Superconductivity

Anomalies of the Y$_{1-x}$Ca$_x$Ba$_2$Cu$_3$O$_y$ crystal structure in the temperature range 80–300 K

S. V. Pryanichnikov^a, S. G. Titova, L. A. Cherepanova, G. A. Dorogina

^a Institute of Metallurgy, Ural Division of the Russian Academy of Sciences, Yekaterinburg

Abstract: The effect of doping on the temperature evolution of the crystal structure of the YBa$_2$Cu$_3$O$_y$ high-temperature superconductor has been investigated. The crystal structure of Y$_{1-x}$Ca$_x$Ba$_2$Cu$_3$O$_y$ ($x$ = 0, 0.1; $y$ = 6.6, 6.8, 6.95) has been studied using the full-profile analysis with X-ray powder diffraction data in the temperature range 100–300K. The unit cell parameters, the bond lengths, and the calculated linear and volume coefficients of thermal expansion are characterized by a nonmonotonic behavior in the temperature range $\sim$160–225 K. Samples with the oxygen content $y$ = 6.6–6.8 in both systems (with $x$ = 0 and 0.1) have negative linear coefficients of thermal expansion at low temperatures. A possible reason for the anomalous behavior can be the change in the state of the electronic subsystem. The data analysis confirms that the doping mechanisms upon oxygen introduction, and when Y is substituted for Ca are different.

Received: 07.12.2010
Accepted: 22.03.2011

 English version: Physics of the Solid State, 2011, 53:10, 1991–1996

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