Swift heavy ion induced structural modifications in zircon and scheelite phases of ThGeO(4)

Structural modifications in the zircon and scheelite phases of ThGeO(4) induced by swift heavy ions (93 MeV Ni(7+)) at different fluences as well as pressure quenching effects are reported. X-ray diffraction and Raman measurements at room temperature on the irradiated zircon phase of ThGeO(4) indicate the occurrence of stresses that lead to a reduction of the cell volume up to 2% followed by its transformation to a mixture of nano-crystalline and amorphous scheelite phases. Irradiation of the zircon phase at liquid nitrogen temperature induces amorphization at a lower fluence (7.5 x 10(16) ions/m(2)), as compared to that at room temperature (6 x 10(17) ions/m(2)). Scheelite type ThGeO(4) irradiated at room temperature under goes complete amorphization at a lower fluence of 7.5 x 10(16) ions/m(2) without any volume reduction. The track radii deduced from X-ray diffraction measurements on room temperature irradiated zircon, scheelite and low temperature irradiated zircon phases of ThGeO(4) are, 3.9, 3.5 and 4.5 nm, respectively. X-ray structural investigations on the zircon phase of ThGeO(4) recovered after pressurization to about 3.5 and 9 GPa at ambient temperature show the coexistence of zircon and disordered scheelite phases with a larger fraction of scheelite phase occurring at 9 GPa. on the other hand, the scheelite phase quenched from 9 GPa shows crystalline scheelite phase pattern. (c) 2009 Elsevier B.V. All rights reserved.