Specific features of praseodymium-doping induced changes in the critical temperature and energy spectrum parameters of YBa$_2$Cu$_3$O$_y$ in the presence of calcium ions in the lattice
Abstract:
The results of the experimental study of the specific features of changes in the temperature and concentration dependences of the thermopower coefficient and the critical temperature in the Y$_{0.85-x}$Ca$_{0.15}$Pr$_x$Ba$_2$Cu$_3$O$_y$ system as the praseodymium content increases are presented. The results obtained have been analyzed based on the narrow band model, the energy spectrum and charge carrier system parameters have been determined, and their behavior with an increase in the doping level has been analyzed. It has been found that both superconducting properties and parameters of the normal state of Y$_{0.85-x}$Ca$_{0.15}$Pr$_x$Ba$_2$Cu$_3$O$_y$ vary differently in various doping ranges. Based on a comparison of the results obtained with the available data for the case of single doping of YBa$_2$Cu$_3$O$_y$ with praseodymium, conclusions have been drawn regarding the mechanism of the energy spectrum modification in the studied compound. The Fermi-level pinning effect has been revealed in the region of a local peak of the density-of-states function, and the energy position of this peak has been determined. It has been shown that the consideration of the Fermi level dynamics caused by the specific features of the structure and transformation of the Y$_{0.85-x}$Ca$_{0.15}$Pr$_x$Ba$_2$Cu$_3$O$_y$ energy spectrum upon doping makes it possible to explain the observed dependence of the critical temperature on the praseodymium content.
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