共查询到16条相似文献,搜索用时 62 毫秒
1.
2.
本文用中子飞行时间方法对C-15相的超导材料V_2Hf,V_2Ta和V_2Hf_(0.8)Ta_(0.2)以及V_2Zr_(0.5)。Hf_(0.5)和V_2Zr_(0.5)Hf_(0.33)Ta_(0.17)的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V_2Zr和V_2(Hf_(0.5)Zr_(0.5))系列声子性能的影响一致:声子频率随超导转变温度T_c增加而软化,随T_c减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高T_c起了作用。结果还进一步表明V_2Zr或V_2Hf与V_2(Zr_(0.5)Hf_(0.5))之间有着质的差别,V_2Hf加Ta后,T_c增加,声子频率软化,而V_2(Zr_(0.5)Hf_(0.5))加Ta后,T_c减小,声子频率则略有硬化。这与V_2Zr和V_2(Hf_(0.5)Zr_(0.5))加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。 相似文献
3.
本文用中子飞行时间方法对C-15相的超导物质V_2Zr,V_2Zr_(0.95)Nb_(0.05)及V_2Hf_(0.5)Zr_(0.5),V_2Hf_(0.5)Zr_(0.3)Nb_(0.2)的热中子非弹性散射谱作了测量,发现Nb的添加对V_2Zr和V_2Hf_(0.5)Zr_(0.5)系列的作用不同,V_2Zr添加第三组元Nb后,超导临界温度Tc增加,声子频率“软化”,而V_2Hf_(0.5)Zr_(0.5)系列添加第四组元Nb后,Tc略有下降,声子频率则“硬化”。V_2Zr_(0.95)Nb_(0.05)声子频率比V_2Zr“软化”的结果与以前磁化率下降几何平均声子频率上升的结果不一致。对于V_2Hf_(0.5)Zr_(0.5)加Nb后声子频率“硬化”的现象用角动量分波表象的能带论方法分析电-声作用得出的杂化理论作了解释 相似文献
4.
本文中研究了C-15结构V2Hf1-xNbx,V2Zr1-xNbx和V2Hf0.5Zr0.5-xNbx系列的超导转变温度Tc与Nb合量x的关系,发现V2Zr,V2Hf加Nb后与V2Hf0.5Zr0.5加Nb后性能显著不同。测定了V2Zr,V2Hf和V2Hf0.5Zr0.5的X射线光电子能谱。结果表明,当Hf原子和Zr原子共存于AB2化合物的A位上时,发生了一种增强原子间相互作用的新的电荷转移。这个事实支持由角动量分波表象能带论方法分析电声耦合超导原理的结果对四元V2(HfZrNb)系列的超导行为提出的一种可能解释:4d-5d原子配位可能有助于提高4d导带的杂化程度,从而有利于提高超导Tc。
关键词: 相似文献
5.
本文研究了C-15结构化合物(Zr0.5Hf0.5-xTax)V2(x≤0.2)和(Hf0.5Zr0.5-xNbx)V2(x≤0.2)的超导转变温度Tc及其压力效应?Tc/?P。报道了实验方法与结果。与(Hf1-xTax)V2和(Zr1-xTax)V2的情况不同,在(Zr0.5Hf0.5-xTax)V2中Ta的引入使常压下的Tc下降,然而(?)Tc/(?)P却大为提高。因此高压下Zr0.5Hf0.45Ta0.05V2的Tc反而比Hf0.5Zr0.5V2更高。导出了一个基于角动量分波表象能带论方法的描述压力效应的新关系式。它指出导带电子波函数中的高角动量成分变化对Tc的压力效应影响比较重要。这个公式有助于理解上述复杂的实验现象,并能合理地解释某些元素(如Cs,Ba,La等)的Tc随压力剧增的事实。
关键词: 相似文献
6.
7.
8.
