Crystal Structure and Magnetic Properties of a New Iron(III) Silicophosphate Fe3P5SiO19 Studied by Neutron Diffraction and Mössbauer Techniques

✍ Scribed by L.K. Elbouaanani; B. Malaman; R. Gérardin; B. Ouladdiaf

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 528 KB
• Volume: 164
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9449

✦ Synopsis

Fe 3 P 5 SiO 19 has been prepared by solid state reaction of Fe(PO 3 ) 3 , FePO 4 , and SiO 2 at 10003C. The structure has been determined from a single crystal through direct methods and di4erence Fourier synthesis and re5ned to R ‫؍‬ 0.052. The unit cell is hexagonal, space group P6 3 , with a ‫؍‬ 14.4804(8) A s , c ‫؍‬ 7.4256(2) A s , and Z ‫؍‬ 4. The three-dimensional framework is built up from [Fe 2 O 9 ] units of two faces sharing octahedra and Si 2 O 7 disilicates linked by PO 4 tetrahedra. Fe 3 P 5 SiO 19 is isotypic with V 3 P 5 SiO 19 . Fe 3 P 5 SiO 19 is antiferromagnetic below T N ‫؍‬ 35 K. The magnetic structure has been determined by means of powder neutron di4raction methods: the magnetic moments are antiferromagnetically coupled inside the [Fe 2 O 9 ] units, in agreement with the Goodenough rules. These units are linked to each other through several Fe+O+P+O+Fe supersuperexchange pathways and form antiferromagnetic [001] rows. The moment direction lies in the (001) plane ( Fe ‫؍‬ 4.56(5) B at 2 K). There is a competition between the intra-and interunits interactions which all are antiferromagnetic and cannot be simultaneously satis5ed without frustration. Mo4 ssbauer spectra are 5tted with two doublets and two sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive e4ect. The magnetic interactions are discussed.

2002 Elsevier Science (USA)