Influence of Point Defects on the Electrical Conductivity and Dielectric Properties of Langasite

Abstract

The temperature-dependent electrical conductivity and dielectric permittivity and room-temperature optical absorption spectra of La 3 Ga 5 SiO 14 (langasite) crystals grown under different conditions are measured. The resistivity and peak-loss temperature of the crystals are shown to be determined by the concentration of oxygen vacancies, which originate from changes in melt composition during crystal growth. The of langasite is shown for the first time to be anisotropic (measurements on Zand X -cuts). The properties of the crystals are suitable for the fabrication of stable piezoelectric elements capable of operating above 600 ° C. t δ tan t δ tan

High-temperature piezoelectric crystals and devices

“…Advantages of langasite over α-quartz include higher piezoelectric coupling which results in higher resonator quality factors, and thus in reduced phase noise [34][35][36]. A couple years had to pass before the interest turned on langasite's high-temperature properties [37][38][39]. The literature in those days did not contain meaningful data about the high-temperature properties of langasite [6].…”

“…Stoichiometry derivations of the melt composition are commonly compensated by the formation of either cation or anion vacancies [39,47]. For example, the activation energy of the electrical conductivity varies depending on the position where the specimen is taken from the crystal boule (seed end, central part, tail end) by up to about 0.1 eV [39]. The fact underlines that even samples from the same crystal boule exhibit significant differences in their properties.…”

“…• The oxygen sites available in langasite (5 × 10 22 cm −3 ) and • The oxygen vacancy concentration reported in [39] for nominally undoped single crystalline langasite of 10 19 cm −3 .…”

Single-crystal growth of langasite (La3Ga5SiO14) by the vertical Bridgman (VB) method in air and in an Ar atmosphere

“…LGS crystals have generally been grown industrially by the Czochralski (CZ) method using an iridium crucible [3][4][5][6]. During CZ growth, an Ar atmosphere containing several percent of oxygen has normally been applied to avoid evaporation of Ga atoms from the melt and oxidation of the iridium crucible [3][4][5][6].…”

“…During CZ growth, an Ar atmosphere containing several percent of oxygen has normally been applied to avoid evaporation of Ga atoms from the melt and oxidation of the iridium crucible [3][4][5][6]. Electric properties of such grown CZ-LGS crystals were reported [5,6]. Our group succeeded in growing an LGS column crystal, 2 in.…”