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Pressure induced lattice anomalies in pnictides
Affiliation:1. Department of Physics, National Technical University of Athens, GR15780 Athens, Greece;2. Department of Physics, University of Athens, Athens, Greece;3. Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland;1. Department of Physics, Sapienza University of Rome, Roma, Italy;2. Center for the Study of Matter at Extreme Conditions, Florida International University, Miami, USA;3. Department of Physics, Northeastern University, Boston, USA;1. School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, PR China;2. College of Chemistry, Nankai University, Tianjin 300071, PR China;1. Department of Physics, Shivaji University, Kolhapur 416004, India;2. Department of Physics, Rajaram College, Kolhapur 416004, India;1. Departamento de Física, IGCE-Universidade Estadual Paulista – UNESP, C.P. 178, CEP 13500-970 Rio Claro, São Paulo, Brazil;2. Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150, CEP 22290-180 Rio de Janeiro-RJ, Brazil;3. Departamento de Física, Universidade Federal de São Carlos, C.P. 676, CEP 13560-970 São Carlos, São Paulo, Brazil;4. Instituto de Física, Universidade Federal Fluminense, Campus da Praia Vermelha, CEP 24210-340 Niterói, Rio de Janeiro, Brazil;1. Physics Department, University of Gujrat, Gujrat, Pakistan;2. Sustainable Energy Technologies Center, College of Engineering, King Saud University, PO-Box 800, Riyadh 11421, Saudi Arabia;3. Physics Department, Bahauddin Zakariya University, Multan, Pakistan;4. Spintronics Laboratory, Physics Department, International Islamic University, Islamabad, Pakistan;5. Physics Department, Hazara University, Mansehra, Pakistan;1. Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Hangzhou, 310018, PR China;2. State Key Laboratory of Information Photonics & Optical Communication, Beijing University of Posts and Telecommunications, Beijing 100876, PR China
Abstract:Hydrostatic pressure Raman and synchrotron XRD measurements at room temperature have been carried out on a series of NdFeAsO1−xFy (Nd1111) oxypnictides in order to investigate pressure-induced lattice modifications. The synchrotron XRD data indicate that there is an increased deviation of the lattice constants from smooth pressure dependence in the superconducting compound, in close agreement with the results from SmFeAsO1−xFx (Sm1111), although the effect is less pronounced in Nd1111. As in Sm1111 the hydrostatic pressure Raman measurements show that the A1g mode of the rare earth atom deviates from the linear pressure dependence. Anomalous pressure dependence and a hysteresis is observed in the phonon width of the phonon modes. The calculated Grüneisen parameter for the Nd phonon is very similar to the corresponding value for SmFeAsO1−xFx compound and it does not vary with substitution. For the As mode it has a lower value indicating a stiffer phonon with the increased ion size. In connection with the XRD measurements the Raman data show a sudden increase of the pressure-induced lattice anomalies close to doping where the compounds become superconducting.
Keywords:Raman spectroscopy  High pressure  X-ray diffraction  Phonons  Superconductors
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