vol. conference reportdownloads.hindawi.com/journals/apec/1978/703934.pdf · conferencereport 135...

Electrocomponent Science and Technology1978, Vol. 5, pp. 133-135

(C) Gordon and Breach Science Publishers Ltd., 1978Printed in Great Britain

Conference Report

3RD INTERNATIONAL JOINT MEETING ONELECTRICAL AND MAGNETIC CERAMICS ATNOORDWIJKERHOUT, THE NETHERLANDS17th-18th November, 1977.

This was an International Conference with partici-pants from 15 countries; the majority being fromWest Germany and Holland.

The major topics were ferrites, dielectrics, positivetemperature coefficient (PTC), barium titanateresistors, voltage dependent resistors (VDRs) madefrom zinc oxide, and the various forms of piezo-electric lead titanate zirconate.

PTC barium titanate has recently been the subjectof a series of papers from the Philips Aachenlaboratories which have established a model based onthe formation of vacant sites during sintering, theirdiffusion during cooling from sintering and theirsubsequent functioning as sources and traps forcurrent carriers under normal room temperatureconditions. This explainsJmost of the phenomenaassociated with the preparation and use of PTCdevices. It was the basis of the many papers at thepresent meeting and indicated the continued interestby Siemens and Philips. The existence of practicalproblems was indicated by a Siemen’s paperdescribing the mechanical failure of devices used tocontrol the switching surge in motor windings. Thedamage was thought to be associated with thermalstresses.

Zinc oxide VDRs are likely competitors withsilicon diodes and spark gaps for the protection ofintegrated circuits from transients. They are anappreciable advance on the present VDRs based onsilicon carbide and may be less expensive than silicondiodes at higher voltages. Their raw materials arecheap and they are made by the familiar powderpressing and sintering process., It is not entirely clearhow they work so that the manufacturing details arehighly empirical but there may be a considerablemarket for them in, for instance, telephone systems.

There appears to be quite a bit of effort going intothe development of low cost high dielectric constantceramic chip capacitors with the elimination ofplatinum and palladium from the electrodes as a

133

primary objective. One paper described a dielectricwith a K of about 1000 and a sintering temperaturecompatible with the use of silver. The theoreticalmodel referred to above for PTC resistors alsoexplains the way’manganese oxide protects bariumtitanate from the action of hydrogen and so enables itto be sintered along with a nickel electrode system togive an insulating dielectric (K 3000). In thisconnection the BME chip capacitors with nickelelectrodes advertised by Globe Union a year ago offerthe best properties I have yet seen (K 5000:leakage about 2000 sec. at 20C). There is also theTruman Rutt process where a low melting alloy isinjected into porous layers between the dielectriclayers in air-fired monolithic structures. Little hasbeen heard of this in the past 2-3 years: it may haverun into practical problems.

There is a modest revival of interest in very lowloss and very low temperature coefficient ceramics formicrowave cavities. There are several possible systemsand the present concentration on the higher titanatesof barium seems rather arbitrary (a matter offollowing the Bell lead) but it could be a system inwhich the properties are less sensitive to smallcompositional changes than most.

The piezoelectric papers reflect current interestin optically active materials but largely consist ofdotting the i’s in the Sandia work. AEG-Telefunkenseem to be developing a similar material to ours forpyroelectric detectors. One paper on a PZT typeceramic for SAW devices indicates that this approachmay still be of interest.

Below is a complete list of the papers given inthe field of PTC and Varistor Ceramics, DielectricCeramics and Piezoelectric Ceramics. A few notes onpapers of particular interest are appended. All thepapers given at the meeting will be published in aspecial issue of Berichte der Deutschen KeramischenGesellschaft which is due to appear in July, 1978.

PTC and Varistor Ceramics

Heterogeneous microstructure of donor-dopedBaTiO3 by B. Hoffmann and A. S. Janitzki, Instituteof Technology, Karlsruhe.

134 CONFERENCE REPORT

An attempt to explain the properties of positivetemperature coefficient (PTC) barium titanate bypostulating other phases in the grain boundaries.

The PTC effect of semiconducting BaTiO3ceramics as a function of the titanium excess byH. Ihrig, Philips, Aachen.

The PTC effect shows a maximum for a 5 atom %excess of Ti. However, the effects of a grain boundaryphase are supposed to be due solely to its influencingthe surface states of the conducting BaTiO3 grains.

The shock resistance of ’cold conductors’ (PTCresistors) by K. Lubitz, Siemens.

PTC resistors in series’with motor windings tend tocrack during the heating up period in switching on,i.e. after about 0.5 sec. As at this point about kW is

Dielectric Ceramics

Ceramic and dielectric properties of selectedcompositions in the BaO-TiO2-NCI: Oa system byD. Kolar, Z. Stadler, S. Gaberek and D. Suvorov,J. Stefan Institute, Univ. of Ljubljana..A systematic phase diagram investigation yielding

low loss ceramics, but with temperature coefficientsof permittivity greater than -50 ppm/C. Any lowert.c.c, is strongly composition dependent.

