Shin-ichi Shirasaki

Induced emission cross section of Nd:Y3Al5O12 ceramics

Optical absorption and emission spectra have been measured for Nd‐doped Y3Al5O12 ceramics obtained by a urea precipitation method. The optical properties of the ceramics are almost the same as those of single crystals grown by the Czochralski method and floating‐zone method, except for a higher background absorption of 2.5–3 cm−1. The energy‐level structure for Nd3+ in the Y3Al5O12 ceramics is determined for a 1‐at. % Nd concentration. The induced emission cross section for the 1‐at. %‐Nd‐doped ceramic is calculated to be 4.9×10−19 cm2, which falls in the range reported for the Nd:Y3Al5O12 single crystals. The Nd concentration dependence of the emission decay time at the 1064‐nm laser wavelength was also measured, and typical concentration quenching was observed. The decay time of the 1‐at. %‐Nd‐doped ceramic is 219 μs, which is slightly smaller than the reported values for single crystals.

OPTICAL SPECTRA OF UNDOPED AND RARE-EARTH-( = PR, ND, EU, AND ER) DOPED TRANSPARENT CERAMIC Y3AL5O12

Undoped and rare‐earth‐ (Pr, Nd, Eu, and Er) doped transparent Y3Al5O12ceramics have been prepared, and their optical spectra have been measured. It is found that absorption coefficient of the undoped ceramic Y3Al5O12 is almost independent of wavelength with 0.258 cm−1, which gives transmittance of the undoped ceramic Y3Al5O12 to be, for example, 95% for a 2‐mm height. Peaks in the absorption and emission spectra of Pr:Y3Al5O12 are assigned to the transitions in 4f 2 configuration. The transitions from the multiplets with total angular momentumJ=0 to multiplets with even J momentum are strong as predicted by Judd–Ofelt theory. The overall and detail structure of the absorption and emission spectra of Nd:Y3Al5O12 is the same as those in a previous publication. However, the absorption coefficient at nonabsorbing wavelengths by Nd3+ is reduced from more than 1.7 to 0.25 cm−1. A simple estimation of the population inversion threshold of the Nd:Y3Al5O12ceramic reveals that the threshold is still about 25 times larger than that of single‐crystal Nd:Y3Al5O12. Peaks in the absorption and emission spectra of Er:Y3Al5O12ceramic are assigned to the transitions in 4f 11 configuration. The transition energies agree well with those reported for single‐crystal Er:Y3Al5O12 and the other hosts within 30 cm−1. A Stark splitting scheme for some multiplets has been constructed. Peaks in the emission, absorption, and excitation spectra of Eu:Y3Al5O12ceramic are assigned to the transitions in 4f 6 configuration. The transition energies are in very good agreement with those of single‐crystal Eu:Y3Al5O12 within 8 cm−1 for the emission peaks and 3 cm−1 for the absorption and excitation peaks. Spectralcharacteristics and derivation of a broad peak in the absorptionspectrum at around 280 nm are discussed in some detail.

Preparation of lead magnesium niobate by a coprecipitation method

The ferroelectric complex perovskite lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 (PMN), was prepared by a coprecipitation method. As the niobium component, niobium oxalate was used. Among the various precipitants, tetramethylammonium hydroxide was effective for the formation of single-phase PMN without pyrochlore phase. The dielectric constant and the dissipation factor of PMN changed either the sintering temperature or the grain size. The maximum dielectric constant at the Curie point was obtained by sintering at 1220 °C in air for 2 h.

Effects of Mn ions on the piezoelectric property of (Pb, La)(Zr, Ti)O3

The effects of sintering temperature and manganese concentration on microstructure and electromechanical property were studied in [Pb0.9La0.1][Zr0.5Ti0.5]O3 piezoelectric ceramics with the substitution of the B-site by manganese by means of scanning electron microscope (SEM) and electron spin resonance (ESR). Grain growth is enhanced by increasing temperature but suppressed by manganese substitution. There was no relationship between Qm (inverse of mechanical vibration loss) and the grain size. Some part of manganese is considered to be reduced to Mn2+ ions during sintering. Qm is considered to be affected by the reduction of manganese ions because it was proportional to Mn2+ concentration, not to total manganese content.

