Abstract
A high-transparency and large-size single crystal, up to 0.5 cm(3), of the piezoelectric phase of GeO2 was grown by the top seeded solution growth method from a high-temperature solution using K2Mo4O13 as solvent. The obtained volume makes this flux-grown GeO2 single crystal, with the metastable alpha-quartz like structure, the largest reported in the literature to our knowledge. Several oriented plates, X-, Y-, and Z-cut according to the dielectric frame, were obtained from the grown crystal, which exhibits a typical hexagonal morphology. The presence of hydroxyl groups as chemical impurities, known to damage the piezoelectric property, was not detected by infrared spectroscopy in transmission mode or Raman spectroscopy on the resulting oriented plates of alpha-GeO2. The effect of a prolonged annealing (up to five months) at high-temperature (800-900 degrees C) was followed by Raman spectroscopy: no structural evolution as well as no macroscopic modification of the transparency or the morphology of the alpha-GeO2 single crystal were observed. These results were consistent with a high optical quality crystal as checked by UV-vis-NIR spectroscopy.