Co,Zn元素对YBa_2Cu_3O_(7-δ)的不同的掺杂效应

THE DIFFERENCE OF DOPING EFFECTS BETWEEN YBa_2Cu_(3-x)Co_xO_y AND YBa_2Cu_(3-x)Zn_xO_y

对单相掺杂样品YBa_2Cu_3 x^(Co_xO_y)(x=0.00,0.025,0.05,0.075,0.10,0.125,0.15,0.20,0.25,O.275,0.30,0.325,0.35,0.375,0.40)和YBa_2Cu_(3-x)Zn_xO_y(x=O.025,0.05,0.075,0.10,0.15,0.20,0.30)作了室温下的晶体结构,正常态时电阻-温度关系,以及低温下的Hall系数的测量,随着杂质含量的增加发现:1)掺Co样品显示出一从正交到四方的连续的结构转变,而掺Zn样品只有在较大的Zn含量时才开始出现此结构转变的趋势;2)掺Co样品呈现出金属-半导体转变,但所有被测的单相掺Zn样品则呈现出金属性行为;3)掺Co样品的空穴载流子浓度单调下降,而掺Zn样品的则在x=0.15处出现一极大值。用局域化的能带图象以及受主杂质的概念对实验现象作了解释,并对各种可能的拆对机制作了讨论。

The measurements of X-ray diffraction, d.c. resistance versus temperature and Hall coefficients at low temperature have been performed forYBa2Cu3-xMxOy systems. (x = 0.00, 0.025,0.05,0.075,0.10,0.125,0.15,0.20,0.25,0.275,0.30,0.325,0.35,0.375,0.40 for M = Co; x=0.025,0.05,0.075,0.10,0.15,0.20,0.30 for M = Zn)The crystallographic data show that an orthorhombic-tetragonal phase transition takes place as Co content increases, while the crystal structure exhibit drastic changes with Zn content. The measurement of resistances indicates that a metal-semiconductor transition occurs at certain x for Co dopant hut not found for Zn dopant. The hole carrier concentration raduces with Co content monotoneous-iy but varies nonmonotoneously with Zn content, giving a maximum at about x= 0.15 The concepts of localization and acceptor are used to explain these phenomena. The suppression of Tc for both systems is discussed with various possible suppression mechanisms.