Structural, dielectric and electro-caloric properties of Ba(Ti,Zr)O3-(La,Sr)MnO3 composite multiferroic

Abstract

Dielectric and electrocaloric (EC) properties of sol-gel synthesized BaTi0.84Zr0.16O3 (BTZ) and La0.78Sr.0.22MnO3 (LSM) composite in 80:20 molar ratio is reported. We discuss the dielectric analysis based on the electric modulus M*(=1/ϵ*) with the aim to differentiate the orientational and interfacial/carrier contribution and to explain their temperature and frequency dependence. Frequency dependence of imaginary part of M, i.e., M″(ω) of the composite exhibits a broad relaxation peak in MHz range while ϵ″(ω) graph is typical of interfacial/carrier polarization dominated: ϵ″ is as high as 7k at 20 Hz, decreases to 300 at 2 MHz measured at 25°C. M″-max shifts to higher frequencies with the increase in the temperature. The M″-peak, associated with BTZ-dipoles, is fitted using Cole-Cole (CC) equation to estimate the dielectric parameters, static and high-frequency dielectric constants ϵs and ϵꝏ respectively, relaxation time, τ, and the CC parameter, α, which is related to the distribution of relaxation time. Temperature dependence of physical parameters obtained from the fitting reflected the attributes of orientational polarization of the parent BTZ. These analyses indicate that M* is a more suitable parameter to consider for the ferroelectric-ferromagnetic composites.