Pergamon J. Phys. Chem So/ids Vol58, No. 3, pp. 421-425, 1997 PIk zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE SOO22-3697(96)00157-6 0 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0022-3697/97 $17.00 + 0.00 STRUCTURAL AND DIELECTRIC PROPERTIES OF SOL-GEL PREPARED PZT(La, K) FERROELECTRIC CERAMICS J. MAL and R. N. P. CHOUDHARY Department of Physics, Indian Institute of Technology, Kharagpur 721 302, India zyxwvutsrqponmlkjihg (Received 21 May 1996; accepted 22 July 1996) Abstract-Polycrystalline samples of Pbo.g(Lat _Z~jKJ,,t(Zr0,53Ti0.47)0.s7503 where (z = 0.0, 0.1, 0.3, 0.5, 0.7) complex perovskite compounds (abbreviated as PLKZT) have been synthesized by sol-gel technique. Preliminary X-ray powder diffraction studies of the compounds suggest the formation of single-phase PLKZT compounds of tetragonal structure at room temperature. Detailed studies of the dielectric constant and loss of PLKZT as a function of temperature (from room temperature to 350°C) at 10 kHz exhibit a ferroelectric phase transition of diffuse type. The transition temperature (7-J is found to increase with increasing K concentration. Electrical resistivity and its temperature variations are measured for all these compounds. 0 1997 Elsevier Science Ltd. All rights reserved Keywords: ferroelectrics, dielectric constant, diffuse phase transition. PLKZT. 1. INTRODUCTION Lead zirconate-titanate (PZT), a solid solution of ferroelectric PbTiOs (T, = 490°C) and antiferroelec- tric PbZr03 (T, = 23O”C), belongs to the ferroelectric family of perovskite structure of a general formula ABOs (A = mono or divalent; B = tri or hexavalent ions). From the extensive work on synthesis and characterization of pure and complex or modified PZT, it has been found that these compounds have wide industrial applications, such as transducers, computer memory and display, light valves, electro- optical modulators, oscillators and sensors. In the past, systematic and extensive studies of structural, electrical and piezoelectric properties of La modified PZT or PLZT (10/35/65: La;Ti,Zr) with different dopants (such as alkali or Bi ions) at A site have already been completed [l-3], but all the compounds were found to be charge deficient. It has been found by Jaffe et al., and others [4-4 that PLOT prepared near morphotropic phase boundary (MPB) using sol-gel technique is very useful for piezoelectric technology. As no work has been done on the effect of double doping (La, alkali ions or Bi) at Pb-site on structural, electrical and piezoelectric properties of PZT near MPB, we have carried out this work. In this paper, we report the structural, dielectric, d.c.-resistivity studies of the composition Pbo.&ai -z/3Wo,1(~0.53 Ti.47)o.97@3 (z = 0.0, 0.1, 0.3,0._5,0.7) prepared by sol-gel technique. 2. EXPERIMENTAL Polycrystalline samples of Pbo.s(Lai -z,3Kz)~.i (Zro,aTi0,47)0,g7503 (abbreviated as PLKZT) with (z = 0.0, 0.1, 0.3, 0.5, 0.7) were prepared by the following sol-gel technique: lead acetate (GR grade, M/s. E. Merck (India) Limited), lanthanum acetate (GR grade, M/s. Johnson Chemical Co., India), and potassium chloride (99.8%, Glaxo Lab. (India) Ltd) were taken together in proper stoichiometry and dis- solved in a minimum quantity of water. As the addi- tion of K+ dopant is less than 1% of the total composition by weight, the anion (chloride or acetate) is not so effective on the synthesis. To obtain zirconyl acetate, an aqueous solution of zirconyl nitrate (GR grade, Loba Chemie, India) was converted first into its hydroxide by addition of dilute ammonia solution (M/s. S.d Fine-Chem Pvt. Ltd, India). The hydroxide was then filtered, dried and dissolved in acetic acid (GR grade, M/s. E. Merck (India) Limited) in a water bath to obtain a clear solution of zirconyl acetate. It was then transferred into a beaker containing the aqueous mixture of potassium chloride and acetates of lead and lanthanum. The resultant mixture contain- ing four cations were then slowly added to the desired volume of titanium isopropoxide (97%, M/s. E. Merck- Schuchardt, Germany) dissolved in an equal volume of n-butanol (99%, E. Merck (India) Limited) were stirred constantly with the help of a magnetic stirrer. Finally, citric acid (99.5%, M/s. E. Merck (India) Limited) and glycerol (GR grade, M/s. E Merck (India) Limited) taken in the ratio of 1.5 and 1 mole, respectively, for each mole of PLKZT, were added to the above resultant mixture as a chelating agent. The mixture was dried at 100°C in an air oven 421