Effect of oxygen partial pressure on nonlinear optical and electrical properties of BNT–KNNG composite thin films
Composite thin films of 1–x [Bi0.5Na0.5TiO3] – x [K0.5Na0.5NbO3 + 1 wt% Gd2O3] (BNT–KNNG); (x = 0.01) have been deposited at various O2 pressures from 0.1 to 10 Pa by pulsed laser deposition, and their crystal structure, surface morphology, optical, dielectric, and ferroelectric properties were investigated. X-ray diffraction analysis of thin films deposited at 0.1 Pa revealed a single phase of BNT–KNNG and further (> 0.1 Pa), film crystallinity gradually increased with a rise in O2 pressure. The improvement in the refractive index and a reduction in optical bandgap are observed with O2 pressure and are estimated to be 2.28–2.42 and 4.08–3.65 eV, respectively. The third-order nonlinear optical coefficients estimated using the Z-scan technique are found to be enhanced with O2 pressure. The film deposited at 10 Pa exhibited a higher nonlinear refractive index (n2 = 6.188 × 10− 6 cm2/W) and a strong absorption coefficient (β = 1.043 cm/W). The temperature-dependent dielectric response displayed two structural phase transitions from rhombohedral to tetragonal phase at 165 oC and tetragonal to cubic phase at 298 oC. The enhanced dielectric (εr = 411, tanδ = 0.156 @ 1 kHz), Microwave dielectric (εr = 317 and tanδ = 0.0074 @ 10 GHz), and ferroelectric (Pr = 25.31 µC/cm2, EC = 42.62 kV/cm @ 1 kHz) properties with low leakage current are observed for the film deposited at 10 Pa which followed a space charge limited conduction behavior. The obtained microwave and nonlinear optical properties of BNT–KNNG composite films are suitable for tunable microwave and optical photonic device applications.
KeywordsPulsed laser deposition Microwave dielectric properties Ferroelectric properties Linear and nonlinear optical properties
The work was financially supported by DAE BRNS [37(1)/14/33/2015/BRNS], India. The authors are grateful to Central Instruments Facility (CIF) and Centre for Nanotechnology, Indian Institute of Technology Guwahati, India for providing experimental facilities.
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