Effect of Lanthanum Substitution on the Structural, dielectric, Ferroelectric and Piezoelectric Properties of Mechanically Activated PZt Electroceramics

Abstract

IntroductIonLead based and lanthanum substituted PZT (PLZT) ceramic systems show all the aspects of the dielectric, piezoelectric, pyroelectric, ferroelectric and electro-optic properties desired in such materials. These best properties make them used widely in numerous devices such as different types of sensors, actuators, nano-positioners and transducers [1][2][3] . The amount of lanthanum substitution in the basic PZT system was selected on the basis of morphotropic phase boundary (MPB, a region of maximum piezoelectric and dielectric response) [3][4][5] , that depends on the Pb/La ratio [6][7] . At the vicinity of the MPB, PLZT ceramics show outstanding piezoelectric properties, which can be attributed to the unique structural feature of the coexistence of tetragonal and rhombohedral phases. In the vicinity of the MPB region, the six domain states of the tetragonal structure along the (100) direction (90° and 180° domains) coexist with the eight domain states of the rhombohedral along (111) , counteract the natural p-type conductivity of the PZT and thus, increase the electrical resistivity. The donors are usually compensated by A-site vacancies, which enhance domain reorientation and as a result ceramics show square hysteresis loops, low coercive fields, high remnant polarisation, high dielectric constants, maximum coupling factors, higher dielectric loss, high mechanical compliance, and reduced aging 2 . Due to high volatility of lead, to ensure good electrical properties, ceramics should be prepared at low calcination and sintering temperatures. This condition was achieved by the synthesis of nano sized fine powders by using the mechanical activation method 9-11 with optimised high energy mechano-chemical (HEM) ball milling parameters because the properties of ferroelectric ceramics are greatly affected by the milling parameters [12][13] . The main advantage of this HEM ball milling method is that no excess PbO was added in the starting composition because of lower calcination and sintering temperatures, without compromising the electrical properties of electro-ceramics. Usually, to carry out dielectric and electrical measurements, ceramic powders are first mixed with binder and then uniaxially pressed in to the shape of ceramic disks but in this study no binder was added. Instead, ceramic powders were cold isostatically pressed (CIP). This eliminated the binder addition and binder burnout steps that help to increase the density, electrical properties and reduced the contamination risk. Effect of Lanthanum AbStrActDifferent compositions of (Pb 1-x La x ) (Zr 0.60 Ti 0.40 )O 3 (abbreviated as PLZT x/60/40; x=0, 0.07, 0.08 and 0.10) ceramics were prepared by a combinatorial approach of high energy mechano-chemical ball milling and cold isostatic pressing (CIP). X-ray diffraction patterns and transmission as well as scanning electron microscopy images were used for the micro-structural and morphological studies. The average particle size of PLZT milled powders was measured from the TEM images and was found...

Development of PLZT Electroceramics with Ultrahigh Piezoelectric Properties by a Novel Material Engineering Approach

“…SEM was also used for the microstructural and morphological studies of sintered PLZT ceramics. The base composition of PZT shows larger grains (~9 μm) compared to La-substituted ones with a less dense microstructure [38]. The grain shape for the PZT system was also not uniform which is detrimental to the electrical properties.…”

“…Figure 1b shows the newly proposed phase diagram of PZT ceramics. La substitution into PZT ceramics also modifies the MPB, and the influence of La doping on the MPB of PZT ceramics was studied and reported by many researchers [10,16,[31][32][33][34][35][36][37][38]. As per the phase diagram, PLZT 8/60/40 ceramics lie close to the MPB and were selected for further studies [7].…”

Dielectric, Ferroelectric, Energy Storage, and Pyroelectric Properties of Mn-Doped (Pb0.93La0.07)(Zr0.82Ti0.18)O3 Anti-Ferroelectric Ceramics

“…The shape of the P-E hysteresis loops is also affected by the measurement temperature (PE and FE), the doping in the original ceramic composition (A-and B-sites), and the microstructure of the ceramics (grain size and porosity). 11,35,36) Moreover, P-E loops can also be used for an estimation of the energy density and efficiency of the ceramics. The values of P r and E c also help understand the microstructure of the ceramics.…”