Effective substitution of aluminum for gallium in langasite-type crystals for a pressure sensor use at high temperature

Aluminum-substituted La3Ga5SiO14 (LGS)-type crystals, La3Ga5-xAlxSiO14 (LGAS(x)) and La3Ta0.5Ga5.5-xAlxSiO14 (LTGA(x) were successfully grown by the Czochralski technique. These crystals were 18-23 mm in diameter and 70-100 mm in length. The piezoelectric modulus d(11) values (6.21 and 6.92 pC/N) of the LGAS(x=0.9) and LTGA(x=0.5) crystals were slightly larger than that of the pure LGS and La3Ta0.5Ga5.5O14 (LTG) ones (6.08 and 6.89 pC/N), respectively. The LTGA(x=0.5) crystals showed the lowest temperature dependence of d(11). The electric resistivity rho values of the Al-substituted crystals at 400 degrees C were significantly higher than those of the pure LGS and LTG crystals grown in an oxygen-containing atmosphere. The aluminum substitution is effective for improving the electrical properties of the LGS and LTG, and the LTGA(x=0.5) crystals are suitable for combustion pressure sensor materials.