[Paper Review] New Iron-based oxyarsenides Sr4M2Fe2As2O6(M = Sc, Cr)

Hiraku Ogino, Yukari Katsura+3 more|arXiv (Cornell University)|Mar 30, 2009

Iron-based superconductors research2 references3 citations

TL;DR

This study reports the synthesis and characterization of new iron-based oxyarsenides Sr4M2Fe2As2O6 (M = Sc, Cr), which adopt a tetragonal P4/nmm structure with anti-fluorite FeAs layers and perovskite-type blocking layers. The compounds exhibit the longest Fe-Fe interlayer distance (15.8 Å) in iron-based oxypnictides, and the absence of superconductivity is attributed to insufficient carrier concentration, similar to undoped REFeAsO systems.

ABSTRACT

We have discovered new layered oxyarsenides (Fe2As2)(Sr4M2O6) (M = Sc, Cr: M-22426). These materials are isostructural with (Fe2P2)(Sr4Sc2O6), which was found in our previous study. The new compounds are tetragonal with a space group of P4/nmm and consist of the anti-fluorite type FeAs layer and perovskite-type blocking layer. The lattice constants are a = 4.050 A, c = 15.809 A for M = Sc and a = 3.918 A, c = 15.683 A for M = Cr. These compounds have long interlayer Fe-Fe distances corresponding to the c-axis length, the 15.8 A in Sc-22426 is the longest in the iron-based oxypnictide systems. Chemical flexibility of the perovskite block in this system was probed by chromium containing (Fe2As2)(Sr4Cr2O6). Different trends were found in bond angle and bond length of the new oxypnictides compared to the reported systems, such as REFePnO. Absence of superconductivity in these compounds is considered to be due to insufficient carrier concentration as in the case of undoped REFeAsO.

Motivation & Objective

• To explore new iron-based oxypnictide systems with enhanced structural flexibility through substitution of rare earth elements with transition metals.
• To investigate the structural and electronic properties of layered oxypnictides with FeAs and perovskite-type blocking layers.
• To determine the role of carrier concentration in suppressing superconductivity in these materials.
• To compare bond angle and bond length trends in the new oxypnictides with established systems like REFePnO.

Proposed method

• Synthesis of Sr4M2Fe2As2O6 (M = Sc, Cr) via solid-state reactions under controlled conditions.
• Structural characterization using X-ray diffraction to determine crystal structure and lattice parameters.
• Analysis of the crystal structure to identify the anti-fluorite FeAs layer and perovskite-type blocking layer.
• Comparison of bond angles and bond lengths in the new compounds with those in REFePnO systems.
• Evaluation of electronic behavior to assess superconducting transition temperature and carrier concentration.

Experimental results

Research questions

• RQ1 What is the crystal structure and lattice parameter of Sr4M2Fe2As2O6 (M = Sc, Cr) and how does it compare to known oxypnictides?
• RQ2 How does the incorporation of Cr into the perovskite block affect the structural and electronic properties of the compound?
• RQ3 Why is superconductivity absent in these oxypnictides despite the presence of FeAs layers?
• RQ4 How do the bond angles and bond lengths in Sr4M2Fe2As2O6 differ from those in REFePnO systems?
• RQ5 What is the role of interlayer Fe-Fe distance in determining electronic properties in iron-based oxypnictides?

Key findings

• The Sr4M2Fe2As2O6 (M = Sc, Cr) compounds crystallize in a tetragonal structure with space group P4/nmm.
• The lattice constants are a = 4.050 Å, c = 15.809 Å for M = Sc and a = 3.918 Å, c = 15.683 Å for M = Cr.
• The Fe-Fe interlayer distance in the Sc-containing compound (15.8 Å) is the longest observed in iron-based oxypnictide systems.
• The compounds feature an anti-fluorite type FeAs layer and a perovskite-type blocking layer.
• Chemical flexibility in the perovskite block is demonstrated by successful incorporation of Cr into the structure.
• The absence of superconductivity is attributed to insufficient carrier concentration, consistent with undoped REFeAsO systems.