Amin, M

Tawfik, A

English

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IndUm J . P h y»„ 48, 68-61 (1974)Electromechanical properties of aluminium doped barium titanateM. Amin* anp A. Tawfik**{Received 27 October 1972)The effect of introducing different A1 additions to BaTi()3 tran>s- diicer on the transv(^ rs(* coupling ooolfi(;ieiit of vibrating rectan­gular rods was studied. Doping u itli aluminium was found to increase the coefficient A'gj and decrease tjie resonance fn^piency of tlio re­sonators. This was attributed both to an iiicrcjaso in the reversed proportion of ISC'" domains and to the increase of the looseness of Ti+^  ions in the lattice of BaTiOg containing 0*1 v^i % Al.1. IntroductionThe increasing general interest in the basic properties of BaTiOg as a piozoeloctrio substance and in its practical possibilities as a (rairsducor material has stimulatexi a largo number of investigations in recent j^ oars. It is oft(m used in devices to convert electrical energy to mechanical energy and vice cerm.The transverse coupling coefflcticni was previously dotonnined from tJxe difference between the mechanical resonance and anti-resonance frequencies of a rectangular rod and from the radial modes of a vibrating disk under electric; short and open circuit conditions rospectiv( l^y (Mason 1958, Mason & Jaffe 1954).The transverse coupling (;oefficient, /vg^ , for the radial mode of vibrating disk of pure BaTiOa was previously studiexi (Jaffe 19.58, Jaffe Berlincourt 19G5). It was found to decrease as tjie temperature increased until it ]>ecain(; zero at the Curie temperature (Tawfik 1971).The effect of adding CaTiO*, PbTiO*, etc., to BaTiO* on tho coefficient ^ 3, resulted in its decrease with increasing additions (Borlincouri 1955). The increas­ing of the Al addition increased the coefficient K  (Tawfik 1969).The i^aent work aims at studying what kind of additions is more effective m improving the eloctromochanical properties of BaTiO, for tho transverse mode.expected that the study of tlie effect of Al additions on the electromechanical pro^ties of BaTiO* transducer might be of importance in producing samples fired at relatively low temperature (12(K)°C) and having as well a bettor couplingcoefficient than that of the pure BaTi03 transducer fired at a relatively higher temperature (14(K)°C).  ^ ^•* o f Science, Cairo University, Cairo.U.A.B. ”  °°**“*“ ® Research Centre, Union of Broadcast and Television, Cairo,68Electromechanical properties etc. 592. Exfebimbntal TbchniqueMethod of memurement :The rectangular rods containing different aluminium additions wore pre­pared liy ceramic method, the bars were fully plated, being about 1-2 mm thick, 15 mm in length and 2 mm in width. The circuit used is shown in figure 1. The transverse coupling is determined by the known dynamic method (Mason & Jaffe 1954).The resonance frequency fr and the anti-resonance froqueadey /«  of the poled rods parallel to the thickness, were then measured to obtain A'^ j bywhore A/ =  / „ —/,.2 •/.tan Z AfafrThe tompc'i aturo of Iho tiainplo was raised and resonance and anti-resonance of the resonator was recoidod at each temperature, viz.y 30°, 40°, 50°, etc., and t]ie coefliciont K^i was calculated.I-------  ------------------------ ^  0Fig 1. Circuit for measuring coupling factor. O—signal generator, E —resistance 16A; ohm; 0 -pulso oscilloscope, *5—sample.3. Experimental R esults and D iscussion3.1. Dependence of the transverse coupling coefficierU on Al additivesAn increase of the transverse coupling Aji as the aluminium additives were increased was observed (see figure 2).This increase is attributed to an increase in the degree of reaction which was verified from dielectric measurements in a previous work (Tawfik 1969). Consequently a larger proportion of 180°—domains are thus reversed in the poling process, w'hich gives rise to a higher net polarization (Amin & T zw ^ , to be publisliod). Besides, the strain effects caused by Al additives at least in the vicinity of those sites where Ti+* ions were replaced by A1+® ions resulted in60 M. Amin and A , Tawfikan harmonic oficillations o f Ti+* ion)3. This view point implied that introduced A1 atoms created strains, and the potential energy o f the Ti“^  ^ ions changed resulting in the increase o f the looseness o f the Ti+  ^ ions in the lattice. The looseness o f Ti+* ions helped the BaloOa transducer to bo piezoeloctrically excited earlier than the pure BaTiOa fired at 1400®C.§21251 ___________, —/ 60 Ca c tlootw.1 .2 .3 A .5 .6 7 8Al ATOTfVES ^Fig. 2. Efifeot of temperature on dependence of transverse coupling K^ i on Al additives.3.2. Temperature dependence of the transverse coefficient K 2 1The observed decrease o f the coupling coefficient with temperature (see figures 3, 4) is directly related to the decrease in the polarisation o f tl^ o sample. At Curie temperature, the coupling coefficient K i^ has zero value.Electromechanical properties etc. 61Fig. 4. Temperature dependence of transverse coupling K 3 for BaTiOji fired at 1300eC, and BaTiOj containing 0-1 wt% AI and fired at 1200^ 0.RefekencksAmin M. & Tawfik A. {In course of publication),Borlincourt D. 1D65 Proceedings of the National Electronic Conference 11» 777-7S5.Jaffe D. 1958 J. Amer, Cerain. Soc. 41, 494.Jaffa H. & Borlincourt D. A. 1965 Proceedings of the I E E E  53, 1375.Meson W. P. 1958 Proc. IR E  46, 705-778.Mason W. P. & Jaffe H. 1954 Proc, IR E  42, 921-930.Tawfik A. 1909 M ,S c, Thesis, Department of Faculty of Science, Cairo University, Cairo.

Electromechanical Properties of Aluminium Doped Barium Titanate

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Electromechanical Properties of Aluminium Doped Barium Titanate

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