JOURNAL OF MATERIALS SCIENCE 27 (1992) 5244-5246 Structural, SEM and dielectric properties of PLZT K. L. YADAV, R. N. P. CHOUDHARY, T. K. CHAKI* Department of Physics, and *Rubber Technology Centre, Indian Institute of TechnOlogy, Kharagpur 721 302, India Powder of lanthanum-modified lead zirconate titanate (PLZT) with the composition La/Zr/Ti = 8/65/35, was synthesized from aqueous nitrate solutions. A single-phase PLZT was obtained at ~ 550 ~ The reactivity of the powder during low-temperature heating was determined using X-ray diffraction and various thermal analysis techniques. The dielectric properties of the compound were also studied at 1 and 10 kHz frequency from room temperature to 200 ~ Diffuse phase transition (DPT) in the material was observed around 1 36 ~ at 1 kHz. An increase in peak-permittivity temperature (i.e. the transition temperature) with increasing frequency (a characteristic of relaxer ferroelectrics) was also observed. 1. Introduction Lead zirconate titanate (PZT) ceramics are widely used for some electronic devices because they have excellent piezo- and ferroelectric properties [1]. Gen- erally, PZT is fabricated by the conventional high- temperature solid-state reaction technique from PbO, TiO2 and ZrOz. It has been found that the properties of PZT synthesized by this technique are very sensitive to compositional fluctuations near the morphotropic phase boundary [2], particle size [3], calcination tem- perature [4], doping [5] and sintering temperature [6]. It has also been observed that the particle dis- tribution and size have a significant effect on the PZT properties. Chemically prepared (Pb, La) (Zr, Ti)O 3 (PLZT) powder is usually finer and less easily pro- cessed because, on a submicrometre scale, the smaller the particles the greater is their tendency to aggregate during calcination. This particle size precludes the dense packing and uniform small pore size which, in turn, permit 100% relative density at relatively low temperature. This chemical method involves the phy- sico-chemical reaction of the precursor compounds of the required oxides, such as alkoxides, oxalates, ni- trates, sulphates, etc. In this work, fine PLZT powders were prepared by a chemical method which differs slightly from previously reported techniques [7-9]. In the present paper, we report structural (X-ray), micro- structure, thermal and dielectrical properties of PLZT which have provided better and improved properties of this compound in comparison with other works. 2. Experimental procedure The starting materials were Pb(NO3)2, La(NO3)3" 6H20 , ZrO(NO3)2"2H20 and C12H2aO4Ti of AR grade. The powder of composition (Pbo.92Lao.os) (Zr0.6sTio.35)O 3 i.e. PLZT (8/65/35), was prepared by dissolving lead, lanthanum and zirconyl nitrates in distilled water in the desired ratio. Liquid tetra isopro- 5244 pyl titanate was then added directly to the nitrate solution while stirring. The titanium hydrolysed to an intermediate Ti(OH)4 phase and slowly redissolved. The intrinsic acidity of the solution was kept at pH < 1, which is a controlling factor of the rate at which the precipitate dissolved. Then nitric acid was added to obtain a clear solution. Later, the desired PLZT powder was obtained by heating the above nitrate solution at 130~ until it dried up. The res- ulting precipitate sticks to the glass beaker, so it was again heated at 230 ~ to break the bonds between the powder and the glass. The powder was calcined at 550 ~ and 920 ~ for 16 h in air in alumina crucibles. The phases formed were identified by X-ray diffraction (XRD) using CuK~ radiation. The size, shape and microstructure of particles were determined by scan- ning electron microscopy (SEM). The chemical com- positions were determined using an energy dispersive X-ray detector (EDX) attached to the SEM. Differ- ential scanning calorimetry (DSC) and thermogravi- metric analysis (TGA) of the powders prepared were carried out using model 9000 M/S DuPont Instru- ments, USA. For DSC analysis, ~ 15 20 mg powder was used, together with a reference material (empty aluminium pellets). The heating rate of the furnace was 20 ~ min-1. In TGA, the weight loss of the PLZT powder was recorded as a function of temperature, together with the DTG curves. The powder calcined at 920~ was cold pressed into a disc (pellet) sample under 6 x 107 kg m- 2 pressure using a hydraulic press. Sintering of the pellets was carried out at different temperatures (920-1200~ and sintering times (120-150 rain). In order to prevent PbO vaporization, an equilibrium PbO vapour pressure was established using PbZrO3 as setter, and placing everything in an alumina crucible covered with another small crucible. After sintering, the samples were subjected to an- nealing at 970 ~ to provide further evidence to con- firm the effect of the dopant. The density of the sample 0022-2461 9 1992 Chapman & Hall