In-Seon Kim

Dielectric properties of a-site deficient perovskite-type lanthanum-calcium-titanium oxide solid solution system [(1 − x)La23TiO3 − xCaTiO3 (0.1 ≤ x ≤ 0.96)]

Solid solution system of the double perovskite La23TiO3 and the GdFeO3-type perovskite CaTiO3, (1 − x)CaTiO3 — xLa23TiO3, has been prepared to investigate the crystal structure and the dielectric properties. In this system, the structure changed from pseudo-cubic perovskite to tetragonal double perovskite at x ≈ 0.7, and to orthorhombic double perovskite at x ≈ 0.9. Microwave dielectric measurement showed a decrease in dielectric constant and temperature coefficient of the resonant frequency and an increase in Q value with increasing x. The sample with x = 0.96 showed excellent microwave characteristics, especially high Q(2700) along with high er(90) at 10 GHz. In the low frequency dielectric measurement, dielectric relaxation could be observed in the composition range x ≤ 0.3. The dielectric relaxation showed strikingly different behaviors depending on the annealing process in oxygen after sintering.

Electrical conductivity and metal-nonmetal transition in the perovskite-related layered system Can+1TinO3n+1−δ (n = 2, 3,and∞)

Abstract A series of dielectric compounds having perovskite-related structures Ca 3 Ti 2 O 7 , Ca 4 Ti 3 O 10 , and CaTiO 3 with the general formulaCa n +1 Ti n O 3 n +1 ( n = 2, 3,and∞) showed a metallic conductivity when electron carriers were doped by reduction under H 2 atmosphere. The temperature dependence of the metallic resistivity up to 300 K was found to be a linear function of T 2 in a wide temperature region. The system showed a metal-nonmetal transition as a function of temperature below 120 K. An activation type hopping conduction was observed down to a few tens kelvin, and a variable range hopping conduction below that temperature was observed. The electrical transport phenomena of the system showed a strong dependence on the oxygen deficiency δ, but little dependence of the stacking number of the perovskite slab n .

Composition dependence of carrier concentration and conductivity in (Ba1-xSrx)PbO3-δ system

Abstract Measurements of electrical resistivity, Hall coefficient, lattice parameter for the system (Ba1−xSrx)PbO3−δ(0.0 ≤ x ≤1.0) were carried out. This system is orthorhombic and probable space groups in 0.0 ≤ x ≤ 0.5 and 0.5 ≤ x ≤ 1.0 are Imma and Pbnm, respectively. The resistivity increases with x and metallic behavior disappears at x = 0.5. The carrier concentration decreases with x and decreases rapidly in x ≥ 0.5. The mobility of electrons in this system shows a minimum at x = 0.5, being correlated with the randomness of A-site containing ions with different sizes. These electric properties are considered to be closely related with the tilting of PbO6 octahedra, affecting the overlap between orbitals Pb 6s and O 2p which is the origin of the metallic conductivity of this system.

Structural and dielectric studies on the new series of layered compounds, strontium lanthanum scandium oxides

Abstract A new series of K 2 NiF 4 related layered compounds SrLaScO 4 and SrLa 2 Sc 2 O 7 have been synthesized. Structural parameters were determined by X-ray powder Rietveld analysis. The results showed both compounds have orthorhombic lattice symmetry with the constants a = 5.7657(5) A , b = 5.7513(4) A and c = 12.467(1) A for SrLaScO 4 and a = 5.7818(5), b = 5.7367(5) and b = 20.534(2) A for SrLa 2 Sc 2 O 7 . Although pure phases were not obtained for compounds BaLaScO 4 and BaLa 2 Sc 2 O 7 , their X-ray diffraction patterns could be indexed as a tetragonal lattice symmetry, respectively. The orthorhombic nature of crystal distortion in Srcompounds at room temperature was attributed to be the tilting of ScO 6 octahedra in perovskite layer. Two types of reorientation of the octahedra occurred with increasing temperature for both SrLaScO 4 and SrLa 2 Sc 2 O 7 , along the sequence of symmetry O → O → T. During these transitions dielectric anomalies were observed. The anomalies are considered to be accompanied by a zone-boundary phase transition attributed to the ScO 6 octahedra rotation.

