Mitsunori Yokoyama

Flux growth of perovskite-type La2/3TiO3-x crystals

Crystals of perovskite-type lanthanum titanate La2/3TiO3-x were grown from a flux of the system KF-Na2B4O7. Cubic crystals were obtained above 1000°C and tetragonal crystals were obtained below 950°C. Oxygen deficiency seemed to be not so much a problem as has been reported for powdered sample. Growth conditions, X-ray diffraction analysis, crystal morphology and dielectric properties are described.

Vapor phase growth of titania whiskers by hydrolysis of titanium flouride

Abstract The chemical vapor deposition of TiO 2 crystals from the system TiF 4 −H 2 O was studied at elevated temperatures. When Na 2 TiF 6 was used as a TiF 4 source, rutile-type TiO 2 needles grew to 30 mm in length in a comparatively short time over the melt in a platinum crucible in air. The needles were mostly skeletal or twinned intergrowths of acicular crystals. Rutile gradually changed to Na 2 Ti 6 O 13 by the reaction with NaF and moisture in the air. The formation of Na 2 Ti 6 O 13 was inhibited by addition of TiO 2 to the raw material. The rutile whiskers were grown under controlled conditions by means of a flow method from the system Na 2 TiF 6 −TiO 2 −H 2 O. The needles or whiskers were found to grow preferentially in the [001] direction.

Flux growth of rare-earth stabilized zirconia and hafnia crystals

Abstract Crystals of zirconia and hafnia stabilized with rare-earth oxides (Nd 2 O 3 , Sm 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Yb 2 O 3 ) were grown from a flux of the system KF - Na 2 B 4 O 7 . Flourite-type or pyrochlore-type crystals were obtained according to the kind of rare-earth oxide doped. The rare-earth oxide content in the grown crystal was estimated by precision lattice parameter measurement. Crystal morphology and growth process are described.

Flux growth of yttria-stabilized zirconia crystals

Abstract Flux growth of stabilized zirconia single crystals is reported. Among some conventional stabilizers, only yttria formed a cubic zirconia solid solution. Various fluxes previously employed to grow monoclinic zirconia crystals were investigated. The system KF-Na 2 B 4 O 7 proved to be suitable for crystal growth of an yttria-stabilized zirconia solid solution. Starting compositions and growth conditions for the KF-Na 2 B 4 O 7 system are reported.

Vapor phase growth of fibrous potassium titanates from fluorine containing melts

Abstract Fibrous crystals of K 2 Ti 6 O 13 and K 2 Ti 4 O 9 were grown from the vapor phase by the reaction of K 2 TiF 6 or KF -TiO 2 mixture with moisture at elevated temperature. K 2 Ti 6 O 13 fibers and a small amount of rutile needles were grown with K 2 TiF 6 as the starting material. The deposition of the rutile phase was considered to relate to the vapor pressure of water. Fine fibers of K 2 Ti 4 O 9 were grown from KF-TiO 2 as the starting material. In order to obtain K 2 Ti 6 O 13 crystals from KF-TiO 2 mixture, it was necessary to prevent an evaporation of excess KF.

GaAs surface passivation with MBE grown GaS thin film

We report on the successful GaAs surface passivation with GaS thin film grown by MBE employing the single precursor, tertiarybutyl-gallium sulfide-cubane ([(t-Bu)GaS]/sub 4/). GaAs bandgap PL intensity increased by passivating with GaS and has been maintained for a year. Furthermore, we investigated the relationship between the interface state density and the GaAs surface reconstruction before GaS passivation. The PL intensity for c(4/spl times/4)As was largest among the surface reconstructions investigated. Also, a minimum interface state density as low as 5/spl times/10/sup 10/ eV/sup -1/ cm/sup -2/ was obtained for an Al/GaS/n-GaAs MIS structure of c(4/spl times/4)As. In addition, we demonstrated the feasibility of GaS passivation for device applications.

Flux growth of some rare-earth titanate crystals

Rare-earth titanate crystals of perovskite-type R2/3TiO3-x (R = Nd, Sm and Gd) and pyrochlore-type R2Ti2O7 (R = Dy, Er and Yb) have been grown from a flux in the system KF-Na2B4O7. The crystal forms corresponded to each crystal symmetry. XRD analysis showed that perovskite-type R2/2TiO3-x has cubic, tetragonal or orthorhombic modifications according to the growth conditions. The lattice parameters have been determined by precision XRD measurements.

Vapor phase growth of stabilized zirconia crystals by hydrolysis of zirconium fluoride

Abstract The vapor phase growth of ZrO2 crystals by the hydrolysis of ZrF4 gas at elevated temperatures is reported. A suitable ZrF4 vaporization rate for crystal growth was obtained with a starting melt containing ZrF4 and alkalifluoride. Stabilized cubic ZrO2 crystals were grown by adding Y2O3 to the melt. The crystal faces were well developed under low water vapor pressures.