Abstract
In the field of piezoelectric crystals, quartz is one of the widely used materials in industry for electronic device application as oscillators for the time-frequency domain. alpha-Quartz SiO2 shows a decrease of its piezoelectric properties above 250°C, an alpha-quartz to beta-quartz phase transition at 573°C and a low electromechanical coupling factor of about 8%. Although its nonlinear optics properties are well known, its low chi2 coefficient prevent it to be used in frequency doubling devices. The goal of this study is to increase the structural distortion and the polarizability of this material by substituting part of the silicon atoms with larger atoms such as germanium or other elements. In order to grow centimeter-size single crystals we use hydrothermal methods in high-pressure autoclaves. Crystal growth of mixed alpha-quartz Si(1-x)GexO2 crystals was successfully performed on pure alpha-quartz SiO2 (001) seeds. Large crystals with different germanium content were obtained and analyzed by infrared spectroscopy and EPMA. Piezoelectric and nonlinear optical properties were measured on these crystals, which exhibit a improved physical properties. Then crystal growths with larger elements than germanium were performed in order to further improve their physical properties. Substitution by the following elements: Mn, V, Ti and Sn were investigated.