Crystal structure and thermal stability of new iron phosphates KMFe(PO4)2 (M = Ni, Mg, and Co)

Abdessalem Badri (1) , Mourad Hidouri (1) , María Luisa López (2) , Maria Luisa Veiga (2) , Carlos Pico Marín (2) , Jacques Darriet (3) , Mongi Ben Amara (1)

1 Matériaux Inorganiques
2 Departamento de Química Inorgánica I
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

Three isostructural iron monophosphates KNiFe(PO4)2 (KNi), KMgFe(PO4)2 (KMg-LT, where LT means “low-temperature stable phase”), and KCoFe(PO4)2 (KCo-LT) are synthesized and structurally characterized from X-ray diffraction data. They crystallize in the monoclinic system with the space group P21/c. Their structures have in common a three-dimensional framework, built up by infinite zigzag chains of edge-sharing MO6 (M = Ni, Mg or Co) octahedra, linked by FeO5 and PO4 polyhedra via vertices and edges to form a rigid skeleton. The K+ ions are located in formed tunnels. DTA showed that KNi has a congruent melting at 941°C, whereas KMg-LT and KCo-LT undergo irreversible phase transitions from P21/c to different high-temperature structures with the C 2/c symmetry. IR absorption bands are assigned to different vibrations of the PO4 tetrahedron.

Mots clés: iron phosphates; synthesis; crystal structure; phase transitions; IR

Domaines: Matériaux

Abdessalem Badri, Mourad Hidouri, María Luisa López, Maria Luisa Veiga, Carlos Pico Marín, et al.. Crystal structure and thermal stability of new iron phosphates KMFe(PO4)2 (M = Ni, Mg, and Co). Journal of Structural Chemistry, 2015, 56 (4), pp.714-722. ⟨10.1134/S0022476615040150⟩. ⟨hal-01216356⟩