microgravity condition the primary phase was granular and the eutectic was peculiar network. Detailed analysis showed that the differences in morphologies of the microstructure were due to the existence of gravity-induced buoyancy convection on the earth which increased the mass transport abilities and decreased the thickness of the solute boundary in front of the solid-liquid interface during solidification under normal gravity condition.     

空间l1(Xn)中的弱紧性

本文首先讨论空间l₁(X_n)中的弱收敛性，然后给出了l₁(X_n)中弱紧性的几种等价刻画，同时对l_p(X_n)（１＜ｐ＜∞）中的弱紧性也得到了类似的结果．     

Dolbeault Cohomology for G2-Manifolds

Cocalibrated G₂-manifolds are seven-dimensional Riemannian manifolds with a distinguished 3-form which is coclosed. For such a manifold M, S. Salamon in Riemannian Geometry and Holonomy Groups (Longman, 1989) defined a differential complex related with the G₂-structure of M.In this paper we study the cohomology of this complex;it is treated as an analogue of a Dolbeault cohomologyof complex manifolds. For compact G₂-manifoldswhose holonomy group is a subgroup of G₂ special propertiesare proved. The cohomology of any cocalibrated G₂-nilmanifold \K is also studied.