Function Of Dc Electric Field Research Articles

ELECTRORHEOLOGY OF DISPERSIONS OF BaxSr(1-x)TiO3 IN SILICONE OIL UNDER AC OR DC ELECTRIC FIELD

Electrorheology (ER) of ferroelectric materials such as nanometric BaTiO 3 is still not fully understood. In this paper, nanoparticles of Ba x Sr (1-x) TiO 3 (where x = 0.8, 0.9 or 1.0) were synthesized using the method of Pechini, calcinated at 950°C, and after, lixiviated under pH 1 or pH 5. A controlled stress rheometer (MCR-301) was used to make the ER characterization of dispersions made of Ba x Ti 1-x O 3 in silicone oil (30% w/w), where (a) shear stress as a function of DC electric field (under constant shear rate) or (b) shear stress as a function of shear rate (under constant AC or DC electric field) were measured. We observed that electrophoresis occurred under electric field DC, creating a concentration gradient which induced phase separation in ER fluid. On the other hand, under AC fields above 1 kV/mm, the ER effect is stronger than for DC field, and almost without electrophoresis. Furthermore, there is an AC frequency, dependent on the disperse phase, where the ER effect has a maximum.

Photoinduced Phenomena in Quantum Paraelectric Oxides by Ultraviolet Laser Irradiation

A photo-induced effect in the quantum dielectric system, such as SrTiO3, KTaO3, and CaTiO3, has been investigated under rather small external DC electric field. The dielectric measurement was performed under ultraviolet (UV) laser excitation combined with DC electric field. The gigantic photo-induced effects of dielectric properties of the quantum paraelectric systems have been firstly observed in the perovskite-type materials. The photoinduced dielectric effect was obtained as a function of DC electric field under constant UV irradiation.

SrTiO3 Thin Film Varactors on Si for Microwave Applications

ABSTRACTDielectric properties of SrTiO3 (STO) thin films in Au/Pt/STO/Pt/TiO2/SiO2/Si structure are studied at microwave frequencies. STO films with thickness of 300 nm were grown by laser ablation at different temperatures on templates of Pt/TiO2/SiO2 on Si with resistivity of 5 kQ-cm. XRD measurements reveal highly textured (111)STO films with small amount of (100) and (110) domains. The full with at half maximum of the rocking curve of (11 1)STO domains is about 2 degrees. Circular Au/Pt top electrodes with diameters in the range of 10–60 μm were formed by e-beam evaporation and lift-off process. The on chip microwave impedance of devices was measured in the frequency range of 45 MHz-45 GHz as a function of DC electric field in the range of 0–800 kV/cm. The loss tangent is less than 0.06 in the whole frequency range. Application of DC bias results in resonant absorption of microwave power at frequencies of 1.3, 3.0, 4.7, 6.4, and 9.7 GHz. The relative change of the dielectric permittivity under 800 kV/cm DC field is more than 20% in the whole frequency range. The results indicate that the varactors based on these STO films are suitable for tunable microwave applications.

Conduction mechanisms in some graphite - polymer composites: the effect of a direct-current electric field

This paper deals with the possible conduction mechanisms in highly anisotropic composites comprising 0 - 10 vol% graphite flakes within a polymer host. Conductivity measurements as a function of DC electric field have been made. In most cases, a non-linear behaviour of the current - voltage relationships is observed. A number of theoretical models are considered and we show that none of them is, by itself, able to explain our results. We further develop several arguments which lead us to consider the existence of a combined tunnelling effect and ionic conduction mechanism.

Hot-electron magnetic susceptibility of degenerate semiconductors at low temperatures

An analytical investigation of the effect of a dc electric field on the magnetic susceptibility of conduction electrons in a degenerate semiconductor at low temperatures has been made. From energy balance considerations, the electron temperature (Te) as a function of the strength of the dc electric field has been determined. Ionized impurity scattering has been assumed to be the dominant momentum relaxation process; the energy loss has been attributed mainly to the scattering by acoustic phonons (via both screened deformation and screened piezoelectric potentials), and by polar optical phonons. Numerical results have been presented for a typical case of an n-type InAs sample for fields up to 10 V/cm. It is found that susceptibility decreases with increasing field strengths. The plot of susceptibility (χ) as a function of dc electric field (E) leads to a kink at a field strength of about 450 mV/cm. This is explained on the basis of the spontaneous emission of polar optical phonons. It is further suggested that the measurement of susceptibility may be usefully employed as a tool for investigation of hot-electron phenomena.

Anomalous Resistivity in a Steady-State, Current-Carrying Discharge-Tube Plasma

The dc conductivity in a turbulent discharge-tube plasma has been measured as a function of dc electric field over the range 0.06 to 300 V/cm. Below approximately 60 V/cm the conductivity can be interpreted quantitatively in terms of the ion-acoustic wave instability. Above 60 V/cm the conductivity is approximately constant and about an order of magnitude lower than that calculated by Buneman for the two-stream instability.

A One-GHz Ferroelectric Limiter

The design and analysis of a 1-GHz limiter which uses voltage variation of the dielectric constant of a ferroelectric material to achieve limiting is described. An RF electric field derived from the input power is used to change the relative dielectric constant /spl epsiv//sub r/ of the material; the resulting nonlinear change of capacitance of a small element of the material is used to change the condition of a tuned circuit. The tuned circuit terminates a quarter-wavelength stub which shunts the main transmission line, thereby providing a power-dependent mismatch at the junction of the two transmission lines. The degree of this mismatch is controlled by the condition of the tuned circuit and, therefore, the magnitude of the input power. Theoretical analysis and experimental results for small signal and large signal operation are presented. Limiter analysis is based on the measured change of ferroelectric (nonlinear) capacitance as a function of dc electric field. The ferroelectric element is 0.011 by 0.013 by 0.020 (inches) machined from polycrystalline (Pb/sub 0.315/-Sr/sub 0.685/) TiO/sub 3/ material.