We study the effect of onium salts (benzyl triphenyl phosphonium chloride, BTPC; tetrabutyl ammonium perchlorate, TAP) on the crystallization of polyvinylidene fluoride (PVDF) from a melt. The beta phase of PVDF crystals is polar and has excellent piezoelectric properties, in contrast to the nonpolar alpha phase. Processing of PVDF results in the formation of predominantly alpha-phase crystals. Different amounts of the onium salts were melt-mixed into PVDF using a microcompounder. PVDF containing about 0.5 wt % of BTPC is found to have predominantly beta-phase crystals in compression molded PVDF films, with an increase in the melting temperature by about 7 degrees C. A significant increase in the toughness of PVDF is obtained by the addition of BTPC. Polarizing microscopy indicates that the onium salts act as nucleating agents and result in significant reduction in spherulite size. Similar results were observed for samples prepared with TAP. The results of the study indicate a facile method for producing beta-phase PVDF films. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1339-1344, 2011