Electron-irradiation-induced crystallization orthophosphates

Amorphous LaPO4, EuPO4, GdPO4, ScPO4, LuPO4, and fluorapatite [Ca-5(PO4)(3)F] were irradiated by the electron beam in a transmission electron microscope. Irradiations were performed over a range of temperatures from -150 to 300 degrees C, electron energies from 80 to 200 keV, and current densities from 0.3 to 16 A/cm(2). In all cases, the materials crystallized to form a randomly oriented polycrystalline assemblage. Crystallization is driven dominantly by inelastic processes, although ballistic collisions with the target nuclei can become important at energies higher than 175 keV, particularly in apatite. Using a high current density, crystallization is so fast that continuous lines of crystallites can be ''drawn'' on the amorphous matrix.