Co-optimization of Na and K doping for improved room-temperature TCR of La0.7(Na0.3-xKx)MnO3 polycrystalline ceramics. Issue 17 (1st September 2022) - Yan, Yixin
Abstract: Polycrystalline La0.7 (Na0.3- x K x )MnO3 (LNKMO, x = 0.10, 0.15, 0.20, 0.25, and 0.26) ceramics were successfully compounded by adopting conventional sol-gel technology. The physical properties of as-prepared specimens were closely related to their morphology and internal structure, which were characterized and analyzed via X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Results confirmed that La + ions located at A-sites in crystal lattice were partially substituted by doped Na + and K + ions, which resulted in rotation and distortion of MnO6 octahedron. Lattice distortion was primary factor behind double exchange (DE) mechanism and Jahn-Teller (JT) effects. In addition, Na and K dopants altered relative amount of Mn 3+ and Mn 4+ ions, causing intensity variation in DE effect. These changes contributed to a decline in resistivity and an increase in peak resistance temperature ( T k ) with increasing K doping level. Meanwhile, optimal temperature coefficient of resistance ( TCR ) value of LNKMO ceramics reached 8.48% K −1 at 292.14 K when x = 0.25. This work reveals the mechanism of Na and K co-doping to optimize electrical transport properties of LNKMO manganese oxides and provides excellent material for the fabrication of uncooled infrared bolometers.