Read on our recent publication at Chemistry-Methods, a Wiley journal:
“ Lead-Free (K0.50Na0.50)NbO3 Unmodified Piezoceramics: Reduction in the Energetic Budget of Solid-State Synthesis and Sintering» by MARIA DORE, JOSÉ F. BARTOLOMÉ, SONIA LÓPEZ-ESTEBAN, MARZIA MUREDDU, COSTANTINO CAU, STEFANO ENZO, ÁLVARO GARCÍA, SEBASTIANO GARRONI and LORENA PARDO. Chemistry-Methods, 2500038 (2025)
DOI: 10.1002/cmtd.202500038
In this work, we reveal that the temperature of the solid-state synthesis of pure (K0.50Na0.50)NbO3 (KNN) piezo-composition is severely reduced by using the appropriated niobium reactant after attrition milling for only 3h of the mixture of reagents for the solid-state reaction: a majoritarian (57 wt.% of the total Nb2O5 content) orthorhombic polymorph Pbam.
After calcination of this mixture at only 450°C/2h, a 60 wt.% of KNN was achieved. Moreover, after 850°C/2h the calcined powder became a pure KNN. A second ball-milling of powder calcined at 700°C-850°C gave place to populations of nanostructured particles (380-40 nm, respectively). The milled powder calcined at 700°C was pressureless sintered in air for 2h at 1050°C and 1100°C, leading to coarse grained ceramics. Milled powder calcined at 750°C and 850°C, sintered at the same conditions, produced fine grain homogeneous microstructures. Ceramics showed an orthorhombic Amm2 pure KNN perovskite phase, as seen by x-ray diffraction and Rietveld analysis. The piezoelectric values (d33=115 pC/N, d31=-22 pC/N, kp=20%, kt=40%) are exceptional when derived from such a straightforward solid-state route.
