掺杂YBa_2Cu_(3-x)M_xO_y(M=Fe,Al,Zn)红外光谱的研究

STUDY OF INFRARED ABSORPTION SPECTRA IN THE YBa_2Cu_(3-x)M_xO_y(M=Fe, Al, Zn)SYSTEM

首先报道并系统地研究了掺杂YBa_2Cu_(3-x)M_xO_y(M=Fe,Al,Zn)体系的红外光谱,证明了YBa_2Cu_3O_(7-δ)中:p1(630cm^(-1))红外峰在正交相中确实属于一维Cu—O链上氧空位诱导的准局域模和α轴上Cu_1—O_5—Cu_1局域模的叠加;p2(580cm^(-1))红外峰在高氧相中不能观测到是由于受二维电子气的屏蔽,而并非是二维CuO_2网络中氧空位诱发的Cu—O准局域振动模;p3(550cm^(-1))红外峰即沿c轴O_4—Cu_1—O_4局域振动模,由于YBa_2Cu_3O_(7-δ)的二维特性不受二维电子气的屏蔽效应的影响,因此它在正交相和四角相强度变化不明显。同时还讨论了掺杂对YBa_2Cu_3O_(7-δ)超导电性及结构的影响。

The infrared absorption spectra of the doped YBa_2Cu_(3-x)M_xO_y(M=Fe, Al, Zn) systems are systematically and unprecedentedly investigated. It is verified that the p_1(630cm^(-1)) IR peak in the YBa_2Cu_3O_(7-δ) orthorhombic phase is indeed corresponding to two overlapped peaks, i. e. a quasi-localized vibrational mode induced by the oxygen-vacancy in one-dimensional Cu—O chain on axis b and a Cu_1—O_5—Cu_1 localized vibrational mode on axis a. The p_2(590cm^(-1)) IR peak, which is undetectable in high oxygen content phase in YBa_2Cu_3O_(7-δ), is completely screened by free carriers of two-dimensional CuO_2 networks instead of being a quasi-localized vibrational mode induced by the oxygen vacancies in the two-dimensional CuO_2 networks. Because of the quasi-two-dimensional structure of YBa_2Cu_3O_(7-δ), the p_3(550cm^(-1)) peak belonging to the localized vibrational mode of the O_4—Cu_1—O_4 vibrational complex along axis c is weakly influenced by the screening effect of two-dimensional free carriers, which results in the intensity of this peak hardly affected by the thermal-equilibrium quenching temperature. The effects of dopants on the superconductivity and structure of YBa_2Cu_3O_(7-δ) are also investigated.