Microwave quality factor improved by ordering of Ba and rare-earth on the tungsten bronze-type Ba/sub 6-3x/R/sub 8+2x/Ti/sub 18/O/sub 54/ (R=La, Nd and Sm) solid solutions

Abstract

A new approach has been developed to numerically calculate solid angles of the ligands in organometallic complexes. The novelty of the method is in using atomic radii corresponding to the distance where the Morse potential becomes zero, rather than in using the "typical" atomic van der Waals radii corresponding to the minimum of the Morse function. The calculated values include the ligand solid angles, the corresponding cone angles (rather than Tolman cone angles), the ligand special overlaps, ligand overshadowing, and the molecular solid angle. In addition, the calculated solid and cone angles are normalized to a Metal-Ligand distance of 2.28 Å to allow facile comparison of ligand steric demands in complexes of different metals with different compositions of coordination spheres. The new approach has been implemented in the program Solid-G and solid angles parameters with standard deviations have been computed for most common ligands such as cyclopentadienyl and tri-substituted phosphines. The new approach allos to evaluate the conformational flexibility of the ligands. The epitaxial cubic symmetric CrPt 3 films exhibit a perpendicular magnetic anisotropy (PMA) with large Kerr rotation angles. In order to understand the PMA effect of such a cubic CrPt 3 thin film, the directional chemical order parameters S and polarization dependent x-ray absorption fine spectroscopy (XAFS) were measured in both in-plan and plane-normal directions. The best PMA effect can be found when the plane normal order parameter is largest while the in-plane one is still low. At the same time, Cr-Cr bond-distance have slight distortion by XAFS analysis. This anisotropic directional long range chemical order might be due to the anisotropic interdiffusion and the compound formation between the Cr and Pt layer. For a short-range order analysis, the PMA effect might be attributed to the difference of the Cr-Cr bond-distance between plane-normal and in-plane directions. Tungstenbronze-type-like (Ba 1-Sr) 6-3x R 8+2x Ti 18 O 54 (R = rare earth) solid solution is one of the microwave dielectric materials. The crystal data is as follows: orthorhombic, Pbnm (No. 62), a 12, b 22, c 7 Å and Z = 2. The crystal structure of the solid solution is composed of two kinds of large cation sites: four pentagonal sites with Ba ions and ten rhombic sites with Ba, Sr and R ions in the framework formed by TiO 6 octahedron. These single crystals for R = Sm and Nd system were synthesized by conventional cooling method and FZ method, respectively. The X-ray diffraction data were obtained by a diffractomater with imaging plate (Rigaku; R-AXIS RAPID). Structural parameters were refined by full-matrix least-squares (RADY) [1]. All Sr ions occupied rhombic sites. Especially, one rhombic sites had more amount of Sr ions as compared with another rhombic sites in both of the R = Sm and Nd system. These solid solutions have relationship between distribution of cations and microwave dielectric properties [2]. Therefore, improvement of these properties with increasing compo...

Microwave dielectrics with enhanced permittivity

“…[4][5][6] Whereas a change in the lanthanide ion from La to Gd results in a decrease in both the permittivity (ε) and the dielectric loss tangent (tg δ) of the BLTss at a fixed value of x, the temperature coefficient of the permittivity (τ ε ) increases and changes its sign when passing from Nd to Sm. 4,5 When investigating Ba 6−x Sm 8+2x/3 Ti 18 O 54 (x = 1.5) using the dielectric resonator method in the frequency range of about 10 10 Hz, we revealed, for the first time, anomalies in the temperature dependence of permittivity 7 . More recently, we observed anomalies in the temperature dependencies of the dielectric parameters (ε, tg δ) in the entire range of Smcontaining BLTss.…”

Microwave dielectric properties of tungstenbronze type like (Ba1−αSrα)6−3xR8+2xTi18O54 (R=Sm, Nd) solid solutions

“…Tungstenbronze type like Ba 6−3x R 8+2x Ti 18 O 54 (R = La, Sm and Nd) is a possible candidate for the applications, [1][2][3][4] since this dense ceramics possesses high dielectric constant ε r as well as high quality factor Q·f.…”

Microwave dielectric properties and crystal structure of the tungstenbronze-type like (Ba1−αSrα)6(Nd1−βYβ)8Ti18O54 solid solutions

“…Ohsato et al 1,2 studied the relation between the quality factor Q × f and their crystal structures in the Ba 6 − 3x R 8 + 2x Ti 18 O 56 (R = rare earth) solid solutions (Table 1). They found that the Q × f value of those solid solutions have the maximum value at x = 2/3 because of a good ordering of Ba ions occupied all in large cations sites A2 and R ions occupied A1 sites.…”