Electron microscopy of iron chalcogenide FeTe(Se) films
- PDF / 1,826,966 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 17 Downloads / 206 Views
TRUCTURE OF CRYSTALS
Electron Microscopy of Iron Chalcogenide FeTe(Se) Films I. O. Shchichkoa, c, M. Yu. Presnyakova, E. A. Stepantsovb, S. M. Kazakovc, E. V. Antipovc, I. P. Makarovab, and A. L. Vasil’eva, b a
b
National Research Centre “Kurchatov Institute”, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia c Moscow State University, Moscow, 119992 Russia e-mail: [email protected] Received December 23, 2013
Abstract—The structure of Fe1 + δTe1 – xSex films (х = 0; 0.05) grown on single-crystal MgO and LaAlO3 substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe1.11Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe0.5Se0.5 film grown on a LaAlO3 substrate is single-crystal and that the FeTe0.5Se0.5/LaAlO3 interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case. DOI: 10.1134/S1063774515030165
INTRODUCTION Interest in iron chalcogenides and pnictides increased after discovering superconductivity in LaO1 – xFxFeAs compounds (x ≈ 0.11) at a temperature Тс = 26 K [1] and in α-FeSe at Тс = 8 K [2]. Pnictides have higher critical temperatures than chalcogenides; however, the latter are very attractive for practical applications, because they are synthesized under relatively safe conditions (in the absence of toxic and volatile arsenic), are characterized by a large value of upper critical field (approaching to 50 T), and exhibit low anisotropy [3]. The critical temperature of α-FeSe increases to 37 K under a pressure of 7 GPa [4]. A similar effect of pressure on the transition temperature was established for FeTe1 – xSex [5]. The crystal structure of FeSe under pressure was analyzed using synchrotron radiation [4, 6]; these studies revealed a monotonic decrease in the lattice parameters and the distance between Fe and Se atoms with an increase in pressure, as well as a decrease in the angle between the Se‒Fe‒Se bonds from 104.53° (0.25 GPa) to 103.2° (9 GPa). Strains arise in a thin film on a substrate because of their lattice mismatch; this circumstance allows one to imitate the presence of external pressure. It was shown in [7] that the FeTe compound (which is nonsuperconducting under conventional conditions), being shaped as a thin film, may exhibit superconducting properties. The transition temperature is Тс = 13 K,
which exceeds the Тс value for α-FeSe. One of the differences of thin FeTe films from the bulk material is the larger Fe‒Te‒Fe angles. Elevated angles between the bonds formed by iron
Data Loading...