通过sol-gel法在Si (111) 基片上分别制备了LaNiO3(LNO)底电极和LaNiO3/La0.3Sr0.7TiO3 (LNO/LSTO)底电极.然后采用sol-gel 方法,在两种衬底上分别制备了Pb (Zr0.5Ti0.5)O3 (PZT)铁电薄膜.XRD分析表明,两种PZT薄膜均具有钙钛矿结构,且在LNO底电极上的PZT薄膜呈(100) 择优取向,而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明,相对LNO衬底上制备的PZT薄膜,在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强,同时矫顽场也增大.介电常数和漏电流的测试表明,LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流.
关键词:
PZT薄膜
铁电性
漏电流
0.3Sr0.7TiO3')" href="#">La0.3Sr0.7TiO3 相似文献
9.
本文利用单晶与粉末衍射方法测定了V2Ga5的晶体结构。V2Ga5属四方晶系,其单相区约为VGa2—V2Ga5。在18℃的点阵常数是a=8.9540?,c=2.6892?,每个晶胞含有二个化合式量,空间羣为D4h5—P4/mbm。V原子与Ga原子分别占据在4(h)与8(i),2(d)的等效位置上。参数为:x相似文献
10.
11.
INVESTIGATION OF THE EFFECT OF SLOW NEUTRON IRRADIATION ON HALOGEN-DOPED HIGH-Tc SUPERCONDUCTORS AND ITS MECHANISM 下载免费PDF全文
Irradiation effect of low-fluence (-108 n/cm2 ) slow neutrons on halogen-doped superconductors is presented in this paper. And the mechanism of the effect is also described from the viewpoint of nuclear physics for both fast and slow neutrons on high-temperature superconductors (HTSC). It is shown ex-perimentally and theoretically that slow neutrons of low fluence has a similar irradiation effect to that of fast neutron beams with an energy En>0.1 MeV and fluence 1016-1018 n/cm2-However,quite differ-ent mechanisms are involved in them: Fast neutrons transfer their energies through elastic scattering in HTSC, whereas slow neutrons give off their energies during the slow neutron capture (n,γ) reaction. 相似文献
12.
13.
The temperature dependences of the sound velocity of the pseudobinary (Hf, Zr)V2 compounds show the evidence of lattice instability. The inverse relation between the superconducting transition temperature and the deduced transformation temperature is shown. 相似文献
14.
15.
16.
Mahfoud Ziyad Rachid Ahmamouch Mohamed Rouimi Slimane Gharbage Jacques C. Vdrine 《Solid State Ionics》1998,110(3-4):311-318
Phosphates of general formula M0.5Hf2(PO4)3 with M=Cd2+, Ca2+, Sr2+ and Cu2+ were prepared by coprecipitation and characterized by several physical techniques. The compounds containing Cd2+, Ca2+, Sr2+ belong to the Nasicon-type structure, whereas Cu0.5Hf2(PO4)3 exhibited substantially different DRX patterns. Combined temperature programmed reduction (TPR) and temperature-programmed oxidation (TPO) showed that the copper in Cu0.5Hf2(PO4)3 was distributed between two energetically different sites in proportions respectively equal to 40 and 60%. Electron Paramagnetic Resonance (EPR) investigations confirmed the TPR/TPO results and revealed that the two sites hosting the Cu2+ ions are of orthorhombic symmetry. Moreover, the Cu2+ ions might be reduced by hydrogen to Cu+. These results were also supported by the UV–visible studies that showed the disappearance, under reducing conditions, of the band corresponding to crystal field transitions of Cu2+ ions and the emergence of a new peak attributed to the transitions between (3d)10 and (3d)9(4s)1 Cu+ levels. At the same time, IR spectroscopy confirmed that protons entered the open lattice framework of the material and gave rise to a new protonated phase containing monovalent copper Cu0.5IH0.5Hf2(PO4)3. This redox process was proven to be reversible without any subsequent change in the network of the phosphate. 相似文献