Hz For Temperatures Research Articles

Waste heat energy harvesting using the Olsen cycle on 0.945Pb(Zn1/3Nb2/3)O3– 0.055PbTiO3 single crystals

This paper reports on direct thermal to electrical energy conversion by performing the Olsen (or Ericsson) cycle on [001]-poled 0.945PbZn1/3Nb2/3O3–0.055PbTiO3 (PZN-5.5PT) single crystals. The cycle consists of two isothermal and two constant electric field processes. The energy density was found to decrease with increasing cycle frequency while the power density increased. The maximum energy density obtained was 150 J/l/cycle for temperatures between 100 and 190 °C and electric field between 0 and 1.2 MV m−1 at frequency 0.034 Hz. The maximum power density reached 11.7 W l−1 at 0.1 Hz for temperatures between 100 and 190 °C and electric fields between 0.2 and 1.5 MV m−1. Moreover, the dielectric constant and saturation polarization of PZN-5.5PT are reported for the first time at 0.1 Hz for temperatures between 100 and 190 °C. Finally, the experimental results agree relatively well with predictions by a recently developed temperature-dependent property model already validated with PMN-32PT. Inter-sample variability and sample durability are also discussed.

Anomalous low-frequency resonance-type behaviour and negative capacitance in doped glasses

It has been found that the dielectric capacitance response of doped silica glasses measured in the frequency range 10-3-105 Hz for temperatures between 500 and 1100K displays anomalous thermally activated resonance-type behaviour. This response is linked to time domain oscillations reported in similar materials. It is shown that negative capacitance can result from these time domain oscillations under certain conditions. One material in which negative capacitance has been seen, a doped boric oxide glass, is also discussed.

The Dielectric Behavior of Straight Chain Alcohol Blends

Time Domain Spectroscopy (TDS) has been used in this study to determine the dielectric relaxations of several mixtures of normal alcohols. The complex permittivity ?* (?) was determined in the frequency range from 106 to 5×109 Hz for temperatures ranging from -20 to 500C. Mixtures of n-octanol and n-butanolin mole concentrations of 95, 75, 50 and 25% were studied. From plots of the primary relaxation time, Tl, against temperature, activation energies ?H of 0.45± 0.02 eV were found for all mixtures investigated, and values of static dielectric permittivity were seen to follow a linear mixing law. Two relaxations were observed with both mixtures and neat alcohols. The primary relaxation time Tl, which characterizes the low frequency dispersions, ns, changed substantially with varying proportions, while the secondary relaxation time Ti did not. Resolution ution of the data for T2 was, however, poorer than those for Tl. There was no indication of change in the relaxing species with temperature below 40°C, while some evidence of dissociation was found at temperatures above 40°C.

Dielectric relaxation in concentrated solutions of poly(methyl methacrylate)

AbstractMeasurements of dielectric relaxation have been made for a series of solutions of poly(methyl methacrylate) in toluene. A range of concentrations between 2% and 20% was used for a number of polymers of differing molecular weights. The dispersion was studied over the frequency range 103‐106 Hz for temperatures between −90°C and +20°C. It has been found that both the distribution of relaxation times and the activation energy increase with increasing concentration. The magnitudes of the effects vary with molecular weight. A significant observation is that the increase in dielectric constant with concentration is not linear.

The polarization impedance of sodium chloride crystals

The polarization impedance of NaCl both pure and doped with 2.2-4.4*10-4 mole fraction of SrCl2 was measured in the frequency range 102-2*104 Hz for temperatures between 480 degrees C and 790 degrees C, using rubbed graphite electrodes. Results depend on the thermal history but are relatively reproducible on cooling from 790 degrees C for the first time. Even then they do not agree overall with the linearized electrode blocking theory of Friauf (1954) and Macdonald (1953) which has been partially satisfactory for KCl. The discrepancies are difficult to explain in terms of the effects of gaps between crystal and electrode proposed by Miliotis and Yoon (1969) but this may be because of the lack of an adequate mathematical formulation of their model.

Ionic conductivity and low frequency dispersion in hexagonal silver iodide

Measurements are reported for the temperature variation of ionic conductivity in single crystals of hexagonal silver iodide. Both nominlly pure and Cu 2+ doped crystals were studied and analysis of the measurements for conduction both parallel and normal to the c-axis leads to a formation energy for Frenkel defects of 0·60eV, activation energies for diffusion of Ag + interstitials parallel and normal to the c-axis of 0·61 and 0·29eV respectively and corresonding activation energies for Ag + vacancies of 0·50 and 0·39eV. Similar measurements performed on thin films of Agl grown expitaxially on mica show varying behaviour but the activation energy for conduction is about 0·4 eV, which agrees with the value expected from the single-crystal results if the conductivity is vacancy controlled. Dielectric measurements in the frequency range 10–10 5 Hz at temperatures between 193 and 304°K show anomalous dispersion peaks at about 10 4 Hz for temperatures above 300°K which are tentatively interpreted in terms of trapped Frenkel defects and interfacial polarization. At temperatures below about 290°K a series of sharp resonant absorptions is observed whose orgin is uncertain. The static dielectric constant approaches the value 6·8±0·2 at temperatures below-40°C.