The possibility of introducing additional states in the conduction band ofYBa2Cu3Oy by Ca doping

Measurements of the temperature dependences of the resistivity and Seebeck coefficient S, as well as of the Hall coefficient R-H at T = 300 K are repo rted for two series of ceramic Y1-xCaxBa2Cu3Oy samples with oxygen contents in the initial sample close to stoichiometric and then lowered by annealin g. It has been found that an increase in calcium content in the first serie s results in a drop of the critical temperature T-c, a weak variation of S (300 K), and an increase of R-H (300 K), whereas in the second series T-c i ncreases, S (300 K) decreases, and R-H (300 K) remains practically constant . The S (T) relations acquire additional features with increasing doping le vel, which are not typical of the YBa2Cu3Oy system for other types of subst itution. An analysis of the data obtained made in terms of the phenomenolog ical band model permits a conclusion that calcium is capable of introducing additional states in the conduction band. Based on this assumption, we hav e succeeded in providing a qualitative explanation for the unusual features in the behavior of the transport coefficients and critical temperature in Y1-xCaxBa2Cu3Oy. (C) 1998 American Institute of Physics. [S1063-7834(98)001 12-9].