Single-Step Synthesis of Ultrafine PLZT from Polymer Gel Precursor:  Synthesis, Consolidation, and Dielectric Properties

Abstract

Ultrafine Pb0.93La.07Zr0.60Ti0.40O3 powder was synthesized by autoignition of a metal−polymer gel precursor on a hot plate at very low temperatures without an additional calcination step. The X-ray diffraction result of the as-burnt powder obtained after ignition showed the presence of rhombohedral lead lanthanum zirconate titanate (PLZT) with minute amounts of unreacted PbO. The average particle size calculated from the transmission electron microscopy micrograph of the as-burnt powder was 1.75 nm. The as-burnt ultrafine PLZT powder was sintered directly to 94 and 96% of its theoretical density at 1100 and 1200 °C without any additional calcination. The PLZT sample with 94% theoretical density and grain sizes 0.4−1.0 μm showed a very high dielectric permittivity of ∼5000 and a completely diffused phase transition near the Curie point. This sample exhibited a remnant polarization (P r) of ∼34.6 μc/cm2. The permittivity of the 1200 °C sintered sample decreases drastically to ∼800. Both of the sintered samples showed very low dielectric loss.

Effect of oxidant-to-fuel ratios on phase formation of PLZT powder; prepared by gel-combustion

“…4 that the lead nitrate initially decomposes to lead oxide and then reacts with other constituents to form crystalline PLZT powder. It is known that the flame temperature during auto-ignition increases with increase in fuel content [8,9,19]. Therefore, the lead nitrate decomposes into PbO and forms PLZT at higher fuel content.…”

“…The amount of each chemical was calculated for 5 g of PLZT(9/65/35) powder. The stoichiometric nitrate (oxidant)-to-glycine (fuel) ratio was calculated by balancing the oxidizing and reducing valances of glycine and metal nitrates [8].…”

“…Usually the powder obtained from the gel-combustion has to be calcined for getting single phase PLZT powder. However, Roy et al [8] have reported single step synthesis of PLZT powder using metal-PVA combustion. Gel-combustion involves an intimate blending of constituent ions and suitable fuel or complexing agent (citric acid, urea, glycine, etc.)…”

“…in an aqueous media and an exothermic redox reaction between fuel and oxidizer (metal nitrates) [9]. The exothermic decomposition of fuel-oxidant precursors results in either the fine powder with required phase or semi-decomposed precursor with a considerable carbonaceous residue depending upon the nature of the fuel, pH of starting solution and oxidant-to-fuel ratio [8][9][10][11][12][13]. The powder characteristics are preliminary dependent on the flame temperature generated during the combustion which in turn is a function of nature of fuel and oxidant-to-fuel ratio.…”

Frequency-temperature dependent dynamics of dielectrics in ferric oxoborate Fe3BO6 of cocktail structure of nanorods

“…As compared in Table 1, it stands reasonably larger in comparison to most of well-known high-" r dielectrics [23][24][25][26][27][28][29]. Such high " r -value can be explained in presence of electrical conductivity of the sample when it designs a model resistor-capacitor network in terms of a bonded v-B 2 O 3 surface layer (insulator) on the individual Fe 3 BO 6 crystallites (a rather conductor).…”