Sc2o3

For the solid-state synthesis of NASICON compounds, typical metal oxides or hydroxides (HfO₂ (Aldrich, 99.8%), MgO (Aldrich, ≥99.99%), Sc₂O₃ (Sigma, 99.9%), Zr(OH)₄ (Aldrich, 97%), SnO₂ (Alfa Aesar, 99.9%), CaO (Sigma-Aldrich, 99.9%)) were used as precursors to introduce metal cations. SiO₂ (Sigma-Aldrich, nanopowder) and NaH₂PO₄ (Sigma, >99%) were used as silicate and phosphate sources. Na₂CO₃ (Sigma-Aldrich, >99%) was used as an extra sodium source. In addition, 10% excess NaH₂PO₄ was introduced to compensate for the possible sodium and phosphate loss during the high-temperature treatment. The powder mixtures were wet ball-milled for 12 h using a Planetary Ball Mill PM200 (Retsch) to achieve a thorough mixing before pressed into pellets. The pelletized samples were first annealed at 900 °C under Ar flow, then grounded with mortar and pestle, wet ball-milled, pelletized, and re-annealed at 1100 °C. The crystal structures of the obtained materials were analyzed using X-ray diffraction (Rigaku Miniflex 600 and Bruker D8 Diffractometer) with Cu Kα radiation.

(1 − x − y)KNN-xBNKLZ-yBS (x = 0–0.05, y = 0–0.03) ternary ceramics including (1 − x − y) KNN-xBNKLZ-yBNT (x = 0.03, y = 0–0.04) and (1 − x − y)KNN-xBNKLZ-yBG (x = 0.045, y = 0–0.01) were prepared using the conventional solid-state powder method. The starting powders were K₂CO₃ (≥99.0%, 150 μm, Sigma-Aldrich), Na₂CO₃ (≥99.5%, 10 μm, Sigma-Aldrich), Li₂CO₃ (99.997%, 20 μm, Sigma-Aldrich), Nb₂O₅ (99.9%, 2 μm, Sigma-Aldrich), Bi₂O₃ (99.9%, 10 μm, Sigma-Aldrich), ZrO₂ (99.0%, 5 μm, Sigma-Aldrich), Sc₂O₃ (≥99.9%, 10 μm, Sigma-Aldrich). TiO₂ (≥99.9%, 5 μm, Sigma-Aldrich) and Ga₂O₃ (≥99.99%, 10 μm, Sigma-Aldrich). With an eye to practical applications, toxic Sb and high-cost Ta, although in common use and useful as doping elements for KNN, were avoided in this work.