Jae Dong Byun

Crystal structure of La(Mg2/3Nb1/3)O3 ceramics

The crystal structure of La(Mg2/3Nb1/3)O3 has been analyzed by high-resolution transmission electron microscopy (HRTEM) and Rietveld refinement using X-ray and neutron powder diffraction patterns. According to our analysis, La(Mg2/3Nb1/3)O3 has the 1:1 ordered monoclinic P21/n structure, contrary to the results of previous works which suggest a 1:1 ordered rhombohedral R3 or orthorhombic Pbnmstructure. The lattice parameters of La(Mg2/3Nb1/3)O3 are a = 5.6052, b = 5.6482, c = 7.9414 A, and β = 89.9501°. Monoclinic La(Mg2/3Nb1/3)O3 is distorted by the inphase and the antiphase tilting of octahedra with the a−a−c+ tilting system. The antiparallel shift of A-site cations was also found in La(Mg2/3Nb1/3)O3.

Characterization of (Ba0.65Sr0.35)(Ti0.65Zr0.35)O3 thin film

Abstract The crystal structure and dielectric properties of (Ba 0.65 Sr 0.35 )(Ti 0.65 Zr 0.35 )O 3 (BSTZ) films were investigated. The films were deposited on Pt/Ti/SiO 2 /Si(100) substrates by metal–organic decomposition (MOD) method and rf magnetron sputtering. The crystal structure of the BSTZ film was cubic perovskite, and the preferred orientation of the film varied with annealing temperature. The MOD film annealed at 750°C exhibited excellent dielectric properties of dielectric constant, k ≈ 1,000 and dissipation factor, tan δ ≤ 0.04. The films also showed a very stable leakage current behavior vs. applied field. The leakage current density, J, increased smoothly with field, up to E = 0.3 MV/cm, and was 3.47 × 10 −7 A/cm 2 at 1.25 V.

Compositional dependence of luminescence of lithium zinc gallate phosphor

The photoluminescence (PL) and cathodoluminescence (CL) characteristics of lithium gallate and lithium zinc gallate were investigated as a function of composition and firing temperature. As Li/Ga of lithium gallate decreased, the emission peak shifted from about 420 to 390 nm under ultraviolet (UV) excitation. Similar results were obtained under cathode ray (CR) excitation. PL spectra of lithium gallates fired at high temperature were most similar to those of Li-deficient lithium gallate. This result clearly indicates that lithium gallate fired at high temperature is Li deficient. The PL and CL emission spectra of lithium zinc gallate consisted of a single broadband under UV and CR excitation. The emission peak of the composition of (1−x)Li0.5Ga2.5O4–xZnGa2O4 shifted from 406 to 440 nm as x increased under UV excitation and the peak intensity decreased with x. However, the intensity increased with x under CR excitation. When the composition of lithium zinc gallate was 0.4Li0.5Ga2.5O4–0.6ZnGa2O4, the brigh...

Crystal structure refinement of (Ba1−xLax)[Mg(1+x)/3Nb(2−x)/3]O3 with 0.3 ≤ x ≤ 0.7 by Rietveld method

Abstract Crystal structures of (Ba1−xLax)[Mg(1+x)/3Nb(2−x)/3]O3 (BLMN) with 0.3 ≤ x ≤ 0.7 were analyzed using the X-ray Rietveld refinement. The evolution of the X-ray powder pattern could be explained by the presence of 1:1 ordering of the B-site cation and the antiphase tilting of the oxygen octahedra, which were further confirmed by the observation of the antiphase boundary (APB) for the ordering and the ferroelastic domain boundaries for oxygen tilting by TEM. The crystal structure, which has only the 1:1 ordering of the B-site cation, has the space group of Fm 3 m (225), and that which has both the 1:1 ordered and the antiphase tilting of oxygen octahedra has the space group of I4/m (87). For the quantitative analysis of X-ray diffraction data, a new concept of the two-phase mixture of phase (Fm 3 m) and phase (I4/m) was employed in these systems. The obtained results were better than others, which employed only one single phase. The molar weight of the I4/m phase in a mixture increased as the La content in the BLMN system increased from 11.5% (x = 0.3) to 24.3% (x = 0.7).

Crystal structure of (Ba1−xLax) [Mg(1 + x)/3Nb(2−x)/3]O3 ceramics

The crystal structure of (Ba1−xLax)[Mg(1 + x)/3Nb(2−x)/3]O3 (BLMN) ceramics with 0 ≤ x ≤ 1 was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). When the La content, x, was above 0.1, the 1:2 ordered hexagonal structure found in Ba(Mg1/3Nb2/3)O3 (BMN) was transformed into the 1:1 ordered cubic structure. The 1:1 ordered cubic structure was maintained up to x = 0.7. When x exceeded 0.7, however, BLMN exhibited a 1:1 ordered monoclinic structure, rather than a 1:1 ordered cubic structure. La(Mg2/3Nb1/3)O3 (LMN) has a 1:1 ordered monoclinic P21/n structure with a = 5.6004 Å, b = 5.6414 Å, c = 7.9346 Å, and β = 89.9819°. The monoclinic LMN has the in-phase and the anti-phase tilt of oxygen octahedra. The anti-parallel shift of A-site cations was also found in LMN.

A new type of ordering in Ba(Zn1/3 Ta2/3)O3 ceramics

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