Yoshio Furuhata

The congruent melting composition of strontium barium niobate

The congruent melting composition of strontium barium niobate has been investigated over the ternary composition region by DTA, X-ray fluorescence, Curie temperature and lattice parameter measurements. The composition of congruent melt was found to be close tox=0.61,y=0.4993 for the formula (Srx Ba1−xO)1−y. (Nb2O5)y. Striation-free single crystals are grown from the melt with this composition. The conceivable reasons for the discrepancy between the results of this work and the previous data are briefly discussed.

High‐sensitive holographic storage in Ce‐doped SBN

High optical sensitivity is observed in 0.1 wt% Ce‐doped strontium barium niobate (SBN) crystals in the absence of an external electric field. Only 5–10 mJ/cm2 of incident 0.488‐μm radiation is required to produce 10% diffraction efficiency, while the energy to erase holograms from the 80% to its 1/e diffraction efficiency level is 30–40 mJ/cm2 at the same wavelength. Holograms stored in Ce‐doped SBN persist at least one month (decay time constant) if kept in the dark at room temperature.

Phase equilibrium diagram for the system Gd2O3-MoO3

Phase equilibria have been established in the binary system Gd2O3MoO3 including Gd2(MoO4)3 with ferroelectricity and ferroelasticity below 159°C, by means of differential thermal analysis and X-ray powder diffraction techniques. It is shown that Gd2(MoO4)3 has no solubility of other compounds in this system and melts congruently on its stoichiometric composition. Three distinct intermediate compounds were found. Gd2O3.6MoO3 and Gd2O3.4MoO3 are formed by a peritectic reaction at 730°C and 825°C, respectively. The remaining compound Gd2O3.MoO3 with the structure closely related to Eu2O3.MoO3 does not decompose below 1400°C.

A New Second Harmonic Type Ferroelectric Modulator for Electrometer

The authors examined the possibility of using a second harmonic type modulator made of ferroelectric material with an electrometer. It was established that if modulation is carried out at a temperature slightly above the Curie point utilizing the odd symmetry of the relationship between voltage and charge of a ferroelectric capacitor, then the delay in response to a large input signal (memory effect) is eliminated, both zero drift and noise are reduced, and carrier amplitude is diminished largely in contrast to the results obtained at room temperature. In the experiments, triglycine sulfate single crystal (TGS) whose Curie point lay around 50°C was used with a carrier frequency of 50 kHz, reducing zero drift to the order of 10 μV/day and realizing low noise as characterized by 6 μV p‐p with 1 MΩ input resistance and in the bandwidth from dc to 1 Hz. This modulator is solid state, and its input resistance is about 1013 Ω as determined by the specific resistance of a TGS single crystal. Owing to the absence...

Dislocations in Strontium Barium Niobate

The distribution of dislocations in strontium barium niobate (SBN) crystals is examined by etching and by optical microscopy, and the sources of the dislocations are also investigated. The dislocations can be put into three categories according to the characteristics of distribution patterns. The dislocations concentrated in the central region of the crystal originate from the dislocations and the residual surface damages in the seed. The dislocations aligned radially in the outer region of the crystal are generated by the lattice mismatching or thermal stress at the groove bottoms in the shoulder part of the crystal. Finally, the dislocations distributed randomly in the outer region are generated at the positions where Pt or SBN were adsorbed on the surface of the crystal body. Methods for eliminating the dislocations are also described.