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Title: Transition to collapsed tetragonal phase in CaFe2As2 single crystals as seen by 57Fe Mössbauer spectroscopy

Journal Article · · Physical Review B
 [1];  [2];  [3];  [1];  [3];  [1]
  1. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
  2. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States); Lanzhou Univ., Gansu Province (China)
  3. Goethe-Univ. Frankfurt, Frankfurt am Main (Germany)

Temperature dependent measurements of 57Fe Mössbauer spectra on CaFe2As2 single crystals in the tetragonal and collapsed tetragonal phases are reported. Clear features in the temperature dependencies of the isomer shift, relative spectra area, and quadrupole splitting are observed at the transition from the tetragonal to the collapsed tetragonal phase. From the temperature dependent isomer shift and spectral area data, an average stiffening of the phonon modes in the collapsed tetragonal phase is inferred. The quadrupole splitting increases by ~25% on cooling from room temperature to ~100 K in the tetragonal phase and is only weakly temperature dependent at low temperatures in the collapsed tetragonal phase, in agreement with the anisotropic thermal expansion in this material. In order to gain microscopic insight about these measurements, we perform ab initio density functional theory calculations of the electric field gradient and the electron density of CaFe2As2 in both phases. By comparing the experimental data with the calculations we are able to fully characterize the crystal structure of the samples in the collapsed-tetragonal phase through determination of the As z coordinate. Furthermore, based on the obtained temperature dependent structural data we are able to propose charge saturation of the Fe-As bond region as the mechanism behind the stabilization of the collapsed-tetragonal phase at ambient pressure.

Research Organization:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-07CH11358; SPP 1458
OSTI ID:
1239156
Alternate ID(s):
OSTI ID: 1235760
Report Number(s):
IS-J-8883; PRBMDO
Journal Information:
Physical Review B, Vol. 93, Issue 2; ISSN 2469-9950
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 14 works
Citation information provided by
Web of Science

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Cited By (6)

Study of the Rare Earth Effects on the Magnetic Fluctuations in RbLn2Fe4As4O2 (Ln = $=$ Tb, Dy, and Ho) by Mössbauer Spectroscopy journal May 2018
57 Fe Mössbauer study of stoichiometric iron-based superconductor CaKFe 4 As 4 : a comparison to KFe 2 As 2 and CaFe 2 As 2 journal July 2017
Preserved entropy and fragile magnetism journal July 2016
Impact of concomitant Y and Mn substitution on superconductivity in La 1 y Y y Fe 1 x Mn x AsO 0.89 F 0.11 journal February 2018
Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: Persistent magnetism with interlayer As–As bond formation in Rh-doped $Ca_{0.8}Sr_{0.2}Fe_{2}As_{2}$ text January 2018
Preserved entropy and fragile magnetism text January 2016

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