Acharya, H N

Choudhary, R N P

Shannigrahi, S R

English

IACS Institutional Repository

Indian J. Phys. 71A (5), 545-554 ( 1997)IJP A— an international journalX -ray, therm al and dielectric properties o f  A i5L a38T i7202i 6 (A = C a, Sr, Ba) ceram icsS R Shannigrahi, R N P Choudhary and H N Acharya Department of Physics, Indian Institute of Technology, Kharagpur-721 302, West Bengal, IndiaReceived II October 1996 accepted 6 May 1997Abstract : The polycrystalbne samples of A|^La^gT 172^ 216  = Ca. Sr, Ba) wereprepared by high temperature solid-stale reaction technique. Preliminary structural analysis of the compounds from the X-ray powder data show that these compounds are orthorhombic at room temperature. Detailed dielectric and thermal studies in a wide temperature range did not show any anomaly which could support the predicted feiToelectnciry in the above compoundsKeywords : Polycrystalline ceramics, structural analysis, dielectric and thermal studies PACS Nos. : 77 22.Gm, 61.10.Nz, 77 80.Bh1. IntroductionSince the discovery of an interesting ferroelectric properties in perovskite BaTi03 [1], the crystal structure and physical properties of a large number of pure and complex oxides of different structures and chemical compositions have been examined [2-8], in search of new ferroelectric for device applications. Some compounds ( i .e . BaTi03, LiNbO*, KTa03, Pb(ZrTi)03, LaTiC ,^ PbNbO  ^e tc . )  of perovskite and tungsten bronze families [9-13] have been found very useful for many devices such as computer memory, display, electro-optic modulator, transducer, pyroelectric detector, IR sensor etc . Though the crystal structure of the tungsten bronze (TB) is much more complicated [14] compared to the perovskite structure [15], a large number and variety of compounds of TB family with large variation of physical properties can be prepared which can be useful for devices. In search of new materials of the TB family, ferroelectricity in one of its large molecule numbers ^ai5Pf38Ti7202i6 has been predicted recently [16], on the basis of its crystal structure. As a part of the systematic and extensive studies of ferroelectric properties of TB family, we have carried out structural, thermal and dielectric properties of the titled compounds to find out the existence of predicted ferroelectric properties in them.© 1997 1ACS546 S R Shannigrahi, R N P Choudhary and H N Acharya2. ExperimentalThe polycrystalline samples of A |5 La3 8 Ti7 3 0 3 | 6  (A = Ca, Sr, Ba) were prepared by high temperature solid-state reaction technique using high purity CaC03 (M/S Glaxo Laboratories (1) Ltd.), SrC03 (M/S Burgoyne Urbiages & Co.), BaCC  ^ (AR Grade BDH), La20 3 (M/S Indian Rare Earth Ltd.) and T i03 (M/S s.d.fine-chem. Pvt. Ltd.) in a stoichiometry. The weighted ingredients were thoroughly mixed in an agate mortar for two hours. The powders of these compounds were calcined at 1000°C in pure alumina crucibles for 24 hours in an air atmosphere. The calcined powders were again ground and calcined at the same temperature in order to complete the reaction and'formation of the desired compounds. Finally, the fine homogeneous powders of all the ^iree compounds were used to make cylinderical pellets of 10 mm diameter and 1-2 mi  ^ thickness at a pressure of 6 x 107 kg/m2 using hydraulic press. As it was difficult \o  make pellets with very fine powders, polyvinyl alcohol (PVA) was used as binder. The pellets were then sintered at 1200°C for 24 hours in silicon carbide high temperature furnace and in alumina crucible. The formation of the single phase compound were checked by X-ray diffraction profile.For