Effects of chemical treatment on loss quality ofmicrowave dielectric ceramics by H.. M. O’Bryan Jr.,J. Thomson and J. K. Plourde, Bell Laboratories.A very low temperature coefficient of permittivity

has been found for the material Baz Ti90 o and thevalue is not acutely dependent upon composition..

being dissipated in an 18 mm diameter 7 mm thick Interaction between metallic films and dielectricpiece of ceramic, high thermal stresses are clearly possible, ceramic substrates during sintering of the ceramics

by A. Peigniez, M. Marchal and N. G6rard, UniversityBehaviour of ZnO varistors at low temperature

by Lo M. Levinsen and H. R. Phillipp, G. E.Schenectady.

3.5 to 300K measurements confirm the useful-ness of a model in which conducting grains of zincoxide are immersed in a semiconducting matrix.

The preparation and properties of ZnO varistors byB. Knecht and H. P. Klein, Brown Beveri & Co.

There was nothing on preparation but a modelwas introduced in which the interstitial material wasmerely given the role of controlling the surfacestates of the ZnO grains. This led to an appreciationof the effect of grain size on properties.

Doping effects in metal oxide-varistors byR. Einzinger, Siemens.

The author ascribes the behaviour to oxygendeficiencies in the ZnO lattice. These can be renderedunstable by the presence of Mn4/ ions. Mn4/ can bereplaced by Co:/ which gives stable material. Co istherefore the really essential doping ion, the otherscontrolling such parameters as grain size. On thismodel the function of the intergranular phasebecomes insignificant.

Direct determination of barrier voltage in ZnOvaristors by J. T. C. van Kemenade and R. K.Eijnthoven, Philips, Eindhoven.

Quite definite potential barriers can bemeasured at grain boundaries averaging about 3.5 V.Other values (down to 2 V) were claimed duringdiscussion but the great significance of grainboundaries seemed to be firmly establishedexperimentally.

of Dijon and Thomson C. S. F.This was concerned with chip capacitors and the

way in which thin metal layers break up into globulesduring sintering. Thus a 1.5 micron thick layer of Pdwill give 90% cov6rage of a surface after sintering at1400C while a 1.0 micron layer only gives 20%coverage. This is all part of the problem of econo-mising in precious metal.

Electrical properties of acceptor doped BaTiO3ceramic by H.-J. Hagemann, Philips, Aachen.A model which explains why capacitors can be

made with base metal electrodes. The objective ischeaper chip capacitors.

The influence of microstructure on the electricalproperties of intergranular capacitors by R. Wernicke,Philips, Aachen.A model for barrier layer capacitors which operate

in the 10 V region.Liquid phase sintering of barium titanate by

D. Hennings, Philips, Aachen.The objective is to reduce the sintering temperature

of barium titanate to a level where silver might besubstituted as electrode material in chip capacitors.It appears difficult to control crystal growth using themethod discussed.

Low sintering ceramic dielectrics by H. Hoppertand H. G. Hoffmann, Dralovie Electronic GmbH.

Again the objective is to reduce the sinteringtemperature of barium titanate and this is done byusing a relatively large proportion of a glassy phase.Chip capacitors with silver electrodes with permittivi-ties of 1000 have been made.

CONFERENCE REPORT 135

P’ezoelectn’c Ceramics

The influence of the geometry of piezoelectricceramic plates on the properties of bending modeoscillation by J. Deckert. AEG-Telefunken.A very specialised paper on mechanical oscillation

for 10 to 100 kHz filters.

Grain growth in PLZT ceramics by G. Wolfram,Siemens.

An optical examination of the small signal responseof 90 domain walls in transparent PLZT-ceramics,by P. Gerthelm and R. Send, Karlsruhe University.

An explanation of 90 domain wall motion in finegrained PLZT ceramic.

Ageing phenomena in reduced PLZT ceramics byJ. Gentner, Kadsruhe University.

Gives a model for ageing effects based on thediffusion of oxygen vacancies.

Dielectric properties of rare earth (III)’substitutedlead titanate ceramics by K. Keizer and A. J. Burggraft,Twente University of Technology.

The permittivity is calculated as a function oftemperature with some success (below the Curiepoint).

Ternary systems based on P6 (Ti, Z003 for pyro-electric applications by R. R. Zeyfang and R. M.Henson, AEG-Telefunken.

A preferred system is established for pyroelectricelements, namely Pb(Zr, Ti (Fe,/2Ta,/2))O3

Piezoelectric ceramics for surface wave elements byW. Christoffens, E. Eckert and H. Schichl, SEL-Research Centre.

Permittivities of less than 300 and frequencyconstant temperature coefficients of about 30 ppm/Care claimed for compositions rather similar to thosediscussed by Zeyfang and Henson.

Relaxation phenomena connected with the pyro-electric effect in the paraelectric phase of bariumtitanate by P. Sasko. Material and ElectrotechnicalInstitute, RWTH, Aachen.

Largely a confirmation of the established model.

J. M. HERBERTThe Plessey Co Ltd

Allen Clark Research CentreCaswell

NorthantsU.K.

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