Effect of Double Doping in Lead Zirconate Titanate (PZT) Lattices by Sol-Gel Technique for MEMS Applications

Abstract

We report on the effect of double doping (La²⁺ and Sm³⁺) in PZT lattices in thin film form, keeping La (mol%) fixed at 8 mol% [Pb_0.92-x La _0.08 Sm_x(Zr_0.65Ti_0.35)O₃: x = 0, 0.02, 0.04, 0.06, 0.08]. Both the cation substitutions are being substituted at A site only. The thin films were grown on Pt/Si<111> substrates by sol gel technique. XRD diffractogram shows single phase for the films for x = 0.02. Thereafter, an unidentified phase starts appearing which increases with further substitution of Sm³⁺. Surface morphology was studied using atomic force microscope (AFM). The films show well-defined ferroelectric behaviour. The dielectric constant decreases with Sm substitution initially and then increases slowly as the Sm substitution is increased but never attains the pure PLZT (8/65/35) dielectric value. The loss tangent (tanδ) initially increases and then decreases. The phase transition temperature (T_c) increases drastically with 2 mol% Sm substitution and decreases slightly as the Sm substitution is increased further. The I-V behaviour shows a consistent shift towards the –ve bias voltage as the Sm substitution is increased from 2 mol% to 8 mol%. The logI-logV curve show ohmic behaviour with the electrode for all the samples. The P-E loop shows more hysteresis for the 2 mol% Sm substitution. The appearance of P-E loop qualitatively shows the piezoelectric nature of the films. Optical band gap was calculated from transmittance studies using a UV-Vis-NIR spectrophotometer. The optical band gap was estimated from (αhυ)² vs hυ curve. The band gap decreases first with Sm substitution and then increases as the Sm substitution is increased. The results are discussed.

Keywords:

• PZT
• thin films
• double doping
• samarium
• optical

Acknowledgments

We are grateful to K. Zimik, Laser Science and Technology Centre, Metcalfe House, Delhi for doing AFM measurements. We also thank Dr. V. R. Balakrishnan and Anshu Goyal for their help in I-V and XRD measurements respectively.