Structure and magnetic properties of nanophase- LiFe1.5 P2 O7

Abstract

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2 Fe3 P2 O7) 2 or LiFe1.5 P2 O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2 Fe3 (P2 O7) 2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and Β=111.83° (P 21 /c space group). Infrared spectroscopic measurements indicate the presence of P2 O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2 Fe3 (P2 O7) 2 is a weak antiferromagnetic material with TN =20 K exhibiting a Curie constant Cp =3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (p =-15 K). The absence of higher valence state Fe impurities and antiferromagnetic interactions due to the greater distance between two equivalent magnetic ions, which vanishes the Fe-O-Fe superexchange interactions, is confirmed. © 2009 American Institute of Physics.