Hole doping by pressure on the 1111 pnictides CaFeAsF and SrFeAsF

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. Fil: Freitas, Daniele C.. Centre National de la Recherche Scientifique; Francia. Universite Joseph Fourier; Francia Fil: Garbarino, Gaston Leonel. European Synchrotron Radiation Facility; Francia Fil: Weht, Ruben Oscar. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sow, Amadou. Universite Joseph Fourier; Francia. Centre National de la Recherche Scientifique; Francia Fil: Zhu, Xiyu. Chinese Academy of Sciences; República de China Fil: Han, Fei. Chinese Academy of Sciences; República de China Fil: Cheng, Peng. Chinese Academy of Sciences; República de China Fil: Ju, Jing. Chinese Academy of Sciences; República de China Fil: Wen, Hai Hu. Chinese Academy of Sciences; República de China Fil: Nunez Regueiro, Manuel Daniel. Universite Joseph Fourier; Francia. Centre National de la Recherche Scientifique; Francia