Transition to collapsed tetragonal phase in CaFe2 As2 single crystals as seen by 57Fe Mössbauer spectroscopy

Thumbnail Image
Bud’ko, Sergey
Ma, Xiaoming
Tomic, Milan
Ran, Sheng
Valenti, Roser
Major Professor
Committee Member
Journal Title
Journal ISSN
Volume Title
Canfield, Paul
Distinguished Professor
Research Projects
Organizational Units
Organizational Unit
Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

Organizational Unit
Physics and Astronomy
Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.
Journal Issue
Is Version Of

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. 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.


This article is published as Bud'ko, Sergey L., Xiaoming Ma, Milan Tomić, Sheng Ran, Roser Valentí, and Paul C. Canfield. "Transition to collapsed tetragonal phase in CaFe 2 As 2 single crystals as seen by Fe 57 Mössbauer spectroscopy." Physical Review B 93, no. 2 (2016): 024516. DOI: 10.1103/PhysRevB.93.024516. Posted with permission.

Subject Categories
Fri Jan 01 00:00:00 UTC 2016