preliminary structural analysis of all the compounds at room temperature. X-ray powder diffraction profiles were recorded using X-r^y powder diffractometer (Miniflex JXR, Japan) with CuKa radiation (A = 0.15418 nm) in an wide range of Bragg angle 2 6  (10° < 2 6   ^ 90°) at a scanning rate of 2°/minute. To examine the grain/particle size and their distribution on the surfaces of the compounds, the scanning electron micrographs (SEM) at a particular magnification were taken using a computer controlled Stereoscan/CAMSCAN S-180 scanning electron microscope. To study the electrical/dielectric properties of the compounds, both the flat surfaces of the pellets were polished and electroded with high purity fine particle silver paste. The capacitance and the dissipation factor of all the samples were measured using GR 1620 AP capacitance measuring assembly as a function of frequency (103 Hz to 10* Hz) and as a function of temperature (-160°C to 250°C). In order to check the thermal stability of the title compounds, thermal curves (TG, DTA) were recorded from room temperature to 600°C.3. Results and discussionIn Figure 1, room temperature X-ray diffraction patterns of all the three compounds have been compared of which sharp single peaks suggest the formation of single phase compound. All the observed peaks are different in position and intensity from their starting materials. With the observed ^-values obtained from diffraction patterns, reflection peaks of the compounds were indexed and their unit cell parameters were determined in different cell configuration/crystal systems. A suitable unit cell of the compounds were selected on the basis of the best agreement in the observed and calculated d-values. Finally, the selected cell dimensions of the compounds were refined using different options of the standard computer programme, "POWDER PACKAGE". With the refined cell parameters. The d-X-ray, thermal and dielectric properties etc 547values of all the reflections were again calculated and compared with their observed values. The orthorhombic cell parameters of all the compounds have been tabulated and comparedFigure I. Comparison of room temperature X-ray diffraction patterns of Ai5La3gTi7202i6 (A = Sr, Ba, Ca) compounds.in Table l . The observed and calculated d-values of all the compounds were found in very good agreement (Tables 2-4) which suggest the correctness of the selected unit cell andTable 1. Comparison of lattice parameters, particle size from X-ray patterns and SEM in parenthesis, density and activation energy of A i5La3gTi720 2 i6 (A = Ca, Sr and Ba).Compound Lattice parameters(A)Particle size(A)Density(gm/cc)Activation energy (ev)Cat 5^38^720216 a 08.3814 b 12.2075 c 12.9230424 (540) 6.41 0.164S n s ^ a T ^ f h ie a 09.6243 b 12 .112 0  c 13.0380383 (490) 6.59 0 239Ba15U3gTi7202i6 a 10.0238 b 12.9268 c 09.7061256 (337) 6.77 0 095structure. From the preliminary structural analysis, it has been found that the crystal structures of all the compounds are orthorhombic at room temperature.548 S R Shannigrahi, R N P Choudhary and H N  AcharyaTable 2 . Comparison of observed and calculated d-values (A) and intensity ratio of some reflections of Sri5La3gTi7 2 0 2 i<>.SI No h k l dobs (^) deal,n (A)1 . 0 2 0 7.7618 7.7618 102 . 2 0 0 6.4634 6.4634 33. 2 I 1 4 2104 4.2104 114. 0 3  1 3.9001 3 9022 75. 3 0  1 3 4795 3.4795 86 0 4  1 3 2549 3.2492 f 117. 4 0 0 3 2090 3.2317 \ 128 4 1 0 3 1644 3.1639 \ 89. 4 2  0 2 9980 2 9834 \ 2410 0 5 1 2 7466 2 7517 1 10011 1 2 2 2.7142 2 7129 1612 4 2  1 2 6671 2 6662 713 3 4 1 2.5996 2.5943 314 4 3 1 2 4946 2 4890 215 4 5 0 2 2432 2 2389 2216 1 7 0 2 1859 2.1857 217. 