Carl Andeen

Effect of high pressure on electrical relaxation in poly(propylene oxide) and electrical conductivity in poly(propylene oxide) complexed with lithium salts

Audio frequency electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer and Parel 58 elastomer complexed with a variety of lithium salts. The measurements have been carried out in vacuum over the temperature range 5–380 K and at pressures up to 0.65 GPa over the temperature range 230–380 K. Both the electrical conductivity for the complexed material and the electrical relaxation time associated with the α relaxation in the uncomplexed material exhibit VTF or WLF behavior. From a VTF analysis for both the vacuum electrical relaxation time and electrical conductivity, Ea is found to be about 0.09 eV and T0 is found to be about 40 °C below the ‘‘central’’ glass transition temperature. In addition, it is found that the activation volumes for the electrical relaxation time and the electrical conductivity are the same when compared relative to T0. These results imply that the mechanism controlling ionic conductivity is the same as that for the α relaxation, namely large‐scale ...

Low‐frequency dielectric constants of α‐quartz, sapphire, MgF2, and MgO

The 1000‐Hz 300°K dielectric constants were measured for crystalline α‐quartz, sapphire, MgF2, and MgO, and polycrystalline sapphire (Lucalox), magnesium fluoride (IRTRAN 1), and magnesium oxide (IRTRAN 5). The measurements were performed using the method of substitution (two‐fluid method). The results are as follows: single‐crystal α‐quartz, es∥=4.6368±0.001 and es⊥=4.5208±0.001; single‐crystal sapphire, es∥ = 11.589±0.005 and es⊥=9.395±0.005; polycrystalline sapphire (Lucalox), es=10.154±0.007; single‐crystal MgF2, es∥ =4.826±0.01 and es⊥=5.501±0.01; polycrystalline MgF2 (IRTRAN 1), es=5.289±0.001; single‐crystal MgO, es=9.830 ±0.001; and polycrystalline MgO (IRTRAN 5), es=9.833±0.001, where es∥ and es⊥ are the dielectric constants parallel and perpendicular, respectively, to the c axis.

NMR, DSC, DMA, and High Pressure Electrical Conductivity Studies in PPO Complexed with Sodium Perchlorate

Abstract : Audio frequency electrical conductivity, DSC, DMA, and 23 Na nMR measurements have been carried out on Parel 58 elastomer complexed with sodium perchlorate. (As Parel 58 is primarily poly(propylene oxide), it will be referred to as PPO.) The DSC and DMA measurements yield similar values for Tg which are about 72 C higher than the central Tg for uncomplexed PPO. In addition, the DSC studies show that the sodium perchlorate is insoluble above about 140 C. The conductivity measurements have been carried out in vacuum over the temperature range 290-370K. From a VTF analysis Ea is found to be about 0.09 eV and T0 is found to be about 45 C below the central glass transition temperature which is the same behavior observed previously for PPP complexed with lithium salts and for the alpha relaxation in uncomplexed material. In addition, it is found that the vacuum activation volumes for the electrical conductivity and the alpha relaxation are approximately the same when compared relative To. The 23Na NMR measurements reveal the presence of both bound and mobile sodium species, the relative concentrations of which change by about a factor of ten over the temperature range -90 to +90 C. In addition the mobile 23Na resonance becomes motionally narrowed above Tg. The NMR results combined with the conductivity data imply that ion motion is controlled by large scale segmental motions of the polymer chains.

The low temperature electrical properties of some anisotropic crystals

Abstract The principal complex dielectric constants have been studied at audio frequencies over the temperature range 5.5–380K for α-quartz, sapphire, magnesium fluoride, and calcite. For some samples, the imaginary part of the dielectric constant revealed the presence of dipolar or thermally activated loss mechanisms which are attributed to trace impurities. The effects of these impurities are considered in arriving at values of the real part of the dielectric constants for each of the materials.

Accurate Determination of the Dielectric Constant by the Method of Substitution

A substitution method for highly accurate determination of the static dielectric constant of solids is presented along with techniques for refining capacitance measurements. The results for some alkaline earth fluorides are CaF2, 6.799; SrF2, 6.466; and BaF2, 7.359; and an alkali halide KCl is 4.818.

