Structure and conductivity of tetragonal and rhombohedral lanthanum oxyfluoride compounds

Lanthanum oxyfluoride compounds can form on the electrodes of LaF3-based oxygen sensors, so transport through these compounds can affect sensor performance. At high temperatures, lanthanum oxyfluoride forms a cubic fluorite structure, which orders into either a tetragonal or rhombohedral structure during cooling. In this paper, results on the structure and conductivity of lanthanum oxyfluoride (LaO1-xF1+2x) compounds With different ordered structures (tetragonal and rhombohedral) and compositions (x = 0-0.75) are reported. X-ray powder diffraction results indicate that the value of x in tetragonal LnO(1-x)F(1+2x) ranges from 0 to 0.43. Impedance spectroscopy results indicate that the minimum conductivity occurs near the stoichiometric LaOF composition (i.e.. x = 0), where the fewest anion point defects are present. (C) 2000 The Electrochemical Society. S0013-4651(00)05-060-6. All rights reserved.