4 2 2 2 1034 2 1052 618 6 2 0 2.0758 2 0760 319. 5 0 2 1.9489 1 9503 3320 5 5 1 1 8842 1 8842 82 1 . 6 5  0 1 7712 1.7700 222 4 0  3 1 6894 1 6687 623 7 3 1 1.6695 1.6692 324. 7 5 0 1.5851 1 5871 30Tabic 3. Comparison of obsc/ved and calculated d-values (A) and relative observed intensity ot some reflections of Ba^La^gT^C^ie-SI No. h k l dobs *n dca| in (A) IUq1 1 2 0 5 1257 5.1257 182 1 2 1 4 7703 4 7703 93 2 1 1 4 2302 4.2302 164. 03  0 4 0401 4 0373 105. 2 0 2 3.8667 3.8716 116 0 2  3 3.49jJ 3 5309 47 3 0 0 3.1977 3.2081 208. 1 0 4 3.0789 3.0872 369 1 1 4 2 9980 2.9916 910 0 3  3 2.9592 2.9579 2111 2 2 3 2 8488 2.8468 100X-ray, thermal and dielectric properties etcFigure 2. Comparison of SEM micrographs of the A^LaagT^Ojifi tA * Sr, Ba, Ca) ceramic compounds.X -ray, therm al a n d  d ielectric  p ro p erties  etc  549T able 3. (Cant'd.).SI No. h k l ^obs in (A) ^calin (A) i / i01 2 . 2 3 2 2 7967 2 7944 1813 0 4 2 2 7303 2.7462 4514. 2 0 4 2 6983 2 6987 415 2 1 4 2 6367 2 6367 1816 0 1 5 2.5495 2.5492 417 4 1 0 2.3559 2.3600 418 2 0  5 2.2924 2 2926 2719 1 5 2 2.2115 2 .2 1 0 0 92 0 2 5 1 2 1317 2 1345 1 12 1 4 2 2 2.1127 2 I 151 142 2 2 4 4 2.0144 2 0147 923 0 4  5 1 9770 1.9759 724 4 4 0 1 9371 1.8838 3425 0 2  7 1 8842 1 7803 426. 5 1 3 1 7814 1 7417 927. 0 7  0 1 7429 1 7303 1 l28. 2 2 7 1.7303 1 6697 729 1 5 6 1 6695 1.5952 430 2 7  2 . 1 5951 l 5797 27T ab le  4. Comparison o f  observed  reflections o f  C a[5La3gTi7 2 0 2 i6 .and calculated rf-values (A) and intensity ratio o f  som eSI. No h k l ^obs ,n dcai in (A) W 01 . 0 0  1 4 1907 4 1907 272 l 1 1 3.8833 3 8833 133 1 2 1 3.4012 3 4012 104. 6 0 0 3.2203 3 2308 335 4 0  1 3.1754 3.1699 276 . 6  1 0 3.1210 3.1232 107. 1 4 0 2.9980 3 0147 678 . 0 3  1 2.9214 2 9194 179. 5 1 1 2.7714 2.7716 531 0 . 3 4 0 2.7385 2.7596 10 01 1 . 4 3 1 2.4946 2.5007 31 2 . 8 2 0 2.2539 2 2521 1713. 6 4 0 2.2325 2.2185 13Dielectric per mittivity (£ )550 S R Shannigrahi, R N  P Choudhary and H  N AcharyaTabic 4. (Cont'd.).SI No h k l 4>bs in (M <*cal »n (A ) III014 9 1 0 2.1317 2 . 1 2 1 1 715 0 5 1 2.1034 2.1096 1716. 5 4  1 2.0758 2 .0814 1317 3 5  1 2 .0060 2.0054 1 018 6 4  1 1 9529 1.9607 2419 4 5 1 1.9332 1 9343 332 0 9 I 1 1 8879 I 8925 -i 132 1 6  5 1 1.7744 1.7664 \ 1 02 2 6 2 2 1 6893 1.6893 l 1 023 3 4 2 1 6695 1 . 6 6 8 8  \ 1 024 4 4 2 1 6260 16271 725 5 4 2 1 5801 1 5779 2 0I44 -42* STttLajiriaOat° BokLo* 117, 07%Figure 3 . V ariation ol £  and tan <5 ol A|4jLa^gTi7202 \ 1, (A  = Srv Ba. Ca) compound as a function o f  frequencylimV - t r 2 6Kio70 *— I02 I01 104F r ec uenc y in HzThe linear particle size of the samples were calculated from some strong reflections of different 20 angle using Scherrer’s equation, the average value of those are given in Tabic 1, which are consistent with the particle size obtained from SEM. The SEMX-ray, thermal and dielectric properties etc 551micrographs obtained from gold coated pellets at 3 pm magnification for different compounds have been compared in Figure 2 which show uniform distribution of spherical particles. However, some holes/voids have been found which confirm low density of the pellets. Measured densities of the pellet samples for different compounds are given in Table 1.In Figure 3, the variation of dielectric constant (£) and dielectric loss (tan 8) of the compounds with frequency have been compared. The normal trend and behaviour of a dielectric are found in studied compounds. At 10 KHz, the variation of £ and tan 5 from -160°C to 250°C of all the compounds have been compared in Figure 4. It is observed thatFigure 4. Comparison of temperature dependent c and tan S of