NbZr multilayers. I. Structure and superconductivity
NbZr multilayers. I. Structure and superconductivity
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NbZr 多层膜。
DOI：
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发表时间：
1984
期刊：
影响因子：
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通讯作者：
T. Geballe
中科院分区：
文献类型：
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作者：
W. Lowe;T. Geballe
采用磁控溅射方法制备了NbZr多层膜。样品是用调制波长制备的.从200A到4A的范围内，用X射线散射研究了它的结构性质。由x射线散射得到的合成波表明，沉积时的方波不是方波，而是部分扩散到Nb组分中。认为Zr替代了Nb位，扩展了Nb层的晶格常数。成分的振幅在..波长以上增加..=31 A，并降低到..。=31A.通过低至..λ的x射线散射检测到成分调制。=13A以上，或=31A，Nb沿生长方向与(110)面呈体心立方，而锆沿生长方向与(002)面呈体心立方。这一区域的T/subc/线性下降为..。增加。在……或=31A区域，Zr经历了结构相变，形成了与Nb晶格共格的体心立方晶格。一旦多层膜变得共格，超导转变温度随温度的降低而急剧升高。这增加了更多的T/subc/，接近9.7K，这是50at的值。%NbZr固溶体。在库珀极限中应用三层模型来解释临界温度。这个模型意味着超导相干长度约为100埃。
Multilayers of NbZr have been made by the process of magnetron sputtering. The samples were prepared with modulation wavelengths ..lambda.. ranging from 200 A down to 4 A. The structural properties have been studied using x-ray scattering. The composition wave constructed from the x-ray scattering shows that the as-deposited square wave is not square but rather the Zr component has partially diffused into the Nb component. The Zr is believed to substitute on Nb sites and expand the lattice constant of the Nb layer. The compositional amplitude increases above ..lambda.. = 31 A and decreases below ..lambda.. = 31 A. A composition modulation was detected by x-ray scattering as low as ..lambda.. = 13 A. Above ..lambda..> or =31 A the Nb is bcc with the (110) along the growth direction and the Zr is hcp with the (002) along the growth direction. The T/sub c/ in this region decreases linearly as ..lambda.. increases. In the region ..lambda..< or =31 A the Zr undergoes a structural phase transition to form a bcc lattice that is coherent with the Nb lattice. Once the multilayer becomes coherent there is a sharp increase in the superconducting transition temperature with decreasing ..lambda... This increasemore » in T/sub c/ approaches 9.7 K which is the value for a 50 at. % solid solution of NbZr. A trilayer model is applied in the Cooper limit to explain the critical temperatures. This model implies a superconducting coherence length of approximately 100 A.« less