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2005
Iron
I 7100
11- 033
Thermal Transformation of (NH4)[Fe(AsO4)F] into the New Textural Porous
Orthorhombic Fe(AsO4) Phase. Crystal Structures, Thermal Behavior, and Spectroscopic and Magnetic Properties. — Light-green single crystals of
(NH4)[Fe(AsO4)F] (I) are synthesized hydrothermally from FeCl 3, As2O5, HF, and
NH4OH (H2O, autoclave, 170 °C, 5 d) and are converted to Fe(AsO4) (II) by heating at
525 °C in air. Compound (I) crystallizes in the orthorhombic space group Pna21 with
Z = 8 and compound (II) in the orthorhombic space group Imam with
Z = 12 (single crystal XRD). The structure of (I) consists of a three-dimensional framework with chains formed by alternating FeO4F2 octahedra and AsO4 tetrahedra. The
structure of (II) consists of a three-dimensional skeleton, constructed from sheets
stacked along the [001] direction interconnected by chains of alternating vertex-sharing
FeO6 octahedra and AsO4 tetrahedra. Transmission electronic microscopy indicates the
existence of unconnected external and internal cavities. Magnetic measurements at low
temperatures indicate the predominance of antiferromagnetic interactions with Néel
temperatures of 68.0 and 54.5 K for compounds (I) and (II), respectively. For both phases the existence of weak ferromagnetic components, giving rise to small hysteresis
loops, is also detected at very low temperatures. — (BAZAN, B.; MESA*, J. L.;
PIZARRO, J. L.; RODRIGUEZ-FERNANDEZ, J.; SANCHEZ-MARCOS, J.; ROIG,
A.; MOLINS, E.; ARRIORTUA, M. I.; ROJO, T.; Chem. Mater. 16 (2004) 25,
5249-5259; Dep. Quim. Inorg., Fac. Cienc., Univ. Pais Vasco, E-48080 Bilbao, Spain;
Eng.) — W. Pewestorf
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