A| (A = Sr, Ba, Ca) at 10 KHz.all the compounds have low dielectric constant and tangent loss at room temperature. In general, £ of all the compounds decrease with increase of temperature whereas dielectric loss (tan S) increases with increase of temperature. Careful and reapeated measurements of € and tan 8, even in small temperature interval, did not show any anomaly in any of these title compounds which clearly suggests the non-existence of ferroelectric properties in them.The temperature dependence of electrical conductivity (Tand activation energy Ea of all the samples have been calculated from the dielectric data collected at different temperatures using standard formulao  = £ co tan 8 and a =  Ob c*P i-E jkp T )  respectively,7lA(5)-6552 S R Shannigrahi, R N P Choudhary and H N Acharyawhere Eq is the dielectric at free space, (O is the angular frequency and kp is Boltzmann constant. The activation energy (Ea) of all the compounds have been obtained from the slope of the plots In a  vs T-1 (Figure 5). The values of the activation energies are tabulated in Table 1. It is observed that (in Figure 5) the conductivity of the samples increases rapidly at high temperature region. So it is clear that at high temperature, there is some oxygen vacancies created and due to this, ionisation takes place inside the samples.Figure 5. Comparison of electric conductivity (log O) of A| 5La3gTi72021$ v.v inverse of temperature (7w|)Figure 6 shows the thermal studies (TG, DTA) upto 600°C on powder samples of the titled compounds. The TG and DTA curves did not show any exothermic or endothermic peaks. Howevei, the compounds were found quite stable in this wide temperature range. Finallv. it is concluded that the title compounds are in orthorhombic crystal system at room temperature and have no ferroelectric phase transition in the temperature range -160°C to 250°C and are thermally very much stable from room temperature to 600°C.W'.gMI'/.) _ W.,gh<(V.)X-ray, thermal and dielectric properties etc 553Tamp *CTemp, *CFigure 6. DTA and TG curves of A15^35^720216 (A = Sr, Ba, Ca).AcknowledgmentThe authors are thankful to Mr. R P Mukherjee and Mr. Shyamal Mukherjee for their kind experimental help.References[1] B Wul and L M Goldman C. R Acad. Sci. 46 123 (1945)12] H Iwasaki. S Niyazawa, S Koisumi, H Sugii and Nuzckj J. Appi Phys. 43 4907 (1972)[31 N K Misra, R Saii and R N P Choudhari Indian J. Pure Appl Phys 34 (1996)14] S Namamatsu. M Kimura, K Doi and M Takahasi J Phys. Sac. Jpn. 30 300 (1971)[5] T Yamada and H Iwaski Acta Cryst. 28A 8181 (1972)[6] S Bera and R N P Choudhary Matter. Lett. 22 197 (1995)17] M L Nanda Goswami, R N P Choudhary and S Sarma Indian J. Phys. 71A 153 (1997)[8] M Kimura, S Namamatsu, T Kawamwra and S Matsushita Jpn. J. Appi Phys. 13 1473 (1974)[9] G Goodman J. Am. Ceram. Soc. 36 368 (1953)1101 G Shirame, H Danner and R Pepinsky Phys. R*v. 105 856 (1957)IU] CM Horiwing. E Wienger-Avner and S P S Porto Phys. Rev. 135 79 (1972)[12] P B Jamieson, S C Abrahams and J L Bernstein J. Chem. Phys. 48 5048 (1968)[13] S Namamatsu, M Kimura, K Doi, S Mats use hit a and N Yamada Ferroelectrics 8 511 (1974)[14] M H Franeombe and B Lewis Acta Cryst 11 696 (1958)[ 15] Bams and J R Carruthers /  Appl. Crystallo3 395 (1970)[16] SC Abrahams Acta Cryst B45 228 (1989)554 S R Shannigrahi, R N  P Choudhary and H  N  Acharya

X-Ray, Thermal and Dielectric Properties of A15La38Ti72O216 (A = Ca, Sr, Ba) Ceramics

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X-Ray, Thermal and Dielectric Properties of A15La38Ti72O216 (A = Ca, Sr, Ba) Ceramics

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