Electron-irradiation-induced amorphization in coesite was observed {ital in} {ital situ} as a function of temperature (15-750 K) at incident electron energy of 1.0 MeV by TEM. Amorphization induced by ion-beam irradiation (1.5 MeV Kr{sup +}) in coesite was studied {ital in} {ital situ} as a function of temperature (15-875 K) using the high-voltage electron microscope (HVEM) Tandem Facility at Argonne National Laboratory. Electron-irradiation-induced amorphization in coesite was also observed at 200 keV and 300 K. Previously, effect of temperature on amorphization was considered to only result in annealing, ie recovery of damaged region. This study shows that temperature has an enhancing effect on amorphization and may even play a dominant role in radiation-induced amorphization of some crystalline materials. The effect of temperature in enhancing amorphization was first theoretically and experimentally recognized in electron- and ion-beam-irradiation-induced amorphization of coesite. Coesite has a melting temperature, {ital T}{sub {ital m}} (875 K), below its glass transition temperature, {ital T}{sub {ital g}} (1480 K). A thermodynamic analysis has been made to model the critical amorphization dose-temperature dependencies of electron- and ion-beam irradiations. We propose that the thermodynamic contributions to amorphization include the free-energy increase due to defect accumulation caused by irradiation and chemical disordering,more » {Delta}{ital G}{sub def} and {Delta}{ital G}{sub dis}, and a thermal contribution, {Delta}{ital G}{sub therm}. The thermodynamic condition for amorphization is generalized by the expression {Delta}{ital G}{sub total}={Delta}{ital G}{sub therm}+{Delta}{ital G}{sub def}+{Delta}{ital G}{sub dis}{ge}{Delta}{ital G}{sub am }, where {Delta}{ital G}{sub total>} is the total free-energy increase for the irradiated crystal, and {Delta}{ital G}{sub am} is the free-energy level required for solid-state amorphization. (Abstract Truncated)« less