Tacl5

Sr_1–xBO₃ (SBO) nanoparticles were synthesized using a two-step coprecipitation/oxygen-controlled
crystallization approach described elsewhere.^{7 (link)} Briefly, A-site (Sr(NO₃)₂, Alfa Aesar, 99.0%,
ACS grade), and B-site (NbCl₅, Alfa Aesar, 99.0% metals
basis; (NH₄)₆Mo₇O₂₄·4H₂O, Sigma-Aldrich; TaCl₅, Alfa Aesar, 99.99% metals
basis) salt precursors were precipitated using ammonium hydroxide
(NH₄OH, 28–30%, ACS grade) at a pH of 9.5. Next,
the as-prepared powder was ground with a eutectic molar ratio of NaNO₃ (high purity grade, VWR Amresco, 99.0%) and KNO₃ (ACS grade, VWR Amresco) to form a homogeneous powder. The mixture
was then transferred to a porcelain boat and heated in a tube furnace
at 600 °C under 0.2 Torr pressure for 2 h. After cooling, the
resultant powder was washed several times with deionized water and
dried overnight at 100 °C. Finally, as-synthesized NPs were annealed
in a tube furnace at 800 °C under a H₂/Ar (5/95%)
atmosphere with varying times (0–6 h).

YbCl₃, GdCl₃, EuCl₃, LuCl₃, ErCl₃, and TaCl₅, (purity > 99.99%) were obtained from Alfa Aesar (Haverhill, MA, USA). Octadecene, oleic acid, ammonium fluoride, and formamide were purchased from TCI Chemicals (Portland, OR, USA). Poly(acrylic acid) 1800 g/mol and sodium diatrizoate were purchased from Sigma-Aldrich (St. Louis, MO, USA).