title: Conventional empirical law reverses in the phase transitions of 122-type iron-based superconductors.
abstract: Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations undergo same pressure-induced phase transitions but at progressively lower pressures as the cation radii increases. However, we discovered that this conventional law reverses in the structural transitions in 122-type iron-based superconductors. In this report, a combined low temperature and high pressure X-ray diffraction (XRD) measurement has identified the phase transition curves among the tetragonal (T), orthorhombic (O) and the collapsed-tetragonal (cT) phases in the structural phase diagram of the iron-based superconductor AFe2As2 (A = Ca, Sr, Eu, and Ba). The cation radii dependence of the phase transition pressure (T → cT) shows an opposite trend in which the compounds with larger ambient radii cations have a higher transition pressure.
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai, 201203, China.
authors.forename: Zhenhai
authors.initials: Z
authors.lastname: Yu
authors.affiliation: 1] Center for High Pressure Science and Technology Advanced Research, Shanghai, 201203, China [2] State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China [3] High Pressure Synergetic Consortium, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, United States of America.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Harbin Institute of Technology, Harbin 150080, China.
authors.forename: Luhong
authors.initials: L
authors.lastname: Wang
authors.affiliation: 1] Center for High Pressure Science and Technology Advanced Research, Shanghai, 201203, China [2] Harbin Institute of Technology, Harbin 150080, China.
authors.forename: Haozhe
authors.initials: H
authors.lastname: Liu
authors.affiliation: Harbin Institute of Technology, Harbin 150080, China.
authors.forename: Jinggeng
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai, 201203, China.
authors.forename: Chunyu
authors.initials: C
authors.lastname: Li
authors.affiliation: High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, United States of America.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Sinogeikin
authors.affiliation: Beijing National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
authors.affiliation: 1] Beijing National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China [2] Collaborative Innovation Center of Quantum Matter, Beijing, China.
authors.forename: Jianlin
authors.initials: J
authors.lastname: Luo
authors.affiliation: 1] Collaborative Innovation Center of Quantum Matter, Beijing, China [2] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
authors.forename: Nanlin
authors.initials: N
authors.lastname: Wang
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Yang
authors.affiliation: High Pressure Science and Engineering Center, University of Nevada, Las Vegas, Nevada 89154, United States of America.
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: 1] Center for High Pressure Science and Technology Advanced Research, Shanghai, 201203, China [2] High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, United States of America [3] Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015, United States of America.
authors.forename: Ho-kwang
authors.initials: HK
authors.lastname: Mao