Synthesis and Characterisation of L-Phenylalanine-alkaline niobate- (KNN) Based Composites

Abstract

Amino acid biomolecules such as L-Phenylalanine (L-P.A) are attracting researchers’ attention because of their reported electrical properties, albeit low which can be improved with the addition of lead-free piezoelectric ceramics to produce dielectric composites. However, the combined physiochemical properties of L-P.A and (K0.45Na0.51Li0.04)(Nb0.85Ta0.1Sb0.05)O3 (KNNLST) has not been fully evaluated, hence the reason for this study. The appropriate composition of KNNLST powder was ball milled and calcined at 900oC. After calcination, ball milling was repeated, pressed, and heat-treated for onward composite formation. In this research, composites from L-P.A and KNNLST ceramics with compositions from 0 wt.% of the ceramics to 100 wt.% have been produced. The density, morphology, and phase changes in the composite were determined using geometric measurement, field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. The bulk density results gradually increased from 1.25 g/cm3 in L-P.A to 4.68 g/cm3 in ceramics. The XRD studies revealed phase changes from the monoclinic phase in L-P.A to the two-phase orthorhombic-tetragonal phase coexistence in the ceramics. The morphology of the composites revealed that polymerisation occurred during processing. A bi-modal grain size distribution was obtained for the ceramics, with most of the grain in the sub-micron region while a few were above 1 μm, respectively. Stable dielectric constant values across the measured frequency range were obtained while the values increased with increasing ceramics content. The values increased from 2 @ 1 kHz for L-P.A to 50 in the composite containing 80 wt.% ceramics and 943 in the ceramics. The dielectric loss and ac conductivity graphs revealed increasing values with increasing ceramics content. The dielectric loss values increased from 0.02 @1 kHz for L-P. A to 0.1 for the composite containing 60 wt. % ceramics while the ac conductivity increased from 8*10-8 S/m @1 kHz in L-P. A to 1*10-7S/m in the composite containing 80 wt.%. Moreover, polarisation hysteresis graphs indicate some level of piezoelectric response in the composites.