Anomalous chemical pressure evolution in ThFePnN (Pn for pnictogens

The layered compound ThFeAsN is the only member in the 1111-type iron-arsenides which exhibits su-perconductivity without chemical substitution or physical pressure. The unique properties of ThFeAsN were attributed to built-in chemical pressure. In this paper, we investigate the effects of iso-valent substitution of P/Sb for As in ThFePnN systems to modulate the chemical pressure. The physical properties are char-acterized by measuring magnetic susceptibility, electric resistivity, and specific heat. Our findings indicate that in the P-doped ThFeAs1-xPxN system, superconductivity disappears at x = 0.3, and we did not observe a second superconducting dome in the phase diagram. Instead, a possible low-temperature magnetic/charge ordering state emerges around the end member ThFePN. In the case of the Sb-doped ThFeAs1-ySbyN samples, superconductivity is gradually suppressed at y = 0.25, and the expected long-range anti-ferromagnetic transition does not occur thereafter. Thus, the physical properties of ThFePnN samples sig-nificantly differ from those of LaFePnO, regardless of P or Sb doping. Structural analysis reveals that the key parameters, such as the height of the pnictogens and the two-fold Fe-Pn-Fe bond angle, vary non-mono-tonically with doping. The inconsistency between ThFePnN and LaFePnO is discussed based on the crystal structure evolution.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

In this paper, the effects of iso-valent substitution of P/Sb for As in ThFePnN systems to modulate the chemical pressure were investigated. It was found that superconductivity in the P-doped ThFeAs1-xPxN system disappears at x = 0.3, while in the Sb-doped ThFeAs1-ySbyN samples, superconductivity is gradually suppressed at y = 0.25. The physical properties of ThFePnN samples significantly differ from those of LaFePnO, regardless of P or Sb doping.