N.m.r., d.s.c., t.m.a. and high-pressure electrical-conductivity studies in solid, crosslinked dimethylsiloxane-ethylene-oxide copolymer networks containing sodium

Abstract Audio frequency electrical conductivity and 23 Na n.m.r. studies have been made on solid, crosslinked dimethylsiloxane-ethylene-oxide copolymer networks containing sodium. Electrical measurements were made in vacuum over the temperature range 5 K to 380 K at pressures up to 0.65 GPa over the temperature range 230 K to 380 K. The electrical conductivity for the complexed material and the electrical relaxation time associated with the α-relaxation in the uncomplexed material exhibit Vogel-Tamman-Fulcher (V.T.F.) or Williams-Landel-Ferry (W.L.F.) behaviour. From a V.T.F. analysis of the electrical conductivity, the activation energy, E a , is found to be about 0.11 eV and T 0 is found to be about 45°C below the ‘central’ glass transition temperature as determined by both d.s.c. and t.m.a. Also, T 0 is found to increase by about 50 K GPa −1 and E a to increase significantly with pressure. In addition, the high-pressure studies show that the activation volume associated with electrical conductivity decreases from 44 to 23 cm 3 mol −1 over the temperature range 262 K to 323 K. The 23 Na n.m.r. measurements reveal the presence of both bound and mobile sodium species, the relative concentrations of which change by about a factor of 10 over the temperature range −100°C to +100°C. Broadening of the bound 23 Na line above room temperature suggests the possible presence of ion pairs or higher aggregates in the complex.

Temperature and pressure variation of the refractive index of diamond

The temperature and pressure variations of the refractive index for a Type IIa diamond have been measured at audio frequencies using capacitance techniques. Measurements have been made at zero pressure over the 5.5-340-K temperature range and at pressures up to 1.4 x 10(8) Pa (1.4 kbar) at room temperature. At room temperature, (1/n)(dn/dT)(p) = +4.04 x 10(-6)/K and (1/n)(dn/dp)(T) = -0.36 x 10(-12)/Pa. In addition, the curvature in the refractive index with temperature has been determined. The first-order derivatives are compared with previous experimental data and the recent theoretical calculations of Van Vechten and Yu and Cardona.

The dielectric spectrum of erbium doped CaF2

The complex dielectric constant has been measured at five audio frequencies (102-104 Hz) over the temperature range 4.2-400K for eight concentrations (0.001-3.0 mol%) of erbium in calcium fluoride. Relaxation processes with activation energies of about 0.15, 0.4, 0.5 and 0.7 eV have been observed which correspond to previously reported dipolar complexes in rare-earth doped alkaline-earth fluorides. In addition, a previously unreported relaxation with an activation energy of approximately 0.028 eV has been found at low temperatures and high rare-earth concentrations. It is concluded that this relaxation is cluster-associated.

The temperature variation of the dielectric constant of ’’pure’’ CaF2, SrF2, BaF2, and MgO

Improved values of the real part of the low‐frequency dielectric constant are presented for ’’pure’’ CaF2, BaF2, SrF2, and MgO over the temperature range 5.5‐400 K. Accurate measurements of both the real and imaginary parts of the dielectric constant were made so that corrections could be made to allow for dipolar impurities. The final results are thought to be accurate to better than 0.1% over the full range of temperatures.

Effect of OH− on the low‐frequency dielectric constant of vitreous silica

The 1000‐Hz 300°K dielectric constant, es, of 24 kinds of commercially available vitreous silica has been measured to an accuracy of 0.01% and a precision of about 1 part in 300 000 by the method of substitution (two‐fluid technique). The observed dielectric constant ranges from 3.8073 to 3.8304. These results are correlated with hydroxyl ion content and other imperfections. It is found that es=3.8073+2.72×10−22 N where N is the hydroxyl concentration in ions/cm3, and observed deviations from this rule are attributed to metallic impurities and inclusions. From the results it appears that 3.8073 closely approximates the low‐frequency dielectric constant of pure vitreous silica.