Change of the Oxidation State of Phosphorus in sputtered Li3±xPO4±y and Li3±xPO4±yNz Films

Thin Li(3 +/- x)PO(4 +/- y)N(z)Li(+)-eleclrolyte films prepared by reactive rf-magnetron sputtering of Li(3)PO(4) incorporate a certain amount of nitrogen which is made responsible for increased Li(+)-conductivity as well as at least kinetic stability with lithium metal. A possible change of the oxidation state +5 of phosphorus as a result of the sputter process has not yet been considered for explanation. We have found out that it cannot be generally assumed that reactive low power rf-magnetron sputtering of Li(3)PO(4) results in fully oxidized films, even when pure O(2) is employed as sputtering gas. Our films immediately react with H(2)O releasing a garlic smelling gas. The reaction area is surrounded by a white crust afterwards. CuSO(4) and AgNO(3) aqueous solutions become reduced. Impedance measurements yield an ionic conductivity of 2.10(-6) S/cm at 25 degrees C and an activation energy of 0.62 eV.