Dielectrics orthorhombic

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Bluish-black orthorhombic crystals refractive index 3.34 density of solid 4.933 g/cm3 at 20°C density of the element in liquid form at 120°C 3.96 g/cm melts at 113.6°C to a black mobile liquid the solid can be sublimed to vapor below its melting point vapor pressure of solid at 25°C 0.3075 torr vapor pressure at 113.6°C 90.5 torr the liquid boils at 184.3°C giving violet vapors vapor density 6.75 g/L critical temperature 545.8°C critical pressure 48.9 atm critical volume 155 cm /mol dielectric constant of solid 10.3 at 23°C and... 

The efficient mechanism for translative motion of a stem through an orthorhombic crystal discovered by dielectric relaxation measurements has... 

The complex dielectric response of crystal 1 can be described in terms of a number of distributed dynamic processes separated by different frequency and temperature ranges. The ferroelectric phase transition is observed at 295.6 K. It is followed by tetragonal to orthorhombic and orthorhombic to rhombohedral transitions occurring at 291.1 K and 230 K, respectively. A comparison of these transition temperatures with the undoped crystal 2 revealed that the second and third transitions (tetragonal to orthorhombic and orthorhombic to rhombohedral) were shifted by approximately 40 K toward the lower temperatures (see Fig. 19). 

In the compounds that are close to PbZr03 in composition, room-temperature structures are orthorhombic (Fig. 12), but the octahedral cations do not uniformly displace parallel to [110]. Rather, for very Zr" cation that displaces parallel to [110], a neighboring Zr" shifts parallel to [TTO]. The net polarization therefore is zero, and the material is classified as antiferroelectric. Antiferroelectric materials also exhibit higher-than-average dielectric constants, but they are not so extreme as those observed in ferroelectric compounds. 

KNbOs shows the closest resemblance to BaTiOa, having three transitions (to tetragonal, orthorhombic, and rhombohedral forms), while NaNb03 shows quite different dielectric behaviour, its transitions (at 350°, 520°, and 640°C) being of a different kind from those in KNb03 and BaTi03. - ... 

The role of crystal imperfections in the dimerization of substituted anthracenes has been described in the case of l,8-dichloro-9-methylanthracene.178 Similar studies have now been conducted for the 10-methyl isomer.179 In order to explain how the topochemically forbidden / -dimer (head to tail) is produced from irradiation in the solid phase, optical and electron microscopic examinations of the (010) faces of the orthorhombic crystals of the monomer have been carried out, together with differential-enthalpic and dielectric measurements. Again it is shown that the dimer nuclei appear at emergent dislocations. 

The dielectric parameters are tensors, and consequently it is essential to use polarized radiation when recording the infrared absorption and reflection spectra of all but cubic crystals. Thus, with an orthorhombic crystal the reflection has to be measured with the electric vector parallel to the a, Z , and c axes. When obtaining the reflection spectra from the be plane of a monoclinic crystal, it is necessary to rotate the plane of polarization of the electric vector. The longitudinal optic (LO) frequency [see discussion of Equation (4)] can be found for q = 0 by noting that it is the frequency for which = 0. It can be measured directly in cubic crystals by a method due to Berriman [114]. 

Figure 4.24. The change in the dipole moments and the physical properties of BaTi03 at different temperatures. At the phase transitions between rhombic (Rh), orthorhombic (Or), tetragonal (T), and cubic (C), the dielectric constants (e), the cell constants (c), the heat capacity Cp, and the piezoelectric parameter d change discontinuously.

Practical interest in rare earth aluminates as microwave dielectric materials remains high. Recently, Shevlin et al. (2005) reported that La cYi- AlOs solid solutions (0.2 possible application as gate dielectrics (which would offer an alternative to silicon dioxide in complementary metal-oxide semiconductor devices) when stabilized in the rhombohe-dral perovskite structure. The needed properties are lost in the orthorhombic modification. Flowever, our previous consideration of the crystal structure (see Section 2.3.1) together with the results of Kyomen and Itoh (2002) reveal that this feature is difficult to realize in practice, that is the rhombohedral modification of Laj Yi j A103 solid solution only exists in a narrow concentration range with X > 0.85, while in the range 0.2 < x < 0.4, the crystal structure will remain orthorhombic. 

Liu XQ, Wu SY, Chen XM, Zhu HY (2009) Temperature-stable giant dielectric response in orthorhombic samarium strontium nickelate ceramics. J Appl Phys 105 054104... 

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