Activation energies for crystallization of 50 glasses, with x = 0, 5 and 10 mol%, were determined by differential thermal analysis (DTA). The structure was investigated by infrared and Mössbauer spectroscopy. Samples with x = 5 mol% of show larger activation energy . Absorptions at P-O-P, P=O, and units are presents in these glasses. P=O absorptions disappear at compositions with x = 5 and 10 mol% of , which shows absorption around , attributed to units. According to Mössbauer results high spin and at distorted octahedral sites are present in samples with x = 5 and 10 mol% of , thus working as a network modifier.