摘要:

Temperature dependences of dielectric, ferroelectric, elastic, piezoelectric, and optical properties of a new ferroelectric crystal, SrTeO3, have been measured. Ferroelectricity in this crystal is confined to the temperature range between 312 and 485°C. All the measured constants exhibit abrupt changes at 312°C, which shows the phase transition at this temperature to be of the first order. The electromechanical coupling factorsk21andk22at 312°C are 0.34 and 0.37, respectively, which are large in spite of the small value of the spontaneous polarization; 0.037 C/m2. The temperature dependence of the piezoelectric constantd22is well explained by the dielectric constant and the spontaneous polarization, while that ofd21seems to be peculiar; i.e., it monotonically decreases to nearly zero at the upper transition point. The elastic compliancesS11DandS22Dshow no anomaly in the ferroelectric temperature range. The obtained value of 17.3 eV for the dispersion energy of the refractive indexnbindicates that this crystal may be built up by the tetrahedral framework. Phase‐transition temperatures in the solid‐solution systems Sr1−xBaxTeO3and Sr1−xCaxTeO3are studied on ceramic samples. The two transition points decrease with increasingxin both systems.

ISSN:0021-8979    

DOI:10.1063/1.1662875

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

By using techniques developed by many workers to study streamer mechanism in air between metallic electrodes, the phenomena of partial discharges in insulating walls were studied. It is shown that the luminous evolution of partial discharges consisted of the development of a primary and a secondary streamer, for positive pulses. The velocity of propagation of the primary streamer was about 5 × 105m/s as for metallic electrodes. The electrically induced pulses and photon pulses have shown a correspondence between electrical and luminous phenomena for positive pulses, while Trichel pulses were observed for negative pulses. A cathodic zone was shown, and then a mechanism of erosion of insulating materials was conceived.

ISSN:0021-8979    

DOI:10.1063/1.1662876

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have studied acoustic anharmonic effects in lead molybdate using a 150‐MHz fundamental acoustic wave. When sampling the amplitude of the second harmonic acoustic wave with a laser probe, the light scattered by the fundamental acoustic wave may lead to severe mistakes in the determination of nonlinear coupling constants if care is not taken. This measurement can be carried out so as to get not only the true acoustic second harmonic amplitude but also to get an experimental proof of the phase lag −&pgr;/2 between second harmonic and fundamental acoustic waves.

ISSN:0021-8979    

DOI:10.1063/1.1662877

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An effective permittivity is defined which characterizes the electrical coupling properties of acoustoelectric surface waves. Relationships are established between this quantity and other parameters, such as &Dgr;v/v, used in evaluating active and passive surface‐wave devices. A simple method for computing the effective permittivity is described which is shown to be more accurate than other methods used to date.

ISSN:0021-8979    

DOI:10.1063/1.1662878

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In a previous paper, the simple Maxwell‐Garnett theory of aggregated metal systems was analyzed in the free‐electron regime for low damping (&ohgr;p&tgr;>1). Expressions were derived for the magnitude and resonance frequencies of plasma and conduction resonances as functions of particle constants and the aggregation parameter. In this paper the effect of moderate and high damping(&ohgr;p&tgr;≲1)and the effect of a dielectric interparticle matrix withn> 1 is examined, and the results are compared with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1662879

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A theory of the strip coupled acoustic surface wave amplifier, the acoustic surface wave strip coupler, and the strip coupled acoustic surface wave parametric device is given. This theory makes use of a space harmonic expansion and variational techniques to determine the impedance looking into an individual strip. The resulting model accurately predicts the experimental results obtained with strip couplers and indicates that for optimum coupling the ratio of strip width to gap spacing should be unity. Strips can be used to couple from the piezoelectric medium to a semiconductor to make amplifiers and nonlinear signal processing devices. When used in amplifiers, strip coupling should reduce the power dissipation for a given gain by orders of magnitude and greatly increase the gain at low frequencies. In parametric devices, the strips eliminate the need for microscopic air gaps and should increase the processing efficiency by orders of magnitude.

ISSN:0021-8979    

DOI:10.1063/1.1662880

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The third‐order elastic constants of lithium niobate have been measured by small‐amplitude ultrasonic waves as a function of applied stress, including the piezoelectric effects.

ISSN:0021-8979    

DOI:10.1063/1.1662881

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper presents a method for determining the electron density and electron collision frequency in a cylindrical plasma column by placing an rf coil coaxially around the plasma and measuring the coil impedance. Simplified expressions relating the impedance to plasma parameters are found to be valid under certain suitable conditions. The plasma of a hot‐cathode low‐pressure dc discharge in argon has been studied by an rf coil probe. The dependence of electron collision frequency on electron velocity has been taken into account. The values of the electron density and average collision frequency, as obtained from the rf probe under different discharge conditions, are in fairly good agreement with those given by a cylindrical Langmuir probe.

ISSN:0021-8979    

DOI:10.1063/1.1662882

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In the positive column of low‐pressure gas discharges, the electron energy distribution can be markedly non‐Maxwellian, in particular in the tail of the distribution at low degrees of ionization. A method is described which enables one to account for large deviations from a Maxwellian distribution when calculating collision rates, energy flow terms, excited‐state densities, and the radiation output. Illustrative examples are given for Cs&sngbnd;Ar, Ar, and Hg&sngbnd;Ar discharges. Possible extensions and applications of the method are briefly discussed. Analytical formulas are derived for (i) the Coulomb relaxation between the electrons and (ii) the cross sections for ionization from excited states.

ISSN:0021-8979    

DOI:10.1063/1.1662883

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The usual geometry of an axially symmetric parallel flow Pierce‐type gun is criticized and some shortcomings underlined. The general equation defining the family of field forms ensuring parallel flow is carried out and a particular solution selected. The shape of electrodes providing the chosen field form is calculated in a simple and reliable way.

ISSN:0021-8979    

DOI:10.1063/1.1662884

出版商:AIP    

年代:1973

数据来源: AIP