Structural and conductivity studies in LiFeP 2 O 7 , LiScP 2 O 7 , and NaScP 2 O 7

Structural studies of LiScP2O7 by Rietveld refinement confirm that this material is isostructural with LiFeP2O7 studied previously. However, NaScP2O7 shows a structure different from the structural types of the basic group of NaIMIIIP2O7 known thus far. Systematic ranges for the six structural types of AIMIIIP2O7 are presented in terms of ion radii sums and ratios. The framework of LiMP2O7 (M=Sc, Fe) has rather wide tunnels running along the crystallographic c-axis. This feature has determined our interest to check the ion conductivity in AIMIIIP2O7 (A=Li, Na; M=Sc, Fe). The bulk conductivity, however, is low in these compounds, 10−6–10−7 S/cm at 300 °C, as determined by impedance spectrosc…