Preparation and characterization of new ruthenium compounds with perovskite structure

Abstract New perovskite compounds Sr(Li 1 4 Ru 3 4 ) O 3 , Sr(Na 1 4 Ru 3 4 ) O 3 , ( Sr 1 2 La 1 2 )( Mg 1 4 Ru 3 4 ) O 3 and ( Sr 7 8 La 1 8 )( Mg 1 4 Ru 3 4 ) O 3 have been prepared. The crystal structures of these compounds were determined by powder X-ray Rietveld analysis. The crystal structure of these compounds was orthorhombic with space group Pnma . Electrical resistivity and magnetic susceptibility were measured for the samples with the nominal ruthenium valences from 4.0+ to 5.0+. In this study, the crystal structure, electrical conductivity and magnetic properties of the new ruthenium perovskite compounds are discussed.

Electrical properties of the A(Pb1−xBx)O3−δ (A=Ba, Sr, B=Sb, Bi) system

Abstract Measurements of electrical resistivity, Hall coefficient, magnetic susceptibility, and lattice parameter of the polycrystalline samples for the system A (Pb 1− x B x )O 3−δ ( A =Ba, Sr, B =Sb, Bi) were carried out. The Sr(Pb 1− x Sb x ) 3−δ , Ba(Pb 1− x Sb x )O 3−δ , Sr(Pb 1− x Bi x )O 3−δ systems, respectively, show metallic conductivity in the ranges x ≤0.2, x ≤0.30, and x ≤0.05, and a maximum carrier concentration at x =0.10, 0.30 and 0.05. In these three systems, only the Ba(Pb 1− x Sb x )O 3−δ system shows a maximum superconductivity with T c =3.5 K. The lattice symmetry remained orthorhombic in the Sr(Pb 1− x Sb x )O 3−δ and Sr(Pb 1− x Bi x )O 3−δ systems through the substitution, but changed to tetragonal in the Ba(Pb 1− x Sb x )O 3−δ system at x =0.25.

Structural study on new ordered potassium-nickel fluoride-type oxides, strontium lanthanum magnesium manganese oxide and strontium lanthanum zinc manganese oxide

The crystal structure of two new K2NiF4-type oxides, SrLaMg0.5Mn0.5O4 and SrLaZn0.5Mn0.5O4, have been determined with space group both 14mmm and P422 using Rietveld refinement profile. An improvement in reliability factor on the basis of space group P422 suggested that they have ordered structure and unit cell parameters be a ≅ a0√2 = 5.4428(1) A, c ≅ c0 = 12.6084(2) A for SrLaMg0.5Mn0.5O4 and a ≅ a0√2 = 5.4588(1) A, c ≅ c0 = 12.6247(3) A for SrLaZn0.5Mn0.5O4. Comparing lengths of (Mnue5f8O) bonds calculated with space group P422, the local symmetry of (MnO6) octahedron is strongly dependent on competing Mg and Zn ions in the perovskite-type plane.

Metal-Nonmetal Transition in La2/3+xTiO3-δ (x<0.2) by Carrier Doping

Carrier concentration dependency of the electronic transport properties for the A-site deficient double perovskite La2/3TiO3−δ with quasi-two dimensional structure was investigated. The lightly doped samples showed a semiconducting behavior, while the heavily doped samples showed a metallic conductivity. This carrier concentration dependent metal-nonmetal transition has been found at 3d 1 electron density of 0.33 per unit formula with a simultaneous occurrence of a crystal symmetry change from P4/mmm to Pnma. Some of the heavily doped La2/3+xTiO3−δ single crystals showed a sign of superconductivity around 3 K, being confirmed by the resistivity and magnetic susceptibility measurements. La2/3+xTiO3−δ system shows a Mott-Hubbard type metal-nonmetal transition around x=0.33 with the change in the carrier concentration.