Dielectric and ferroelectric properties of lanthanum doped SrBi4Ti4O15 ferroelectric ceramics

Bismuth layer structure ferroelectrics (BLSFs) have attracted intensive investigation for the potential use in non volatile ferroelectric random access memory (FeRAM) and piezoelectric devices suitable at high temperature. Bismuth layere structured compounds with general formula of (Bi₂O₂)²⁺ (A_m-1B_mO_3m+1)^2- are firstly found by Aurivillius^1-3. The structure of these compounds can be described as pseudo-pervoskite (A_m-1B_mO_3m+1)^2- slabs separated by (Bi₂O₂)²⁺ layeres along the crystallographic c-axis⁴. The 12-coordinated A site can be occupied by such cations as La³⁺, Bi³⁺, Ba²⁺, Sr²⁺, Pb²⁺, Ca²⁺, Na⁺, etc. While the octahedral-coordinated B site can be occupied by W⁶⁺, Nb⁵⁺, Ta⁵⁺, Ti⁴⁺, etc. Lanthanum substituted BiT (Bi₄Ti₄O₁₂) known as BLT has been extensively investigated. With this substitution, BLT shows relatively large P_r, low synthesis temperature and good fatigue endurance which makes it a potential candidate for FeRAM application. So, lanthanum doping is an effective way to improve the ferroelectric and fatigue properties of Bi₄Ti₄O₁₂. Lanthanum doped Bismuth layer structure ferroelectrics (BLSFs) ceramics SrBi_4-xLa _xTi₄O₁₅ (x=0, 0.025, 0.050, 0.075, 0.1) were prepared by solid state reaction method. X-Ray diffraction pattern showed that single phase was formed when x=0- 0.1. Morphological studies were carried out by SEM analysis. It was found that crystal lattice constant, dielectric and electrical properties of SBT ferroelectrics varied appreciably with amount of doping. Dielectric measurements in the frequency range 100Hz-1MHz were made using a n impedance analyzer (Wayne Kerr 6500P) and the measurements were carried out from RT to 600°C. The ferroelectric hysteresis loop was traced at room temperature by a standard P-E loop tracer based on sawyer-tower circuit.