Tetsuo Kudo

Crystal Growth of Ca3Nb(Ga1−xAlx)3Si2O14 Piezoelectric Single Crystals with Various Al Concentrations

Ca3Nb(Ga1−xAlx)3Si2O14 (CNGAS) single crystals with various Al concentrations were grown by a micro-pulling-down (µ-PD) method and their crystal structures, chemical compositions, crystallinities were investigated. CNGAS crystals with x = 0.2, 0.4 and 0.6 indicated a single phase of langasite-type structure without any secondary phases. In contrast, the crystals with x = 0.8 and 1 included some secondary phases in addition to the langasite-type phase. Lattice parameters, a- and c-axes lengths, of the langasite-type phase systematically decreased with an increase of Al concentration. The results of chemical composition analysis revealed that the actual Al concentrations in as-grown crystals were almost consistent with the nominal compositions. In addition, there was no large segregation of each cation along the growth direction.

Growth of Ca 3 Ta(Ga 0.5 Al 0.5 ) 3 Si 2 O 14 piezoelectric single crystal and the piezoelectric properties

We grew Ca3Ta(Ga0.5Al0.5)3Si2O14 piezoelectric single crystal with a diameter of 1 inch by Czochralski method and the physical properties were investigated. The grown crystal indicated high transparency with the yellow color. In addition, there was no crack in the crystal. By the powder X-ray diffraction measurement, the grown crystal was a single phase of langasite-type structure and lattice parameters, a- and c-axes lengths, were decreased by the Al substitution. The back-reflection Laue image revealed that the grown crystal was single crystal and crystalline facets derived from (0 0 1) plane. Actual chemical composition of grown crystal was little different from the nominal composition with stoichiometric composition.

Scintillation Properties of a Non-Doped

In order to search for a new scintillation material consisting of tantalum (Ta) with a high atomic number of 73, we have investigated scintillation properties of langasite type crystal containing Ta. Non-doped Ca3TaGa3Si2O14 (CTGS), which is well known as a piezoelectric material, was grown by the Czochralski method. Radio-luminescence spectrum of this crystal peaked around 340 nm. Its light output was approximately 1,200 photons/MeV. This crystal is expected to be a scintillation host material.

{\rm Ca}_3{\rm TaGa}_3{\rm Si}_2{\rm O}_{14}

One inch Ca3NbGa3Si2O14 (CNGS) and Ca3Nb(Ga1?xAlx)3Si2O14 (CNGAS) bulk crystals with an ordered langasite-type structure were grown by a Czochralski method. CNGS bulk single crystals without cracks could be grown, while CNGAS bulk crystals with x = 0.25 and 0.50 included some cracks even under improved growth conditions. Lattice parameters and anisotropy on the structure of grown crystals were systematically decreased and increased by increasing the Al concentration, respectively. Although the density and dielectric constant ?11 of an X-cut sample of the CNGAS crystal with x = 0.25 were decreased by Al substitution, the electromechanical coupling factor k12 and piezoelectric constant d11 were increased. The effects of Al substitution on piezoelectric properties were almost consistent with previous reports on the disordered langasite-type crystals except for their amount of change.

Crystal

The acoustic properties of Ca3Ta(Ga1− x Al x )3Si2O14 (CTGASx) were experimentally studied as a function of the Al substitution content x in the ranges from x = 0 to 0.50. Five specimens, X-, Y-, Z-, 35°Y-, and 140°Y-cut, were prepared from each crystal of CTGASx (x = 0, 0.25, and 0.50) grown by the Czochralski technique. Longitudinal wave and shear wave velocities for CTGASx linearly increase with Al content for all propagation directions. Dielectric constants and density were measured and then elastic and piezoelectric constants were determined from the measured velocities for each crystal. The results revealed that all of the constants change linearly with Al content. From the relationship, the constants for CTAS (x = 1) were estimated. Calculations of the velocities using the determined constants also suggested that the maximum electromechanical coupling factor k 2 for the slow shear wave mode propagating along the rotated Y-axis direction of CTAS was improved to 4.42% compared with 3.83% for CTGS, owing to the Al substitution effect.

