Instabilities at 1/8 Doping in La_<2-x>Ba_xCuO_4 and Related Compounds : II-A Instability and Substitution Effects : II Oxide Superconductors; Experiments II : Electronic States :

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In this report, we will discuss the p=1/8 problem in high-temperature superconductor La_<2-x>Ba_xCuO_4(LBCO) and its related compounds. It has been known that striking suppression of superconductivity of LBCO in narrow range of x around 0.125 is caused by a structural transition to a low-temperature tetragonal (TLT) phase at about 60 K. We will show that in Th-doped LBCO, La_<2-y-x>Th_yBa_xCuO_4,the development of the TLT phase, as well as the sharp suppression of superconductivity, is centered at x-y=0.125, instead of x=0.125. Therefore, the anomalous low-temperature behavior is precisely governed by the condition p=1/8 for the density of carriers per Cu, rather than local ionic forces, which couples with the lattice instabilities. We will next discuss the role of the ionic radii of the cations in the La site by comparing the low-temperature instabilities in La_<2-x>Ba_<x-y>Sr_yCuO_4 and La_<2-y-x>Nd_ySr_xCuO_4.

Journal

  • JJAP series

    JJAP series 7 91-98, 1992-02-29

    Japanese Journal of Applied Physics

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