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

Abstract

Three isostructural iron monophosphates KNiFe(PO 4 ) 2 (KNi), KMgFe(PO 4 ) 2 (KMg-LT, where LT means "low-temperature stable phase"), and KCoFe(PO 4 ) 2 (KCo-LT) are synthesized and structurally characterized from X-ray diffraction data. They crystallize in the monoclinic system with the space group P2 1 /c. Their structures have in common a three-dimensional framework, built up by infinite zigzag chains of edge-sharing MO 6 (M = Ni, Mg or Co) octahedra, linked by FeO 5 and PO 4 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 P2 1 /c to different high-temperature structures with the C2/c symmetry. IR absorption bands are assigned to different vibrations of the PO 4 tetrahedron.

The rich crystal chemistry of theAMM′(PO4)2morphotropic series: NaZnAl(PO4)2, the first Na representative with a new structure type

“…The calculations were made without considering the splitting of the Na position and 'dilution' of the positions of Zn and Al. study (Badri et al, 2015) revealed a congruent melting of KNiFe(PO 4 ) 2 at 941 C and an irreversible phase transition from the low-to the high-temperature stable phases at 778 and 840 C for isotypic KMgFe(PO 4 ) 2 -LT and KCoFe(PO 4 ) 2 -LT, respectively. For RbCuAl(PO 4 ) 2 , the spontaneous magnetization and antiferromagnetic ordering at T N = 10.5 K was shown (Yakubovich et al, 2016).…”

Crystal growth, structure elucidation and CHARDI/BVS investigations of β-KCoFe(PO4)2

“…Whereas the environments around the two TM sites are tetrahedral in the title compound, an octahedral coordination is found for one site (Co) in the -form. The crystal structure of -KCoFe(PO 4 ) 2 is isotypic with that of KZnFePO 4 ) 2 (Badri et al, 2014), while that of -KCoFe(PO 4 ) 2 is isotypic with those of KNiFe(PO 4 ) 2 and KMgFe(PO 4 ) 2 (Badri et al, 2015).…”

“…The title compound crystallizes isotypically with KZnFe(PO 4 ) 2 (Badri et al, 2015). The principal building units of -KCoFe(PO 4 ) 2 are shown in Fig.…”