Growth and piezoelectric properties of Ca3Nb(Ga1?xAlx)3Si2O14 (x = 0.25 and 0.50) single crystals

Acoustically related physical constants were experimentally determined for Ca₃Nb(Ga_0.75Al_0.25)₃Si₂O₁₄ (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y-, Z-, 40.24° Y-, and 144.98° Y-cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients for CNGAS were determined from longitudinal wave and shear wave velocities at around room temperature, measured by the ultrasonic microspectroscopy system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave velocity. The piezoelectric constants for CNGAS were a 7.2% increase in e₁₁ and a 1.7% decrease in e₁₄ due to Al-substitution effect, compared with those of Ca₃NbGa₃Si₂O₁₄. The appropriate cut angle for thickness-shear mode resonator with zero temperature coefficient of velocity was estimated to be around 150° Y-cut from calculations using the determined constants of CNGAS exhibiting electromechanical coupling factor k² of 3.19% and power flow angle of -1.70°.

Dependence of acoustic property on Al substitution for Ca3Ta(Ga1− x Al x )3Si2O14 single crystals

Ce-doped garnet-type single crystals with improved dopant distribution were grown by the micro-pulling-down method using a modified Iridium crucible and effects of dopant distribution improvement on the optical and scintillation properties were investigated. Ce-doped Y3Al5O12 (Ce:YAG) and Gd3(Ga,Al)5O12 (Ce:GGAG) single crystals with improved dopant distribution could be grown by a Iridium crucible with five capillaries (5C). The Ce:YAG and Ce:GGAG single crystals (5C) showed higher transmittance than the single crystals grown by an original Iridium crucible with one capillary (1C). In addition, a clear photo-peak could be observed in the pulse-height spectrum of the Ce:YAG single crystal (5C) under γ-ray irradiation while there was no peak in the spectrum of the Ce:YAG single crystal (1C).

Evaluation of Acoustic Properties for Ca 3 Nb(Ga 0.75 Al 0.25 ) 3 Si 2 O 14 Single Crystal Using the Ultrasonic Microspectroscopy System

Acoustical physical constants were experimentally determined for Al-substituted Ca3NbGa3Si2O14 (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y-, Z-, 40.24°Y-, and 144.98°Y-cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients were determined from longitudinal wave and shear wave velocities measured for the CNGAS specimens at around room temperature using the ultrasonic micro-spectroscopy (UMS) system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave (LSAW) velocity.

Effects of dopant distribution improvement on optical and scintillation properties for Ce-doped garnet-type single crystals

We grew a Al 25% substituted Ca₃NbGa₃Si₂O₁₄, Ca₃Nb(Ga_0.75Al_0.25)₃Si₂O₁₄ (CNGAS) bulk single crystal with a diameter of 1 inch by Czochralski (Cz) method. Cracks in the crystal were dramatically decreased by the optimization of temperature gradient. Result of powder X-ray measurement indicated the grown CNGAS bulk single crystal was a single phase of langasite-type phase and lattice parameters, a- and c-axes lengths, decreased by the Al substitution. X-ray rocking curve of polished CNGS specimen indicated the grown CNGS bulk single crystal had great crystallinity.

Measurements of acoustical physical constants for Ca 3 Nb(Ga 0.75 Al 0.25 ) 3 Si 2 O 14 single crystal using the ultrasonic microspectroscopy system

A new method for evaluating homogeneities of Ca₃Ta(Ga_0.5Al_0.5)₃Si₂O₁₄ (CTGAS) single crystal was investigated using leaky surface acoustic wave (LSAW) velocities measured by the line-focus-beam ultrasonic material characterization (LFB-UMC) system. LSAW velocity changes due to Al-substitution effect were successfully extracted by using a relationship between two LSAW velocities propagating along different directions for Ca₃TaGa₃Si₂O₁₄ (CTGS) and Al-doped CTGS. Al-concentration variation of 0.219 at% was detected in diameter direction of the crystal ingot through the LSAW velocity measurements for Y-cut CTGAS specimen. The velocity resolution to Al-concentration is estimated to be ±0.0046 at% for Y-cut Z-propagating LSAW.