Kazushige Tota

Shaped crystal growth of langasite-type piezoelectric single crystals and their physical properties

We have grown shape-controlled langasite-type crystals by the micro-pulling-down (μ-PD) method. Columnar shaped La₃Ta_0.5Ga_5.5O₁₄ (LTG), Ca₃NbGa₃Si₂O₁₄ (CNGS), Ca₃TaGa₃Si₂O₁₄ (CTGS), Sr₃NbGa₃Si₂O₁₄ (SNGS), and Sr₃TaGa₃Si₂O₁₄ (STGS) crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die at the bottom. All grown crystals showed high transparency except for the peripheral area and diameter of approximately 3 mm. The chemical phases at the central parts of the grown crystals were identified as a single phase of langasite-type structure and their lattice parameters were almost the same as those of crystals grown by the Czochralski (Cz) method; however, some impurity phases were observed in the peripheral area. In X-ray rocking curve measurements, the grown crystals indicated equivalent crystallinity to the crystal grown by the Cz method. The piezoelectric constant d₁₁ of the CNGS crystal was 3.98 pC/N; this value is well correlated with those of previous reports.

Shape-controlled crystal growth of Sr 3 NbGa 3 Si 2 O 14 and Sr 3 TaGa 3 Si 2 O 14 piezoelectric crystals by the micro-pulling-down method

We grew column-shaped Sr₃NbGa₃Si₂O₁₄ (SNGS) and Sr₃TaGa₃Si₂O₁₄ (STGS) langasite-type piezoelectric single crystals by the micro-pulling-down (μ-PD) method. 3-mm-diameter SNGS and STGS crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die. According to X-ray rocking curve measurements, the grown crystals had crystallinity equivalent to that of crystals grown by the Czochralski (Cz) method. The crystals were single-phase materials with langasite-type crystal structure. The lattice parameters of the grown crystals were almost consistent with those of crystals grown by the Cz method.

Annealing Effects for Ca3NbGa3Si2O14 Piezoelectric Single Crystals Grown by Micro-Pulling-Down Method

The langasite-type Ca3NbGa3Si2O14 [CNGS] piezoelectric crystals grown in Air and Ar were annealed under various temperatures and atmospheres and the effects of annealing on various properties were investigated. The absorption peaks around 360 and 500 nm of CNGS crystals grown in Air decreased by the annealing at 1300°C in Ar. On the other hand, the annealing at 1300°C in Air decreased transmittance in the range from 300 to 500 nm for the CNGS crystal grown in Ar. The results suggest that the absorptions around 350 and 500 nm originate from the excess oxygen and the post-annealing can control the oxygen content in the crystals.

Study on Phase Diagram of Ca3NbGa3Si2O14 Piezoelectric Material by Differential Thermal Analysis and X-Ray Diffraction Measurement

Ca3NbGa3Si2O14 (CNGS) Is One of the Langasite-Type Crystals and it Is Known as a Piezoelectric Material. We Have Successfully Grown the Shaped CNGS Crystal Using Micro-Pulling-down (μ-PD) Method with Shape Control. However, the Impurity Phases such as Ca-Nb-O Related Compounds Were Detected in the Grown Crystals. The Creation of the Impurity Phases Is Related to Difference in Stoichiometric and Congruent Compositions. Therefore, the Detailed Investigation of Phase Diagram on CNGS Was Carried Out to Prevent the Impurity Phases Creation. It Follows from the TG-DTA Measurements that the Melting Point Systematically Changed with the Ca/Ga Ratio in the Ca3-xNbGa3+xSi2O14±δ Cmpositions. The CNGS Phase with Ca/Ga = 1.02 Indicated the Maximum Melting Point which Suggests that the Stoichiometric Composition of CNGS Is Different in the Congruent Composition. Furthermore, in the DTA Measurements the Peaks of Impurity Phases Were Detected around 1550 °C for the CNGS Sample with Ca/Ga = 1.02.