Tawfik, A

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Pyroelectricity in sodium benzoyl acetonateA. T a w f ikDfiparlmpnt of Physics, Faculty of Fcicncc, Tania TJniversiiy, Egypt {Received 25 October 197G)Indian J .  Phya. 52A, 126-12» (1978).Data liav(» benii obiaiiiod on the pyroclocirio behaviour of polarized speciimcniH of Hodmrn lieiizoyl acetonate in an effort to detorminr the total pyro(doctrio eff(;ct. Near the curie temperature the tota ]>yroelectrie effect was inforrod from capacitance change. Thi niveiHal fif 180" domains on heating interacts with the vohimotn change yic'Jding a pc^ ak value of pyroelectric curi'ont near the euri temperatuni.1. INTIIOIITICTIONAccording l.o the terminology introduced by Cadj  ^ (194G) the primary pyro­electricity is defined as tlu^  change of polarization of a diclectiic with tempera­ture. Since all substanee-s that could exhibit primary pyroelectrieii.y are also jiiezoolectrie, there is, in gmioral, some c!ontribution to the polarization change with temperature due to the tpliermal expansion or contraction of the dielectric. I f  such a piezoele(d,ric contribution is produced by a uniform temperature change through the sample, it is designated as the sccondaiy pyroelectricity. Experi­ments intended to verify the existence of primary pyroelectricity were performed by Voigt (191G) on tourmaline crystals. Experimental evidence at present seems to indicate that the primary pyroelectricity docs indeed exist, the iippei limit for its contribution, however, being only about 10-12% in the case of the pyroiilectric substances, like tourmaline and Rochelle salt. In fact, in both barium titanate (Pearls 1958, Tawfik 19G9) and lead zirconate (Cook 1963, Tawfik 1974) titantae and sodium acetylacetonate (Tawfik 1974) near room temperature, the secondary effect is small. The purpose of the present investiga­tion Avas to derive higher pyroeh^ctric current from our sjiecimons near room temperature, which were to be used in a convertor, for conversion of heat to electrical power.2. E x p e r im e n t a l  P r o c e d u r eSodium benzoyl acetonate specimens were prepared b}^  chemical method. The prepared poAvder was pressed int.o tablets at 1000 kg/cm’*, having diameter 12 mm and thickness 1 mm. Tavo electrodes of silver were used and the speci­mens were polarized by applying different values of electric fields'^1000 V/cm for different times ranging from 10-120 minute Eor the pyroelectric measure­ments a shunted ammoter was placed in parallel with the test specimen. The126Pyroelectricity in sodium benzoyl acetonate 127spocM'mon was heatod in a boakew coiilaiiiing silicont' oil and tho reading ammeter Avas recorded as a function of tomjioratine, tlic heating being about 10°C per minute.3 R esults anu  D iscussionThe pyroelectric currents produced liy the spocimeiis figure I aiose as a consoquciico of its capacitance change due t.o phase transit-ion. This is sodium beuzoylacetonato could be the result of t-wo factors, viz. the primary effect of aligned domains, and sivitching ol domains by 180°.20 40 60 80 100TOlKBlUVTnRS (T*’C)Fig. 1120Secondary pyrooleetiicity could result from 90° domain switching and the secondary effect in aligned domains. The secondary pyroelectricity has the same sign as the total effect on first heating. Switching of the aligned domains by 180” during heating would eontributo to primary iiyroclectricity. It appears, therefore that appreciable 180“ domain switching took jilacc only close to the curio point. However, near the curie kimperature on account of the close coupling between spontaneous polarization and spontaneous strain, one must consider the effect of increased non-polar alignment- by 90”. This makes a128 A. Tawfikposi1iiv'(i contribution to the strain parallel to the polar axis with a consequent contribution to charge flow.The cffccl< of the polarizing field and time of polarization on the generated pyroelectric current is shown in figures 2 and 3. The pyroelectric current^Mjiincreased by increasing the polarizing field and time ol polarization, This can bo explained by an increase in the remaining 180“ domains after poling process.Fig. 3pyroelectricity in sodium benzoyl acetonate 129Tho maintaming domains reversed during heating the spoeinien which caused a greater displacement of tlui charges constituting dipoles, and this resulted in a higher flow of electrje charge i.o tlie surfaci  ^ of tlio polarized specimen.ItEFERTSNCESGaily W G 1946 Fiezodccii u ilif. MoGmw-Hill Bonk (Company Ixic , YoikCook AV> 11 Jt., & Boiliii Court D A J A/ipl P/njn 34, i:i92.Foils T A , Diosnlt. J. Dolnov VV I I9RS J. A ppl P/iys. 29, 1297.Tawlik A. 1900 M Sc, Thosis, Fliymcs Jlcp,, Faculty ol Sciomu, Oaiio IJnivorhilyTaw/ik A 197  ^ IntL J Phi/s. 48, 291Vmgt W lOin Jnw. Ph}].silc, 66, 1900; ISOS ihhi 46, 221.A o^iyt W 1916 PhysiL. Z 17, 2S7 aud :J07

Pyroelectricity in Sodium Benzoyl Acetonate

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Pyroelectricity in Sodium Benzoyl Acetonate

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