Koji Maiwa

POTASSIUM-SODIUM-RUBIDIUM NIOBATE SINGLE CRYSTALS AND ELECTRIC PROPERTIES

Potassium-sodium-rubidium niobate single crystals are grown using an original pulling down method, to improve their composition change during a crystal growth, by means of co-doping of small ionic size sodium and large ionic size rubidium into potassium niobate. Even by the co-doping, single crystals can be grown with orthorhombic single-phase at room temperature, as well as pure potassium niobate. Their electric properties, such as the dielectric constant and the impedance, are changed depending on the doping ions.

Crystal Growth and Characterization of Pb2KNb5O15

Lead potassium niobate crystals were grown by our pulling down method and tube-seed Czochralski method. Evaporation of lead and potassium was observed. Crystal growth was not so difficult despite the evaporation. Grown crystals were brownish and transparent. Cleavage was observed in the Czochralski grown crystals on the c-plane. After heat treatment, the dielectric constant along the c-axis was about 500–1000. A large dielectric constant above 10000 was observed on the ab-plane. On the ab-plane, almost isotropic properties were obtained on the basis of the dielectric constant and the thermal expansion coefficient.

Crystal Growth and Electric Properties of Bismuth Titanate Fibers

Bismuth titanate (Bi4Ti3O12) crystals were grown by our original floating-zone pulling down (Fz-PD) method. The shape of the grown crystals was fiberlike with dimensions of 15×1×0.34 mm3. The dielectric properties and impedance of the grown fiber crystals were determined. A large difference in the dielectric constant was observed along the c- and a-axes.

In situ observation of the crystallization via incongruent melting and peritectic reaction in Sr(NO3)–H2O system

Abstract The crystallization via incongruent melting and peritectic reaction was investigated in the Sr(NO 3 ) 2 –H 2 O system. The dissolution processes of the secondary β phase (Sr(NO 3 ) 2 ·4H 2 O) and the primary α phase (Sr(NO 3 ) 2 ) in water above and below the peritectic temperature T p =29.3°C were observed in situ, respectively, by optical microscopy. Around the β phase dissolving above 61°C, α phase formed. With the depletion of the β phase, the α phase stopped growing and dissolved. On the other hand, β phase formed on the α phase dissolving below −13°C. After a while, ice crystals (γ phase) formed and enclosed the β phase. The result shows that the incongruent melting and the peritectic reaction are the sequential processes of the dissolution of the metastable solid phase and the formation of the stable solid phase in the liquid. A possible driving force for the crystallization is originated from the difference in the solubility of the two solid phases at a given temperature. The formation of γ phase on the α phase dissolving below 0°C was also observed, instead of the peritectic reaction. In this process, the α phase acted as the site for both melting and regrowth of the γ phase. This resulted in a zonal structure of the γ phase around the α phase.

Synthesis of KNbO3 Films from K2NbO3F Solution on Oxide Substrates

Method to synthesize KNbO3 crystals using K2NbO3F solutions is of interest. In this paper, films of KNbO3 crystals are synthesized on several oxide substrates from K2NbO3F solutions. The films have some orientation due to a reaction with the substrates. The reason is expected the solution after the synthesis is strongly basic.

Li(Ga1-xMx)O2 (M: B or Al) Single Crystals Grown by Floating Zone Method

Li(Ga1-xMx)O2 (M: B or Al) single crystals are grown by Floating zone method. These crystals are characterized from the viewpoint of the substitution of M, such as lattice parameter (lattice volume) change, piezoelectric properties and nonlinear optics. The lattice volume is decreased with the increase of Al content for Al-substitution largely, but the change is a little for B-substitution.