Structural Distortion and Chemical Bonding in TlFeO3: Comparison with AFeO3 (A=Rare Earth)

✍ Scribed by Seung-Joo Kim; Gérard Demazeau; Igor Presniakov; Jin-Ho Choy

• Book ID: 102611224
• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 444 KB
• Volume: 161
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9292

✦ Synopsis

The crystal structure and the magnetic properties for thallium orthoferrite, TlFeO 3 , were characterized and compared with those of rare earth orthoferrites, AFeO 3 (A ‫؍‬ rare earth). TlFeO 3 has a GdFeO 3 -type perovskite structure (a ‫؍‬ 5.3172(2) A s , b ‫؍‬ 5.4465(2) A s , and c ‫؍‬ 7.7927(3) A s ; space group, Pbnm). Its cell parameters and unit-cell volume considerably deviate from a trend observed in the rare earth orthoferrites, which are attributed to a speci5c coordination of Tl 3؉ ion. According to magnetization measurements, TlFeO 3 shows an antiferromagnetic behavior accompanied with weak ferromagnetism. The magnetic ordering temperature, T N (560 K), for TlFeO 3 is lower than that for any other orthoferrite while the Fe+O+Fe superexchange angle (144.03) in TlFeO 3 is comparable to that in ErFeO 3 . The MoK ssbauer spectrum reveals a single Fe 3 ؉ quadrupole doublet with an isomer shift ‫؍‬ 0.18 ؎ 0.02 mm/s and a quadrupole splitting value ‫؍‬ 0.47 ؎ 0.02 mm/s at 623 K (> T N ), whereas it shows a magnetic hyper5ne sextet with ‫؍‬ 0.47 mm/s and a hyper5ne 5eld H hf (Fe 3 ؉ ) ‫؍‬ 535 kOe at 80 K (< T N ). The magnetism and the MoK ssbauer results underline a signi5cant competing e4ect of the Tl+O bond with the covalency of the Fe+O one. Despite the anomalous character of TlFeO 3 in structure and magnetism, it is found that the T N values for all orthoferrites, including TlFeO 3 , are strongly correlated with their crystallographic axial ratio, c/(2a. Through this type of analysis, the electronic e4ects of A cation on structural distortion and magnetic behavior in perovskite are discussed.