Synthesis, structure, and superconductivity of La7+2x Sr1-4x K x Na x Cu4O16-δ

Sodium and potassium have been doped into La7SrCu4O16-δ to form La7+2x Sr1-4x K x Na x Cu4O16-δ solid solutions by a solid-state reaction, which crystallizes in the I4/mmm space group when 0 ≤ x < 0.16 and Fmmm when 0.16 < x ≤ 0.25. With the equivalent replacement of four Sr2+ by one Na+, one K+ and two La3+, it is very interesting to find that T zero c (the definition is presented in the introduction part) of La7+2x Sr1-4x K x Na x Cu4O16-δ does not remain constant with an increase in x but first increases from 14.8 K for x = 0.00 to 33.9 K for x = 0.10 and then decreases to 18.5 K for x = 0.175.Sodium and potassium have been doped into La7SrCu4O16-δ to form La7+2x Sr1-4x K x Na x Cu4O16-δ solid solutions by a solid-state reaction, which crystallizes in the I4/mmm space group when 0 ≤ x < 0.16 and Fmmm when 0.16 < x ≤ 0.25. With the equivalent replacement of four Sr2+ by one Na+, one K+ and two La3+, it is very interesting to find that T zero c (the definition is presented in the introduction part) of La7+2x Sr1-4x K x Na x Cu4O16-δ does not remain constant with an increase in x but first increases from 14.8 K for x = 0.00 to 33.9 K for x = 0.10 and then decreases to 18.5 K for x = 0.175.