Planar faults and grain boundary precipitation in non-stoichiometric (Sr, Ca)TiO3 ceramics

Microstructures of non-stoichiometric-composition (Sr0.85Ca0.15O)xTiO2 ceramics (with x=0.98 and 1.02) were observed using high-resolution transmission electron microscopy and scanning transmission electron microscopy. Precipitation of Magneli-phase was found at the grain boundary in the specimen for x=0.98, and Ruddlesden-Popper-type insertion layers in that for x=1.02. The crystallographic site occupancy of impurity atoms determined by ALCHEMI (Atom Location using CHanneling-Enhanced MIcroanalysis), showed that the excess TiO2 was precipitated as Magneli phase in the specimen for x=0.98, and similarly that excess SrO formed insertion planar faults of NaCl type in that for x=1.02. No anti-site point defects were formed in either of the specimens.

Defect ferroelectrics of type Pb1−xTiO3−x

Abstract A series of new ferroelectric substances of type Pb1−xTiO3−x or Pb 1−x Na y TiO 3−x+( y 2 ) with perovskite-type structure was prepared by simple solid state reaction among powdered mixtures of PbO, TiO2, and in a several cases, Na2CO3, with TiO2 in an excess. The defect materials are characterized in terms of inhomogeneously distributed vacancies, □pb and □O at the respective equivalent lattice positions. Their ferroelectric properties are discussed in relation to those of the same type of materials precipitated aqueously and followed by firing at elevated temperatures

Microstructure of SnO2 Conductive Film Prepared by Pyrohydrolytic Decomposition onto a Glass Substrate

The microstructure of a thin SnO2 film prepared by pyrohydrolytic decomposition onto a glass substrate was studied by scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HR-TEM) of cross-sectional specimens, and the findings were correlated with the low resistivity shown by this material when employed as a transparent electrode. The thin film was found to consist of three regions: a region which showed reaction with the glass substrate, a non-oriented polycrystalline region and an oriented columnar polycrystalline region showing a crystallographic shear (CS) structure which was thought to contribute to the low resistivity.

Single‐crystal preparation and some characterizations of the superconducting Y‐Ba‐Cu oxide

Single crystals of Ba2YCu3O7−δ were prepared from melts of a BaO‐Y2O3‐CuO mixture and characterized by the x‐ray microprobe analyzer and x‐ray diffraction. Electrical resistivity was measured by the standard four‐terminal method. Some crystals have the critical temperature above 77 K. After annealing in oxygen, the crystals behave like a semiconductor.

Magnetic and electrical properties in the defect perovskite system La1−xNaxFeO3−δ

Abstract Magnetic and electrical properties were studied for the defect perovskite system La 1− x Na x FeO 3−δ . X-Ray diffraction showed that the materials with a composition range x = 0.0–0.25 were monophasic perovskite-like compounds with orthorhombic symmetry. The present ferrite solid solution showed a parasitic-ferromagnetic property, accompanying the antiferromagnetism. Values of both ferromagnetic moment and magnetic susceptibility increased with increase in Na content. Furthermore, the magnetization was strongly affected by oxygen partial pressure. These experimental facts seem to have a close relation with the oxygen vacancies. Electrical conductivity measurements suggested the presence of mixed valencies of Fe 3+ and Fe 4+ on a basis of the compositional dependence of the conductivity and its activation energy.

Magnetic properties of lanthanum orthoferrites containing lattice defects

Abstract Polycrystalline lanthanum orthoferrites were prepared by firing coprecipitated hydroxides of La 3+ and Fe 3+ at elevated temperatures. The materials fired at temperatures below 1100°C were characterized by the coexistence of such lattice vacancies that the concentration ratio of V La : V Fe : V o is always equal to that of the constituent atoms of LaFeO 3 . They exhibited a large magnetic susceptibility, a low Neel temperature, and a small spontaneous magnetization, in comparison with lanthanum orthoferrite without these vacancies. These characteristics originated essentially from a local reduction in anisotropic superexchange interaction at vacant sites. The lowering of Neel temperature characteristic of these materials was interpreted in terms of a decrease in the number of Fe 3+ OFe 3+ linkages due to the existence of oxygen and iron vacancies.