The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P(2)O(5)-30PbBr(2)-30PbF(2) (mol%)] were investigated by differential thermal analysis (DTA) and X-ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP2O4, and the minor phase was PbP2O6. The average activation energy for crystallization, E, for two different particle sizes of this glass was determined to be 119 +/-4 kJ/mol by the Kissinger method and 124 +/- 4 kJ/mol by the Augis-Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 [cm, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 mum, respectively, by the Augis-Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation-rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/T-P, or the height of the crystallization peak, (deltaT)P, as a function of nucleation temperature, T-n. The temperature where nucleation can occur for this glass ranges from 360degrees-450degreesC and the maximum nucleation rate is at 420degrees +/- 10degreesC.