The compositions of lead lanthanum zirconate titanate PLZT [Pb(Zr_0.57Ti_0.43)O₃ + 𝑥 at% of La, where 𝑥 = 3, 5, 6, 10 and 12] have been synthesized using mixed oxide route. The temperature dependent electromechanical parameters have been determined using vector impedance spectroscopy (VIS). The charge constant 𝑑₃₁ and elastic compliance $s^{E}_{11}$ show a peak in all the samples at a temperature 𝑇_mt much below the ferroelectric – paraelectric transition temperature, whereas the series resonance frequency 𝑓_s shows a dip at these temperatures. The Poisson’s ratio 𝜎^𝐸 increases with temperature 𝑇 showing a broad peak at a temperature higher than 𝑇_mt. The voltage constant 𝑔₃₁ decreases and the planar coupling coefficient 𝐾_p remains constant up to half of the 𝑇_mt and then falls sharply with 𝑇. Half of the 𝑇_mt can, therefore, be used for specifying the working temperature limit of the piezoceramics for the device applications.

The dielectric properties of lead lanthanum zirconate titanate (PLZT) ceramics [Pb(Zr_0.57Ti_0.43)O₃ +𝑥 at% of La, 𝑥 = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz–1 MHz using the vector impedance spectroscopy (VIS) at different temperatures. All the compositions show both non-dispersive and dispersive dielectric responses in different temperature regions. The non-dispersive region obeys the universal dielectric response. A low frequency (< 1 kHz) relaxation phenomenon with a high value of distribution parameter `ℎ’ (∼0.4 to 0.6) has been observed in all the compositions around the temperature corresponding to themaximum dielectric constant (𝑇_m). The activation energies as calculated from the relaxation and d.c. conduction processes are comparable. The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content.