P-T phase diagram of iron arsenide superconductor NdFeAsO0.88F0.12

NdFeAsO0.88F0.12 belongs to the recently discovered family of high-TC iron-based superconductors. We have studied the influence of high pressure on transport properties of this material at low temperatures using the four-probe electrical conductivity technique in a diamond cell. Contrary to La-based compounds, we did not observe a maximum in TC under pressure. Under compression, TC drops rapidly as a linear function of pressure with the slope k = −2.8 ± 0.1 K GPa. Under decompression, the behavior is completely reversible. The extrapolated value of TC at zero pressure is about TC (0) = 51.7 ± 0.4 K. At pressures higher than ∼18.4 GPa, the superconducting state disappears at all measured temperatures, although electrical resistance changes slope dramatically and shows a concave behavior. These observations may be related to the Kondo effect or to a weak localization of two-dimensional carriers at high pressures and low temperatures below ∼45 K, indicating a competition mechanism with the superconducting phase. On the bases of our experimental data, we propose a tentative P-T phase diagram of NdFeAsO0.88F0.12.