Top Seeded Solution Growth and Structural Characterizations of α-Quartz-like Structure GeO2 Single Crystal

Abstract

A high-transparency and large-size single crystal, up to 0.5 cm3, 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 α-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 α-GeO2. The effect of a prolonged annealing (up to five months) at high-temperature (800–900 °C) was followed by Raman spectroscopy: no structural evolution as well as no macroscopic modification of the transparency or the morphology of the α-GeO2 single crys...