A wide range of material properties can be accessed by tuning the size and shape of nanocrystals (NCs). Cations incorporated into the crystal lattice of indium oxide (In_(2)O_(3)) NCs as dopants have been shown to impact electronic, optical, and magnetic properties and also sometimes influence the NC shape, but the effects of nonincorporative cations have not been investigated. In this work, we found that nonincorporative alkali cations greatly affect the size and shape of In_(2)O_(3) NCs. In particular, addition of sodium ions in the reactant mixture significantly increases the NC size and induces a rhombic dodecahedral (RDH) shape, which has not been observed in previous reports. By changing the volume of the precursor, we demonstrate size tunability from 17 to 45 nm, where shape is independently controlled by the sodium concentration. Finally, a progressive shape evolution from RDH to cubes is observed by incrementally replacing sodium in the precursor with potassium ions.
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