X. Z. Ding

Charge trapping on different cuts of a single‐crystalline α‐SiO2

A scanning electron microscope is employed for the investigation of charging on different cuts of an α‐SiO2. A method for the determination of trapped charges is proposed. Charging on different cuts is observed to decrease in the order of z cut, 30° cut, 45° cut, and 60° cut of the α‐SiO2. This phenomenon is related to permittivity, defect density, and stress of the samples. Details of the experiments and the method of charge determination are given.

Dielectric and electrical properties of ordinary Portland cement and slag cement in the early hydration period

The dielectric constant and electrical conductivity of ordinary Portland cement (OPC) with water-cement ratios (w/c) of 0.30, 0.35 and 0.40 were measured for the first 30 h hydration, using a microwave technique in the frequency range 8.2–12.4 GHz. It was found that both the dielectric constant and electrical conductivity of the cement paste are sensitive to the water-cement ratio, the higher the w/c value, the greater the dielectric constant and electrical conductivity, and the longer the hydration time. We also found that the higher the frequency the greater the electrical conductivity but the smaller the dielectric constant. The dielectric constant and electrical conductivity of high- and low-slag cement with water-solid ratio (w/s) of 0.40 were measured in the first 30 h after mixing. The changes in dielectric constant and electrical conductivity of low-slag cement with time are similar to that of OPC, but the high-slag cement shows very different dielectric and electrical properties compared with OPC and low-slag cement. The relationship between the dielectric and electrical properties of cement paste and cement hydration was also discussed.

Microwave study of hydration of slag cement blends in early period

Microwave technique were used to investigate the early hydration of slag cement with different slag percentages, different activators and different amount of activator. It is found that higher slag cement causes a higher dielectric constant E and a shorter induction period. But higher slag cement samples have very different electrical conductivity (3 compared with that of pure cement, their o curves have two extra bumps in 9-14 h and 22-24 h. We found that the addition of 2% NaOH and Na.

Dielectric polarization relaxation measurement in α‐SiO2 by means of a scanning electron microscope technique

O, results in large changes in E whereas the addition of 2% Ca(0I-Q causes a little change in E. Addition of 2% Ca(OH), decreases the o but addition of 2% NaOH and Na.

Study of dielectric and electrical properties of mortar in the early hydration period at microwave frequencies

O, increases the o. We also found that the greater the amount of Na

Effects of impurity concentration on dielectric loss in Zn‐doped InP at microwave X‐band frequencies

O, the smaller the E but the greater the (T. The relation between the compressive strength results and the E and o results are also discussed.

MICROWAVE DIELECTRIC RESONANCE OF A FLUORIDE GLASS

A scanning electron microscope is used as a tool to study dielectric relaxation processes in α‐SiO2 by measuring the leakage current in the sample surrounded by a metallic aperture. A transient time (t t ) of the order of a few seconds appears before the steady‐state current is established. The time dependence of the trapping rate is found to follow a power law and to be related to relaxation processes of a dielectric under electrical and thermal stress.

Effects of impurities on dielectric properties of fluorozirconate glasses at microwave frequencies

The dielectric constant, ɛ, and electrical conductivity, σ, of mortars with various sand-cement ratios,s/c, were measured for the first 30 h hydration using microwave techniques in the frequency range 8.2–12.4 GHz. The ɛ and σ of the mortars were found to increase linearly with increasing water-solid ratiow/(s + c), but decrease with increasings/c. It was found that as long as thes/c values were the same, the rate of changes in ɛ and σ of the mortars were the same. It appears that thes/c is the key factor controlling the rates of changes in dielectric and electrical parameters of cement hydration in mortar. The relationship between compressive strength and dielectric and electrical properties of mortars was also discussed.

A vacuum pump coaxial probe system for measurement of dielectric properties of materials with smooth surfaces

Microwave dielectric measurements have been performed on various Zn‐doped InP crystals using a vector network analyzer. There are two kinds of dielectric response in Zn‐doped InP crystals depending on their Zn concentration. The general dielectric response in InP in the microwave frequency region is dielectric relaxation, which is related to the dipolar species formed from the ionized substitutional ZnIn−. The other dielectric response of InP crystals doped with a higher Zn concentration is dielectric loss. The crystal doped with Zn to a concentration of 2.14×1018 cm−3 shows a strong dielectric loss at 11 GHz, but no dielectric loss peaks are found in crystals doped with a lower Zn concentration of 4.36×1017 cm−3. The dipolar species, which gives rise to the dielectric loss in Zn‐doped InP crystals, is believed to be a result of vacancy complex defects of neutral substitutional ZnIn and two P vacancies.

Microwave dielectric relaxation of silicon crystals

The dielectric properties of a fluorozirconate glass are investigated in the frequency range from 0.5 to 13.5 GHz using a microwave vector network analyzer. A prominent dielectric resonance is observed around 7.0 GHz. The resonance may be due to a fundamental interunit vibrational mode of the basic structural ZrFn polyhedral units of the fluorozirconate glass.