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Low-k dielectric materials were prepared by sintering ZSM-5 zeolite powder compacts at temperatures ranged 1200-1300°C, and the microwave dielectric characteristics were investigated together with the structure evolution during sintering. It was failed to obtain ZSM-5 ceramics by high temperature sintering because the densification could never occur below the tolerable temperature and the ordered porous structure completely collapsed above the tolerable temperature. The structure changed from ZSM-5 zeolite to SiO2-Al2O3 glass at 1240°C, and finally to SiO2-based cristobalite ceramics above 1275°C.Alow dielectric constant (2.63-2.78) combined with low dielectric loss (< 0.0005 at 18GHz) and small temperature coefficient of resonant frequency (varied from -18.6 to -8.1 ppm/°C) was achieved in the present materials, and the value of dielectric loss was the lowest one achieved so far in the dielectric materials with a dielectric constant lower than 3. With the structure evolution fromZSM-5 zeolite to SiO2-Al2O3 glass and finally to SiO2-based cristobalite ceramics, the dielectric constant increased from 2.27 to 2.78, while the Qf value indicated a complicated variation tendency, and the higher Qf values were achieved in the amorphous and crystalline states, while significant drop was determined in the partial amorphous state. It should be a great challenge to prepare dense zeolite ceramicswithout collapse of ordered porous structure, and then the ultra-low dielectric constant materials with high Q could be expected. [ABSTRACT FROM AUTHOR]

Effects of the radius difference (ΔR) between A1 and A2 site cation on the crystal structure and the dielectric properties were investigated for Sr5RTi3Nb7O30 (R=La, Nd, Sm, and Eu) tungsten bronze. The tetragonal tungsten bronze structure was determined for all compounds, and the octahedral distortion significantly varied with the composition. In the Ti/Nb(2)O6 octahedra, besides the off center displacement of the Ti/Nb(2) cations along the c-axis, the four oxygen ions in the equatorial plane were gradually driven to different planes with decreasing R cation radius, while displacement of the Ti/Nb(2) cations in the ab plane decreased. For the Ti/Nb(1)O6 octahedra, the equatorial plane deviated from the center of the octahedron when the R cation radius became smaller. The ferroelectric transition in Sr5RTi3Nb7O30 was also dominated by the radius difference between A1 and A2 site cation. When the R cation radius became smaller, the dielectric anomaly of Sr5RTi3Nb7O30 changed from relaxor-like behavior into firstorder ferroelectric transition. Structural analysis indicated that compounds with larger radius difference between A1 and A2 site cation exhibited severer octahedra distortion, which was helpful for the ferroelectric transition. The low temperature relaxation observed in Sr5RTi3Nb7O30 (R5Nd, Sm, and Eu) was attributed to the freeze-out of polarizability in the ab plane, which originated from the Ti/Nb(2) cation displacement in the ab plane of the Ti/Nb(2)O6 octahedra. [ABSTRACT FROM AUTHOR]

Ba5NdFe1.5Nb8.5O30 tungsten bronze ceramics were prepared, and the dielectric and ferroelectric characteristics were evaluated together with the structure. The filled tungsten bronze structure in space group P4bm was confirmed. Two obvious dielectric relaxations were observed in the temperature range from 163 to 623 K, and there was a dielectric constant plateau with weak temperature dependence between them. A Debye-type dielectric relaxation in temperature range from 163 to 410 K is identified to originate from combination effect of the reorientation of the off-center Fe/Nb ions coupling with charge carrier hopping. The high-temperature (550-623 K) relaxation can be attributed to the Maxwell-Wagner effects. Moreover, another weak dielectric relaxation was determined below 200 K. The present ceramics exhibited room-temperature ferroelectric property with Pr=1.0 μC/cm². [ABSTRACT FROM AUTHOR]

The crystal structure and dielectric characteristics were evaluated for Ba4Sm2Ti4Ta6O30 and Ba5SmTi3Ta7O30 ceramics. The X-ray diffraction patterns confirmed the tetragonal tungsten bronze structure with space group P4 bm. A normal ferroelectric phase transition was observed at 332 K for the former, while the typical relaxor ferroelectric behavior with a spin glass nature was determined for the latter, where a broad permittivity peak with a strong frequency dispersion was observed around 150 K, which followed the Vogel–Fulcher relationship well. These different dielectric behaviors originated from the different crystal structures governed by the occupancy configuration of cations at A1 and A2 sites. [ABSTRACT FROM AUTHOR]

The title compound, C20H15N3O3, consists a phthalo­nitrile group and an iso­indole-1,3-dione group connected by a flexible butoxy chain. The dihedral angle between these two groups is 70.47 (3)°. Partial face-to-face overlap between the phthalo­nitrile groups of centrosymmetrically related mol­ecules is observed. In addition, the crystal packing is stabilized by C—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]