The interplay of electron doping and chemical pressure in Ba(Fe_1−yCo_y)₂(As_1−xP_x)₂

Department Chemie der Ludwig-Maximilians- Universität München - Butenandtstr- 5-13 (Haus D), 81377 München, Germany, EU

^a johrendt@lmu.de

Received: 12 March 2011
Accepted: 14 May 2012

Abstract

The effects of internal chemical pressure on electron-doped iron arsenide superconductors are studied in the series Ba(Fe_1−yCo_y)₂(As_1−xP_x)₂. Combinations of both dopants induce superconductivity also in areas where only one would not suffice, and can move the system into an overdoped state, while the highest critical temperature is not raised above 31 K in BaFe₂(As_1−xP_x)₂. The T_c(x, y) phase diagram contradicts the creation of holes by P-substitution, but supports the finding that P-substitution is charge neutral. Chemical and physical pressure act similarly in Ba(Fe_1−yCo_y)₂(As_1−xP_x)₂, but our data reveal that the most important control parameter is the length of the Fe-As bond and not the unit cell volume. This emphasizes that differences between chemical and physical pressure, which manifest themselves as the non-linear reduction of the Fe-As distance in (As_1−xP_x)₂, are strongly linked to the superconducting properties also in the Co-doped compounds.