Hole doping by pressure on the 1111 pnictides CaFeAsF and SrFeAsF

• Published in: Journal of physics. Condensed matter Vol. 26; no. 15; p. 155702
• Main Authors: Freitas, Daniele C, Garbarino, Gastón, Weht, Ruben, Sow, Amadou, Zhu, Xiyu, Han, Fei, Cheng, Peng, Ju, Jing, Wen, Hai Hu, Núñez-Regueiro, Manuel
• Format: Journal Article
• Language: English
• Published: England 16-04-2014
• Subjects: Arsenicals - chemistry; Atmospheric Pressure; Calcium Compounds - chemistry; Electric Conductivity; Ferrous Compounds - chemistry; Models, Chemical; Phase Transition; Strontium - chemistry; Transition Temperature; X-Ray Diffraction
• ISSN: 1361-648X
• DOI: 10.1088/0953-8984/26/15/155702

We determine the pressure phase diagram of the 1111 compounds CaFeAsF and SrFeAsF, up to 20 GPa and down to 4 K by electrical resistivity measurements and the change of structure up to 40 GPa at room temperature. The antiferromagnetic transition temperature, as determined by the derivative peak, shows a minimum at ~5 GPa (10 GPa) for the Ca (Sr) compound. For CaFeAsF, superconductivity appears at this minimum, coincident with the development of a previously reported monoclinic phase. For SrFeAsF, where the orthorhombic and the monoclinic phase were reported to coexist, superconductivity exists above P≥1 GPa. Both phase diagrams can be scaled by a shift of ~10 GPa pressure at which the volume of SrFeAsF and that of CaFeAsF at ambient pressure coincide. The difference of our phase diagram with that of electron-doped 1111 samples is accounted for by hole doping under pressure, which we verified through electron band structure calculations.