Ferroelectric ordering and energy storage capacity in lead-free Ba(Zr0.2Ti0.8)O3 nanoscale film capacitors fabricated using pulsed laser deposition technique

Abstract

Dielectric thin film capacitors, storing large charge density, are useful in electric energy storing devices. Highly oriented lead-free BaZr0.20Ti0.80O3 (BZT20) thin films were grown on a conducting bottom layer La0.7Sr0.3MnO3 deposited on a MgO (100) substrate under an oxygen atmosphere using a pulsed laser deposition technique. X-ray diffraction studies indicate that BZT20 films were stabilized in a (100) oriented tetragonal phase. Microstructural studies on thin films indicate a smooth film (a roughness of ∼1.25 nm) with a thickness of around 320 nm. The structural sensitive A1(TO2) Raman band exhibits a discontinuous change across the tetragonal-cubic phase transition temperature Tc ∼275 K. The appearance of the broad Raman band in the cubic (Pm-3m) phase at an elevated temperature suggests the activation of symmetry forbidden Raman active bands. The temperature dependent band frequency and integrated intensity of the structural sensitive A1(TO2) band show anomaly across Tc. Temperature dependent dielectric studies (100-650 K) carried out in a wide range of frequencies 102-106 Hz on a fabricated Pt/BZT20/LSMO metal-insulator-metal capacitor suggest a broad dispersive peak of around 290 K. The polarization relaxation follows the Vogel-Fulcher relation with an activation energy of Ea = 0.047 eV and a freezing temperature of Tf= 246 K. The slim polarization P-E loops with a remanent polarization of ∼89.6 μC/cm2 and an EC value of ∼0.29 MV/cm were observed, suggesting its local ferroelectric ordering in corroboration with Raman and dielectric findings. From the P-E loop analysis, a large energy storage density of 31.9 J/cm3 and an energy storage efficiency of 56% were obtained. Our experimental results revealed that the BZT20 thin film capacitors have potential for energy storage device applications.